Early follicle growth in the juvenile macaca monkey ovary: the effects of estrogen priming and follicle-stimulating hormone

Sphingosine-1-phosphate and its mimetic FTY720 do not protect against radiation-induced ovarian fibrosis in the nonhuman primate†

Oocytes are highly radiosensitive, so agents that prevent radiation-induced ovarian follicle destruction are important fertility preservation strategies. A previous study in rhesus macaques demonstrated that ovarian treatment with antiapoptotic agents, sphingosine-1-phosphate (S1P) and FTY720, its long-acting mimetic, preserved follicles following a single dose of 15 Gy X-ray radiation, and live offspring were obtained from FTY720-treated animals. However, it is unknown whether these antiapoptotic agents also protected the ovarian stroma from late effects of radiation, including vascular damage and fibrosis. Using ovarian histological sections from this study, we evaluated the vasculature and extracellular matrix in the following cohorts: vehicle + sham irradiation, vehicle + irradiation (OXI), S1P + irradiation (S1P), and FTY720 + irradiation (FTY720). One ovary from each animal was harvested prior to radiation whereas the contralateral ovary was harvested 10 months post-treatment. We assessed vasculature by immunohistochemistry with a PECAM1 antibody, hyaluronan by a hyaluronan binding protein assay, and collagen by picrosirius red and Masson's trichrome staining. Disorganized vessels were observed in the medulla in the OXI and S1P cohorts relative to the sham, but the vasculature in the FTY720 cohort appeared intact, which may partially explain fertoprotection. There were no differences in the hyaluronan matrix among the cohorts, but there was thickening of the tunica albuginea and fibrosis in the OXI cohort relative to the sham, which was not mitigated by either S1P or FTY720 treatment. Thus, the fertoprotective properties of S1P and FTY720 may be limited given their inability to protect the ovarian stroma against the late effects of radiation-induced fibrosis.

Usage of pharmaceutical contraceptive drug for controlling Eobania vermiculata snails by baits technique

The present study focused on evaluating the effects of oral administration of three different concentrations of Yasmin® combined contraceptive pills (estrogen and progesterone) on reproductive hormones levels, histology of the ovotestis and rate of oviposition of E. vermiculata for two months using baits technique. The levels of anti-müllerian hormone (AMH), Follicle stimulating hormone (FSH), Luteinizing hormone (LH), Estradiol (E2), Progesterone(PRG), Thyroid-stimulating hormone (TSH) and Testesterone (T) of treated snails were decreased with increasing the drug concentrations by percentages of -83.3%, -78.9%, - 59.6%,- 98.3 %, - 79.6 %, - 86.7% and 8.2%, respectively. Prolactin (PRL) level was significantly increased (86.9%) compared to control snails after 8 weeks of exposure. Histological investigations on the hermaphrodite glands of snails treated with 909 μg/gm. showed glandular hyperplasia, sloughing of germinal epithelium, acini sizes reduction, suppression of follicular growths, decreased luteinization and vasodilation. Male acini revealed histolytic of spermatogonia and mature sperms. The lowest concentration (303 μg/gm.) caused gradual decrease of the total egg counts that reach 50% at the 8^th week of treatment. Higher doses (606 and 909 μg/gm.) resulted in dramatic dwindling of egg numbers and inspiring complete egg cessation at the 7^th and 3^rd weeks of treatments, respectively. The applications of combined contraceptive drugs as baits give promising results for controlling high population densities of E. vermiculata snails at Sharkia Governorate, Egypt.

Direct actions of androgen, estrogen and anti-Müllerian hormone on primate secondary follicle development in the absence of FSH in vitro

STUDY QUESTION

What are effects of androgen, estrogen and anti-Müllerian hormone (AMH), independent of FSH action, on the development and function of primate follicles from the preantral to small antral stage in vitro?

SUMMARY ANSWER

Androgen and estrogen, but not AMH, promote follicle survival and growth in vitro, in the absence of FSH. However, their growth-promoting effects are limited to the preantral to early antral stage.

WHAT IS KNOWN ALREADY

FSH supports primate preantral follicle development in vitro. Androgen and estrogen augment follicle survival and growth in the presence of FSH during culture.

