FSH induction of aromatase in cultured rat granulosa cells measured by a radiometric assay

Unkeito promotes follicle development by restoring reduced follicle-stimulating hormone responsiveness in rats with polycystic ovary syndrome

Background

Polycystic ovary syndrome (PCOS) is a common disorder resulting in irregular menstruation and infertility due to improper follicular development and ovulation. PCOS pathogenesis is mediated by downregulated follicle-stimulating hormone receptor (FSHR) expression in granulosa cells (GCs); however, the underlying mechanism remains elusive. Unkeito (UKT) is a traditional Japanese medicine used to treat irregular menstruation in patients with PCOS. In this study, we aimed to confirm the effectiveness of UKT in PCOS by focusing on follicle-stimulating hormone (FSH) responsiveness.

Methods

A rat model of PCOS was generated by prenatal treatment with 5α-dihydrotestosterone. Female offspring (3-week-old) rats were fed a UKT mixed diet or a normal diet daily. To compare the PCOS phenotype in rats, the estrous cycle, hormone profiles, and ovarian morphology were evaluated. To further examine the role of FSH, molecular, genetic, and immunohistological analyses were performed using ovarian tissues and primary cultured GCs from normal and PCOS model rats.

Results

UKT increased the number of antral and preovulatory follicles and restored the irregular estrous cycle in PCOS rats. The gene expression levels of FSHR and bone morphogenetic protein (BMP)-2 and BMP-6 were significantly decreased in the ovarian GCs of PCOS rats compared to those in normal rats. UKT treatment increased FSHR staining in the small antral follicles and upregulated Fshr and Bmps expression in the ovary and GCs of PCOS rats. There was no change in serum gonadotropin levels. In primary cultured GCs stimulated by FSH, UKT enhanced estradiol production, accompanied by increased intracellular cyclic adenosine monophosphate levels, and upregulated the expression of genes encoding the enzymes involved in local estradiol synthesis, namely Cyp19a1 and Hsd17b. Furthermore, UKT elevated the expression of Star and Cyp11a1, involved in progesterone production in cultured GCs in the presence of FSH.

Conclusions

UKT stimulates ovarian follicle development by potentiating FSH responsiveness by upregulating BMP-2 and BMP-6 expression, resulting in the recovery of estrous cycle abnormalities in PCOS rats. Restoring the FSHR dysfunction in the small antral follicles may alleviate the PCOS phenotype.

Effect of oestrogen on mouse follicle growth and meiotic resumption

Many studies have shown that oestrogen affects late follicular development, but whether oestrogen is involved in other aspects of folliculogenesis remains unclear. In this study, two antagonists of oestrogen, tamoxifen and G15, were used to determine the effects of oestrogen on folliculogenesis. Mouse preantral follicles and cumulus-oocyte complexes (COCs) were cultured in vitro. The results showed that follicle growth stimulated using pregnant mare serum gonadotrophin (PMSG) was inhibited using tamoxifen, whether in vivo or in vitro. The average diameters, the maximum diameters of follicles and the numbers of follicles with a diameter of more than 300 μm decreased significantly following a 4-day culture with tamoxifen. G15, the antagonist of oestrogen via the membrane receptor, did not change follicular growth stimulated by PMSG in vitro. Results of in vitro maturation of COCs showed that germinal vesicle breakdown (GVBD) occurred spontaneously (95.1%) after 2 h in culture, and the GVBD ratio changed little with the addition of either oestrogen or 10 μM G15. However, first polar body (PBI) extrusion was driven by oestrogen markedly and supplementation with 10 μM G15 inhibited PBI extrusion (82.4% vs 55.0%) significantly. These results demonstrated that oestrogen promotes follicle growth through the nuclear receptor during follicle growth and then triggers the transition of metaphase to anaphase through the membrane receptor during meiotic resumption. So oestrogen plays a progressive role in the two phases of follicle growth and oocyte meiotic resumption.

Molecular mechanism of FSHR expression induced by BMP15 in human granulosa cells

PURPOSE

Follicle-stimulating hormone receptor (FSHR) expression in granulosa cells is critical in enabling follicles to achieve accelerated growth. Although FSHR expression has been reported to be epigenetically regulated, the mechanism is unclear. Cooperation between oocytes and granulosa cells is also essential for normal follicular growth. Among oocyte-derived factors, bone morphogenetic protein 15 (BMP15) promotes follicular growth and is suggested to have epigenetic effects. We examined the role of BMP15 in the acquirement of FSHR in human granulosa cells.

METHODS

Immortalized non-luteinized human granulosa (HGrC1) cells were stimulated with trichostatin A (TSA) or BMP15 to analyze FSHR expression, histone modifications, and USF1/2 binding at the FSHR promoter region. Histone acetyl transferase (HAT) activity and phosphorylation of Smad 1/5/8 and p38 MAPK were examined with or without BMP15, SB203580, and LDN193189. CYP19A1 expression and estradiol production were also studied.

RESULTS

TSA and BMP15 induced FSHR mRNA expression in a dose-dependent manner and histone modifications were observed with increased binding of USF1/2. BMP15 increased FSHR protein expression, which was suppressed by LDN193189. BMP15 increased phosphorylation of Smad 1/5/8 and significantly increased HAT activity, which was inhibited by LDN193189, but not by SB203580. BMP15 increased phosphorylation of p38 MAPK and USF1. LDN193189 suppressed BMP15-induced phosphorylation of both p38 MAPK and USF1, whereas SB203580 suppressed the phosphorylation of USF1. BMP15 increased CYP19A1 mRNA expression and estradiol production.

