Understanding the physiology of folliculogenesis serves as the foundation for perfecting diagnosis and treatment of ovulatory defects

PURPOSE

To discuss updated physiologic information concerning the mechanism of folliculogenesis.

METHODS

Physiology studies involving the growth of primordial follicular growth and pre-antral growth to the development of the corpus luteum are discussed.

RESULTS

Benefits in aiding fertility potential and pitfalls of these drugs in preventing embryo implantation are discussed with reference to the physiologic processes required for folliculogenesis.

CONCLUSIONS

Knowledge of the physiology of folliculogenesis can provide further understanding of luteal function when taking follicle maturing drugs and complications, as premature luteinization and the luteinized unruptured follicle syndrome. Also, this knowledge helps to create novel therapies to prevent ovarian hyperstimulation syndrome, endometrial receptivity defects, and treating women with diminished oocyte reserve.

Male hypogonadism and germ cell loss caused by a mutation in Polo-like kinase 4

The genetic etiologies of male infertility remain largely unknown. To identify genes potentially involved in spermatogenesis and male infertility, we performed genome-wide mutagenesis in mice with N-ethyl-N-nitrosourea and identified a line with dominant hypogonadism and patchy germ cell loss. Genomic mapping and DNA sequence analysis identified a novel heterozygous missense mutation in the kinase domain of Polo-like kinase 4 (Plk4), altering an isoleucine to asparagine at residue 242 (I242N). Genetic complementation studies using a gene trap line with disruption in the Plk4 locus confirmed that the putative Plk4 missense mutation was causative. Plk4 is known to be involved in centriole formation and cell cycle progression. However, a specific role in mammalian spermatogenesis has not been examined. PLK4 was highly expressed in the testes both pre- and postnatally. In the adult, PLK4 expression was first detected in stage VIII pachytene spermatocytes and was present through step 16 elongated spermatids. Because the homozygous Plk4(I242N/I242N) mutation was embryonic lethal, all analyses were performed using the heterozygous Plk4(+/I242N) mice. Testis size was reduced by 17%, and histology revealed discrete regions of germ cell loss, leaving only Sertoli cells in these defective tubules. Testis cord formation (embryonic day 13.5) was normal. Testis histology was also normal at postnatal day (P)1, but germ cell loss was detected at P10 and subsequent ages. We conclude that the I242N heterozygous mutation in PLK4 is causative for patchy germ cell loss beginning at P10, suggesting a role for PLK4 during the initiation of spermatogenesis.

[Bone and calcium metabolism in menopause transition]

Menopause, or estrogen deficiency, predispose women towards fragility fractures resulting from impaired bone strength, as the composite consequence of : (1) increased bone resorption caused by proliferation and activation of osteoclasts ; (2) dissociation of coupling bone formation with resorption ; (3) deterioration of bone quality ; (4) decreased calcium absorption from intestines and resorption from renal tubules. The current explanation of each phenomenon is described in this article, although the exact mechanisms have not been unanimously defined.

The role of androgens in follicle maturation and ovulation induction: friend or foe of infertility treatment?

BACKGROUND

Effects of androgens on follicle maturation have been controversial for some time. Here, we review the potential of their applications in improving human ovulation induction, based on human and animal data, reported in the literature.

METHODS

We reviewed the published literature for the years 2005-2011, using relevant key words, in PubMed, Medline and Cochrane reviews, and then performed secondary reviews of referenced articles, which previously had not been known or preceded the searched time period. A total of 217 publications were reviewed.

RESULTS

Contrary to widely held opinion, recent data, mostly developed in the mouse, convincingly demonstrate essential contribution of androgens to normal follicle maturation and, therefore, female fertility. Androgens appear most engaged at preantral and antral stages, primarily affect granulosa cells, and exert effects via androgen receptors (AR) through transcriptional regulation but also in non-genomic ways, with ligand-activated AR modulating follicle stimulating hormone (FSH) activity in granulosa cells. While some androgens, like testosterone (T) and dehydroepiandrosterone (DHEA), appear effective in improving functional ovarian reserve (FOR) in women with diminished ovarian reserve (DOR), others may even exert opposite effects. Such differences in androgens may, at least partially, reflect different levels of agonism to AR.

