Number Of Healthy Antral Follicles Research Articles

Long-term chronic stress exposure induces PCO phenotype in rat.

Thus far the effects of chronic stress on the ovary were studied for shorter durations. However, responses of the ovary may vary with durations of exposure to stress. Hence, we investigated the responses of the ovary following exposure to different durations of chronic stress. Exposure of rats to restraint (1 h) and after a gap of 4 h to forced swimming (15 min) daily for 4 or 8 weeks resulted in significant decreases in the activities of the ovarian antioxidant enzymes, 3β-hydroxysteroid dehydrogenase and percentage of healthy granulosa cells with concomitant increases in the number of atretic follicles, the percentage of apoptotic granulosa cells and ovarian malondialdehyde concentration. However, the response of the ovary to similar stress regime for 12 weeks was paradoxical as there were increases in the activities of ovarian antioxidant enzymes and 3β-hydroxysteroid dehydrogenase, the number of healthy antral follicles, and decreases in ovarian malondialdehyde concentration and percentage of apoptotic granulosa cells. These changes were accompanied by hyperglycaemia and an increase in the serum levels of insulin, testosterone and oestradiol. In addition the cystic follicles were found in the ovaries of these rats. However, the number of oestrous cycles and active corpora lutea showed significant decrease in all the durations of stress exposure. The results demonstrate a differential response of ovary to short- and long-term exposure to chronic stress.

Follicle development, endocrine profiles and ovulation rate in adult Merino ewes: effects of early nutrition (pre- and post-natal) and supplementation with lupin grain

In adult ewes, we tested whether ovarian function, including the response to short-term supplementation, was affected by the nutrition of their mothers during the pre-/post-natal period. A 2×2 factorial design was used with nutrition in early life (low or high) and a 6-day supplement (with or without) as factors. All ewes received three prostaglandin (PG) injections 7 days apart, and the supplement (lupin grain) was fed for 6 days from 2 days after the second until the third PG injection. We measured reproductive and metabolic hormones, studied follicle dynamics (ultrasonography), and evaluated granulosa cell numbers, aromatase activity and oestradiol (E2) concentrations in follicular fluid in healthy follicles at days 3 and 7 of supplementation. Ovulation rate was increased by 25% by exposure to high pre-/post-natal nutrition (1.5 vs 1.2; P<0.05), in association with a small decrease in FSH concentrations (P=0.06) and a small increase in insulin concentrations (P=0.07). The number of healthy antral follicles was not affected. Acute supplementation increased the number of granulosa cells (3.7±0.2 vs 3.0±0.2 million; P<0.05) in the largest follicle, and the circulating concentrations of E2 (4.6±0.3 vs 3.9±0.3 pmol/l; P<0.05) and glucose (3.4±0.03 vs 3.3±0.03 mmol/l; P<0.01). Both early life nutrition and acute supplementation appear to affect ovulation rate through changes in glucose-insulin homoeostasis that alter follicular responsiveness to FSH and therefore E2-FSH balance.

The Yin and Yang of WNT4 Signaling in the Adult Gonad.