CONCLUSION

BMP15 induced FSHR expression in human granulosa cells through Smad and non-Smad pathways. This mechanism of FSHR induction by BMP15 may be utilized for controlling follicular growth.

Elevated progesterone during ovarian stimulation for IVF

There is an ongoing debate regarding the impact of premature progesterone rise on the IVF outcome. The objective of this review is to assess evidence of poorer ongoing pregnancy rate in IVF cycles with elevated serum progesterone at the end of follicular phase in ovarian stimulation. It also explores the origin of the progesterone rise, potential modifying factors and possible methods to prevent its rise during ovarian stimulation. This review draws on information already published from monitoring progesterone concentrations at the end of follicular phase in ovarian stimulation. The databases of Medline and PubMed were searched to identify relevant publications. Good-quality evidence supports the negative impact on endometrial receptivity of elevated progesterone concentrations at the end of the follicular phase in ovarian stimulation. Future trials should document the cause and origin of premature progesterone in stimulated IVF cycles. There is an ongoing debate regarding the impact of premature progesterone rise on the IVF outcome. The objective of this review is to assess evidence of poorer ongoing pregnancy rate in IVF cycles with elevated serum progesterone at the end of follicular phase in ovarian stimulation. It also explores the origin of the progesterone rise, potential modifying factors and possible methods to prevent its rise during ovarian stimulation. This review draws on information already published from monitoring progesterone concentrations at the end of follicular phase in ovarian stimulation. The databases of Medline and PubMed were searched to identify relevant publications. Good-quality evidence supports the negative impact on endometrial receptivity of elevated progesterone concentrations at the end of follicular phase in ovarian stimulation. Future trials should document the cause and origin of premature progesterone in stimulated IVF cycles.

Aromatase expression in Xenopus oocytes: a three cell-type model for the ovarian estradiol synthesis

In contrast to the classical model describing the synthesis of androgens and estrogens as restricted to somatic cells, a previous study demonstrated that Xenopus laevis oocytes participate in androgen synthesis. The objective of our study was to determine whether Xenopus oocytes are also involved in estrogen synthesis. More precisely, we analyzed aromatase expression by in situ hybridization and RT-QPCR and measured aromatase activity. Aromatase, the enzyme responsible for estrogen synthesis, appears to be expressed and active not only in the follicular cells but also in the vitellogenic oocytes. During late oogenesis, aromatase oocyte expression and activity decreased concomitantly with the trend observed in surrounding follicular layers. In order to investigate the role of estradiol-17β (E(2)), we studied its effect on oocyte meiotic resumption. It appears that, as in Rana pipiens, E(2) inhibited the follicle-enclosed maturation of Xenopus oocytes, likely through inhibition of LH-induced maturation-inducing steroid synthesis. In addition, E(2) exerted a slight enhancing action on denuded oocyte maturation whose biological significance remains unclear. Together, our results demonstrate that Xenopus oocyte significantly participates in ovarian E(2) synthesis and this may be a common feature of vitellogenic vertebrates.

Follicle-stimulating hormone regulates steroidogenic enzymes in cultured cells of the chick embryo ovary

This investigation addresses the potential regulation of enzymes involved in the biosynthesis of steroid hormones during early stages of gonadal development by follicle-stimulating hormone (FSH). Gonadal cells of 10-day-old chick embryo and cells of the left ovary of 18-day-old chick embryo were cultured for 60 h in a defined medium with or without the addition of FSH (2.0 IU/ml). At the end of the culture, cells were recovered and evaluated by biotransformation of tritiated steroid precursors and mRNA levels were evaluated by RT-PCR. The production of estrone from androstenedione was increased in the FSH-treated cells, both human FSH (hFSH) and recombinant human FSH (rhFSH), indicating a stimulatory effect on aromatase (P450arom). Similarly, the intensity of the band corresponding to P450arom mRNA was higher in hFSH and rhFSH than in control and chorionic gonadotropin (hCG) groups. The P450arom stimulation was observed in the ovary of 10- and 18-day-old chick embryo. The transformation of dehydroepiandrosterone to androstenedione was taken as evidence of 3beta-hydroxysteroid dehydrogenase function. This enzyme was stimulated in the cultured ovarian cells of 18-day-old chick embryos treated with hFSH and rhFSH compared with controls. The production of pregnenolone in the mitocondrial fraction of 18-day-old chick embryo ovary was increased when cultured with hFSH and rhFSH. This observation together with the increase in the band intensity corresponding to mRNA of P450 cholesterol side-chain cleavage indicates stimulation by FSH treatment; hCG produced a similar effect. Somatic cells of the medullary cords are proposed to be FSH target cells in the ovary of the chick embryo.

Effect of follicle-stimulating hormone on steroid secretion and messenger ribonucleic acids encoding cytochromes P450 aromatase and cholesterol side-chain cleavage in bovine granulosa cells in vitro

We determined 1) whether the previously observed induction of estradiol secretion in bovine granulosa cells cultured in serum-free conditions is associated with an increase in cytochrome P450 aromatase (P450(arom)) mRNA abundance and 2) whether P450(arom) mRNA levels are responsive to FSH in vitro. Granulosa cells from small (2-4-mm) follicles were cultured in serum-free medium. Estradiol secretion increased with time in culture and was correlated with increased P450(arom) mRNA abundance. Progesterone secretion also increased with time in culture, but P450 cholesterol side-chain cleavage (P450(scc)) mRNA abundance did not. FSH stimulated estradiol secretion and P450(arom) mRNA abundance; the effect was quadratic for both estradiol and P450(arom) mRNA. Estradiol secretion and P450(arom) mRNA levels were correlated. FSH stimulated progesterone secretion and P450(scc) mRNA abundance, although the minimum effective dose of FSH was lower for estradiol (0.1 ng/ml) than for progesterone (10 ng/ml) production. Insulin alone stimulated estradiol secretion and P450(arom) mRNA levels but not progesterone or P450(scc) mRNA abundance. We conclude that this cell culture system maintained both estradiol secretion and P450(arom) mRNA abundance responsiveness to FSH and insulin, whereas P450(scc) mRNA abundance and progesterone secretion were responsive to FSH but not insulin.