DISCUSSION

Selective androgens appear capable of improving early stages of folliculogenesis. They, therefore, may represent forerunners of a completely new class of ovulation-inducing medications, which, in contrast to gonadotropins, affect follicle maturation at much earlier stages.

Mechanisms of follicle selection and development

Follicle recruitment and selection, the process that gives rise to the dominant follicle (DF) and the physiological state of the DF are important areas of research. The selection of a single ovarian follicle for further differentiation and finally ovulation is a shared phenomenon in monovulatory species including humans. The DF is different from other follicles because it can escape atresia (the fate of all other follicles). The DF cells develop corpus luteum if exposed to the luteinizing hormone (LH) surge. Several mechanisms for DF selection have been proposed. Rising follicle stimulating hormone (FSH) concentrations induce the emergence of a follicle wave and cohort attrition occurs during declining FSH concentrations, resulting in DF selection. Cohort secretions are initially responsible for the decline in FSH, which is subsequently suppressed by the selected DF lowering it below the threshold of FSH requirements of all other cohort follicles. The DF acquires relative FSH-independence in order to continue growth and differentiation during further declining FSH concentrations. A transition from FSH- to LH-dependence is postulated as the mechanism for the continued development of the selected DF. In addition, FSH and insulin-like-growth factor (IGF) enhance each other's ability to stimulate follicle cell function. Access of IGF II to their receptors is regulated by IGF binding proteins that are in turn regulated by specific proteases; all of which have been ascribed a role in DF development. One other shared mechanism recently proposed for DF selection is the possible differential regulation of blood vessel formation. Anti-Müllerian hormone (AMH) also plays a critical role in selection of the DF. AMH levels decline as the size of the follicle increases. Once follicles reach a size at which they are dominant, it has largely disappeared. From the time a follicle has been selected, the follicle destined to ovulate greatly enlarges and shows marked changes in its steroidogenic activity. LH surge causes a significant decline in gap junctions leading to dissociation of mural granulosa cells (GC) and expansion of the cumulus-oocyte complex (COC). The oocyte resumes its meiosis and progresses from prophase 1 to metaphase 2 at the time of ovulation. The concept of DF selection could be applied to the in-vitro maturation (IVM) program. Understanding the mechanism of DF selection in menstrual cycles is the key to planning the optimal timing of oocyte retrieval in order to obtain competent oocytes and embryos. Although the timing of oocyte retrieval is still open to debate, there is evidence to suggest that it may be better to retrieve oocytes before the small cohort follicles complete the process of atresia following selection of the DF.

Endocrinology of the aging male

The endocrinology of the aging male is complex, with multiple hormones along the hypothalamic-pituitary-testicular (HPT) axis interacting with one another in feedback. As men age, there is a small and progressive (not precipitous, as in women) decline in several sex hormones, in particular testosterone and dehydroepiandrosterone, and related increases in luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin. The importance of these changes is wide-ranging because of the ubiquitous role of sex hormones in male physiology. This chapter discusses the endocrinology of the aging male. We provide an overview of the regulation of the HPT axis with an emphasis on the changes that occur with aging and the measurement of gonadal steroids, including hormone pulsatility, within-subject and circadian variations. The difficulties of assessing the symptoms of late-onset hypogonadism are highlighted. There is a comprehensive discussion of the epidemiology of sex hormone changes, including their age associations, prevalence of symptomatic hypogonadism, secular changes, risk factors, and the association of sex hormones with outcomes.

Regulation of Sertoli cell activin A and inhibin B by tumour necrosis factor α and interleukin 1α: interaction with follicle-stimulating hormone/adenosine 3',5'-cyclic phosphate signalling

