Academic literature on the topic 'Corpus luteum. Pituitary hormones. Hormones'

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF2αand appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF2αof uterine origin in most subprimate species. The role played by PGF2αin primates remains controversial. In primates, if PGF2αplays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF2αappear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

ABSTRACTOral contraceptive (OC) pills contain estrogen and progestin that are synthetic analogs of natural hormones. These synthetic hormones affectthe hypothalamus-pituitary-gonadal axis of the female reproductive system. There are many types of contraceptives; most of the OC pills preventpregnancy by inhibiting ovulation. Estrogen and progestin are two female reproductive hormones that are critical. Typically, estradiol is producedby growing follicle (ovaries) which stimulates the hypothalamus to produce the gonadotropin-releasing hormone, which further stimulates theanterior pituitary to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH). LH production triggers the ovulation. Similarly, theprogesterone is produced by corpus luteum (ovaries), which triggers the production of FSH and LH. There are many types of progesterone available.Long-term usage of synthetic estrogen and progesterone can disturb the balance between the level of these hormones in the body. This imbalance maylead to severe side effects such as breast cancer, cervical cancer, thrombosis, direct impact on the brain, and infertility.Keywords: Estrogen, Progesterone, Contraceptives, Herbal contraceptives.

Abstract Pituitary hormones are essential for the maintenance of the corpus luteum in the pregnant mouse during the first half of gestation. Thereafter, hormones from the placenta take over the luteotropic role of the pituitary hormones. Mouse placental lactogen-I (mPL-I) and mPL-II, two PRL-like hormones produced in the placenta, are probably necessary for the maintenance of the corpus luteum in the latter half of pregnancy. A culture system of luteal cells from pregnant mice was developed to investigate the role of hormones from the placenta that may be important for the function of the corpus luteum. Mice were killed on days 10, 14, and 18 of pregnancy, and the corpora lutea were excised from the ovaries and digested in 0.1% collagenase, 0.002% DNase for 1 h. The resulting luteal cell suspension was plated onto 96-well plates coated with fibronectin (1 × 105 cells/well) and cultured for 1–3 days. Medium was changed daily. The cells were treated with various concentrations and combinations of mPL-I, mPL-II, mouse PRL, androstenedione, dihydrotestosterone, 17β-estradiol (E2), testosterone, hydroxyflutamide, cycloheximide, actinomycin D, and fadrozole to study the effects of these different treatments on progesterone (P4) production. The three lactogens (mPL-I, mPL-II, and mouse PRL) all stimulated the release of P4 from the luteal cells. The potency of the lactogens was similar and did not depend on the stage of pregnancy at which the luteal tissue was obtained. However, the responsiveness of the cells to all hormone-stimulated P4 release was gradually reduced the later in pregnancy the tissue was collected. Androgens also stimulated the release of P4 from the luteal cells, and when administered together, the lactogens and the androgens acted synergistically to stimulate P4 release. The androgens acted directly but not through conversion to E2, as determined by the findings that 1) the effects of the androgens could not be reproduced by E2 administration, 2) nonaromatizable androgen dihydrotestosterone was as effective as aromatizable androgens, and 3) aromatase inhibitor did not prevent the action of the androgens to stimulate the P4 release. The effect of the androgens on the P4 release was rapid, occurring within 15 min of hormone administration. It was not prevented by inhibitors of protein and RNA synthesis, and the intracellular androgen receptor antagonist hydroxyflutamide did not affect the androgen action. Therefore, the androgen effects were not mediated through the intracellular androgen receptor and de novo protein synthesis was not needed for androgen-stimulated P4 release.

The present study investigated the pituitary oestrogen (ER) and progesterone (PR) receptor concentrations in ewes during the oestrous cycle in the breeding season (n = 19), and in anoestrous ewes treated with gonadotrophin-releasing hormone (GnRH) (n = 11) and anoestrous ewes treated with progesterone + GnRH (n = 11). The pituitary ER and PR concentrations at the expected time of ovulation and in the early and late luteal phases were measured by binding assay. The pattern of pituitary ER and PR concentrations in the progesterone + GnRH-treated ewes resembled the pattern found during the normal oestrous cycle, with ER and PR concentrations decreasing from the time of ovulation to the early luteal phase. In contrast, in ewes treated with GnRH alone, ER and PR concentrations increased in the early luteal phase, which may increase the inhibitory effects of steroid hormones on luteinising hormone secretion, ultimately leading to the development of subnormal luteal phases.

There is increasing interest in the role of oxygen conditions in the microenvironment of organs because of the discovery of a hypoxia-specific transcription factor, namely hypoxia-inducible factor (HIF) 1. Ovarian function has several phases that change day by day, including ovulation, follicular growth and corpus luteum formation and regression. These phases are regulated by many factors, including pituitary hormones and local hormones, such as steroids, peptides and cytokines, as well as oxygen conditions. Hypoxia strongly induces angiogenesis because transcription of the potent angiogenic factor vascular endothelial growth factor (VEGF) is regulated by HIF1. Follicular development and luteal formation are accompanied by a marked increase in angiogenesis assisted by HIF1–VEGF signalling. Hypoxia is also one of the factors that induces luteolysis by suppressing progesterone synthesis and by promoting apoptosis of luteal cells. The present review focuses on recent studies of hypoxic conditions, as well as HIF1-regulated genes and proteins, in the regulation of ovarian function.