Developmental and hormonal regulation of hepatocyte growth factor expression and action in the bovine ovarian follicle

Ovarian hormones (i.e., estrogen and LH) may promote folliculogenesis by regulating the local production of mesenchymal "inducer proteins" that mediate theca cell-granulosa cell interactions. Theca cells produce hepatocyte growth factor (HGF) that can stimulate granulosa cell growth. In order to investigate the physiological role of HGF in the ovarian follicle, the developmental and hormonal regulation of HGF was examined during follicular development in the bovine ovary. Reverse transcription-polymerase chain reaction (RT-PCR) analysis was used to examine HGF expression in theca cells and the HGF receptor (HGFR or c-met) in granulosa cells. Both HGF and HGFR were detected throughout follicular development in small (< 5 mm)-, medium (5-10 mm)-, and large (> 10 mm)-sized follicles. Steady-state levels of HGF and HGFR mRNAs were determined using sensitive quantitative RT-PCR assays. Developmental regulation of HGF in theca cells and HGFR in granulosa cells was analyzed in freshly isolated small-, medium-, and large-sized follicles. Observations demonstrate that expression of HGF (in theca cells) and HGFR (in granulosa cells) was highest in large-sized follicles. Hormonal regulation of HGF was analyzed in hormone-treated theca cell cultures. Steady-state levels of HGF mRNA in theca cells were increased by treatment with hCG (an LH agonist), but estradiol had no effect. These results suggest that LH may promote ovarian follicular growth (i.e., granulosa cell proliferation) in part by stimulating the local production of HGF by theca cells. Effects of HGF on granulosa cell differentiated functions were examined. Treatment with HGF reduced basal and FSH-stimulated levels of aromatase activity in bovine and rat granulosa cells. In addition, HGF inhibited the ability of hCG to stimulate progesterone production by granulosa cells. The inhibition of granulosa cell steroid production by HGF is proposed to be the indirect effect of promoting cellular proliferation. Therefore, HGF directly stimulates granulosa cell proliferation and indirectly inhibits granulosa cell differentiated functions. The developmental and hormonal regulation of HGF and HGFR during folliculogenesis provides evidence that HGF may be important for hormone-induced granulosa cell proliferation. As a result, HGF may be essential for establishing the granulosa cell population and microenvironment required for oocyte maturation in the female.

Developmental and hormonal regulation of keratinocyte growth factor expression and action in the ovarian follicle

The developing ovarian follicle is one of the most rapidly proliferating normal tissues in vivo. Mesenchymal-epithelial cell interactions between theca cells and granulosa cells are essential for this follicular expansion. Ovarian hormones (i.e. estrogen and LH) may promote follicular development by regulating the local production of mesenchymal inducer proteins that mediate theca cell-granulosa cell interactions. Recently, theca cells were shown to produce keratinocyte growth factor (KGF) that can act in a paracrine manner to stimulate granulosa cell growth. In this study, the developmental and hormonal regulation of KGF was examined during follicular development in the bovine ovary. Expression of KGF in theca cells and the KGF receptor (KGFR, or splice variant of the fibroblast growth factor family receptor family, FGFR-2) in granulosa cells was examined using RT-PCR. Both KGF and KGFR were detected throughout follicular development in small (<5 mm), medium (5-10 mm), and large (>10 mm) follicles. Quantitative RT-PCR assays were used to determine steady-state levels of KGF and KGFR messenger RNAs. Developmental regulation of KGF and KGFR was analyzed in freshly isolated theca cells and granulosa cells from small, medium, and large follicles. Observations demonstrated that expression of KGF (in theca cells) and KGFR (in granulosa cells) was highest in large follicles. These results suggest that KGF actions are important for the rapid proliferation of granulosa cells in large follicles. Estrogen and LH are the primary endocrine hormones that regulate theca cell function in vivo. Therefore, hormonal regulation of KGF was analyzed by treating serum-free theca cell cultures with estrogen and human CG (hCG, an LH agonist). Results showed that both estrogen and hCG stimulated KGF gene expression in theca cells. These results suggest that estrogen and LH may promote follicular growth (i.e. granulosa cell proliferation), in part, by stimulating the local production of KGF. Effects of KGF on granulosa cell differentiated functions were examined. Treatment with KGF reduced basal levels and FSH-stimulated levels of aromatase activity in bovine and rat granulosa cells. In addition, KGF inhibited the ability of hCG to stimulate progesterone production by granulosa cells. The inhibition of granulosa cell steroid production by KGF was likely the indirect effect of promoting cellular proliferation. Therefore, KGF directly stimulates granulosa cell proliferation and indirectly inhibits granulosa cell differentiated functions. Combined results suggest that theca cell production of KGF may be important for ovarian folliculogenesis. This is the first report of the regulation of KGF expression in the ovary. The developmental and hormonal regulation of KGF and KGFR during folliculogenesis provides evidence that KGF may be important for hormone-induced granulosa cell proliferation. As a result, KGF may be essential for establishing the microenvironment required for oocyte maturation in the ovary.