The WNTs are a family of secreted glycoprotein signaling molecules best known for the multiple roles that they play during embryonic development. WNT signaling first attracted the attention of the reproductive biology research community a little over a decade ago, when a groundbreaking study by Vainio et al. demonstrated that the ablation of Wnt4 in female mice causes partial sex-reversal and oocyte loss. More recently, the regulated expression of several WNTs and WNT signaling effectors has been shown to occur in adult male and female gonads. For instance, in mice, WNT4 expression persists in ovarian granulosa cells after birth, and is markedly induced during ovulation/luteinization, strongly suggesting a role for WNT4 in adult ovarian physiology. To define the function(s) of WNT4 in postnatal granulosa cells, we used a conditional gene targeting approach. We showed that Wnt4flox/-;Amhr2tm3(cre)Bhr/+ mice had reduced ovary weights, produced smaller litters, and had only a quarter of the normal number of healthy antral follicles at puberty. RTPCR analyses of Wnt4flox/-;Amhr2tm3(cre)Bhr/+ granulosa cells and cultured granulosa cells that overexpress WNT4 demonstrated that WNT4 regulates the expression of Star, Cyp11a1 and Cyp19, steroidogenic genes previously identified as downstream targets of the WNT signaling effector CTNNB1 (β-catenin). Decreased serum progesterone levels were found in immature, gonadotropin-treated Wnt4flox/-;Amhr2tm3(cre)Bhr/+ mice. Together, these data indicated that WNT4 is required for normal antral follicle development, and may act by regulating granulosa cell functions including steroidogenesis. In male mice, ourselves and others have shown that constitutive activation of CTNNB1 in the Sertoli cells of the Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ model results in progressive germ cell loss and sterility. More recently, we sought to determine if the latter phenotype could be due to a loss of spermatogonial stem cell (SSC) activity. Reciprocal SSC transplants between Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ and wild-type mice showed that Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ testes lose SSC activity over time, and cannot support colonization by donor SSCs. Microarray analyses showed that CTNNB1 induces the expression of genes associated with the female sex determination pathway in Sertoli cells, including Wnt4. We therefore tested the effects of exogenous WNT4 on SSC-enriched germ cell cultures, and found that WNT4 reduced germ cell numbers due to increased apoptosis and reduced SSC capacity to colonize recipient testes. Conversely, conditional inactivation of Wnt4 in the Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ model rescued spermatogenesis and male fertility, indicating that WNT4 is the major effector downstream of CTNNB1 responsible for germ cell loss. Taken together, our data indicate diametrically opposed functions for WNT4/CTNNB1 signaling in the adult female and male gonad: a powerful positive regulator of follicle development on the one hand, an equally powerful negative regulator of spermatogenesis on the other. (Supported by the Canadian Institutes of Health Research and the National Sciences and Engineering Research Council of Canada). (platform)

Methoxychlor Induces Atresia and Decreases Estradiol Levels in Antral Follicles Simultaneously.

The endocrine disruptor methoxychlor (MXC) is a chlorinated organic pesticide which was first registered for use in 1948 and now is widely used in many countries against various species of insects that attack field crops, trees, vegetables, fruits, gardens, stored grain, livestock and domestic pets. MXC exposure is highest in people working in manufacturing industries, people living near farms, livestock, and in pet owners treating pests with MXC. MXC exposure causes adverse effects on reproductive functions in adult females, including altered estrous cyclicity, reduced fertility, and ovarian atrophy. MXC has been shown to target antral follicles. Specifically, it decreases the number of healthy antral follicles and increases the number of atretic antral follicles in adult female mice. Previous studies have shown that MXC induces atresia and decreases estradiol levels after 96 hours of follicle culture. The goal of the present study was to determine whether MXC induces atresia and decreases estradiol levels earlier than 96 hours of culture. Further, the present study was designed to determine whether MXC-induced changes in atresia precede MXC-induced changes in estradiol levels or vice versa. To complete these goals, antral follicles were mechanically isolated from ovaries of CD1 female mice aged 35-40 days. The isolated antral follicles (10-15 per treatment) were cultured in supplemented alpha-minimum essential media in the presence of dimethylsulfoxide (control; DMSO) or MXC (1, 10, 100 µg/ml) for 24 and 48 hours at 37°C and 5%CO2. After culture, the media was collected and follicles were fixed in Dietrick solution. Fixed follicles were embedded in plastic blocks, cut into 2 µm sections, stained with Lee's methylene blue-basic fuchsin, and graded for atresia on a scale of 1 to 4 based on the percentage of apoptotic bodies (1=0%, 2=<10%, 3=10-30%, and 4=>30% apoptotic bodies). The media was subjected to measurements of estradiol levels by enzyme-linked immunosorbent assays. The results show that MXC does not induce atresia at 24 hours, but it does induce atresia by 48 hours (24 hours: DMSO = 1.73 ± 0.11, MXC1 µg/ml = 1.59 ± 0.16, MXC10 µg/ml = 1.78 ± 0.20, MXC100 µg/ml = 1.90 ± 0.16; 48 hours: DMSO = 1.25 ± 0.14, MXC1 µg/ml = 1.79 ± 0.09, MXC10 µg/ml = 2.22 ± 0.15, MXC100 µg/ml = 4 ± 0; n=3 separate experiments; p ≤ 0.05 for DMSO versus MXC at 48 hours). The results also indicate that MXC does not alter estradiol levels at 24 hours, but it does decrease estradiol levels by 48 hours (24 hours: DMSO = 17.10 ± 4.98, MXC1 µg/ml = 18.73 ± 2.50, MXC10 µg/ml = 26.46 ± 7.95, MXC100 µg/ml = 18.63 ± 4.27 pg/ml; 48 hours: DMSO = 599.38 ± 68.97, MXC1 µg/ml = 225.65 ± 18.79, MXC10 µg/ml = 120.48 ± 35.31, MXC100 µg/ml = 32.85 ± 2.97 pg/ml; n=3 separate experiments; p ≤ 0.05 for DMSO versus MXC at 48 hours). Collectively, these data suggest that MXC decreases estradiol levels and induces atresia as early as 48 hours and that these effects of MXC on antral follicles occur simultaneously. Support: NIH R01 ES012893 and the Environmental Toxicology Program at UIUC. (poster)