Regulation of crucial events during spermatogenesis involves dynamic changes in cytokine production and interactions across the cycle of the seminiferous epithelium. Regulation of activin A and inhibin B production by the inflammatory cytokines, tumour necrosis factor α (TNFα) and interleukin 1α (IL1α), alone and in conjunction with FSH or a cAMP analogue (dibutyryl cAMP), was examined in cultures of Sertoli cells from 20-day old rats. Both TNFα and IL1α stimulated activin A secretion and expression of its subunit (β(A)) mRNA, and suppressed inhibin B secretion and expression of its subunit (α and β(B)) mRNAs. The actions of TNFα and IL1α were opposed by FSH and dibutyryl cAMP. Both cytokines inhibited FSH/dibutyryl cAMP-stimulated inhibin B secretion and mRNA expression as well as stem cell factor mRNA expression. Both cytokines also inhibited FSH-induced cAMP production, and reduced baseline FSH receptor mRNA expression. These data highlight the reciprocal relationship that exists between FSH/cAMP signalling and inflammatory cytokine signalling pathways in the control of Sertoli cell function, and production of activin A/inhibin B in particular. It is anticipated that these interactions play important roles in the fine control of events during the cycle of the seminiferous epithelium and in the inhibition of spermatogenesis during inflammation.

The role of FSH and TSH in bone loss and its clinical relevance

Osteoporosis, a global health problem, is now frequently recognized to be secondary to alterations in the pituitary-bone axis. This review examines the current evidence for how dysregulation of the pituitary-bone axis leads to osteoporotic bone loss. Specifically, perimenopausal bone loss in the context of follicle-stimulating hormone action, and hyperthyroid bone loss in the context of thyroid-stimulating hormone action are explored. From the reviewed scientific findings, recommendations for early diagnosis and better clinical management of bone loss are made.

[Control of bone remodeling by nervous system. Possible roles of pituitary hormones for bone metabolism]

Accumulating evidence clearly indicates both thyroid hormone and estrogen have a pivotal role in bone metabolism. Pituitary hormones, TSH and FSH, regulate circulating levels of thyroid hormone and estrogen, respectively. Recent works raise a possibility that either TSH or FSH also has its own direct effects on bone cells involved in bone resorption and formation. More recently, it is suggested that oxytocin and vasopressin are also involved in bone metabolism. However, several investigations of genetically manipulated model mice and clinical data from patients with certain diseases have provided inconsistent results. Thus, we need more data that answer the question whether or not each pituitary hormone is physiologically and pathophysiologically involved in controlling bone metabolism in human.

Follicle-stimulating hormone regulation of microRNA expression on progesterone production in cultured rat granulosa cells

MicroRNAs (miRNAs) regulate gene expression post-transcriptionally by interacting with the 3' untranslated regions of their target mRNAs. Previously, miRNAs have been shown to regulate genes involved in cell growth, apoptosis, and differentiation, but their role in ovarian granulosa cell follicle-stimulating hormone (FSH)-stimulated steroidogenesis is unclear. Here we show that expression of 31 miRNAs is altered during FSH-mediated progesterone secretion of cultured granulosa cells. Specifically, 12 h after FSH treatment, miRNAs mir-29a and mir-30d were significantly down-regulated. However, their expression increased after 48 h. Bioinformatic analysis used to predict potential targets of mir-29a and mir-30d revealed a wide array of potential mRNA target genes, including those encoding genes involved in multiple signaling pathways. Taken together, our results pointed to a novel mechanism for the pleiotropic effects of FSH.

Undifferentiated primate spermatogonia and their endocrine control

The biology of spermatogonial stem cells is currently an area of intensive research and contemporary studies in primates are emerging. Quantitative regulation of sperm output by the primate testis seems to be exerted primarily on the transition from undifferentiated to differentiating spermatogonia. This review examines recent advances in our understanding of the mechanisms governing spermatogonial renewal and early differentiation in male primates, with a focus on the monkey. Emerging revisions to the classic view of dark and pale type A spermatogonia as reserve and renewing spermatogonial stem cells, respectively, are critically evaluated and essential features of endocrine control of undifferentiated spermatogonia throughout postnatal primate development are discussed. Obstacles in gaining a more complete understanding of primate spermatogonia are also identified.