Cytochrome P-450 levels of immature rat ovaries during early follicular development: quantification, cellular and subcellular distribution, enzymatic activity and response to FSH in vivo and in vitro

Absolute values of cytochrome P-450 (cyt. P-450) content were determined by dual beam spectrophotometry in mitochondrial and microsomal fractions of granulosa cells and stroma (theca and interstitial cells) obtained from ovaries of immature rats treated with diethylstilbestrol (DES) or with DES and FSH. Cholesterol side-chain cleavage activity and aromatase activity were also measured in relevant cell fractions. The cyt. P-450 content in the granulosa cell mitochondria was significantly increased in FSH-treated animals (cyt.P-450 in nmols/mg protein, mean +/- SE: DES-treated 0.027 +/- 0.00213, N = 9; DES/FSH-treated 0.0668 +/- 0.0120, N = 13, P = 0.014). The increased cyt. P-450 content was associated with an increase in cholesterol side-chain cleavage activity confirming the functional relevance of the spectrophotometric measurements. The increase in cyt. P-450 content in stroma after FSH treatment was not statistically significant but there was a significant increase in cholesterol side-chain cleavage activity. The cholesterol side-chain cleavage activity of intact granulosa cells from secondary follicles of DES-treated rats was significantly stimulated by in vitro exposure to FSH during 2 hr assay incubations. A significant cyt. P-450 content was detected in the microsomal fraction of granulosa cells from DES-treated rats which was not associated with aromatase activity. Granulosa cell microsomal cyt. P-450 content was not significantly altered by in vivo FSH treatment despite a dramatic increase in aromatase activity of such microsomal preparations.

Steroidogenesis-inducing protein interacts with transforming growth factor-beta to stimulate DNA synthesis in rat granulosa cells

We have examined the effects of steroidogenesis-inducing protein (SIP), previously isolated from human follicular fluid, on the synthesis of DNA by granulosa cells isolated from diethylstilbestrol-primed immature rats. SIP alone had no effect but in conjunction with transforming growth factor-beta (TGF-beta) there was an increase in [3H]thymidine incorporation into granulosa cell DNA. The increase in [3H]thymidine into DNA was due to an increase in the number of labeled granulosa cells as assessed by autoradiography. Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) interfered with the ability of SIP and TGF-beta to promote DNA synthesis. Previously, we reported that the growth-promoting action of follicle-stimulating hormone (FSH) on rat granulosa cells in vitro was dependent on TGF-beta, and EGF inhibited the actions of FSH plus TGF-beta on [3H]thymidine incorporation into DNA. Since the dependency of SIP on its interactions with TGF-beta and the ability of EGF to interfere with the process were similar to the properties reported for FSH, this raised the possibility that the actions of SIP were mediated through the accumulation of intracellular cAMP. However, when the hypothesis was tested, SIP had no effect on cAMP levels in the presence or absence of TGF-beta, under conditions in which FSH stimulated cAMP accumulation. In conclusion, DNA synthesis in rat granulosa cells is dependent on the presence of TGF-beta. In the presence of TGF-beta, FSH or SIP, acting through cAMP-dependent and cAMP-independent mechanisms respectively, can recruit more cells to enter the cell cycle and initiate DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid production by ovarian follicles of the viviparous guppy (Poecilia reticulata) and its regulation by precursor substrates, dibutyryl cAMP and forskolin

Production in vitro of estradiol-17 beta, testosterone, 17 alpha-20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-P), 17 alpha-hydroxyprogesterone, and progesterone by follicles of the guppy at various stages of oocyte growth and gestation was investigated. Basal production of estradiol-17 beta was highest in 0.8- and 1.2-mm follicles, whereas that of testosterone and 17 alpha,20 beta-P was highest in 1.6-mm (postvitellogenic) follicles. Levels of these steroids declined after fertilization and were undetectable in late gestation and postpartum follicles. 17 alpha-Hydroxyprogesterone and progesterone levels were low at all stages. Thus, none of these steroids appears to be involved in maintaining gestation. Regulation of estradiol-17 beta and 17 alpha,20 beta-P secretion by vitellogenic (1.0 mm) and postvitellogenic follicles by precursor substrates, dbcAMP (0.1 to 10 mM) and forskolin (1 to 100 microM), was also investigated. Vitellogenic follicles synthesized increased quantities of estradiol-17 beta in the presence of exogenous testosterone, whereas estradiol-17 beta production by postvitellogenic follicles was not altered by testosterone. These results suggest decreased aromatase activity in the postvitellogenic follicles. Dibutyryl cAMP and/or forskolin stimulated testosterone and estradiol-17 beta production by vitellogenic follicles but did not stimulate conversion of testosterone to estradiol-17 beta, suggesting that the adenylate cyclase system stimulates estradiol-17 beta production by stimulating testosterone production but does not mediate conversion of testosterone to estradiol-17 beta. Postvitellogenic follicles synthesized increased quantities of 17 alpha,20 beta-P in response to 17 alpha-hydroxyprogesterone in a dose-dependent manner. Although 1 microM of forskolin stimulated 17 alpha,20 beta-P production by postvitellogenic follicles in the absence of exogenous 17 alpha-hydroxyprogesterone, 100 microM of forskolin inhibited 17 alpha,20 beta-P production. Dibutyryl cAMP, however, did not affect 17 alpha,20 beta-P production. In the presence of 50 ng of 17 alpha-hydroxyprogesterone, dbcAMP (10 mM) and forskolin (1 to 100 microM) suppressed 17 alpha,20 beta-P production. It is suggested that cAMP mediates 17 alpha,20 beta-P production up to a certain threshold level, beyond which it inhibits 17 alpha,20 beta-P production.