STUDY DESIGN SIZE, DURATION

Nonhuman primate model; randomized, control versus treatment groups. Rhesus macaque (n = 6) secondary follicles (n = 24 per animal per treatment group) were cultured for 5 weeks.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicles were encapsulated in 0.25% (w/v) alginate and cultured individually in modified alpha minimum essential media with (i) FSH (1 ng/ml; control), (ii) no FSH, (iii) no FSH + estradiol (E2; 100 pg/ml)/dihydrotestosterone (DHT; 50 ng/ml) and (iv) no FSH + AMH (50 ng/ml). In a second experiment, follicles were cultured with (i) FSH (1 ng/ml), (ii) no FSH, (iii) no FSH + E2 (1 ng/ml), (iv) no FSH + DHT (50 ng/ml) and (v) no FSH + E2/DHT. Follicle survival, antrum formation and growth pattern were evaluated. Progesterone (P4), E2 and AMH concentrations in culture media were measured.

MAIN RESULTS AND THE ROLE OF CHANCE

In the first experiment, FSH deprivation significantly decreased (P < 0.05) follicle survival rates in the no FSH group (16 ± 5%), compared to CTRL (66 ± 9%). E2/DHT (49 ± 5%), but not AMH (27 ± 8%), restored follicle survival rate to the CTRL level. Similarly, antrum formation rates were higher (P < 0.05) in CTRL (56 ± 6%) and E2/DHT groups (54 ± 14%), compared to no FSH (0 ± 0%) and AMH (11 ± 11%) groups. However, follicle growth rate after antrum formation and follicle diameter at week 5 was reduced (P < 0.05) in the E2/DHT group (405 ± 25 μm), compared to CTRL (522 ± 29 μm). Indeed, the proportion of fast-grow follicles at week 5 was higher in CTRL (29% ± 5), compared to E2/DHT group (10 ± 3%). No fast-grow follicles were observed in no FSH and AMH groups. AMH levels at week 3 remained similar in all groups. However, media concentrations of P4 and E2 at week 5 were lower (P < 0.05, undetectable) in no FSH, E2/DHT and AMH groups, compared to CTRL (P4 = 93 ± 10 ng/ml; E2 = 4 ± 1 ng/ml). In the second experiment, FSH depletion diminished follicle survival rate (66 ± 8% in control versus 45 ± 9% in no FSH, P = 0.034). E2 plus DHT (31.5 ± 11%) or DHT alone (69 ± 9%) restored follicle survival rate to the control (FSH) level as expected. Also, E2 plus DHT or DHT alone improved antrum formation rate. However, in the absence of FSH, E2 plus DHT or DHT alone did not support growth, in terms of follicle diameter, or steroid (P4 or E2) production after the antral stage.

LIMITATIONS REASONS FOR CAUTION

This study is limited to in vitro effects of E2, DHT and AMH during the interval from the secondary to small antral stage of macaque follicular development. In addition, the primate follicle pool is heterogeneous and differs between animals; therefore, even though only secondary follicles were selected, follicle growth and developmental outcomes might differ from one animal to another.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides novel information on the possible actions of estrogen and androgen during early follicular development in primates. Our results suggest that sequential exposure of preantral follicles to local factors, e.g. E2 and DHT, followed by gonadotropin once the follicle reaches the antral stage, may better mimic primate folliculogenesis in vivo.

STUDY FUNDING/COMPETING INTEREST(S)

Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Center for Translational Research on Reproduction and Infertility 5P50HD071836, and the NIH Primate Centers Program 8P510D011092. There are no conflicts of interest.

Follicle growth, ovulation, and luteal formation in primates and rodents: A comparative perspective

Ovarian function has a great deal of functional overlap between species; antral follicles grow in response to FSH, ovulation involves proteolysis, and the steroidogenic pathway is largely the same. However, embedded in these similarities are important differences that reflect the evolutionary and natural history of species and may focus future research into these critical areas. This review compares ovarian function of rats and mice with primates, focusing on estradiol and follicle growth, steroidogenesis and rupture during the periovulatory interval, and the formation of a functional corpus luteum, drawing the conclusion that careful comparison of species yields more functional information about both than studying them in isolation.