WNT4 is required for normal ovarian follicle development and female fertility.

To study the role of WNT4 in the postnatal ovary, a mouse strain bearing a floxed Wnt4 allele was created and mated to the Amhr2(tm3(cre)Bhr) strain to target deletion of Wnt4 to granulosa cells. Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had reduced ovary weights and produced smaller litters (P<0.05). Serial follicle counting demonstrated that Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice were born with a normal ovarian reserve and maintained normal numbers of small follicles until puberty but had only 25.2% of the normal number of healthy antral follicles. Some Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had no antral follicles or corpora lutea and underwent premature follicle depletion. RT-PCR analyses of Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) granulosa cells and cultured granulosa cells that overexpress WNT4 demonstrated that WNT4 regulates the expression of Star, Cyp11a1, and Cyp19, steroidogenic genes previously identified as downstream targets of the WNT signaling effector CTNNB1. Decreased serum progesterone levels were found in immature, gonadotropin-treated Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice (P<0.05). WNT4- and CTNNB1-overexpressing cultured granulosa cells were analyzed by microarray for alterations in gene expression, which showed that WNT4 regulates additional genes involved in late follicle development via the WNT/CTNNB1 signaling pathway. Together, these data indicate that WNT4 is required for normal antral follicle development and may act by regulating granulosa cell functions including steroidogenesis.

Methoxychlor Reduces Aryl Hydrocarbon Receptor Levels in the Mouse Ovary.

The endocrine disruptor methoxychlor (MXC) is a chlorinated organic pesticide which was first registered for use in 1948 and now is widely used as a replacement for dichlorodiphenyltrichloroethane (DDT). It is available in the form of wettable powders, dusts, emulsifiable concentrates, liquids, and pressurized liquids. It is primarily used against various species of insects that attack field crops, trees, vegetables, fruits, gardens, stored grain, livestock, and domestic pets. MXC exposure has adverse effects on reproductive function in adult females, including altered estrous cyclicity, fertility, and ovarian atrophy. MXC has been shown to target antral follicles; specifically it decreases the number of healthy antral follicles and increases the number of atretic antral follicles. The mechanism by which MXC targets antral follicles is unknown. However, studies have indicated that MXC may bind to estrogen receptors α and β (ERα and β) as well as the aryl hydrocarbon receptor (AhR) in non-ovarian cells. These previous studies raise the possibility that MXC causes ovarian atresia through ERα, ERβ or AhR pathways. As a first step in determining whether this is the case, we hypothesized that MXC induces ovarian toxicity by altering the expression of selected endocrine receptors (ERα, ERβ, and AhR). To test this hypothesis, CD-1 female mice aged 39 days were dosed with sesame oil (control) or MXC (16, 32, and 64 mg/kg/day) daily for a period of 20 days. After dosing, whole ovaries were collected from the mice, snap frozen, and subjected to real time PCR analyses for expression of ERα, ERβ, and AhR. In some experiments, antral follicles were isolated from control and MXC-treated mice and subjected to real time PCR for expression of ERα, ERβ, and AhR levels. Our results indicate that MXC does not alter ERα and ERβ expression in the ovary (ERα: sesame control = 1.58 ± 0.27 genomic equivalents (ge), MXC 64 mg/kg/day = 2.20 ± 0.38 ge, n=6, p = 0.68; ERβ: sesame control = 1.20 ± 0.20 ge, MXC 64 mg/kg/day = 1.66 ± 0.23 ge, n=6, p = 0.43). In contrast, MXC significantly decreases the expression of AhR in isolated antral follicles compared to control (sesame control = 0.69 ± 0.17 ge, MXC 64 mg/kg/day = 0.14 ± 0.04 ge, p = 0.012). These data suggest that MXC might be causing antral follicle toxicity by decreasing the expression of the AhR, but not by altering expression of ERα and ERβ.Support: NIH R01 ES012893 and NIH R01 HD047275.