Interactions between activin and follicle-stimulating hormone-suppressing protein and their mechanisms of action on cultured rat granulosa cells

Direct roles of follicle-stimulating hormone (FSH)-suppressing protein (FSP) and activin in regulation of ovarian granulosa cell differentiation have been reported recently. The present study further investigated the effects of these peptides on steroidogenesis and inhibin production as well as cAMP generation in cultured granulosa cells from immature, diethylstilbestrol (DES)-treated rats. In the presence of FSH (20 ng/ml) and activin (30 ng/ml), which enhanced FSH-induced aromatase activity, progesterone production and inhibin production, FSP (1-100 ng/ml) reversed the stimulating activities of activin in a dose-dependent manner. In addition, activin reversed the inhibitory effects of FSP on FSH-induced aromatase activity and inhibin production. In the presence of FSH, activin enhanced FSH-stimulated extracellular cAMP accumulation, and FSP caused a reduction in extracellular cAMP. Activin but not FSP also stimulated basal cAMP level. In the presence of forskolin, a potent stimulant of adenyl cyclase activity which stimulated extracellular cAMP, aromatase activity, progesterone production and inhibin production, activin augmented the effect of forskolin on all four parameters, whereas FSP significantly enhanced progesterone production without changing the other three parameters. Our findings suggest that activin action on rat granulosa cells may be mediated via regulation of cAMP generation. The action of FSP and FSH and/or activin-dependent, consistent with either an action as an activin binding protein or by a direct action of FSP on the granulosa cells.

Dynamics of ovarian follicular development in cattle following hysterectomy and during early pregnancy

Three experiments were conducted to evaluate ovarian follicular dynamics and functional activity during pregnancy in cattle. In 11 pregnant Charolais cows of Experiment I, size of largest follicle, number of follicles and accumulated follicle size were reduced by day 27 of pregnancy on the ovary bearing the corpus luteum (CL) but not on the non-CL bearing ovary. In experiment II, local attenuation of ovarian follicular development on the CL bearing ovary of seven pregnant heifers was evident compared to the contralateral ovary without the CL. However, in four hysterectomized heifers, follicular development was sustained on both the CL- and non-CL bearing ovaries when CL maintenance was achieved without presence of the uterus or conceptus. In Experiment III, steroidogenic characteristics of the largest and second largest follicles at 17 d postestrus were evaluated for seven pregnant and six cyclic cattle. Follicle by physiological status interactions were detected for both aromatase activity of the follicle and follicular fluid concentrations of estradiol and progesterone. In cyclic cows, the largest follicle had appreciably more aromatase activity than did the second largest follicle; whereas, aromatase activity of the largest follicle from pregnant cows was less than that of cyclic cows. However, in pregnant cows the second largest follicle became the estrogen-active follicle, and this follicle occurred with a higher frequency on the ovary contralateral to the CL-bearing ovary. These changes in aromatase activity were reflected by parallel changes in estrogen concentrations of follicular fluid. The higher progesterone concentration in follicular fluid of the largest follicle in pregnant cows provided further confirmation of their atretic status. In conclusion, during early pregnancy the conceptus and/or uterus ipsilateral to the conceptus appear to secrete compounds which alter local follicular steroidogenic activity and attenuate subsequent follicular growth between 17 to 34 d of pregnancy on the CL-bearing ovary. This local mechanism acting within the ovary may contribute to the antiluteolytic effects of early pregnancy in cattle.

Action of LH, FSH and (Bu)2 cAMP on the conversion of [3H]19-hydroxyandrostenedione into oestrogens by foetal and infantile rat ovaries in organ culture

Ovaries from 18-21-day-old foetal as well as from 2-10-day-old infantile rats were cultured in vitro in the presence of [3H]19-hydroxyandrostenedione and in the presence or absence of LH, FSH or (Bu)2 cAMP, and oestrone and oestradiol formed were determined by double isotopic dilution and recrystallization to constant specific activity. In foetal ovaries, the stimulation factor with FSH was 0.9-1.3, which was considered insignificant in comparison with the 8-13-fold stimulation obtained with (Bu)2 cAMP. At infantile stages, aromatase activity was stimulated 1.3-3.5-fold, which was close to the 3.9-fold stimulation obtained with (Bu)2cAMP. LH was ineffective at both foetal and infantile stages.

The effect of bovine activin and follicle-stimulating hormone (FSH) suppressing protein/follistatin on FSH-induced differentiation of rat granulosa cells in vitro

The time- and dose-dependent effects of bovine activin A and bovine follicle stimulating hormone (FSH) suppressing protein (FSP) or follistatin on basal and FSH-induced steroidogenesis and inhibin production were studied in granulosa cells from immature, diethylstilbestrol (DES)-treated rats. In the presence of rat FSH (20 ng/ml) which stimulates aromatase activity and the production of progesterone and inhibin, activin (0.3-100 ng/ml) augmented all three parameters, whereas FSP (0.3-100 ng/ml) enhanced progesterone production and attenuated the other two parameters. In the absence of FSH, the basal parameters were unaffected by treatment with either activin or FSP alone, except for a statistically significant increase in basal inhibin in the presence of activin alone (P less than 0.05, at doses of 30 and 100 ng/ml). Neither activin nor FSP influenced the timing of the maxima of FSH-induced activities over 5 days. These findings suggest that activin and FSP, both present in follicular fluid, may play an important role in the local regulation of granulosa cell differentiation.