Effects of low-dose follicle-stimulating hormone administration on follicular dynamics and preovulatory follicle characteristics in dairy cows during the summer

The well-documented phenomenon of reduced conception rate in dairy cows during the hot season involves impaired functioning of the ovarian follicles and their enclosed oocytes. Three experiments were performed to examine the administration of low doses of follicle-stimulating hormone (FSH) to induce turnover of follicles that are damaged upon summer thermal stress and to examine whether this FSH administration has beneficial effects on preovulatory follicles. In experiment 1, synchronized heifers were treated with 100 mg of Folltropin-V (n = 7) or 4.4 mg of Ovagen (n = 6) on day 3 of the estrous cycle. Treatment with both FSH sources resulted in greater (P < 0.05) numbers of follicles than in control animals (n = 12) on day 6 of the estrous cycle, indicating that low doses of FSH can increase the number of emerging follicles in a follicular wave. In experiment 2, milking cows were assigned to a control group (n = 4) or treated with 2.2 mg (FSH-2.2; n = 6) or 4.4 mg (FSH-4.4; n = 5) Ovagen. Follicle-stimulating hormone was administrated on day 3 or 4 and day 10 or 11 of the estrous cycle, coinciding with emergence of the first and second follicular waves, respectively. The number of follicles emerging during the first wave tended to be higher (P < 0.1) in FSH-4.4-treated cows than in controls. The second-wave dominant follicles emerged 2 d later in the treated cows and were smaller in diameter (P < 0.05) than controls, 2 d before aspiration. Despite being younger, the preovulatory follicles of FSH-4.4 cows expressed a steroidogenic capacity that was similar to controls with a tendency toward greater insulin concentrations (P < 0.09). In experiment 3, milking cows were assigned to a control group (n = 6) or treated with 4.4 mg Ovagen (FSH-4.4; n = 6). Follicle-stimulating hormone was administrated on day 3 and day 12 or 13 of the estrous cycle. The number of emerging follicles was higher (P < 0.05) in the treated vs control cows. However, the features of the preovulatory follicle developed in the subsequent cycle did not differ between groups. In summary, low doses of FSH can efficiently induce follicular turnover accompanied by a modest effect on the preovulatory follicle of the treated cycle. It appears that the administration of low doses of FSH, precisely timed to synchronize with the emergence of follicular waves, might have a beneficial effect on the preovulatory follicle and its enclosed oocyte.

Characterization of the inhibitory roles of RFRP3, the mammalian ortholog of GnIH, in the control of gonadotropin secretion in the rat: in vivo and in vitro studies

RF-amide related peptides (RFRP), as putative mammalian orthologs of the avian gonadotropin-inhibitory hormone (GnIH), have been proposed as key regulators of gonadotropin secretion in higher vertebrates. Yet considerable debate has arisen recently on their physiological relevance and potential mechanisms and sites of action. Present studies were undertaken to further characterize the effects of RFRP on LH and FSH secretion by a combination of in vivo and in vitro approaches in male and female rats. Initial screening via intracerebroventricular (icv) administration of different analogs of RFRP1 (RFRP1-12 and RFRP1-20) and RFRP3 (RFRP3-8 and RFRP3-17), as well as the related neuropeptide FF (NPFF8), to gonadectomized (GNX) female rats evidenced significant, albeit modest, inhibitory effects on LH secretion only for RFRP3-8 and RFRP3-17, which were detectable at the high dose rage (1 nmol for RFRP3-8, 5 nmol for RFRP3-17). This moderate inhibitory action was also documented after icv administration of RFRP3-8 to intact and GNX male rats. In addition, systemic (intravenous) administration of RFRP3-8 decreased the circulating levels of both gonadotropins in GNX male rats. Likewise, RFRP3-8 inhibited basal and GnRH-stimulated LH secretion by pituitaries from GNX males in vitro. This inhibitory effect was blocked by the antagonist of RFRP receptors, RF9. In summary, our results support a putative inhibitory role of RFRP3 as ortholog of GnIH in the regulation of gonadotropin secretion in mammals, which appears to involve direct pituitary actions as well as potential central (hypothalamic) effects.