Reduced recruitment and survival of primordial and growing follicles in GH receptor-deficient mice

GH influences female fertility. The goal of the present study was to obtain more insight into the effect of loss of GH signalling, as observed in humans suffering from Laron syndrome, on ovarian function. Therefore, serial paraffin sections of ovaries of untreated and IGF-I-treated female GH receptor knock-out (GHR/GHBP-KO) mice were examined to determine the follicular reserve and the percentage of follicular atresia in each ovary. Our observations demonstrate that the amount of primordial follicles was significantly elevated in GHR/GHBP-KO mice, while the numbers of primary, preantral and antral follicles were lower compared with wild-type values. The reduced number of healthy growing follicles in GHR/GHBP-KO mice was accompanied by a significant increase in the percentage of atretic follicles. IGF-I treatment of GHR/GHBP-KO mice for 14 days resulted in a reduced number of primordial follicles, an increased number of healthy antral follicles, and a decreased percentage of atretic follicles. The results of the present study suggest that GH may play a role, either directly or indirectly, via for instance IGF-I, in the recruitment of primordial follicles into the growing pool. Furthermore, GH seems to protect antral follicles, directly or indirectly from undergoing atresia.

Intraovarian excess of nerve growth factor increases androgen secretion and disrupts estrous cyclicity in the rat.

A single injection of estradiol valerate induces a form of cystic ovary resembling some aspects of the human polycystic ovarian syndrome. Preceding the development of follicular cysts, there is an increase in intraovarian synthesis of nerve growth factor (NGF) and the low affinity NGF receptor (p75 NGFR). Selective blockade of NGF actions and p75 NGFR synthesis in the ovary restored estrous cyclicity and ovulatory capacity in estradiol valerate-treated rats, suggesting that an increase in NGF-dependent, p75 NGFR-mediated actions within the ovary contributes to the development of cystic ovarian disease. We have tested this hypothesis by grafting NGF-producing neural progenitor cells into the ovary of juvenile rats that have been induced to ovulate precociously by a single injection of PMSG. The NGF-producing cells, detected by their content of immunoreactive p75 NGFR material, were found scattered throughout the ovary with some of them infiltrating the granulosa cell compartment of large, precystic follicles. Ovarian NGF content was 2-fold higher than in the ovary of rats receiving control cells. Estrous cyclicity was disrupted, with the animals showing prolonged periods of persistent estrus, and an almost continuous background of vaginal cornified cells at other phases of the estrous cycle. Morphometric analysis revealed that the presence of NGF-producing cells neither reduced the total number of corpora lutea per ovary nor significantly increased the formation of follicular cysts. However, the ovaries receiving these cells showed an increased incidence of precystic, type III follicles, accompanied by a reduced number of healthy antral follicles, and an increased size of both healthy and atretic follicles. These changes in follicular dynamics were accompanied by a selective increase in serum androstenedione levels. The results show that an abnormally elevated production of NGF within the ovary suffices to initiate several of the structural and functional alterations associated with the development of follicular cysts in the rat ovary.