Non-steroidal low molecular substance from porcine follicular fluid inhibits aromatase activity

To clarify the underlying mechanism of the inhibitory control of the non-steroidal substance from porcine follicular fluid on estradiol secretion by granulosa cells, the suppression of aromatase activity was studied in vitro. Follicular fluid from porcine small follicles was filtered through an Amicon PM-10 membrane and a filtrate with a molecular weight of less than 10,000 was obtained. The filtrate was eluted on a Sephadex G-25 column (1.5 x 70 cm) using 0.01N CH3COOH, pH 4.0 as the elution buffer. The fraction containing the first peak of peptide (Fraction A) was used for subsequent experiments. Human placental microsomal fraction was used for the aromatase source. Aromatase activity was examined by counting the radio-activity of 3H2O converted from (1 beta, 2 beta 3H)-testosterone. The conversion of 3H2O from (1 beta, 2 beta 3H)-testosterone by rat's granulosa cells cultured in serum-free medium was also examined. Fraction A significantly suppressed aromatase activity of placental microsomal fraction by 57% at 120 min, and by 38% at 180 min, in dose and time-dependent manners. The aromatase activity of cultured rat granulosa cells was also inhibited by Fraction A in a dose-dependent manner. These results demonstrate the presence of a low molecular non-steroidal substance in the follicular fluid which is capable of inhibiting aromatase activity. This substance could provide important insights into the regulatory mechanism of differentiated functions of granulosa cells.

The effect of tumor necrosis factor/cachectin on follicle-stimulating hormone-induced aromatase activity in cultured rat granulosa cells

We investigated the effects of tumor necrosis factor (TNF)/cachectin on follicle-stimulating hormone (FSH)-induced aromatase activity in cultured rat granulosa cells using the stereospecific transfer of 3H from [1 beta-3H] androstenedione into 3H2O. TNF (10 pg/ml-10 ng/ml) inhibited FSH (250 ng/ml)-induced aromatase activity in a concentration-dependent manner, and 10 ng/ml of TNF completely abolished the FSH-induced aromatase activity. A time course analysis of the effects of TNF showed that TNF had no effect on induced aromatase activity, but inhibited the further induction of the enzyme by FSH. TNF (10 ng/ml) also inhibited the ability of TGF beta (1 ng/ml) to enhance aromatase activity and increase progesterone synthesis. Thus, TNF is a component of the complex array of proteins that modulate ovarian function and, as such, may play a physiological role in the regulation of the granulosa cell. In view of its association with cachexia, it may also play a pathophysiological role in the suppression of reproductive function during chronic illness.

Cyclosporine differentially affects estrogen and progestin synthesis by rat granulosa cells in vitro

Potential side-effects of the immunosuppressive drug cyclosporine (also cyclosporin A, CsA) on ovarian endocrine function have been investigated using granulosa cells isolated from immature estrogen-primed rats and cultured in a chemically defined medium. The FSH-dependent differentiation of steroidogenic pathways for estrogen and progestin secretion was shown to be differentially affected by CsA in vitro, at drug concentrations that approximate immunosuppressive concentrations in blood of humans or animals. CsA at 0.1-1 microgram/ml synergistically enhanced FSH-stimulated aromatase activity as measured by the conversion of exogenous testosterone to 17 beta-estradiol, while production of the progestins (progesterone + 20 alpha-hydroxypregn-4-en-3-one + pregnenolone) was little affected at up to 0.1 microgram/ml CsA and reduced at higher concentrations. CsA alone did not stimulate basal steroid secretion. The action of CsA to augment FSH-stimulated induction of aromatase activity was seen both in the presence or absence of testosterone. The effects of CsA (1 microgram/ml), either stimulatory on aromatase activity or inhibitory on progestin secretion, were in general increased with greater times of cell exposure throughout the culture period, although the temporal effects on 17 beta-estradiol and the progestins were not identical following delayed addition or removal of CsA from the culture medium. Higher concentrations of CsA (3-10 micrograms/ml) were generally toxic to granulosa cells as indicated by marked decreases in 17 beta-estradiol and progestin secretion and in incorporation of [3H]leucine. These results suggest that therapeutic concentrations of CsA might directly influence ovarian function by differentially modulating the FSH-dependent steroidogenic pathways of granulosa cells.

Rat thecal/interstitial cells produce a mitogenic activity that promotes the growth of granulosa cells

To test the hypothesis that the cells outside the basal lamina of the follicle secrete paracrine factors that influence the cells on the inside of the follicle, two ovarian cell populations were obtained from diethylstilbestrol-treated rats. Granulosa cells were obtained by extrusion from the follicles and an ovarian cell preparation, termed thecal/interstitial, was derived from the granulosa cell-depleted ovaries. Light microscopy showed that each cell population in culture had distinctive morphologies. Electrophoretic examination of the radiolabeled proteins secreted by the two ovarian cell preparations revealed that each secreted unique protein components into the culture medium. Rat thecal/interstitial cell-conditioned medium promoted [3H]thymidine incorporation into normal rat kidney cell line (NRK) DNA and into bovine granulosa cell DNA. The growth-promoting activity was stable to heating at 70 degrees C for 5 min whereas native fibroblast growth factor (FGF) lost its activity, showing that the factor was not characteristic of FGF. To further characterize the growth-promoting activity thecal/interstitial cell-conditioned medium was concentrated and the proteins separated by size exclusion high performance liquid chromatography. The growth-promoting activity eluted with an apparent molecular weight between 15,000 and 25,000. The finding that thecal/interstitial cells in culture secrete growth-promoting factors suggests that those cells that are in close proximity to the granulosa cells may secrete protein factors that diffuse into the follicular antrum and influence granulosa cell proliferation.