Signal pathway of GnRH-III inhibiting FSH-induced steroidogenesis in granulosa cells

Gonadotrophin-releasing hormone type 1 and type 2 have been demonstrated to inhibit follicle-stimulating hormone (FSH)-induced granulosa cell (GC) steroidogenesis. A third type of GnRH (GnRH-III) was also purified from salmon, its action on the FSH-regulated GC function, however is not clear. In the present study we demonstrated that the FSH-induced estrogen and progesterone production in cultured DES-treated GCs was significantly inhibited by GnRH-III. Furthermore, the FSH-stimulated steroidogenic acute regulatory protein and the enzymes for steroidigenesis, such as HSD3B2,aromatase and cytochrome P450 side-chain cleavage were also significantly suppressed by this peptide. The inhibitory action of GnRH-III on the FSH-induced steroidogenenisis was demonstrated via Akt and p38 mitogen-activated protein kinase signaling pathways through suppressing its own receptor expression. Further studies indicated that FSH could stimulate NR5A2 and upstream stimulatory factor (USF) activation, and their induction was significantly suppressed by the GnRH-III. Therefore, it is suggested that GnRH-III inhibiting FSH-induced steroidogenenisis in GCs might be by suppressing FSH-induced its own receptor expression via NR5A2 and USF transcriptional factors.

The ovary: basic biology and clinical implications

The classical view of ovarian follicle development is that it is regulated by the hypothalamic-pituitary-ovarian axis, in which gonadotropin-releasing hormone (GnRH) controls the release of the gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and that ovarian steroids exert both negative and positive regulatory effects on GnRH secretion. More recent studies in mice and humans indicate that many other intra-ovarian signaling cascades affect follicular development and gonadotropin action in a stage- and context-specific manner. As we discuss here, mutant mouse models and clinical evidence indicate that some of the most powerful intra-ovarian regulators of follicular development include the TGF-beta/SMAD, WNT/FZD/beta-catenin, and RAS/ERK1/2 signaling pathways and the FOXO/FOXL2 transcription factors.

Coordinated regulation of follicle development by germ and somatic cells

The continuum of folliculogenesis begins in the fetal ovary with the differentiation of the oogonia and their isolation within the primordial follicles. Primordial follicle activation is an enigmatic process, whereby some follicles enter the growing pool to become primary follicles, thereby embarking on an irreversible progression towards ovulation or atresia. This process is under the coordinated regulation of factors from the oocyte itself, as well as from the somatic cells of the ovary, in particular the theca and granulosa cells, which are structural components of the follicle. These two influences provide the principal stimuli for the growth of the follicle to the late preantral or early antral stage of development. The endocrine effects of the gonadotrophins FSH and LH are essential to the continued progression of the follicle and most atresia can be attributed to the failure to receive or process the gonadotrophin signals. The peri-ovulatory state has received intensive investigation recently, demonstrating a coordinated role for gonadotrophins, steroids, epidermal growth factor family proteins and prostaglandins. Thus, a complex programme of coordinated interaction of governing elements from both germ and somatic cell sources is required for successful follicle development.

[The effect of initial hormonal status of recipient animals on morphological state and endocrine function of ovarian tissue transplant]

The aim of investigation was a comparative analysis of morphofunctional characteristics of allografts of mature ovarian tissue and neonatal ovary depending on initial hormonal status of recipient animals. Rats' mature ovarian tissue and neonatal ovary were transplanted under renal capsule simultaneously with ovariectomy and 2 months later. Data analysis indicated that the development of ovarian tissue transplant was determined by its maturity and initial hormonal status of recipient. Mature ovarian tissue transplants preserve morphology and endocrine function to the 60th day after transplantation to the recipient animals with the initial hormonal status that corresponds to the norm. Neonatal ovary transplants are developed to the mature stage following transplantation to recipients with hormonal status that corresponded to the ovariectomized animals, that is, low concentration of sex hormones and an increased level of follicle-stimulating hormone.