Deviations in the formation of reproductive function, and subsequently menstrual irregularities from the age of menarche, ovarian dysfunction and steroidogenesis disorders can be clinically manifested in remote periods after their direct action. The nature and depth of morphofunctional disorders in this case depends on the degree of maturity of the reproductive system, the initial functional state of the regulation centers (hypothalamus, pituitary gland) and ovaries, and the duration of the action of adverse factors. The accumulated specific research experience indicates that in addition to the pituitary gonadotropin hormones, cytokines (interleukins), which can simulate ovarian function and play an important role in ovulation, are of great importance in the normal functioning of the ovaries. The objective: аccording to laboratory and instrumental methods of research, to study the characteristics of hormonal status and the relationship of ovarian hormones with interleukins (IL) in women with menstrual dysfunction in the puberty. Materials and methods. According to the nature of the violations, the main group of women (n=90) who had a pathology of menstrual function in the puberty period was divided into 3 subgroups (n=30): the first – women with primary oligomenorrhea in the anamnesis, the second – with a late age menarche, the third – with puberty bleeding. The control group included women (n=30) with the correct rhythm of menstruation in puberty. Results. A clinical study found a decrease in the concentration of progesterone in women with a history of primary oligomenorrhea, a decrease in estradiol in the preovulatory period in women with late menarche. When assessing the concentration of follicle-stimulating hormone in the subgroups, an increase was noted in patients with puberty bleeding compared with the control group, due to the low level of antimuller hormone in the blood serum. The correlation between the indicators of these hormones and interleukins (IL-4, IL-8) indicates the influence of cytokines on folliculogenesis and the formation of the corpus luteum. Ovarian reserve parameters are not reduced. Conclusion. An analysis of the hormonal and cytokine status in women with menstrual dysfunction in the puberty allows us to draw an analogy between the processes of ovulation and the inflammatory response. The cytokines produced by certain immune cells are signaling molecules that affect cell proliferation and apoptosis of ovarian cells, folliculogenesis, hormone secretion and thus play an important role in ovulation. Therefore, the immune system may be an additional local regulator of ovarian function. Estradiol and progesterone are of great importance in the secretory transformation of the endometrium, especially during the «implantation window». Keywords: puberty, menarche, oligomenorrhea, pubertal bleeding, folliculogenesis, progesterone, estradiol, interleukins, pituitary gland, anti-varial antibodies.

Oestrus and ovulation occur spontaneously in the majority of marsupials, with behavioural oestrus usually occurring 1-2 days before ovulation. The hormone changes that occur at this time have been described in the most detail for the monovular tammar wallaby Macropus eugenii. The respective roles of the Graafian follicle, corpus luteum and the pituitary in the events leading up to oestrus and ovulation in this species are also reviewed. Recently, various protocols have been developed for superovulation of marsupials, including Australian species, such as the brush-tailed possum, fat-tailed dunnart, brush-tailed bettong and tammar wallaby, and the American laboratory opossum, Monodelphis domestica. These protocols provide an opportunity for studying the regulation of ovarian activity and for the collection of larger quantities of material for the study of gamete maturation, in vitro fertilization and embryonic development.

Management of the ovine oestrous cycle is mainly based on the use of exogenous hormones to mimic or enhance (progesterone and its analogues) or manipulate (prostaglandin F2α and its analogues) the activity of the corpus luteum, combined with the application of other hormones mimicking the pituitary secretion of gonadotrophins (e.g. equine chorionic gonadotrophin). These protocols have been applied without major change for decades but, now, there are two reasons to reconsider them: (1) our greatly improved knowledge of the dynamics of ovarian physiology, following the application of transrectal ultrasonography, indicates that modification of the protocols may improve fertility yields and (2) increasing concerns about animal health and welfare, food safety and the environmental impact of the treatments, as evidenced by public opinion and therefore market forces. Here, we offer an overview of these issues, introduce an updated protocol and suggest ways for future improvements to the protocols.

ABSTRACT The role of the pituitary gonadotrophins in controlling luteal function in the stumptailed macaque has been investigated by examining profiles of serum concentrations of LH, FSH, progesterone and oestradiol in daily blood samples from 13 monkeys during the menstrual cycle, and in blood samples taken at hourly intervals between 09.00 and 21.00 h on different days of the luteal phase in 13 cycles. The effects of acute withdrawal of gonadotrophins was investigated by administering a single injection of 300 μg LHRH antagonist/kg body weight at different stages of the luteal phase during 28 cycles. Although there were high basal values and marked fluctuations of bioactive LH during the first 4 days after the LH peak, progesterone profiles showed no corresponding short-term changes, there being a slow and steady rise in progesterone concentrations during the sampling periods. After day 5, basal LH secretion decreased, but high amplitude LH pulses were identified which were associated with episodes of progesterone secretion. Administration of the LHRH antagonist caused a suppression of bioactive LH and progesterone concentrations at all stages of the luteal phase, although some basal secretion of progesterone was maintained through the 24-h period of effective antagonist gonadotroph blockade. Luteal function recovered apparently normally in all monkeys treated in the early–mid-luteal phase. Serum concentrations of FSH and oestradiol fluctuated comparatively less during the 12-h sampling periods, and the antagonist had less suppressive effects on the concentrations of these hormones. The LHRH antagonist had no apparent effect on prolactin release. It appears that the corpus luteum is relatively unresponsive to the high serum LH concentrations during the early luteal phase, but that responsiveness increases as the corpus luteum develops. The corpus luteum is, however, susceptible to withdrawal of LH not only in the mid–late luteal phase when the relationship with LH is apparent, but also during the early luteal phase. J. Endocr. (1986) 111, 83–90

Three experiments were conducted to examine the regulation of steady-state concentrations of mRNA encoding ovine low density lipoprotein receptor (LDL-R) and high density lipoprotein-binding protein (HBP) in corpora lutea. In Experiment 1, corpora lutea were collected from ewes on Days 3, 6, 9, 12 and 15 (Day 0, oestrus) of the oestrous cycle. Enriched preparations of small and large steroidogenic luteal cells were also obtained on Days 6, 9, 12 and 15 of the oestrous cycle. In Experiment 2, 16 ewes were hypophysectomized on Day 5 of the oestrous cycle and received saline, luteinizing hormone (LH), growth hormone (GH) or a combination of LH+GH until collection of luteal tissue on Day 12 of the oestrous cycle. Corpora lutea were also collected from pituitary-intact control ewes on Day 5 and Day 12 of the oestrous cycle. In Experiment 3, 13 ewes on Day 11 or Day 12 of the oestrous cycle were administered prostaglandin F2 alpha (PGF2 alpha) and corpora lutea were collected 4 h, 12 h and 24 h later. Corpora lutea were also collected from 4 non-injected and 4 saline-injected (at 24 h) ewes. Results demonstrated that concentrations of mRNA encoding LDL-R did not differ throughout the oestrous cycle. Luteal tissue collected on Day 3 of the oestrous cycle had higher concentrations of mRNA encoding HBP than luteal tissue collected on any other day of the oestrous cycle. Hypophysectomy increased concentrations of mRNA encoding LDL-R but had no effect on concentrations of mRNA encoding HBP. Twelve hours following PGF2 alpha injection concentrations of mRNA encoding LDL-R were decreased but concentrations of mRNA encoding HBP were increased. Concentrations of both LDL-R and HBP mRNA were decreased 24 h following injection of PGF2 alpha. Thus, long-term positive and acute negative regulation of progesterone secretion from the corpus luteum by luteotrophic and luteolytic hormones was not mediated by changes in steady-state concentrations of mRNA encoding LDL-R or HBP.