Should androgen supplementation be used for poor ovarian response in IVF?

Poor ovarian response is reported in 9-24% of IVF cycles. Several interventions have been proposed to improve the outcome, although evidence to support these has been scant. There has been interest in the use of adjuvant androgens in this context and a recent worldwide survey showed that nearly a quarter of IVF clinicians used dehydroepiandrosterone (DHEA) in poor responders. We examine the rationale for the use of adjuvant androgens and suggest that the current clinical uncertainty should be addressed by a randomized controlled trial of DHEA in poor responders.

The Macaque Ovary, with Special Reference to the Cynomolgus Macaque (Macaca fascicularis)

Concerning functional and morphological aspects, the ovary of the cynomolgus macaque is representative for the conditions in higher primates like humans and is therefore of major relevance in toxicological research. Against this background, a comprehensive overview about the cynomolgus macaque ovary is given from its embryonic appearance, throughout the adolescent and adult development until old age. The overview includes morphologic characteristics, a description of the different cell types, comparisons between the expression of selected receptors, and some details on hormonal effects if considered necessary for understanding the unit of ovarian morphology and function. The close correlation of hormones and morphological characteristics of the ovary and of the other reproductive organs is emphasized by several schematic drawings and images. Special emphasis is also laid on the comparison to the human organism indicating the similarity of both species and hence underlining the importance of the cynomolgus macaque as a model in toxicological research.

Competing Interests: This article was sponsored by Covance Inc. and Schering-Plough. Martina Zöller and Eberhard Buse are employed by Covance Inc. Eric Van Esch is employed by Schering-Plough. No other competing interests were declared.

Oestrogen receptor α and β, androgen receptor and progesterone receptor mRNA and protein localisation within the developing ovary and in small growing follicles of sheep

A first step to elucidating the roles that steroids may play in the processes of ovarian development and early follicular growth is to identify the cell types that are likely to be receptive to steroids. Thus, cell types expressing receptors for oestrogen (α and β form; ERα and ERβ respectively), androgen (AR) and progesterone (PR) were determined by in situ hybridisation and immunohistochemistry in ovine ovarian tissues collected during ovarian development and follicular formation (days 26–75 of fetal life) as well as during the early stages of follicular growth. Expression of ERβ was observed early during ovarian development and continued to be expressed throughout follicular formation and also during the early stages of follicular growth. ERβ was identified in germ cells as well as in the granulosa cells. At the large preantral stage of follicular growth, expression of ERα was also consistently observed in granulosa cells. AR was first consistently observed at day 55 of fetal life in stroma cells throughout the ovary. Within the follicle, expression was observed in granulosa and thecal cells from the type-2 to -3 stage of follicular growth. PR mRNA did not appear to be expressed during ovarian development (days 26–75 of gestation). However, PR (mRNA and protein) was observed in the theca of type-3 (small preantral) and larger follicles, with mRNA – but not protein – observed in granulosa cells of some type-4 and 5 follicles. Expression of ERβ, ERα and AR, as well as PR, was also observed in the surface epithelium and ovarian stroma of the fetal, neonatal and adult ovary. Thus, in sheep, steroid hormones have the potential to regulate the function of a number of different ovarian cell types during development, follicular formation and early follicular growth.

Ovarian follicular development is initiated during the hormone-free interval of oral contraceptive use

We evaluated ovarian follicular development in women during compliant use of oral contraceptives (OC). Thirty-six healthy women received: [35 microg ethinyl estradiol (21)/180 microg norgestimate (7), 215 microg norgestimate (7), 250 microg norgestimate (7)]; [30 microg ethinyl estradiol (21)/150 microg desogestrel (21)]; or [20 microg ethinyl estradiol (21)/100 microg levonorgestrel (21)] for 3 consecutive 28-day cycles. Transvaginal ultrasonography was performed every third day to monitor follicular development. If a follicle reached > or = 14 mm, ultrasonography was performed daily and blood drawn every other day to determine estradiol-17beta concentrations. Seventeen of 36 women (47%) grew follicles > or = 10 mm. Nine of the 17 women (53%) grew follicles > or = 14 mm, in association with increased serum concentrations of estradiol-17beta. Thirty-seven of 43 follicles > or = 10 mm (86%) emerged during the hormone-free interval (HFI). No ovulations were observed. Our results supported the hypothesis that follicular development to an ostensibly ovulatory diameter occurs during compliant OC use, in association with loss of endocrine suppression during the HFI.

