Neonatal exposure to estradiol valerate programs ovarian sympathetic innervation and follicular development in the adult rat

A single injection of estradiol valerate (EV) to 14-day-old rats (when the ovarian follicle population has been already established) disrupts cyclicity, increases the activity of key enzymes of androgen biosynthesis, and develops polycystic ovary by a causally related increase in ovarian noradrenaline (NA). The current study examined an early window of ovarian development to look for a specific stage of development at which estradiol can induce such changes in sympathetic activity and follicular development. A single dose of EV applied to rats before the first 12 h of life rapidly increases (after 24 h) the ovarian expression of nerve growth factor (Ngfb) and p75 low-affinity neurotrophic receptor (Ngfr) mRNAs. When adults, rats presented early vaginal opening, disrupted cyclicity, appearance of follicular cyst, absence of corpus luteum, and infertility. Total follicles decreased, mainly due to a reduced number of primordial follicles, suggesting that estradiol acts in the first stages of folliculogenesis, when primordial follicles are organizing. These changes paralleled a 6-fold increase in NA concentration. No changes in NA content were found in the celiac ganglia, suggesting a local, non-centrally mediated effect of estradiol. Surgical section of the superior ovarian nerve (the main source of sympathetic nerves to the ovary) to rats neonatally treated with EV decreased intraovarian NA, delayed vaginal opening, and blocked the development of follicular cyst and that of preovulatory follicles. Therefore, we can conclude that early exposure to estradiol permanently modifies ovarian sympathetic activity and causes profound changes in follicular development, leading to the polycystic ovary condition.     

Populations of follicles in F344/N rats during aging

Follicular populations were investigated in female F344/N rats to better understand the aging process of the rat ovary. Ovaries dissected at various ages (spanning 1–36 months old) were submitted for histological examination. The total number of primordial, growing (primary and secondary), tertiary, and atretic follicles as well as corpora lutea (CL) were counted in hematoxylin–eosin- and azocarmine–aniline-blue-stained ovarian sections. The number of healthy follicles including primordial, growing and tertiary follicles decreased rapidly between the first and third months and gradually thereafter. CL were found in 3-month-old rats, and their number remained unchanged until 18 months of age, at which point it decreased. The number of atretic follicles started to increase in rats older than 18 months, which corresponded to the cessation of estrous cyclicity. Several healthy follicles and CL were observed even in 36-month-old rats.     

Inhibin a increases apoptosis in early ovarian antral follicles of diethylstilbestrol-treated rats

The purpose of this study was to evaluate the role of inhibin A in follicular development and apoptosis-related mechanisms in preantral and early antral follicles from prepubertal diethylstilbestrol (DES)-treated rats. Granulosa cells isolated from the ovaries of 23- to 25-day-old rats were cultured in serum-free medium containing FSH (20 ng/ml), transforming growth factor beta (5 ng/ml), and estradiol (50 ng/ml) in the presence or absence of different concentrations of recombinant human inhibin A. (3)H-Thymidine incorporation was decreased in the presence of Inh, but no significant changes were observed in progesterone and estradiol levels in culture medium. An increase in low molecular weight DNA fragmentation indicative of apoptosis and an increase in the levels of Bax protein with no changes in Bcl-2 protein levels were evident in early antral follicles incubated for 24 h with Inh. For each animal, Inh (0.5 micro g/ovary) was injected intrabursally in one ovary, and the contralateral ovary served as a control. Ovarian histology revealed an inhibitory effect of Inh treatment on the follicular development induced by DES. At 24 h after Inh injection, the number of preantral follicles was increased compared with controls, whereas the number of early antral follicles was decreased. In addition, in vivo Inh treatment caused an increase in the percentage of apoptotic cells in preantral and early antral follicles. These results suggest that inhibin produced by the dominant follicle may act as a paracrine factor inhibiting the growth of neighboring follicles, thus participating in the mechanism of follicular selection.     