To increase profitability in beef and dairy cattle operations, adequate reproductive management strategies that provide high service and conception rates, especially at the beginning of the breeding season for beef cattle, and after the voluntary waiting period for dairy herds, are necessary. To achieve these goals various hormonal protocols have been developed to synchronize the emergence of a new follicular wave, estrus and ovulation, thus allowing fixed time artificial insemination (FTAI). Treatment with eCG has been included in FTAI protocols. Considering that eCG is an indispensable tool for reproductive management, a better understanding of its biological action in the final follicular growth process, ovulation and luteal development is crucial to optimize its use in hormonal protocols. At the same time, alternatives for eCG need to be tested. In this regard, it is important a better understanding of how FSH and LH act in the dominant follicle. Based on that, three studies were performed. The first study evaluated effects of eCG on fertility of 679 crossbred lactating grazing cows synchronized for FTAI. Treatment with eCG tended to increase P/AI at 30 and 60 days and increased P/AI at 30 and 60 days for cows inseminated at ≤ 70 DIM but had no effect in cows receiving AI after 70 DIM. The second study evaluated the effect of eCG or different doses of hCG on the final growth of the dominant follicle in 84 Nelore cows submitted FTAI. No differences were observed for the diameter of the largest follicle on D8 or D10. However, the growth rate of the dominant follicle between D8 and D10 was greater for the groups eCG and hCG 300. In addition, more cows from the Groups hCG 300 and hCG 200 SC presented premature ovulation. Treatment with different hCG doses on D8 of a FTAI protocol failed to produce similar effects compared to eCG. The third study evaluated the effect of eCG, FSH, or hCG on follicular growth rate, ovulatory follicle size, CL volume and circulating E2 and P4 concentrations, as well as the number of large and small luteal cells in cows submitted to a protocol for synchronization of ovulation. Seventeen non-lactating Nelore cows were used. Two Latin squares were done, totaling eight replicates. The gonadotropin treatments, eCG, FSH, or hCG, were effective in increasing the follicular growth rate between D7-10 and consequently the follicular diameter on D10 and ovulatory follicle diameter in comparison to Control. In addition, treatment with different gonadotropins increased the number of large and small luteal cells, however, there was no difference in preovulatory E2 peak concentration, CL volume and circulating P4 concentration post ovulation.
Para aumentar a rentabilidade nos sistemas de produção de bovinos de corte e leiteiro, são necessárias estratégias de manejo reprodutivo que proporcionem elevadas taxas de serviço e concepção, especialmente no início da estação de monta em bovinos de corte e após o período de espera voluntária para rebanhos leiteiros. Para atingir esses objetivos, vários protocolos hormonais foram desenvolvidos com o intuito de sincronizar a onda folicular, o estro e a ovulação, permitindo assim inseminação artificial em tempo fixo (IATF). Considerando que a eCG é uma ferramenta indispensável para o manejo reprodutivo, é fundamental uma melhor compreensão de sua ação biológica no processo de crescimento folicular final, ovulação e desenvolvimento luteal, otimizando seu uso em protocolos hormonais. Além disso, alternativas para a eCG precisam ser testadas. Dessa forma é importante uma melhor compreensão de como FSH e LH atuam no folículo dominante. Com base nisso, três estudos foram realizados. O primeiro avaliou os efeitos da eCG na fertilidade de 679 vacas lactantes mestiças em sistema de pastejo sincronizadas para IATF. O tratamento com eCG tendeu em aumentar a P/IA aos 30 e 60 dias e aumentou a P/IA aos 30 e 60 dias para vacas inseminadas com DEL ≤ 70, mas não houve efeito nas vacas que receberam IA após 70 DEL. O segundo avaliou o efeito da eCG ou diferentes doses de hCG no crescimento final do folículo dominante em 84 vacas Nelore submetidas a IATF. Não houve diferença quanto ao diâmetro do maior folículo no D8 ou D10. No entanto, a taxa de crescimento folicular entre D8 e D10 foi maior para os grupos eCG e hCG 300. No entanto, mais vacas dos Grupos hCG 300 e hCG 200 SC apresentaram ovulação precoce. O tratamento com diferentes doses de hCG no D8 do protocolo de IATF não produziu efeitos semelhantes em relação à eCG. O terceiro estudo avaliou o efeito de eCG, FSH ou hCG na taxa de crescimento folicular, tamanho do folículo ovulatório, volume de CL e concentrações circulantes de E2 e P4, bem como o número de células lúteas grandes e pequenas em vacas submetidas a sincronização da ovulação. Foram utilizadas 17 vacas Nelore não lactantes em delineamento com dois quadrados latinos, totalizando oito réplicas. Os tratamentos com as gonadotrofinas eCG, FSH, ou hCG foram efetivos em aumentar a taxa de crescimento folicular entre D7-10 e consequentemente o diâmetro folicular no D10 e o diâmetro do folículo ovulatório em relação ao Controle. Além disso, o tratamento com diferentes gonadotrofinas aumentou o número de células lúteas grandes e pequenas sem, entretanto, se detectar diferenças no pico pré-ovulatório de E2, volume luteal e concentração circulante de P4 após a ovulação.