Effects of testosterone, dihydrotestosterone, and 17β-estradiol on human ovarian tissue survival in culture

OBJECTIVE

To investigate the effects of T, dihydrotestosterone (DHT), and 17beta-estradiol on human ovarian stromal tissue survival in culture and to identify steroids capable of inhibiting cell death in vitro.

DESIGN

Prospective study.

SETTING

Academic research setting.

PATIENT(S)

Thirty women, aged 18-38 years, undergoing gynecological operations for benign conditions and eight women, aged 27-36 years, undergoing IVF because of tubal obstruction or male factor infertility.

INTERVENTION(S)

Cultured tissue was exposed to T, DHT, 17beta-estradiol, or the anti-androgen casodex.

MAIN OUTCOME MEASURE(S)

Immunohistochemistry for androgen receptor (AR), Southern blot analysis of DNA fragmentation, histology, and in situ end labeling of apoptotic DNA.

RESULT(S)

Androgen receptors were detected in the ovarian stroma and granulosa cells of the primordial follicles, although they were more clearly seen in primary follicles and more advanced-stage follicles. Testosterone only marginally suppressed ovarian tissue apoptosis in vitro. DHT was more effective than T, whereas 17beta-estradiol had no notable effect on the viability of the tissue. The effects of androgens on the ovarian tissue may be mediated through ARs, since blocking the receptors with an AR antagonist reversed the suppressive effect of DHT.

CONCLUSION(S)

DHT may be useful for enhancing human ovarian tissue survival in vitro.

The physiology of follicle selection

During the follicular phase of the primate menstrual cycle, a single follicle usually matures to the preovulatory stage and releases its oocyte for fertilization and the potential establishment of pregnancy. In assisted reproductive technology procedures, it is desirable to override the natural process of follicle selection to produce many oocytes that are capable of being fertilized and undergoing normal embryo development. The goal of this chapter is to summarize the current views regarding the natural process of follicle selection in primates and to discuss how this process may be amplified to produce a greater number of oocytes.

Ovarian follicular development during the use of oral contraception: a review

Over the past 40 years, alterations to the composition of oral contraceptives (OCs) have been made in attempts to reduce adverse effects and to improve patient compliance while maintaining contraceptive efficacy. However, there is growing evidence to indicate that reducing the estrogen dose to minimize adverse effects may have compromised the degree of hypothalamo-pituitary-ovarian suppression, particularly during the hormone-free interval (HFI) or following missed doses. Follicle development during OC use appears to occur in association with a loss of endocrine suppression during the HFI. This information provides a rationale for reducing or eliminating the HFI in OC regimens. There is also evidence for an increased risk of follicle development and ovulation in women who use delayed OC initiation schemes, such as the "Sunday Start" method. It is not currently known why some follicles ovulate during OC use while others regress or form anovulatory follicle cysts. Continued research about follicle development during OC use would provide insight into understanding the precise mechanisms of action underlying combined OCs, as well as those of continuous OC formulations and emergency contraceptive regimens.

Vascular endothelial growth factor stimulates preantral follicle growth in the rat ovary

The regulation of preantral follicle growth in mammals is poorly understood. The availability of an adequate vascular supply to provide endocrine and paracrine signals may be important during the early states of follicle growth as well as the later states of follicle selection and dominance. The objective of the present study was to investigate whether vascular endothelial growth factor (VEGF) plays a role in preantral follicular development in the rat ovary. Immature (age, 21 days) Sprague-Dawley rats were injected with 500 ng of VEGF in saline or 50 microg of diethylstilbestrol (DES) in oil under the bursa of one ovary. The contralateral ovary was injected with a corresponding volume of vehicle. Rats were killed 48 h later, and the ovaries were removed and analyzed histologically. Intrabursal administration of VEGF significantly increased the number of primary and small secondary, but not of large secondary, preantral follicles in the ovary, similar to the effect of DES (P < 0.05). The VEGF stimulated preantral follicle growth in a time- and dose-dependent manner. Subcutaneous DES administration increased the number of primary and secondary follicles, and both s.c. and intrabursal estrogen administration stimulated VEGF protein expression in the rat ovary. These data indicate that VEGF stimulates preantral follicular development in the rat ovary, is regulated by estrogen, and may be one of the factors that participate in the regulation of early follicle growth in the rat.