Effects of vitamin E on nicotine-induced lipid peroxidation in rat granulosa cells: Folliculogenesis

In this study, we investigated the mechanism of oxidative damage induced by nicotine and the efficacy of vitamin E, an integral component of cellular membranes, against the damage in follicular/granulosa cells of rat ovaries. The animals were randomly divided into 4 groups; control, nicotine, nicotine + vitaminE, vitamin E (n = 8, per each group). Nicotine and vitamin E were administrated intraperitoneally 1 mg/kg/day and 200 mg/kg/day, respectively, once daily for 2 weeks. Nicotine increased lipid peroxide levels such as lipid peroxide (LPO) and malondialdehyde (MDA) in serum, 4-hydroxynonenal (4-HNE) in granulosa cells and apoptotic granulosa cells in the ovary. Positive correlation occurred between the findings of LPO markers and TUNEL labeling. Level of 17-β estradiol (E₂), number of follicles and granulosa cell proliferation decreased with nicotine treatment and negatively correlated with LPO levels and apoptosis in granulosa cells. Ultrastructural study of nicotine treated rat ovaries showed mitochondrial damage and autophagosomes in the granulosa cells. The administration of nicotine and vitamin E together, revealed an increase in E₂ level, granulosa cell proliferation and the number of healthy follicles associated with decrease in LPO, MDA, 4-HNE levels and TUNEL reactivity in a manner correlated with each other, compared to the nicotine group. Vitamin E showed to alleviate mitochondrial damage and decrease the number of autophagosomes in granulosa cells. These results suggest that lipid peroxidation may be one of the nicotine’ damage mechanisms on folliculogenesis and vitamin E may prevent nicotine-induced follicular damage through reducing lipid peroxidation level in granulosa cells.     

Somatostatin-14 influences pituitary–ovarian axis in peripubertal rats

The effects of multiple somatostatin (SRIH-14) administration on the pituitary-ovarian axis were examined in peripubertal rats. Female Wistar rats received subcutaneously, two daily doses of 20 mug SRIH-14 per 100 g body weight (b.w.) for five consecutive days (from the 33rd to the 37th day of life). Follicle-stimulating (FSH), luteinizing (LH) and somatotropic (GH) cells were examined by the peroxidase-anti-peroxidase immunocytochemical method. Changes in cell volumes, volume densities and number per unit area (mm(2)) of FSH-, LH- and GH-immunoreactive cells were evaluated by stereology and morphometry. Serum FSH and LH levels were determined by RIA. Ovaries were analyzed by simple point counting of follicles. The volumes and volume densities of FSH-, LH- and GH-immunoreactive cells were significantly decreased while their numbers per mm(2) remained unchanged. SRIH-14 induced a significant decrease in serum FSH and LH levels. In the ovary, SRIH-14 induced an increase in the number of primordial follicles, followed by a reduction in the number of small healthy growing follicles and absence of preovulatory follicles. The number of atretic follicles was unchanged. We concluded that treatment with SRIH-14 during the peripubertal period markedly inhibited pituitary FSH, LH and GH cells. In the ovary, SRIH-14 acted by inhibiting folliculogenesis without affecting atretic processes.     

Effect of clomiphene citrate on the ovary of a wild rat, Bandicota bengalensis

The effects of clomiphene citrate (0.3 or 3.0 mg/kg body weight/day) for 10 consecutive days on the ovary of a wild rat, Bandicota bengalensis, were studied. The low dose of clomiphene decreased the number of nonatretic follicles larger than 400 microns in diameter, increased atresia in follicles smaller than 200 microns, inhibited granulosal mitosis in follicles less than 200 microns and between 401 and 600 microns in diameter and inhibited thecal mitosis in follicles smaller than 400 microns and larger than 600 microns. The high dose of clomiphene increased the number of follicles between 201 and 400 microns, decreased the number of follicles larger than 600 microns, increased atresia in follicles of 51-400 microns and increased granulosal mitosis in follicles of 201-400 microns diameter. In both the doses, clomiphene inhibited the ovulation rate (p less than 0.005), with 25 and 35% of the rats being anovulatory in low and high doses, respectively. In addition, clomiphene caused irregularity in the estrous cycles associated with increased cycle length. These results suggest that the clomiphene-induced partial inhibition of ovulation is possibly through its action on follicular growth and atresia mainly in nonantral (less than 200 microns) and mature follicles (401-600 microns).     