Growth hormone and insulin-like growth factor-I accelerate PMSG-induced differentiation of granulosa cells

To investigate the nature of the interactions between growth hormone (GH), insulin-like growth factor-I (IGF-I) and follicle stimulating hormone (FSH), their temporal and dose-related effects on steroidogenesis were studied in granulosa cells from stilboestrol-treated immature rats, stimulated in vitro with pregnant mare's serum gonadotropin (PMSG) or FSH. GH in the presence of PMSG enhanced aromatase activity and progesterone synthesis above that induced by maximally stimulating doses of PMSG alone, and accelerated PMSG-induced peak levels for both progesterone and aromatase activity. IGF-I also enhanced PMSG-induced aromatase activity and progesterone production, and accelerated their peak responses in a similar fashion to the effects observed for GH. The stimulatory actions of IGF-I could still be observed after the removal of FSH from the cultures, and appeared to be partly independent of cAMP. It is concluded that both GH and IGF-I act on FSH-induced granulosa cells to accelerate the differentiation of the follicular cell to a lutein cell.

Aromatase activity in granulosa cells: regulation by growth factors

This study describes the effects of insulin, insulin-like growth factor 1 (IGF1), and epidermal growth factor (EGF) on the aromatase activity of granulosa cells isolated from immature rat ovaries. None of the growth factors alone influenced the basal level of aromatase activity, but did modulate follicle-stimulating hormone (FSH)-induced aromatase activity. Insulin and IGF1 augmented the action of a sub-optimal concentration of FSH (5 ng/mL) on aromatase activity in a dose-dependent manner. In contrast, EGF (1-10 ng/mL) was effective in inhibiting aromatase activity maximally stimulated by FSH. Since insulin and IGF1 had opposing actions to those of EGF on FSH-induced aromatase activity, we examined the interactions between the growth factors. EGF inhibited the actions of both FSH and insulin on aromatase activity. Both IGF1 and EGF increased the [3H]thymidine incorporation into the DNA of bovine granulosa cells in vitro, IGF1 being a more potent mitogen. Whereas EGF inhibited the actions of IGF1 on aromatase activity, it did not inhibit the effects of IGF1 on the growth of granulosa cells. In summary, growth factors influence both the differentiation and growth of granulosa cells, and may be important regulators of follicular development.

Vasoactive intestinal peptide enhances aromatase activity in the neonatal rat ovary before development of primary follicles or responsiveness to follicle-stimulating hormone

We have investigated the factors that regulate aromatase activity in fetal-neonatal rat ovaries. Ovarian aromatase activity (assessed by measuring the amount of 3H2O) formed from [1 beta-3H]testosterone) is low prior to birth (less than 0.5 pmol/hr per mg of protein) and increases to values greater than 30 pmol/hr per mg of protein between days 8 and 12 after birth. The appearance of ovarian aromatase (postnatal days 2-4) coincides with the development of primordial follicles. Fetal-neonatal ovaries maintained in serum-free organ culture do not develop aromatase activity at the expected time. Ovine follicle-stimulating hormone (0.1-1 microgram/ml), ovine luteinizing hormone (0.1 microgram/ml), or their combination failed to induce the enzyme activity in cultured fetal ovaries, whereas follicle-stimulating hormone is effective in preventing the decline in aromatase activity when postnatal day 8 ovaries are placed in culture. In contrast to follicle-stimulating hormone, dibutyryl-cAMP markedly enhances ovarian aromatase in cultured fetal ovaries. Likewise, enhancement of endogenous cAMP formation with forskolin or cholera toxin caused an increase in enzyme activity within 24 hr. Vasoactive intestinal peptide, a peptide known to occur in ovarian nerves, caused a dose-dependent increase in aromatase activity in fetal ovaries prior to folliculogenesis. Of related peptides tested, only the peptide having N-terminal histidine and C-terminal isoleucine amide was capable of inducing aromatase activity in fetal ovaries. The fact that VIP can induce aromatase activity in fetal rat ovaries prior to follicle formation and prior to responsiveness to follicle-stimulating hormone suggests that this neuropeptide may play a critical role in ovarian differentiation.

Actions of growth factors in the follicle

In this paper we have examined the possibility that soluble factors produced by the thecal and granulosa cells may be essential local modulators of follicular development. The observations that insulin could influence both the growth and the differentiation of granulosa cells were important in establishing the concept that peptides could act as amplifiers of the actions of gonadotrophins. Insulin alone did not influence aromatase activity significantly but acted synergistically with FSH to augment aromatase activity in rat granulosa cells. Unlike aromatase activity, insulin alone was able to significantly stimulate 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity, the maximum level achieved approaching that obtained with high concentrations of FSH. To determine if insulin could influence other parameters of granulosa cell function in addition to steroidogenesis, we measured a component of extracellular matrix, fibronectin, previously shown to be inhibited by FSH. Treatment with insulin independently inhibited the increase in fibronectin secretion observed in control cultures. Also, insulin alone was able to stimulate quiescent bovine granulosa cells to incorporate [3H]thymidine into DNA under serum-conditions. The concentration of insulin required in these experiments was higher than physiological levels suggesting that other insulin-like growth factors may be involved. Our work and that of others has shown that IGF1 can mimic the actions of insulin and is effective at lower concentrations. A possible source of IGF1 production in the follicle was sought initially by collecting rat granulosa cell conditioned medium, and assessing biological activity and immunoreactivity. Conditioned medium augmented the actions of FSH on aromatase activity and alone stimulated 3 beta-HSD, indicating the presence of insulin-like bioactivity. A positive reaction on immunoblots using specific antiserum confirmed the presence of immunoreactive IGF1. Conditioned medium from thecal cells contained a growth-promoting activity (TcGF) that did not augment FSH-induced aromatase activity. The production of growth factors locally within the follicle may represent the self-amplifying mechanism that enables the dominant follicle to complete its developmental program and ovulate.