Ovarian follicular differentiation with prepubertal gonadotropin surges and gonadotropin priming in mice

Preantral follicles were mechanically isolated from the ovaries of 1.5 to 8 week old mice and cultured in vitro for 4 days in the presence or absence of either activin A or FSH. Plasma gonadotropin, estradiol and immunoreactive (IR) inhibin levels were measured. Cultured follicles showed stepwise changes in response to recombinant human (rh) FSH, with no response until 11 days, a gradual increase from 2 weeks, culminating in a strong response to rhFSH at 8 weeks. The response to activin A was vice versa. It enhanced the effect of rhFSH on preantral follicular growth of up to 4-week-old mice, but inhibited the effect of rhFSH in 8-week-old mice. The peak of the prepubertal gonadotropin surge was observed on day 11. Seven-day-old mice were treated with either luteinizing hormone releasing hormone (LHRH) or rhFSH or human chorionic gonadotropin (hCG) for 3 consecutive days from day 7, and follicles were collected on day 11. Those follicles showed enhanced response to rhFSH, no response to activin A, and an enhanced response to the combination of rhFSH and activin A, suggesting that the chronological changes in follicular response are a result of the prepubertal gonadotropin surge.

Effects of aromatase inhibition on in vitro follicle and oocyte development analyzed by early preantral mouse follicle culture

In vivo studies on folliculogenesis have documented a relation among intrafollicular steroid content, follicle growth, and oocyte development. This study examined how profound changes in androgen/estrogen ratio would affect mouse in vitro follicular development. Arimidex, a potent follicular aromatase inhibitor was used for this purpose. Early preantral follicles were cultured for 12 days up to the preovulatory stage. Oocyte's meiotic maturation, spindle and chromosome configurations, in vitro fertilization and preimplantation embryo development were evaluated. Compared to controls, Arimidex reduced E2 concentration in follicle culture medium by a factor 1000, and an expected simultaneous accumulation of testosterone was measured in the conditioned medium. Arimidex treatment provoked a dose-dependent earlier differentiation of the granulosa cells as judged by an earlier antrallike cavity formation and slightly elevated basal progesterone secretion. Follicle survival exceeded 98% in all groups and all follicles responded normally to HCG/EGF addition on day 12 by cumulus mucification. By the HCG ovulatory challenge, progesterone output was reduced in Arimidex supplemented groups suggesting preovulatory luteinization. These results indicate that in vitro mouse follicles can develop normally under very low levels of estrogens and that a local androgen increase by a factor 3 is not atretogenic. Oocyte growth did not differ among culture conditions. Arimidex treatment induced a dose dependent enhancement of GVBD and polar body formation rate in response to HCG at the end of culture. Spindle and chromosome analyses demonstrated that in all groups, 90% of the oocytes which extruded a polar body had also reached the MII stage. While most of the cultured MII oocytes had a normal spindle and well aligned chromosomes, significantly less oocytes were fertilized in the groups cultured in the presence of Arimidex. Once fertilized, however, there was found to be no difference for preimplantation embryo development between controls and Arimidex treatment. These data suggest that in mice a pronounced estrogenic environment is not essential for in vitro folliculogenesis. Drastic changes in the intrafollicular steroid concentrations do not disrupt meiotic maturation nor compromise early preimplantation development, but adversely affect fertilization of in vitro grown oocytes.

Are estrogens of import to primate/human ovarian folliculogenesis?