Follicular recruitment in long-term hemicastrate rats

In the long-term hemicastrate rat, the total number of ova shed during estrus is the same as in the intact rat. To determine if the dynamics of follicular development are the same in the hemicastrate rat as in the intact control rat, the remaining ovary was removed from rats 20 to 30 days after hemiovariectomy. Complete serial sections of each ovary were prepared for histological examination. All follicles greater than or equal to 300 micrometers were counted, measured, and examined for signs of atresia. Long-term hemicastrate rats had a total complement of half as many healthy antral follicles compared to intact rats at estrus. At metestrus, there were half as many small and medium antral follicles in long-term hemicastrates as in controls. However, the total number of large antral follicles was the same in hemicastrate and intact rats. Thus, by metestrus, the appropriate number of follicles for ovulation appears to have been achieved in both animals, with all these large antral follicles located in the one remaining ovary of the hemicastrate rat, while they are distributed between both ovaries of the intact rat. Ovaries of the long-term hemicastrate rats contained far fewer attretic follicles than ovaries of intact rats. These findings suggest that the process of follicular recruitment differs greatly between intact and long-term hemicastrate rats. Atresia of small and medium antral follicles (300-400 micrometers in diameter) is apparently a necessary step in achieving the correct number of ovulatory follicles in the intact rat, yet the hemicastrate rat arrives at the correct number of ovulatory follicles without atresia.     

Effect of growth hormone on steroid content,proliferation and apoptosis in the chicken ovary during sexual maturation

The present study was undertaken to examine in vivo the effect of growth hormone (GH) on progesterone and estradiol levels and on cell proliferation and apoptosis in the chicken ovary during sexual maturation. Hy-Line chickens (10 weeks old) were injected three times a week with 200 μg recombinant chicken GH (cGH) per kilogram body weight until sexual maturity. GH treatment significantly increased ovarian weight at 16 weeks of age, i.e., ∼1 week before onset of egg laying. The progesterone content in the ovary just before and at the time of sexual maturity and the estradiol content before onset of egg laying were also elevated after cGH injections. The highest number of proliferating (positive for proliferating cell nuclear antigen) and apoptotic (positive for terminal-deoxynucleotidyl-transferase-mediated dUTP nick-end labeling) cells was found in the ovarian stroma and white follicles (>1-4 mm diameter), whereas the lowest number of these cells was detected in yellow (>8-30 mm) follicles. Administration of cGH significantly stimulated cell proliferation and inhibited cell apoptosis in the ovarian stroma and small ovarian follicles. The number of ovarian follicles and the weight of the ovary prior to the first oviposition were also higher in cGH-injected hens. Thus, prior to and after the onset of egg laying, GH participates in the growth, maturation and hormonal activity of ovarian follicles in the chicken, via the regulation of steroidogenesis, proliferation and apoptosis processes.     