A hiperplasia adrenal congênita (HAC) por deficiência no P450c17 é uma doença de herança autossômica recessiva raramente relatada em pacientes 46, XX. Nosso objetivo foi o de caracterizar o fenótipo e genótipo desta doença rara revendo os dados clínicos, laboratoriais, genéticos, e da função ovariana de pacientes 46,XX de uma coorte brasileira avaliada no HCFMUSP e dos casos já publicados na literatura. Foram avaliados retrospectivamente os dados de 18 pacientes brasileiras pertencentes a 12 famílias avaliadas no HCFMUSP, e revisados os dados de literatura de pacientes de 10 coortes com deficiência da atividade P450c17 (14 pacientes, 6 delas com defeitos no CYP17A1 e 8 com defeitos no POR). Fenótipo: A maioria das pacientes apresentou-se com amenorreia primária (74 %) e 90 % das pacientes não desenvolveram pubarca; 69,5 % das pacientes apresentavam hipertensão arterial no momento do diagnóstico. Observamos uma alta incidência de distúrbios psiquiátricos (76%), como depressão, ansiedade e síndrome do pânico, em nossa coorte, mas não foram encontrados relatos na literatura. O ultrassom mostrou um aumento de pelo menos um dos ovários em 87 % dos pacientes antes do tratamento e macrocistos ovarianos em 65%, 6 pacientes (26%) referiram terem sido submetidas a cirurgia anterior para tratamento de torção ou ruptura de ovário. O tratamento com dexametasona, estrogênio e progesterona resultou em redução efetiva do volume ovariano. Todos os pacientes apresentaram níveis basais elevados de progesterona e LH e redução dos níveis de androgênios. Não observamos correlação entre os níveis de LH, da relação LH/FSH e de progesterona com o volume ovariano nos dois defeitos. Genótipo: O estudo molecular revelou que 17 pacientes de nossa coorte apresentavam mutações inativadoras no gene CYP17A1 e 1 paciente no gene POR. Duas novas mutações foram identificadas no gene CYP17A1, a p.R362H no éxon 6 e a p.G478S no éxon 8. A mutação mais prevalente no CYP17A1 foi a p.W406R identificada em 41 % das nossas famílias. Algumas das mutações no CYP17A1 foram encontradas apenas na coorte brasileira, mas a mutação p.A287P encontrada no gene POR em uma das nossas pacientes é a mais prevalente na literatura. Em relação à etnia, houve um predomínio dos defeitos moleculares no CYP17A1 em pacientes chinesas e brasileiras, enquanto que os defeitos no gene POR foram mais relatados nas pacientes europeias e norte - americanas. Em conclusão, a análise retrospectiva do fenótipo, genótipo e morfologia ovariana de trinta e duas pacientes 46,XX portadoras de deficiência da atividade P450c17, nos permitiu destacar os seguintes aspectos: a importância da dosagem da progesterona basal para este diagnóstico, a alta prevalência de aumento dos ovários com a presença de macrocistos ovarianos com risco de torção, e de transtornos psiquiátricos identificados em nossa coorte. Acreditamos que esta revisão possa contribuir para o diagnóstico mais precoce desta rara doença congênita
Congenital adrenal hyperplasia due to P450c17 deficiency is rarely reported on 46,XX patients. Our aim was to characterize the phenotype and genotype of this rare disorder reviewing the clinical, laboratory, genetic and ovarian imaging of 46,XX patients of our cohort and of other already reported cases. We retrospectively reviewed 32 patients with deficiency of P450c17 activity: 18 Brazilian patients belonging to 12 families and 10 cohorts already published (fourteen 46,XX patients, 6 of them with CYP17A1 defects and 8 with POR defects). Phenotype: most patients had primary amenorrhea (74%) and 90% of the patients did not develop pubarche; 69.5% of the patients had blood hypertension at diagnosis. We observed a high incidence of psychiatric disorders such as depression, anxiety and panic (76%) in our cohort but no reports were found in the literature. Ultrasound showed an increase of at least one of the ovaries in 87% of the patients before treatment and ovarian macrocysts in 65% of them; 6 patients (26%) had had previous surgery for twisting or ovarian rupture. Treatment with dexamethasone, estrogen and progesterone resulted in ovarian volume reduction. All patients showed elevated basal progesterone and LH and levels, and decreased androgen levels. There was no correlation between the levels of LH and progesterone and of LH/FSH ratio and the ovarian volume in both defects. Genotype: the molecular study showed that 17 patients from our cohort had inactivating mutation in the CYP17A1 gene and 1 in POR gene. Two novel mutations were identified in the CYP17A1 gene, the p.R362H in exon 6 and p.G478S in exon 8. The most prevalent mutation in the CYP17A1 was the p.W406R, identified in 41% of our families. Some of the CYP17A1 mutations were found only in the Brazilian cohort, but the mutation p.A287P found in the POR gene is the most prevalent in the literature. Regarding the ethnicity of the defects, there was a predominance of Chinese and Brazilian patients with defects in the CYP17A1 whereas defects in POR were most reported in European and North-American subjects.Conclusion: In this data review of thirty-two 46,XX patients with dysfunction of P450c17 activity we characterized the phenotype and genotype of this rare disorder and emphasize: the importance of basal progesterone measurement for this diagnosis, the high prevalence of ovarian macrocysts with risk of twisting, and the psychiatric disorders. We believe that this review may contribute to the early diagnosis of this disorder