Initiation of the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma) in the rat ovary and the role of FSH

PPARgamma is highly expressed in granulosa cells by 23 days post-partum (pp) and is down-regulated in response to the LH surge. We tested the hypothesis that high levels of FSH during the neonatal period trigger the expression of PPARgamma. To determine when PPARgamma expression is initiated, ovaries were collected from neonatal rats. Messenger RNA for PPARgamma was undetectable on day 1, low from days 5-14, and increased by day 19 pp (p < 0.05). PPARgamma was detected in select granulosa cells in primary/early secondary follicles. Messenger RNA for the FSH receptor was detected as early as day 1 and remained steady throughout day 19 pp. The FSH receptor was detected by immunoblot analysis in ovaries collected 1, 2, and 5-9 days pp. In a subsequent experiment, neonatal rats were treated with acyline (GnRH antagonist) which significantly reduced FSH (p < 0.05) but not levels of mRNA for PPARgamma. The role of FSH in the induction of PPARgamma expression was further assessed in ovarian tissue from FORKO mice. Both mRNA and protein for PPARgamma were identified in ovarian tissue from FORKO mice. In summary, the FSH/FSH receptor system is present in granulosa cells prior to the onset of expression of PPARgamma. Reducing FSH during the neonatal period, or the ability to respond to FSH, did not decrease expression of mRNA for PPARgamma. These data indicate that FSH is not a primary factor initiating the expression of PPARgamma and that other agents play a role in activating its expression in the ovary.

Timing of the ovarian circadian clock is regulated by gonadotropins

The timing of ovulation is critically important to the success of reproduction. Current thinking attributes the timing of ovulation to LH secretion by the pituitary, itself timed by signals from the hypothalamus. The discovery of an internal circadian timer in the ovary raises the possibility that ovulation is in fact timed by an interaction between clocks in the hypothalamus/pituitary and those in the ovary. We asked whether ovarian clocks were influenced by signals from the brain and pituitary. Ovaries of Period1-luciferase transgenic rats display circadian rhythms in vitro. To determine whether the phase of these rhythms is set by neural or endocrine signals, we surgically denervated or heterotopically transplanted ovaries with or without encapsulation in dialysis membranes. Animals' light-dark cycles were phase advanced or delayed 6 h, and the resetting of the ovarian clock was tracked by culturing ovaries at intervals over the next 12 d. Resetting trajectories of control, surgically denervated, and encapsulated ovaries were similar, demonstrating that endocrine signals are sufficient to transmit phase information to the ovary. We next evaluated LH and FSH as potential endocrine signals. Using the phase of Per1-luc expression in granulosa cell cultures, we demonstrated that both of these pituitary hormones caused large phase shifts when applied to the cultured cells. We hypothesize that the ovarian circadian clock is entrained by hormonal signals from the pituitary and that ovulation depends, in part, on the phase in the ovarian circadian cycle at which these signals occur.

The history of assisted human conception with especial reference to endocrinology

This review lecture is primarily concerned with the study of assisted human conception and especially in-vitro fertilization (IVF). It also places in perspective the role of endocrinology in history of IVF. A knowledge of the hypothalamic-pituitary control of ovulation, and of ovarian follicle dynamics is assumed. A detailed consideration of these topics, together with extensive references, are available in a recent textbook (Edwards and Brody, 1995). Many of the early pioneers studying animal reproduction combined reproductive physiology and endocrinology, especially Marshall, who analysed oestrous and menstrual cycles in many mammalian species. The clarification of the roles of pituitary gland and hypothalamus in the menstrual cycle and ovulation, and their regulation by steroidal feedbacks from the gonads gave an immense stimulus to studies on human reproduction (Smith and Engle, 1927; Lewis and Gregory, 1933; Harris, 1970). Three periods of research into assisted human conception are covered in this lecture including the initial work on the introduction of the endocrinology and embryology of human IVF, the rapid advances in technique as it expanded worldwide, and finally some of the recent remarkable advances in the field.

[Hormones and osteoporosis update. Possible roles of pituitary hormones, TSH and FSH, for bone metabolism]

Accumulating evidence clearly indicates both thyroid hormone and estrogen have a pivotal role in bone metabolism. Pituitary hormones, TSH and FSH, regulate circulating levels of thyroid hormone and estrogen, respectively. Recent works raise a possibility that either TSH or FSH also has its own direct effects on bone cells involved in bone resorption and formation. However, several investigations of genetically manipulated model mice and clinical data from patients with certain diseases have provided inconsistent results and we are not yet ready to be convinced whether or not either TSH or FSH is physiologically and pathophysiologically involved in controlling bone metabolism.