Effect of reduced ovarian tissue on cyclicity, basal hormonal levels and follicular development in old rats

Reduction of the number of growing follicles was proposed to contribute to the decline in reproductive performance with aging (Butcher and Page, 1981). To investigate the effects of a reduced number of follicles, rats which maintained regular estrous cycles at greater than 1 yr of age had either unilateral ovariectomy (ULO) or control surgery. Irregular estrous cycles and periods of constant estrus were more frequent during a period of 90 days after ULO than in controls. Follicle-stimulating hormone (FSH) concentration in plasma collected at 0900-1100 h of the metestrus nearest to 20, 50, and 90 days after surgery was increased by ULO; in both treatment groups, FSH increased between 20 and 90 days. Compensation in ovarian weight and number of corpora lutea had occurred by 90 days after ULO. Estradiol, estrone and luteinizing hormone (LH) concentrations did not change with time or treatment. Numbers of small, medium and large antral follicles per ovary at metestrus were increased by ULO, while the number of follicles per rat was decreased. It was concluded that the reduction in ovarian tissue (which decreased the number of growing follicles) resulted in an elevation of basal FSH followed by irregularity in estrous cycles.     

Chronic somatostatin treatment affects pituitary gonadotrophs, ovaries and onset of puberty in rats

The effects of chronic somatostatin (SRIH-14) treatment on the pituitary gonadotrophs (FSH and LH cells) and ovaries of female Wistar rats were examined. Females were given 20 microg/100 g b.w. twice per day from the immature (23rd day) till the adult period of life (71st day). The onset of puberty was determined by daily examination for vaginal opening. The peroxidase-antiperoxidase immunocytochemical procedure was used to study the gonadotrophs. Changes in the number per unit area (mm2), cell volume and volume densities of LH- and FSH-immunoreactive cells were evaluated by morphometry and stereology. Ovaries were analysed by simple point counting of follicles and corpora lutea (CL). Follicles were divided by size according to the classification of Gaytán and Osman. The mitotic indexes of granulosa and theca cells in the follicles were estimated at all stages of folliculogenesis. The number, volume and the volume density of FSH- and LH-immunoreactive cells decreased after chronic SRIH-14 treatment, particularly the latter. In the ovary, SRIH-14 treatment decreased the number of healthy follicles at all phases of folliculogenesis, lowered the mitotic indexes of granulosa and theca cells but increased the number of atretic follicles. Healthy CL were fewer in number, while regressive CL were increased. Vaginal opening occurred at a later age in treated females. It can be concluded that chronic SRIH-14 treatment markedly inhibited LH cells and to a lesser extent FSH cells. In the ovary SRIH-14 inhibited folliculogenesis, enhanced atretic processes and lowered proliferative activity of granulosa and theca cells. It also delayed puberty onset.     

Effect of dihydrotestosterone on the growth and function of ovarian follicles in intact immature female rats primed with PMSG

Intact, immature female rats were primed with PMSG and treated with 4 injections of DHT. DHT given at 0, 12, 24 and 36 h caused a significant decrease in the ovulation rate 72 h after the PMSG treatment. Concurrent treatment with oestrogen reversed the inhibitory effects of the androgen. The androgen effect was apparently exerted directly on the ovary since DHT did not alter the surge of LH and FSH which occurred at 58 h after PMSG treatment. The DHT inhibition of ovulation was observed in the treatment cycle as well as in subsequent cycles which followed a second PMSG injection. This finding suggests that intermediate size follicles were also adversely affected by the androgen. To confirm that androgen affects follicles of all size ranges, follicles less than 200 microns, 200-400 microns and greater than 400 microns in diameter were isolated from the ovaries of rats treated with PMSG and DHT or the vehicle. The follicles were isolated by density gradient separation of follicles followed by filtration with pre-calibrated Teflon sieves. In some experiments, granulosa cells were also harvested from isolated follicles. DHT treatment did not affect the numbers of follicles of any size but did reduce the oestrogen content of follicles of all sizes. Follicles from DHT-treated animals contained fewer granulosa cells and the cells from treated animals had lower aromatase activity than did cells from control rats. Taken together, these findings suggest that DHT reduces the ovulation rate by decreasing the number of granulosa cells/follicle and by altering the oestrogen synthetic abilities of the cells. All follicles, regardless of size, were sensitive to androgen treatment.     