The notion that estrogens play a meaningful role in ovarian folliculogenesis stems from a large body of in vitro and in vivo experiments carried out in certain rodent models, (e.g., rats) wherein the stimulatory role of estrogen on granulosa cell growth and differentiation is undisputed. However, evidence derived from these polyovulatory species may not be readily generalizable to the monoovulatory subhuman primates, let alone the human. Only recently, significant observations on the ovarian role(s) of estrogen have been reported for the primate/human. It is thus the objective of this communication to review the evidence for and against a role for estrogens in primate/human ovarian follicular development with an emphasis toward the application of the concepts so developed to contemporary reproductive physiology and to the practice of reproductive medicine. The role(s) of estrogens will be examined not only by analyzing the physiological evidence to the effect that these hormones control ovarian function and follicular growth, but also by summarizing the molecular evidence for the existence and distribution of the cognate receptors.

Improving in vitro maturation of oocytes in the human taking lessons from experiences in animal species

One to three per cent of infertile women develop severe ovarian hyperstimulation syndrome after superovulation for assisted reproduction treatment (ART). This severe complication can be avoided when oocytes are obtained at an immature stage (germinal vesicle stage) out of small or medium-sized follicles. This hypothesis has been tested in several infertile women, but clinical pregnancies are disappointlingly low. This new approach in ART is still at an experimental phase and this treatment has still to be improved before routine clinical application. Experimental work in animals and humans suggest a beneficial effect in providing a short preliminary pretreatment with follicle-stimulating hormone to select for a developing cohort of follicles. The aspiration of oocyte cumulus complexes is carried out with a short needle applying reduced aspiration pressure. A crucial point is to provide the appropriate culture environment for the immature oocytes. An optimal cumulus-enclosed human oocyte culture system needs to be defined. The composition of the culture medium could be suggested by in vitro work carried out in animal models. As developmental competence is established during the latest phases of oocyte growth and is dependent on the storage of RNA, a prolonged in vitro maturation period (before inducing nuclear maturation) could provide the necessary transcriptional and translational changes. The conditions to achieve this improved cytoplasmic maturation by prolonging the in vitro culture remain to be defined. More objective noninvasive parameters for oocyte maturity are also needed to pursue research in this field.

In vitro manipulation of nonhuman primate gametes for embryo production and embryo transfer

Since nonhuman primates are closely related to humans and share many physical similarities, they are important for use in research areas such as human infectious diseases, reproduction, physiology, endocrinology, metabolism, neurology and longevity. To develop and maintain these animals, we must establish techniques for in vitro manipulation of spermatozoa and eggs. For a decade my research group has been conducting basic research to establish embryo manipulation techniques and to clarify the reproductive phenomena in nonhuman primates. This article summarizes the past research on in vitro manipulation of nonhuman primate gametes, from collection of reproductive cells and in vitro fertilization to the birth of offspring after embryo transfer, as well as the current status of these research areas. The studies summarized here will directly lead to the development of standard techniques for practical and comprehensive use in nonhuman primates.

Follicle culture after ovarian cryostorage

OBJECTIVES

Cryostorage of ovarian cortical tissue, before devastating chemo- and/or radiotherapy for cancer, permits survival of primordial and early preantral follicles. This work aims for a system allowing the long-term maturation in vitro (IVM) of small immature oocytes up to fertilisable metaphase II oocytes.

METHODS

A culture system allowing follicle attachment permitted the growth and maturation of isolated follicles (follicle diameter between 100 and 130 microns) from 14-day-old (prepuberal) mice. Follicle and oocyte development were observed under the inverted microscope and conditioned medium was used for biochemical analysis. Effects of recombinant gonadotrophins and oxygen tensions were studied for their specific effects on follicle development.

RESULTS

A 12-day culture period yielded full-grown oocytes which were able to complete meiosis (metaphase II). Live young were obtained after IVF and intra-uterine transfer of in vitro matured oocytes. Growth and maturation were only successful when recombinant gonadotropins were added and when the incubator had a 20% oxygen tension. This system enabled the growth of early preantral follicles after cryopreservation: 80% of frozen and thawed follicles survived up to culture-day 12 and yielded a comparable blastocyst formation rate as in controls.

CONCLUSIONS

The mouse model suggests that IVM is a valuable option after oocyte storage. The development of a comparable system for long-term culture of human follicles will imply the acquisition of non-invasive techniques to appreciate oocyte's maturity and developmental capacity.