Corpus luteum (CL), a transient endocrine structure formed from the ruptured ovarian follicle after ovulation, secretes progesterone (P4) that is essential for establishment and maintenance of pregnancy in mammals. The biosynthesis and secretion of P4 from CL depends, in general, on trophic hormones of the anterior pituitary gland and on hormones or factors originating from ovary, uterus, embryo and placenta. The structure and function of CL tissue is regulated by intricate interplay between two types of factors, namely, the luteotrophic factors, which stimulate CL growth and function, i.e., P4 secretion, and the luteolytic factors, which inhibit CL function and lead to luteal regression. In monoovulatory species such as higher primates and bovines, a striking diversity in the regulation of CL function exists not only between species, but also within the species during different stages of the luteal phase. In higher primates, unlike other species, one of the important characteristics of CL regulation is that, during non-fertile cycle, circulating LH appears to be the sole trophic factor responsible for maintenance of its function, and during fertile cycle, chorionic gonadotropin (CG), an LH analogue, originating from placenta maintains CL function. In higher primates, the role/involvement of luteolytic factors during luteolysis remains elusive. On the other hand, in the bovine species, the role/involvement of luteolytic factor, prostaglandin (PG) F2α during luteolysis is well established. It should be pointed out that in both the species, the mechanism of luteolysis is still poorly understood and the work presented in this thesis attempts to address these lacunae. Further, in bovines, studies have been carried out to examine potential trophic factor(s) responsible for the maintenance of CL function. Chapter I provides an extensive review of literature on CL structure and function with emphasis on factors that influence its growth, development, function and demise in primates and bovines. In Chapter II, employing bonnet monkey (Macaca radiata) as the representative animal model for higher primates, various studies have been conducted to examine the role of molecular modulators involved in regulation of CL function, particularly during spontaneous luteolysis. Although, it is well established that LH is essential for the maintenance of CL function in higher primates, the mechanism(s) responsible for the decline in serum P4 levels at the end of non-fertile cycles, without a concomitant change in circulating LH milieu, remains to be addressed. Several experiments have been conducted to examine the component(s) of luteotrophic (LH/CG) signaling that is/are modulated during luteolysis in the bonnet monkey CL. To understand the relative lack of responsiveness of CL to the circulating LH during the late luteal phase, LH/CG receptor (R) dynamics (expression of LH/CGR and its various transcript variants) was examined throughout the luteal phase and during different functional states of the monkey CL. The results indicated presence of LH/CGR mRNA, its transcript variants and functional LH/CGR protein in the monkey CL on day 1 of menses. Moreover, the functionality of receptors was tested by confirming the biological response of the CL to bolus administration of exogenous LH preparations, which eventually suggested factor(s) downstream of LH/CGR activation to account for the decline in CL function observed during non-fertile cycle. Studies have been conducted to identify molecular modulators that would selectively exploit intraluteal processes to regulate trophic signaling pathways that are critical to the control of luteal function. Immunoblot and qPCR analyses were carried out to examine presence and activation of Src family of kinases (SFKs) and cAMP-phosphodiesterases (PDEs) during various functional states of CL. The results revealed an increased activation of Src (phosphorylated at Tyr 416) during spontaneous and PGF2α/CET-induced luteolysis that may participate in the regulation of cAMP levels in part by increasing the cAMP-PDE activity observed during spontaneous luteolysis. This observation raised the question on the possible mechanism by which CG, an analog of pituitary LH, rescues CL function during early pregnancy. Thus, subsequent experiments involving LH/hCG administration in CET-treated animals as well as simulated early pregnancy animal model were conducted and the results revealed that, a bolus of LH/hCG decreased Src activation and cAMP-PDE activity accompanying a momentous increase in cAMP levels in both these models that further led to a concomitant increase in P4 secretion. Although the mechanisms of action of LH/CG involve modulation of a number of signaling pathways in the CL, by far, the results from various experiments suggested that it leads to activation of Src kinase and cAMP-PDE, thus causing inhibition of various elements of the primary signaling cascade- AC/cAMP/PKA/CREB during spontaneous luteolysis. One of the consequences of activation of Src kinase and cAMP-PDE was the regulation of expression of genes associated with steroidogenesis and it was observed that expression of SR-B1, a membrane receptor associated with trafficking of HDL-CE into the luteal cells, was lower in the regressed CL. The results taken together suggest that the decrease in responsiveness of CL to LH milieu during non-fertile cycles is not associated with changes in LH/CGR dynamics, but, is instead coupled to the activation of Src kinase and cAMP-PDE, inhibition of molecules downstream of LH signaling, and a decrease in the SR-B1 expression that regulates cholesterol economy of the luteal cell, and in turn, P4 secretion. The control of primate CL function appears to be dominated by the luteotrophic factors (LH/CG) over the luteolytic factors, since the process of luteal regression was overcome by administration of LH/CG. Further, in the primate CL, the molecular modulators of LH/CG signaling (Src kinase and PDE) are maintained in the repressed state by the luteotrophic factor LH/CG for maximum steroidogenic function. In contrast, in non-primate species, without invoking a role for the luteotrophic factor, essentially the synthesis and secretion of luteolytic factor, PGF2α, from the uterus is kept in check during pregnancy by the trophoblast derived IFN- and thus allowing CL to continue to function that is essential for maintenance of pregnancy. In the bovine species, the mechanism of PGF2α-induced luteolysis that involves a change in expression of genes associated with various processes of cellular function is poorly understood. Experiments were conducted utilizing buffalo cows (Bubalus bubalis) as a model system, to determine temporal changes in the global gene expression profile of the CL in response to PGF2α treatment. For this purpose, CL tissues were collected on day 11 of estrous cycle without treatment (designated as 0 h) and at 3, 6 and 18 h post PGF2α treatment for various analyses. Global changes in gene expression pattern in the CL were investigated employing Affymetrix GeneChip bovine genome array and the results are presented in Chapter III. The hybridization intensity values obtained by microarray analysis were subjected to R/Bioconductor tool. Following the application of highly stringent statistical filters to eliminate false positives, a set of differentially expressed genes were identified. The differentially expressed genes were further classified based on a fold change cut-off filter of ≥2, and the analysis revealed 127 genes to be differentially expressed within 3 h of PGF2α administration, of these 64 and 63 genes were up-regulated and down-regulated, respectively. Analysis of microarray data at 6 h post PGF2α administration revealed 774 genes to be differentially expressed, of which 544 genes were up-regulated, while 230 genes were down-regulated. The microarray analysis performed on CL tissues collected at 18 h post PGF2α administration showed that out of the total 939 differentially expressed genes, 571 genes were up-regulated, while 368 genes were down-regulated. Analysis of the ontology report for the biological processes category showed that initially in response to PGF2α administration, genes regulating steroidogenesis, cell survival and transcription were differentially regulated in the CL, but at later time points, differential expression of genes involved in apoptosis, PGF2α metabolism, tissue remodeling and angiogenesis was observed. Further, involvement of molecules downstream of LH/IGF-1 activation was investigated and the results obtained indicated that PGF2α interfered with the LH/IGF-1 signaling since the expression of LH/CGR, GHR and pAkt were down-regulated following PGF2αadministration. Furthermore, the functional luteolysis observed post PGF2αadministration appeared to be due to an interruption in cholesterol trafficking to inner mitochondrial membrane, since StAR expression was inhibited. The results obtained also demonstrated that the expression of AGTR1, VEGFR2 and R3 were down-regulated following PGF 2α administration. Further, the data obtained also suggested modulation of expression of pro- and anti-angiogenic factors upon PGF2α-treatment indicative of an involvement of other autocrine or paracrine factor(s) in the regression of bovine CL. This was an interesting finding as it suggests a novel and potential functional relationship between angiogenesis and the luteolytic response of CL to PGF2α administration. In bovines, despite extensive research being carried out to examine factors involved in the regulation of development and function of the CL, the trophic factor(s) required for maintenance of CL function, especially, P4 biosynthesis and secretion are not well characterized. It was hypothesized that the function of the CL during its finite lifespan must be responsive to LH as well as to various growth factors. Thus, experiments were conducted to examine the effects of increased LH and GH/IGF-I on the maintenance of CL function during mid luteal phase and post PGF2α administration and the results of these studies are presented in Chapter IV. To elucidate the role of LH as a trophic factor in the regulation of CL function, effects of increased endogenous LH through GnRH administration and exogenous hCG injections were examined. The results indicated an absence of noticeable effect of various hCG/GnRH treatments on circulating P4 levels. On the other hand, administration of GH resulted in increased serum IGF-1 and P4 levels. It was further observed that the administration of a combination of hCG and GH increased serum P4 levels better than treatment with GH alone. Further experiments were carried out to examine the complex reciprocal relationship between LH/GH and PGF2α on expression of genes involved in the regulation of luteal structure and function. In buffalo cows, administration of exogenous hCG and/or GH following inhibition of CL function by PGF2α administration did not prevent the PGF2α-induced decline in serum P4 levels, but PGF2-mediated decrease in expression of LH/CGR and GHR genes was prevented upon GH administration. However, the decrease in StAR expression was not restored by hCG and GH treatments, thereby indicating that PGF2 action was not prevented by hCG and/or GH treatments. Taken together, the results of studies carried out in buffalo cows employing various experimental model systems suggest essential role for LH and GH/IGF-1, however, these factors were unable to reverse PGF2α-induced luteolysis. Further, our crucial findings of the effects of increased endogenous LH and IGF-1, in addition to their relationship with luteolytic agents such as PGF2α will open new avenues for studying the mechanisms involved in the regulation of structural and functional properties of the buffalo CL. It is well known that a large number of buffalo cows experience loss of pregnancy and infertility due to inadequate luteal function and/or failure of timely insemination. Results from our studies suggest that the incorporation of PGF2α and hCG or GH/IGF-1 protocols in buffalo cows to be beneficial for improving their breeding efficiency as these protocols are likely to increase luteal function with defined luteolysis. To summarize, the results of studies described in the present thesis provide new insights into the physiological and molecular mechanisms involved in the regulation of CL function during luteolysis in the monoovulatory species. The results suggest that the maintenance of CL function appears to be dependent on both luteotrophic and luteolytic factors, but with a varied degree of dominance between the two species examined. Further, the results indicate that while the luteotrophic factors (LH/CG) dominate the CL regulation in primates, the regulation of CL function in bovines is dominated by the actions of luteolytic factor (PGF2α). In monoovulatory species, the luteotrophic and luteolytic factors following binding to their specific plasma membrane receptors on the luteal cells, would counteract each other and modulate activation of various downstream signaling molecules subsequently leading to regulation of gene expression and P4 secretion (Fig.5.1). LH: luteinizing hormone; CG: chorionic gonadotropin; LH/CGR: LH/CG receptor; Gαs: stimulatory α-subunit of trimeric G-protein; AC: adenylate cyclase; cAMP: cyclic adenosine monophosphate; PKA: protein kinase A; p: phosphorylation: CREB: cAMP response element binding protein; SR-B1: scavenger receptor class B, type I; SF-1: steroidogenic factor 1; LRH-1: liver receptor homologue 1; P4; progesterone; Src; sarcoma; PDE4D: cAMP phosphodiesterase 4D; StAR, steroidogenic acute regulatory protein; PGF2α: prostaglandin F2α; PTGFR: PGF2α receptor; PLC: phospholipase C; CYP19A1: cytochrome P450 aromatase; PTGR1: Prostaglandin reductase 1; AREG: Amphiregulin; RTK: receptor tyrosine kinase; Akt: protein kinase B; FKHR: forkhead transcription factor; DAPL1: death associated protein like 1; ARG2: Arginase, type II Growth factor LH/CGR RR AC Gαs ? Gα TT P? Gα K PKP src cAMP ? P Akt PDE4D P PFKHR FKHR CREB P LRH-1CREB P SF-1 Genes associated with Genes associated with apoptosis ? CYP19A1, apoptosis SR-B1 PTGR1 DAPL1 SF-1, LRH-1 AREG ARG 2 P4 biosynthesis Apoptosis? P4 biosynthesis Apoptosis MONKEY BUFFALO COW Shown here is the diagram depicting intracellular signaling pathways regulated by luteotrophic factor (LH) and luteolytic factor (PGF2α) and their cross talk to counteract changes in the expressions of genes associated with the biosynthesis and secretion of P4 and apoptosis in the CL. In primates, LH/CG activates a multitude of intracellular signaling cascades, primarily Gαs/AC/cAMP/PKA/CREB leading to changes in gene expression. LH during early and mid luteal phase and CG during pregnancy maintain the activation of Src and PDE in an inhibitory state. However, during the late luteal phase of non-fertile cycle, results in present study suggests that activated Src levels and PDE activity increase, with accompanying decrease in cAMP and pCREB levels leading to concomitant decrease in SR-B1 expression, and in turn, P4 secretion. Surprisingly, regulation of apoptotic gene expression and CL regression are still unclear. In bovines, PGF2α of uterine origin mediates changes in luteal gene expression and results in decreased P4 secretion, principally by reduction in StAR level. The present study suggests that during luteolysis PGF2α affects the genes regulated by LH, by interfering with LH (and perhaps IGF-1) signaling leading to alteration in the expression of genes crucial for CL structure and function. (Pl refer the abstract file for figures)