A possible dual mechanism of the anovulatory action of antiprogesterone RU486 in the rat

The purpose of these experiments was to investigate the mechanism of the anovulatory action of antiprogesterone RU486 (RU486) in rats by studying its effects on follicular growth, secretion of gonadotropins and ovarian steroids, and ovulation. Rats with 4-day estrous cycles received injections (s.c.) of either 0.2 ml oil or 0.1, 1, or 5 mg of RU486 at 0800 and 1600 h on metestrus, diestrus, and proestrus. At the same times, they were bled by jugular venipuncture to determine serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17 beta-estradiol (E), and progesterone (P). On the morning of the day after proestrus, ovulation and histological features of the ovary were recorded. Rats from each group were killed on each day of ovarian cycle to assess follicular development. Rats treated similarly were decapitated at the time of the ovulatory LH surge and blood was collected to measure LH. The serum levels of LH increased and those of FSH decreased during diestrus in rats treated with RU486. Neither E nor P levels differed among the groups. Treatment with RU486 caused both a blockade of the ovulation and an increase in ovarian weight in a dose-dependent manner. At the time of the autopsy (the expected day of ovulation), rats treated with 1 mg RU486 had ovaries presenting both normal and post-ovulatory follicles and unruptured luteinized follicles. Rats treated with 5 mg RU486 presented post-ovulatory follicles without signs of luteinization. The number of follicles undergoing atresia increased in rats treated with RU486. Rats treated with 5 mg RU486 exhibited a significant decrease in ovulatory LH release. The mechanism by which RU486 produces the ovulatory impairment in rats seems to be dual: first, by inducing inadequate follicular development at the time of the LH surge and second, by reducing the amount of ovulatory LH released. The physiological events-decreased basal FSH secretion and follicular atresia-that result from use of RU486 cannot be elucidated from these experiments and should be investigated further.     

Immunization of rats and sheep against granulosa cell-inhibitory factor from bovine follicular fluid increases the number of large follicles in rats and the ovulation rate in sheep.

Granulosa cell-inhibitory factor (GCIF), a low molecular weight factor from bovine follicular fluid, inhibits the proliferation of bovine granulosa cells in vitro and the growth of large follicles in rats in vivo. In this study the effects of (1) immunization of rats against GCIF on follicular growth and (2) immunization of sheep against GCIF on ovulation rate were studied. The ability of antiserum from sheep immunized against GCIF to reduce the inhibitory effect of GCIF on bovine granulosa cell proliferation in culture was also examined. Immunization of rats against GCIF increased the number of large follicles (P < 0.001) but decreased the number of small follicles (P < 0.05) per ovary. Ovarian mass (P < 0.05) and uterine wet (P < 0.05) and dry (P < 0.01) masses were increased in immunized rats. Immunization of sheep against GCIF, followed by boosting over two breeding seasons, increased ovulation rate (P < 0.01). Addition of antiserum from sheep immunized against GCIF reduced or abolished the inhibitory effect of GCIF on granulosa cell proliferation (P < 0.01). These data provide further evidence that GCIF has an important role in controlling follicle growth and ovulation in vivo.     

Role of follicle stimulating hormone in the induction of hyperplasia during compensatory ovarian hypertrophy