Hypophysectomy of the cyclic mouse. II. Effects of follicle-stimulating hormone (FSH) and luteinizing hormone on folliculogenesis, FSH and human chorionic gonadotropin receptors, and steroidogenesis.

This study was designed to determine the effects of FSH and LH on ovarian follicular development in adult hypophysectomized (HX) mice. Twelve days after HX, the animals received s.c. injections of ovine FSH (oFSH; 4 micrograms/day) or oFSH (4 micrograms/day) plus ovine LH (oLH; 2 micrograms/day) twice a day for 1 to 4 days. After 4 days of treatment with FSH alone, the number of preantral follicles (stages 1-3) increased significantly compared to that in HX controls and reached cyclic numbers; however, incorporation of [3H]thymidine into these preantral follicles as compared to HX controls did not increase. The number of healthy antral follicles (stages 4-5) and incorporation of [3H]thymidine into stage 5 follicles started to increase after only 1 day of treatment with FSH, and the number of atretic follicles concomitantly decreased. Treatment with both FSH and LH for 1 to 4 days increased the number of healthy follicles and restored DNA synthesis at all stages (1-5) to normal levels. Two days of replacement with FSH or FSH plus LH was required for follicles to attain preovulatory size (stage 6). FSH alone induced FSH and hCG receptors in granulosa cells, but without the induction of thecal LH/hCG receptors; FSH induced production of progesterone and androstenedione by stage 6 follicles, but not estradiol (E2) accumulation in the incubation medium or in the serum. Combined FSH and LH induced hCG receptors in the theca and interstitium, and also restored follicular E2 production to proestrous values. LH alone increased only the number of stage 2-3 follicles. Unexpectedly, LH alone also induced thecal hCG receptors as well as FSH receptors in granulosa cells of preantral and antral follicles. The present results demonstrate that FSH is essential for follicular growth at all stages and for prevention of atretic antral follicles. Both FSH and LH are necessary for regulation of follicular development and differentiation from the earliest preantral to preovulatory stages.

Studies on Regulatory Mechanisms for Gonadotropins Secretion in Lactating Rats

The present study was designed to clarify mechanisms responsible for regulation of FSH and LH secretion and ovarian follicular maturation during lactation in rats. Throughout lactation in rats, plasma levels of follicle-stimulating hormone (FSH) remain within the range normally found during the diestrous phase of the estrous cycle, regardless of litter size, although levels of luteinizing hormone (LH) in plasma are consistently lower in dams nursing 8 pups than in dams nursing 2 pups. All antral follicles larger than 401μm in diameter degenerate during the first half of lactation and do not reappear until the second half of lactation in rats nursing 8 pups. Healthy follicles of this size, however, are always present in mothers nursing 2 pups. These changes in follicular degeneration corresponded with a decrease in concentrations of plasma LH in the first half of lactation, and follicular development was noted with an increase in basal levels of plasma LH in the second half of lactation. Corpora lutea formed after postpartum ovulation secrete a large amount of progesterone under the influence of prolactin released as a result of suckling. Despite continued suckling, plasma concentrations of prolactin and progesterone decline gradually and a slight increase in plasma concentrations of estradiol-17β occurs during the second half of lactation. Concentrations of bioactive and immunoreactive inhibin in plasma vary with the number of healthy antral follicles and no positive correlation has been observed with luteal function throughout lactation in the rat.On the basis of the present results it is indicated that 1) tonic secretion of LH is an important factor in normal follicular maturation and maintenance in lactating rats, 2) the suckling stimulus, rather than ovarian factors, is mainly responsible for the suppression of FSH as well as LH secretion during the first half of lactation in rats nursing 8 pups. On the other hand, during the second half of lactation in rats nursing 8 pups, ovarian inhibin plays a primary role in the suppression of FSH secretion, whereas ovarian steroids act to suppress LH secretion. The present findings also indicate that 3) the suckling stimulus alone suppressed the secretion of both LH and FSH and this effect may be mediated by the inhibition of LH releasing hormone (LH-RH) secretion from the hypothalamus, 4) the suckling-induced inhibition of LH-RH may be primarily mediated by endogenous corticotropin-releasing hormone and opioid peptides and 5) the pituitary-adrenal system is capable of influencing the maintenance of a normal secretion of gonadotropins and prolactin as well as the maintenance of ovarian function during the lactation in the rat.