The control of reproductive cycles in higher primates is largely dependent on negative and positive feedback mechanisms by both steroidal and non-steroidal substances of the ovaries which regulate the function of hypothalamo-pituitary system. To gain insights into the role of INH A, the non steroidal ovarian hormone in the feedback control of pituitary FSH secretion, studies were conducted to examine the interrelationships of hormones throughout the menstrual cycle of the bonnet macaque. The findings of chapter II provide a detailed description of endocrine hormone profile during the menstrual cycle of the bonnet macaques with special attention to the feedback role of INH A on pituitary FSH secretion. To characterize the endocrine profile of different hormones, both ovarian (E2, P4, INH A) and pituitary (FSH, LH) hormones were measured daily for more than 40 days. To further examine the site of secretion of INH A and its relationship with pituitary FSH dynamics, surgical lutectomy and pharmacological induction of luteolysis employing the third generation GnRH R antagonist, Cetrorelix (CET) studies were carried out in the subsequent experiments. The results obtained from these studies suggest that INH A and P4 secreted from the CL during luteal phase regulate pituitary FSH secretion. The selective rise in FSH observed during the late menstrual cycle and during menstruation (referred to as luteo-follicular transition), as has been reported previously in higher primates, considered necessary for initiation of follicular growth and recruitment of follicles for ensuing menstrual cycle was characterized in the monkey. Surgical lutectomy and induction of luteolysis by CET experiments suggested that increased GnRH secretion is essential for this selective rise in FSH following withdrawal of inhibition by P4 and INH A. In clinical cases of reproductive ageing, the shortened follicular phase in human females has been identified to be the result of occurrence of early onset of FSH rise during the luteal-follicular transition period. The cause(s) of declining fertility with age in women who still have regular menstrual cycles are not clear, but issues of relationship between dysregulation of selective FSH rise in the late luteal phase and associated infertility could be examined using bonnet monkey as a model system. INH A is secreted in significant quantities by CL in higher primates and the feto placental unit suggesting its importance during fertility and pregnancy. Apart from the negative feedback regulation of pituitary FSH secretion, the complete repertoire of actions of this hormone during pregnancy is yet to be fully understood. The data presented in this thesis is the first comprehensive report showing the endocrine hormone profile of gonadotropins and ovarian hormones including INH A throughout the menstrual cycle of the bonnet macaque. The characterization of INH A profile in bonnet monkey will be of significant value for studies examining the role of INH A in higher primates. Dimeric inhibin has been suggested to be important for regulation of fertility and reproductive functions. Also, inhibin-α (one of the subunits of the dimeric protein) knock out mice model has provided convincing evidence that it acts as a tumour suppressor. A great deal of new information has been generated in recent years regarding the potential clinical usefulness of monitoring inhibin levels in blood and biological fluids in gynaecological diseases, pathological pregnancies and other disorders. Emerging clinical roles of inhibin have made INH A an important candidate molecule to study its molecular regulation. The results presented in chapter II suggested that LH regulates luteal INH A secretion (induction of luteolysis by CET administration experiment). As a first step towards understanding molecular regulation of inhibin-α expression in the macaque CL, in silico promoter analysis of macaque inhibin-α was performed and it revealed several transcriptional factor binding sites that were conserved across species. In rats FSH up regulates while preovulatory LH surge suppresses inhibin-α mRNA expression in the ovary and this suppression has been suggested to be necessary for occurrence of secondary FSH surge during metestrus. To address differential regulation of inhibin-α by LH and FSH in rat ovary during the periovulatory period, studies employing immature rats were carried out and the results are presented in chapter III. The results suggest that immature rat ovaries respond to exogenous gonadotropins in terms of LH signaling (cAMP production), luteinization (P4 production) and as well induction of ICER expression required for repression of inhibin-α subunit expression. PDE4 inhibitor (rolipram) treatment enhanced the ovarian cAMP concentrations suggesting that PDE4 play a major role in controlling intraovarian cAMP concentrations in rat ovaries. However increased cAMP concentrations did not appear to up regulate the ICER expression at the time point examined in this study. In higher primates time course of second FSH surge and continued synthesis and secretion of INH A in the CL are different from non primate species. In the monkey, the second FSH rise occurs during the late luteal phase and experiments have been carried out to examine the regulation of inhibin-α subunit expression by ICER. Expressions of ICER (mRNA/protein) and INH A were examined during different stages of CL and the results indicated no clear inverse relationship between the ICER and inhibin-α mRNAs. With no conclusive role for the ICER in regulating luteal inhibin-α observed in the study, the role of transcriptional activators in the regulation of inhibin-α like GATA4, SF-1, β-catenin were further examined. Since luteal INH A secretion was dependent on pituitary LH as determined earlier in chapter II, expressions of transcriptional activators were examined in CL of different stages and also during induced luteolysis and the results are described in chapter IV. In conclusion, our results indicate cross talk between WNT, cAMP and P38 MAP kinase signaling pathways in the regulation of luteal INH A secretion. The pituitary gonadotropin, LH, is the primary luteotropin in primate species acting to maintain the structure and function of the CL during the menstrual cycle. However whether the actions of LH are direct or mediated by local factors such as P4 remain unknown. Moreover, P4 secretion which is dominant during luteal phase has any role in regulating CL structure and function is not clearly defined. To address these and issues concerning P4 actions, initially, experiments were performed in the rat model to study the importance of P4 in the regulation of ovarian functions. An antiprogestin, RU486, was employed as a tool to uncover the PR regulated pathways during ovulation in rats and the findings are presented in the chapter V. The results indicated that blockade of PR action by RU486 during gonadotropin-induced superovulation resulted in inhibition of follicular rupture and ovulation in immature rats. Further to understand the downstream effectors of PR action, and to identify the candidate target genes of PR activation, semi-quantitative RT-PCR and western blot analyses were performed. The results obtained indicated that betacellulin, a member of EGF family and MMP-9 a proteolytic enzyme, were markedly repressed in response to RU486 treatment in rat ovaries. Also, the down stream pathway of EGF signaling leading to activation of ERK was markedly repressed in RU486 treated ovaries. It was next examined what role the P4/PR system has in the regulation of CL structure and function. Surprisingly, PR expression is absent in CL of rats, while it is present in higher primates. Experiments were carried out to examine intracrine actions of P4 in the regulation of CL structure and function in monkeys. The recently reported model system of induced luteolysis yet capable of responsive to trophic support from the laboratory provided an ideal opportunity to examine direct effects of P4 on structure and function of CL in the monkey. A series of pilot experiments were carried out in monkeys experiencing summer amenorrhea, to determine dose and mode of administration of exogeneous P4 to simulate mid luteal phase circulating P4 concentrations in monkeys subjected to induced luteolysis. Based on the results of pilot experiments, implantation of Alzet pumps containing 97.5mg of P4 was selected for maintaining mid luteal phase P4 concentrations. The microarray data of induced luteolysis previously deposited by the laboratory in NGBI’s gene expression omnibus were mined for identification and validation of differentially expressed genes of PR and its target genes following LH depletion and LH replacement experiments. Expressions of PR, PR cofactors and expressions of PR downstream target genes through out the luteal phase and in CL from day1 of menses were also examined. Analysis of expressions of genes revealed that of the 45 genes identified to be regulated by LH treatment, 4 genes were found to be responsive to P4, and 14 were identified to be responsive to both P4 and LH. Morphology of CL tissue sections revealed that P4 treatment appeared to have reversed the induced-luteolysis changes. In another experiment, implantation of P4 during late luteal phase (i.e., the period of declining P4 concentrations) for 24h caused changes in expressions of genes associated with tissue remodeling and morphology of luteal cells. Taken together, the results suggest that induced luteolysis plus P4 replacement model is suitable for assessing the effects of P4 on CL function. The results also suggest that CL could serve as target tissue for examining the genomic and non genomic actions of P4. In summary, studies carried out in the present thesis provides a comprehensive endocrine hormone profile throughout the menstrual cycle of the bonnet monkey with special emphasis on time course of INH A and FSH secretion which is very useful for future investigations. Studies have been carried out in rats and monkeys with different experimental model systems to address molecular mechanisms underlying inhibin-α regulation in the ovary in general and CL in particular. Experimental findings in monkeys could help elucidate the underlying molecular nature of CL functionality and extrapolate to understand luteal insufficiency and infertility producing conditions in humans. Also different model systems have been validated to examine the actions of P4/PR system in rats and monkeys and more importantly to address the direct effects of P4 upon monkey CL structure and function were established. Future investigations based on findings of these studies should help clarify relative roles for LH and P4 during maintenance of CL function and luteolysis.