In adult rats, removal of one ovary leads to an acute albeit transient rise in serum follicle stimulating hormone and an increase in the weight of the remaining ovary. In an attempt to correlate the high titre of endogenous follicle stimulating hormone with the changes taking place at the macromolecular level, the phenomenon of compensatory ovarian hypertrophy was studied for one cycle after hemiovariectomy at metoestrus in the adult, cycling female rats derived from the Holtzman strain. The significant finding with respect to hormonal changes was an acute follicle stimulating hormone surge commencing 6h post-unilateral ovariectomy, reaching a maximum at 12 h and declining thereafter, hitherto not reported in the Holtzman strain. Serum luteinizing hormone, prolactin, oestradiol-17β and testosterone remained unaltered while progesterone showed a decline at 6 h after surgery. There was an increase in the number of healthy class III (> 350 μm) follicles with a concomitant drop in atretic class III follicles 24 h post-unilateral ovariectomy. Analysis for DNA, RNA and protein content showed that all three constituents registered a continuous rise in the hypertrophying ovary up to 120h after surgery. When expressed as ?g/mg ovarian weight, the increase in DNA reached a maximum at 24 h and declined thereafter. The kinetics of DNA synthesis was followed by pulse labelling with [³H] thymidine at 18, 24, 36 and 48 h after unilateral ovariectomy. Maximum incorporation occurred at 36 h. Autoradiographic studies showed that the granulosa cells of healthy follicles preferentially incorporated the label. In an extension of this study, it was found that labelling index registered a significant increase following ovariectomy, the maximum being reached at 24 h especially in classIII follicles. The results clearly point out the crucial role of hyperplasia in the response of the contralateral ovary to the surgery and implicate the rise in follicle stimulating hormone as the primary signal for initiation of such a response. This raises the question whether in compensatory ovarian hypertrophy follicle stimulating hormone has a mitogenic role     

Counteraction of testosterone-induced suppression of the pituitary-ovarian axis in rats by flutamide.

Daily administration of 100 micrograms of testosterone to unilaterally ovariectomized rats for 18 days caused a significant decrease in compensatory ovarian hypertrophy. The number of corpora lutea was markedly reduced and many cystic follicles were noticeable. Administration of graded doses (0.5, 1 and 3 mg daily) of flutamide over the same period did not cause any significant change in the weight and histology of the ovary in untreated unilaterally ovariectomized animals. However, treatment with the same doses of flutamide prevented the changes observed in the reamining ovary of testosterone-treated animals.     

Stress inhibits seasonal and FSH-induced ovarian recrudescence in the lizard,Mabuya carinata

Stressors (handling, chasing, and noise) applied randomly five times per day for one month to lizards during the recrudescence phase of the ovarian cycle caused a significant reduction in mean number of oocytes and primordial follicles when compared to those of controls. Further, vitellogenic follicles were absent in the ovary of lizards subjected to stressors. Administration of bovine FSH during post-breeding regression phase of the ovarian cycle induced ovarian recrudescence as shown by significant increases in the mean number of oogonia, oocytes, and primordial follicles compared to controls, as well as vitellogenic growth of follicles. However, lizards treated with FSH and exposed to stressors did not exhibit ovarian recrudescence. Furthermore, FSH administration during the post-breeding regression phase caused a significant increase in serum levels of estradiol compared to controls, which was accompanied by significant increases in the relative weight of the liver and oviduct, as well as vitellogenic growth of follicles. Despite administration of FSH to lizards subjected to stressors, there was neither any increase in serum levels of estradiol and weight of the liver nor vitellogenic growth of follicles. The results indicate that repeated application of stressors inhibits vitellogenic growth of follicles by suppression of steroidogenic activity in M. carinata. This is the first report revealing that the ovary does not respond to gonadotrophin treatment under stressful conditions in reptiles.     

Evidence for a role of androgens in the growth and maturation of ovarian follicles in rats

Changes in the morphology and steroid content of ovaries were studied after 48 h of intravenous injection of 100 microgram of cyproterone acetate or flutamide to diestrus or estrous rats. Treatment with cyproterone acetate at diestrus caused a decrease in the number of small follicles (less than 200 micrometer), freshly formed corpora lutea and the levels of estradiol-17beta in the ovary, suggesting inhibition of ovulation. Following flutamide administration at diestrus, the number of follicles at all stages of development were reduced with a concomitant decrease in the ovarian levels of the hormones. Thus, flutamide suppressed the growth and maturation of follicles. On administration of these drugs at estrous, the steroid content of ovaries was more pari passu with the increase in the number of mature and medium follicles. The differential effects of the two drugs are discussed in the light of these observations.     