Nicotine, cotinine, and anabasine inhibit aromatase in human trophoblast in vitro

Epidemiologic studies suggest that women who smoke have lower endogenous estrogen than nonsmokers. To explore the possible link between cigarette smoking and decreased endogenous estrogens, we have examined the effects of constituents of tobacco on estrogen production in human choriocarcinoma cells and term placental microsomes. In choriocarcinoma cell cultures, nicotine, cotinine (a major metabolite of nicotine), and anabasine (a minor component of cigarette tobacco) all inhibited androstenedione conversion to estrogen in a dose-dependent fashion. Removal of nicotine, cotinine, and anabasine from the culture medium resulted in the complete reversal of the inhibition of aromatase. In the choriocarcinoma cell cultures, a supraphysiologic concentration of androstenedione (73 microM) in the culture medium blocked the inhibition of aromatase caused by nicotine, cotinine, and anabasine. In preparations of term placental microsomes, nicotine, cotinine, and anabasine inhibited the conversion of testosterone to estrogen. Kinetic analysis demonstrated the inhibition to be competitive with respect to the substrate. These findings suggest that some nicotinic alkaloids directly inhibit aromatase. This mechanism may explain, in part, the decreased estrogen observed in women who smoke.

Differential actions of phorbol ester and diacylglycerol on inhibition of granulosa cell maturation

Hormonal induction of granulosa cell maturation is inhibited by phorbol esters and permeant synthetic diacylglycerols, but these activators of protein kinase C differ in their effects on cAMP production and actions. Both agents prevented the induction of luteinizing hormone receptors and progesterone biosynthesis by follicle-stimulating hormone, choleragen, and forskolin, but only diacylglycerol abolished the cAMP responses to these stimuli. Granulosa cell aggregation and aromatase activity were inhibited by phorbol ester but not completely by diacylglycerol. In intact granulosa cells, cytosolic C kinase activity was rapidly decreased by phorbol ester but unaffected by diacylglycerol. Although diacylglycerol has a marked inhibitory action on cAMP production, the more prominent suppression of granulosa cell differentiation by phorbol ester may be related to its rapid and prolonged action on kinase C.

Steroid conversions by the 19-day old foetal rat ovary in organ culture

The ovaries from 19-day old foetal rats were cultured in vitro on Wolff and Haffen's semi-solid medium with radioactive progesterone, dehydroepiandrosterone, testosterone or androstenedione added as precursors, and in the presence or absence of lutropin, follitropin and human chorion gonadotropin. After a 24-h culture period, the media were analysed for the presence of testosterone, androstenedione, oestrone and oestradiol, which were measured by specific activity determination after isotopic dilution.

Aromatase activity in human granulosa cells during follicular development and the modulation by follicle-stimulating hormone and insulin

Granulosa cells were isolated from follicles that ranged in size from 0.4 to 2.0 cm in diameter, obtained from patients during the follicular phase of the menstrual cycle. Aromatase activity, assessed by the release of tritiated water from [1 beta-3H]testosterone, was undetectable in follicles with a diameter of less than 1.0 cm; thereafter, there was a direct correlation between aromatase activity and follicular diameter. When cultured in the presence of 200 ng of National Institutes of Health follicle-stimulating hormone-15 per milliliter, aromatase activity was stimulated in cells isolated from all sizes of follicles from 0.4 to 1.5 cm. Insulin (500 ng/ml) further augmented follicle-stimulating hormone (FSH)-induced aromatase activity, as evidenced both by an increase in 17 beta-estradiol production and by the release of tritiated water from [1 beta-3H]testosterone by granulosa cells. This study further delineates the role of FSH in estrogen production during human follicular development and suggests that insulin or insulin-like growth factors may play a role in modifying the FSH-dependent cellular differentiation of human granulosa cells.

The role of cyclic AMP in the induction of estrogen and progestin synthesis in cultured granulosa cells

The role of cyclic AMP in the induction of enzymes involved in estrogen and progestin biosynthesis in undifferentiated granulosa cells was investigated. When granulosa cells from immature hypophysectomized, DES-treated rats were cultured for 2 days in serum-free medium with aromatase substrate (10(-7) M androstenedione) together with graded doses of FSH, prostaglandin E2 (PGE2), cholera toxin (CT), or dibutyryl cyclic AMP (Bu2cAmP), there was a dose-related increase in estrogen (E) production. The induction of E production by saturating doses of FSH, PGE2, CT, and Bu2cAmP required a lag phase of approximately 24 h, after which the E response increased sharply to maximum levels at day 3, and then declined gradually to day 5. Treatment for 24 h ((day 0-1) with FSH, together with 1 microgram/ml of either actinomycin D or cycloheximide, completely abolished the stimulatory action of FSH on E production. When the inhibitors were removed, the FSH-induced increases in E returned to near normal levels after a 24-h lag period. Similar effects of the inhibitors upon E production by CT, PGE2 and Bu2cAMP were observed. As with E, the production of progesterone and 20 alpha-dihydroprogesterone was markedly stimulated by FSH, PGE2, CT and Bu2cAmP, and the results of the time course, dose response, and inhibitor experiments were similar to those for E production. These results indicate that FSH induces the de novo synthesis of enzymes required for both estrogen and progestin biosynthesis by undifferentiated granulosa cells and suggest that this action is mediated by cyclic AMP.