The production of germ cells is essential for the continuation of a species. In the female this function is accomplished by the ovaries. In addition, the ovaries secrete steroids and nonsteroidal hormones that not only regulate the secretion of anterior pituitary hormones but also act on various target organs, including the ovaries themselves, the uterus, fallopian tubes, vagina, mammary gland, and bone. Morphologically, the ovary has three regions: an outer cortex that contains the oocytes and represents most of the mass of the ovary; the inner medulla, formed by stromal cells and cells with steroid-producing characteristics; and the hilum, which, in addition to serving as the point of entry of the nerves and blood vessels, represents the attachment region of the gland to the mesovarium. The cortex, which is enveloped by the germinal epithelium, contains the follicles, which are the functional units of the ovary. They are present in different states of development or degeneration (atresia), each enclosing an oocyte. In addition to the oocyte, ovarian follicles have two other cellular components: granulosa cells, which surround the oocyte, and thecal cells, which are separated from the granulosa cells by a basal membrane and are arranged in concentric layers around this membrane. The follicles are embedded in the stroma, which is composed of supportive connective cells similar to that of other tissues, interstitial secretory cells, and neurovascular elements. The medulla has a heterogeneous population of cells, some of which are morphologically similar to the Leydig cells in the testes. These cells predominate in the ovarian hilum; their neoplastic transformation results in excess androgen production. The ovary produces both steroids and peptidergic hormones. Whereas the steroids are synthesized in both interstitial and follicular cells, peptidergic hormones are primarily produced in follicular cells and, after ovulation, by cells of the corpus luteum. The initial precursor for steroid biosynthesis is cholesterol, which derives from animal fats of the diet or from local synthesis.