Comparison of granulosa cell proliferation in small follicles of hypophysectomized, prepubertal, and mature rats

The factors that control the rate of granulosa cell proliferation during follicular development are unknown. The object of this study was to test the hypothesis that growth rates of small and medium follicles may be modulated by cyclic alterations in endogenous hormone concentrations. Follicular growth in adult cycling rats was compared with hypophysectomized rats, untreated prepubertal rats, and prepubertal rats treated with exogenous gonadotropins. Cell kinetics was studied using a metaphase arrest technique and by long-term infusion of [3H]thymidine. Many follicles of hypophysectomized rats showed evidence of continued cell proliferation despite the absence of gonadotropins. In hypophysectomized rats, follicular growth was able to proceed to the size of the largest healthy non-preovulatory follicles in the proestrous rat ovary. Follicular growth in prepubertal rats progressed little beyond this same size range. Granulosa cell proliferation rates differed in immature rats and cycling rats. Granulosa cells in small follicles (80-180 cells in the largest cross-section) of cycling rats grew slowly. However, granulosa cells in small follicles of immature rats were among the fastest growing in the ovary. These results suggest that, although gonadotropins are not absolutely required to maintain granulosa cell proliferation in small follicles, the rate at which these follicles grow varies under different hormonal conditions.     

Monoamines and function of ovaries of rats selected for enhancement of catatonic reactivity

There have been studied the contents of dopamine, noradrenalin, and serotonin in thalamus as well as function of ovary (folliculogenesis) at various stages of estral cycle in female rats of the genetic catatonia (GC) line selected for enhancement of catatonic reactivity. The outbred Wistar line was a control. The selection for enhancement of catatonic reactivity has led to a decrease of the number of follicles of all types in ovary of female rats of the GC line at stages of diestrus and proestrus. Meanwhile at the estrus stages of the GC line female rats, on the contrary, there was a tendency for an increase of the number of growing follicles as compared with that in female Wistar rats. It has been shown that on the background of a decrease of the dopamine and noradrenalin content in hypothalamus of the GC line rats the catecholamine level was higher at the estrus and lower at the diestrus stage. Thus, selection for manifestation of excessive protective catatonic type of response in the form of an increase of duration and intensity of freezing leads, by involvement of the brain monoergic system, to inhibition of folliculogenesis that is the key factor in regulation of sexual function.     

Effects of methoxychlor on IGF-I signaling pathway in rat ovary

Follicular development and other ovarian functions are regulated by growth factors that can be affected by exogenous agents. Methoxychlor (MXC) is an organochloride pesticide that causes female infertility. We investigated how MXC affects the distribution of developing ovarian follicles in adult rats after treatment between embryonic day (E) 18 and postnatal day (PND) 7. We also measured insulin-like growth factor-I (IGF-I) and its receptor, IGF-IR, expressions in ovarian follicles and investigated whether MXC changed the levels of IGF-I and IGF-IR in the ovary. Using immunohistochemical (IHC) staining, we detected IGF-I expression in oocytes and granulosa cells of the follicles, luteal cells, interstitial cells, theca externa and theca interna, and the smooth muscle of ovarian vessels. IGF-IR was co-localized with IGF-I in the ovary except for the theca externa. IGF-I expression was decreased in granulosa cells of preantral and antral follicles after treatment with MXC compared to granulosa cells of preantral and antral follicles of the control group. We also observed that oocytes of secondary follicles and granulosa cells of secondary and preantral follicles of the MXC treated groups showed increased IGF-IR expression compared to oocytes of secondary follicles and granulosa cells of secondary and preantral follicles of the control group. We also detected more secondary and preantral follicles, and fewer primordial and antral follicles after MXC administration compared to controls. Therefore, the IGF signaling pathway may participate in MXC induced ovary dysfunction and female infertility.