The recovery of follicular oocytes from the rabbit ovary during prepubertal age and in vitro maturation of their oocytes.

The recovery of oocytes from minced ovarian tissues was examined as well as the ability of their oocytes to mature to Metaphase II in immature rabbits (2-, 3-and 4-month-old), treated with PMSG or not. The number of visible large follicles (over 1 mm in diameter) on the ovary, as well as ovarian weight, increased with advancing age and the increase was remarkable in 3-and 4-month-old PMSG-treated does. Blood follicle formation was marked only in PMSG-treated does 4-month-old. In histology, many antral follicles were grown in 3-and 4-month-old does; especially the number of healthy follicles >700μm in diameter was markedly increased in 3-month-old PMSG-treated does. Ratios of the number of healthy antral follicles >700μm in diameter were still higher in the PMSG-treated does than in non-treated does. In oocytes recovered by mincing ovaries using a pair of razors, only oocytes surrounded by a thick layer of cumulus cells (Type I oocyte) were selected and cultured for in vitro maturation. The number of Type I oocytes was increased by PMSG treatment at each age; the number in 3-month-old does was the highest (3 times that in non-treated does). Ratios of Type I oocytes which emitted the first polar body in in vitro culture increased with advancing age up to 4 months, though the ratios remained at lower levels than in adult does. There were no differences in the maturation ratios between PMSG-treated and non-treated groups. These results show that oocytes to undergo in vitro maturation are obtainable from the ovary in immature rabbits, especially in 3-month-old PMSG-treated does.

Peripheral blood levels of immunoreactive inhibin during pseudopregnancy, pregnancy and lactation in the rat

Concentrations of inhibin in peripheral blood were determined by radioimmunoassay in pseudopregnant, pregnant and lactating rats and correlated with the status of follicular development, luteal function in the ovaries and placental function. In pseudopregnant rats, plasma concentrations of inhibin remained relatively high from days 2 to 12 of pseudopregnancy and no significant changes occurred throughout pseudopregnancy. In pregnant rats, a marked decline in plasma concentrations of inhibin occurred between days 6 and 14 followed by an abrupt increase on days 20 and 21. In lactating rats, plasma concentrations of inhibin were consistently lower in dams nursing eight pups than in dams nursing two pups. Plasma concentrations of inhibin remained low during the early stages of lactation followed by a significant increase during the late stages in dams nursing eight pups. These changes in inhibin during the period of lactation correlated with those of plasma concentrations of LH, but not with those of oestradiol-17 beta, testosterone and progesterone. Throughout pseudopregnancy, pregnancy and lactation, on the other hand, plasma concentrations of FSH were within the range of dioestrous levels. These findings indicate that concentrations of inhibin in peripheral plasma vary with the number of healthy antral follicles and no positive correlation was observed with luteal function during the luteal phase in rats. The results also suggest that inhibin is a more direct index of follicular development than oestradiol-17 beta in rats.

Compensatory ovulatory mechanisms operative after first ovulation in rats unilaterally ovariectomized prepubertally.

Ovarian steroid contents and serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured during the days after first ovulation in rats unilaterally ovariectomized in late prepuberty. In addition, follicle counts were made at second estrus and second metestrus. During the cycle following first ovulation, ovarian estradiol contents in unilaterally ovariectomized (ULO) rats were significantly increased as compared to intact rats on the day of metestrus, on diestrus 1 and on second estrus. Ovarian progesterone was significantly increased on the days of metestrus, on diestrus 1, second proestrus and second estrus, but no differences were seen in ovarian androgen contents. After ULO there was an indication of an augmented FSH surge at the first and the second ovulation. Follicle counts revealed that the total number of healthy as well as of atretic antral follicles on the day of second estrus was significantly increased after ULO, due to increased numbers of the smallest antral follicles. At second metestrus the number of larger antral follicles (350-500 micron 3) and the total number of healthy antral follicles was higher after ULO. It is concluded that the compensatory process after ULO involved increased recruitment of small antral follicles. Activities in the remaining ovary were not simply doubled but a new hormonal balance was established.