Androgens stimulate early stages of follicular growth in the primate ovary

The concept that androgens are atretogenic, derived from murine ovary studies, is difficult to reconcile with the fact that hyperandrogenic women have more developing follicles than normal-cycling women. To evaluate androgen's effects on primate follicular growth and survival, normal-cycling rhesus monkeys were treated with placebo-, testosterone-(T), or dihydrotestosterone-sustained release implants, and ovaries were taken for histological analysis after 3-10 d of treatment. Growing preantral and small antral follicles up to 1 mm in diameter were significantly and progressively increased in number and thecal layer thickness in T-treated monkeys from 3-10 d. Granulosa and thecal cell proliferation, as determined by immunodetection of the Ki67 antigen, were significantly increased in these follicles. Preovulatory follicles (> 1 mm), however, were not increased in number in androgen-treated animals. Follicular atresia was not increased and there were actually significantly fewer apoptotic granulosa cells in the T-treated groups. Dihydrotestosterone treatment had identical effects, indicating that these growth-promoting actions are mediated by the androgen receptor. These findings show that, over the short term at least, androgens are not atretogenic and actually enhance follicular growth and survival in the primate. These new data provide a plausible explanation for the pathogenesis of "polycystic" ovaries in hyperandrogenism.

Steroid receptors and action in the primate follicle

Studies localizing steroid receptor (R) proteins and their mRNAs to the primate ovary are consistent with a local role for progesterone (P) and androgen (A) in modulating follicle growth and/or maturation via classic R-mediated pathways, but data in support of estrogen (E) action remain equivocal. Investigations of the hypothesis that steroids play a pivotal role in folliculogenesis or gametogenesis in macaques receiving inhibitors of steroid enzyme synthesis and in women with congenital steroid enzyme deficiencies reveal that (a) antral follicle growth, maturation, and luteinization, as well as oocyte meiosis, do not require high or increasing E levels; (b) elevated A to E ratios are detrimental to the gametogenic functions of the primate follicle, but do not alter growth and maturation of antral follicles; and (c) ovulation and luteinization of the mature follicle are dependent on local P actions. The genomic actions of steroids likely vary between compartments and with the developmental state of the follicle; however, potential nongenomic actions of steroids in follicles remain largely undefined. Future advances will rely on identification of discrete biochemical, morphological, and functional correlates of steroid hormone action in the somatic and gametogenic compartments of the primate follicle throughout its life cycle.

Ovarian control of follicle development

A variety of ovarian autocrine and paracrine factors may modulate folliculogenesis and steroid production. The developmental program that leads to the production of a dominant follicle involves a precise quantitative and temporal pattern of expression of a large number of genes. Follicle-stimulating hormone plays an essential role in this process, and no other ligand by itself can serve in this regulatory capacity. It is clear that a variety of growth factors can modulate follicle-stimulating hormone action by autocrine and paracrine mechanisms. Advances in the understanding of the role of growth factors, particularly the family of insulin-like growth factor-related proteins, in regulating follicle-stimulating hormone action are discussed. It is likely that complex interactions exist between follicle-stimulating hormone and the growth factors. Significantly, growth factor regulation by pituitary gonadotropins is probably a central feature of their expression. With increased understanding of the ovarian control of follicle development, it is hoped that newer and more effective regimens for synchronous follicular and oocyte maturation can be realized.

Role and site of estrogen action in follicular atresia

Subsequent to an initial understanding that estrogen was only stimulatory to folliculogenesis, we have come full circle to the present recognition that many actions of estrogen are inhibitory to follicular function. The development of this interpretation has frequently been associated with the controversial issue o f the likely site o f estrogen action, especially in primates, where much of the evidence has been amassed. The accumulated findings in a variety of species seem to demonstrate clearly that at least part of the atretogenic effect of estrogen is exerted directly on the ovary, apparently by interaction with the nuclear estrogen receptor. Recent observations include identification of messenger RNAs for the estrogen receptor and for creatine kinase in the macaque ovary, and a current focus is to localize messages within specific compartments of the ovary.