Hormonal regulation of male reproduction (with reference to infertility in man)

In mammals, pituitary control of spermatogenesis varies with age. In the rat, before puberty FSH is highly active whereas LH is not; after puberty it seems that LH alone is able to support spermatogenesis. The mode of action of hormones is discussed. In the human, in case of infertility due to hypogonadotrophic hypogonadism, spermatogenesis can be restored by HCG or HMG. The best results are obtained after simultaneous treatment with both hormones, LH activity being predominant.

Hormones and hormonal target cells in the testis

Studies over the last few years have greatly increased our knowledge about target cells for sex hormones and gonadotropins in the testis. A diagram illustrating our present state of knowledge is given in Fig. 1. LH is the principle stimulus of testosterone secretion by the Leydig cells. Direct effects of estrogens and androgens on these cells might modulate the response to LH. Androgens are apparently influencing the differentiation and the contractility of peritubular cells. FSH is the principle stimulus for Sertoli cell secretory function before puberty, although androgens are acting synergistically with FSH. After puberty, androgens alone are capable of maintaining on optimal secretory function of the Sertoli cells. In addition to normal secretory activity of the Sertoli cells, direct stimulation of the germ cells by androgens is needed in order maintain spermatogenesis.

Expression of bone morphogenetic protein receptor (BMPR) during perinatal ovary development and primordial follicle formation in the hamster: possible regulation by FSH

To understand whether bone morphogenetic protein plays any role in the formation of primordial follicles in the hamster, we examined the temporal and spatial expression of bone morphogenetic protein receptor (BMPR) mRNA and protein in embryonic (E) 13 through postnatal day (P) 15 ovarian cells and a possible regulation by FSH during the formation of primordial follicles on P8. BMPRIA and BMPRII mRNA levels were significantly higher than that of BMPR1B throughout ovary development. BMPRIA and BMPRII mRNA levels increased significantly on E14 and declined by P5 through P6. Whereas BMPRII mRNA increased again by P7, BMPRIA mRNA levels increased through P8 concurrent with primordial follicle formation. In contrast, BMPRIB mRNA levels increased greater than 10-fold on P7-9, with a further 3-fold increase by P10. BMPR proteins were low in the somatic cells and oocytes on E13 but increased progressively during postnatal development. BMPR expression in somatic cells increased markedly on P8. Whereas BMPRII expression declined by P10 and remained steady thereafter, BMPRIA protein expression fluctuated until P15 when it became low and steady. Overall, BMPRIB immunoreactivity also declined by P10 and then remained low in the interstitial cells through P15. FSH antiserum treatment on E12 significantly attenuated receptor mRNA and protein levels by P8, but equine chorionic gonadotropin replacement on P1 reversed the inhibition. Furthermore, FSH in vitro up-regulated BMPR levels in P4 ovaries. This unique pattern of BMPR expression in the oocytes and somatic cells during perinatal ovary development suggests that BMP may play a regulatory role in primordial follicle formation. Furthermore, FSH may regulate BMP action by modulating the expression of its receptors.

Inhibin A inhibits follicle-stimulating hormone (FSH) action by suppressing its receptor expression in cultured rat granulosa cells

Inhibin has long been considered as a suppresser of follicle-stimulating hormone (FSH) secretion from anterior pituitary through pituitary-gonad negative feedback to regulate follicle development. We demonstrated that addition of inhibin A could significantly suppress FSH-induced FSHR mRNA level in cultured rat granulosa cells (GCs) measured by real-time PCR. The inhibin A exerted its action mainly by inhibiting FSHR promoter activity. Furthermore, exogenous inhibin A could dramatically decrease FSH-induced P450arom and P450scc level and suppress progesterone and estradiol production in the cultured GCs, but it did not decrease forskolin-induced steroidogenesis, indicating that the inhibitory effect of inhibin A on FSH action may be upstream of cAMP signaling. Inhibin A was also capable of suppressing FSH-induced expression of steroidogenic factor 1 (SF-1) and androgen receptor, but stimulating DAX-1 expression in the culture. Our study has provided new evidence to show that inhibin A is capable of feedback antagonizing FSH action on GCs by reducing FSHR expression at ovarian level via a short feedback loop. Transcriptional factor receptors, such as SF-1, AR and DAX-1 were involved in this regulation.