Inhibin activity in ovarian venous plasma during pregnancy, pseudopregnancy and lactation in the rat.

Inhibin activity in ovarian venous plasma and concentrations of FSH and LH in peripheral plasma were examined in rats during pregnancy, pseudo-pregnancy and lactation and correlated with the status of the ovarian follicular population. Inhibin activity was assessed in terms of its ability to suppress the 48 h secretion of FSH in a dispersed anterior pituitary cell culture system. FSH and LH were measured by radioimmunoassay. Inhibin activity in ovarian venous plasma was always detected when Graafian follicles were present, such as Days 3, 5 and 10 of pseudopregnancy, Days 5, 10, 20 and 21 of pregnancy, Days 3, 5 and 10 of lactation in mothers with 2 pups and Days 0, 10, 15 and 20 of lactation in mothers with 8 pups. Inhibin activity in ovarian venous plasma was undetectable whenever healthy antral follicles were absent, such as Days 15 of pregnancy and Days 2, 3, 4 and 5 in lactating rats with 8 pups. No FSH surge occurred during these periods of low inhibin activity in ovarian venous plasma, in striking contrast to normal cyclic rats. These results indicate that inhibin activity in ovarian venous plasma of rats varies with the number of healthy antral follicles during the luteal phase. Ovarian inhibin in conjunction with other factors such as steroid hormones or the suckling stimulus may be involved in the regulation of FSH secretion in the luteal phase of the rat.

FOLLICULAR DEVELOPMENT IN THE IMMATURE GUINEA-PIG

A method for making statistical comparisons between populations and types of antral follicles within the ovary of the immature guinea-pig is described. This was used to demonstrate that atresia in the antral follicles first appeared at around 14 days of age, but that the population of healthy antral follicles remained remarkably consistent throughout the second half of the prepubertal period, since neither the total number of healthy antral follicles nor the proportion of atretic follicles changed significantly. However, the maximum diameter of the antral follicles gradually increased with age, from 400 micron at 7 days to 1000 micron at 28 days, 4 days before the vagina first opended. Because the percentage distribution of all types of follicles was so consistent at any age, although individuals showed substantial differences in the numbers of follicles within each ovary, it is suggested that mechanisms operate which regulate the total population of antral follicles within the ovary.

Effect of oestrogen and progesterone on pituitary goandotropic content of the cyclic hamster.

ABSTRACT Oestradiol cyclopentylpropionate (ECP) and progesterone alter the normal pattern of LH synthesis and release in the mature female hamster. Both compounds also inhibit ovulation, but through different mechanisms. A dose of 50 μg ECP, injected s. c. on day 1 of the oestrous cycle, causes atresia of all vesicular follicles within 48 hours. This is related temporally to a decrease in pituitary LH content. On the other hand, 5 mg progesterone, administered at day 1, does not change the normal pattern of follicular development, but inhibits ovulation by preventing the ovulatory surge of LH on day 4. The number of healthy antral follicles is halved between days 3 and 4 of the oestrous cycle in untreated controls and animals given 5 mg progesterone on day 1. This coincides with a decrease in pituitary FSH content of both groups. Animals administered 50 μg ECP on day 1 show no decrease in pituitary FSH between days 3 and 4. Concurrent administration of 50 μg ECP and 5 mg progesterone on day 1 inhibits both synthesis and release of LH, as evidenced by a decreased pituitary content and atrophic ovaries. The present study indicates that ECP causes atresia indirectly via a decrease in LH synthesis and release during the first two days of the oestrous cycle. Progesterone, however, does not alter the normal pattern of follicular development or pituitary LH content until day 4, at which time the release of LH is blocked.