The reproductive organs of male and female giraffes are similar to those of all other artiodactyls. Giraffes have 14 pairs of autosomes and a pair of sex chromosomes. A constant testis temperature depends on countercurrent heat exchange between a large pampiniform venous plexus and the testicular artery. The onset of puberty in males and females occurs at ~3 years of age and is marked by enlargement of testes and the onset of oestrous cycles. Oestrus cycles are ~15 days long. Courtship, conception, and pregnancy are delayed until ~5 years of age. The giraffe placenta is polycotyledonous and epitheliochorial. Pregnancy is sustained by progesterone secreted by a single corpus luteum, the placenta and fetal ovaries and testes. Gestation lasts ~450 days and is ended by hormones secreted by the hypothalamic-pituitary axis of a mature fetus. Birth takes ~30 minutes. Daily milk yield ranges between 2.5 L and 10 L. Protein, fat, and lactose are higher than in cow’s milk. Weaning occurs at ~6 months of age. The average calving interval is ~20 months but varies according to the degree of lactational stress itself partly determined by whether a calf survives. Female giraffes have ~8 calves of which ~3 will reach adulthood. Survival of giraffes as a species depends on fewer adults dying each year than the number of calves reaching adulthood.

The testes are the source of both germ cells and hormones essential for male reproductive function. The production of both sperm and steroid hormones is under complex feedback control by the hypothalamic-pituitary system. The testis consists of a network of tubules for the production and transport of sperm to the excretory ducts and a system of interstitial cells (called Leydig cells) that express the enzymes required for the synthesis of androgens. The spermatogenic or seminiferous tubules are lined by a columnar epithelium composed of the germ cells themselves as well as supporting Sertoli cells surrounded by peritubular tissue made up of collagen, elastic fibers, and myofibrillar cells. Tight junctions between Sertoli cells at a site between the spermatogonia and the primary spermatocyte form a diffusion barrier that divides the testis into two functional compartments, basal and adluminal. The basal compartment consists of the Leydig cells surrounding the tubule, the peritubular tissue, and the outer layer of the tubule containing the spermatogonia. The adluminal compartment consists of the inner two-thirds of the tubules containing primary spermatocytes and germ cells in more advanced stages of development. The base of the Sertoli cell is adjacent to the basement membrane of the spermatogenic tubule, with the inner portion of the cell engulfing the developing germ cells so that spermatogenesis actually takes place within a network of Sertoli cell cytoplasm. The mechanism by which spermatogonia pass through the tight junctions between Sertoli cells to begin spermatogenesis is unknown. The close proximity of the Leydig cell to the Sertoli cell with its embedded germ cells is thought to be critical for normal male reproductive function. The seminiferous tubules empty into a network of ducts termed the rete testis. Sperm are then transported into a single duct, the epididymis. Anatomically, the epididymis can be divided into the caput, the corpus, and the cauda regions. The caput epididymidis consists of 8 to 12 ductuli efferentes, which have a larger lumen tapering to a narrower diameter at the junction of the ductus epididymidis.