Gonadotropin-releasing hormone receptor messenger ribonucleic acid expression in rat ovary.

Rat GnRH pituitary receptor complementary DNA was used to isolate a truncated clone from a rat corpus luteum complementary DNA library that proved to be identical in sequence to the rat anterior pituitary GnRH receptor. The distribution of the GnRH receptor messenger RNA (mRNA) was then determined in rat ovary using in situ hybridization. GnRH receptor expression was investigated in cyclic female rats and in hypophysectomized immature female rats treated with either recombinant human FSH or human menopausal gonadotropin. The expression of LH receptor mRNA was determined in serial sections as an index of the health and differentiation of the follicles. In cyclic animals, GnRH receptor mRNA was detected in granulosa cells at varying stages of follicular development and in the corpus luteum. Ovaries from hypophysectomized animals expressed GnRH receptor mRNA in the granulosa cells of most follicles. The administration of FSH or human menopausal gonadotropin to hypophysectomized animals altered the distribution of GnRH receptor mRNA. During antral development, the signal was most abundant in medium-sized follicles not expressing LH receptor mRNA and showing signs of follicular atresia. However, healthy preovulatory follicles also expressed GnRH receptor mRNA. We conclude that the expression of the GnRH receptor gene in granulosa cells is 1) individually regulated for each follicle, 2) persists in the corpus luteum, and 3) expressed in atretic follicles.

Ovarian thecal/interstitial androgen synthesis is enhanced by a follicle-stimulating hormone-stimulated paracrine mechanism.

To obtain direct evidence for FSH-stimulated paracrine signaling in the ovary, 21-day-old intact or hypophysectomized female Wistar rats received four sc injections of recombinant human FSH (rhFSH; total dose, 16-72 IU) at 12-h intervals. Ovaries were removed 48 h after the first injection to extract total RNA for Northern analysis of 17-hydroxylase/C17-20-lyase (cytochrome P450c17 alpha) mRNA or to isolate thecal/interstitial cells for assessment of basal and hLH-responsive androgen synthesis in vitro. In situ hybridization with a 35S-labeled cytochrome P450c17 alpha cRNA probe confirmed that expression of the cytochrome P450c17 alpha gene was specific to thecal/interstitial cells. The approximately 2.0-kilobase P450c17 alpha mRNA signal in ovarian total RNA from intact animals was increased approximately 5-fold by treatment with rhFSH (total dose, 72 IU) or PMSG (15 IU). This effect was shown to be dose dependent, with a approximately 2-fold increase in response to 16 IU (total dose) rhFSH. P450c17 alpha mRNA levels in isolated granulosa and thecal/interstitial cell total RNA from intact animals were compared to establish which was the principal cellular site of P450c17 alpha mRNA expression. The P450c17 alpha mRNA signal was undetectable in control granulosa cells and only barely discernible after treatment with 72 IU (total dose) rhFSH. In contrast, P450c17 alpha mRNA was abundant in control thecal/interstitial mRNA, and its level was increased 4- to 6-fold by treatment with rhFSH. Treatment of hypophysectomized animals with rhFSH did not consistently alter ovarian P450c17 alpha mRNA levels. During culture for 48 h in serum-free medium, basal androgen (androstenedione plus androsterone) production by thecal/interstitial cells from intact animals was unaffected by treatment with rhFSH in vivo, but hLH-stimulated androgen production by these cells was enhanced approximately 2-fold. Neither basal nor hLH-responsive androgen production by thecal/interstitial cells from hypophysectomized animals was altered by previous treatment with rhFSH in vivo. Treatment of thecal/interstitial cell cultures from both intact and hypophysectomized animals with inhibin (0.1-30 ng/ml), a putative granulosa-derived paracrine factor, did not measurably affect basal androgen synthesis, but potently enhanced LH-responsive androgen synthesis in vitro. Similarly, treatment of thecal/interstitial cell cultures with conditioned medium from FSH-treated granulosa cell cultures significantly enhanced LH-responsive, but not basal, androgen production. We conclude that treatment of pituitary-intact rats with "pure" FSH modulates thecal/interstitial cell androgen synthesis. Granulosa cells, but not thecal cells, possess FSH receptors, and thecal/interstitial cells are the principal ovarian sites of P450c17 alpha expression.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of 3 beta-hydroxysteroid dehydrogenase delta 5/delta 4-isomerase and cholesterol side-chain cleavage cytochrome P450 by activin in rat granulosa cells.

Activin is a dimeric protein implicated in the local control of follicular steroidogenesis. Using cultured rat granulosa cells, we previously showed that the effect of activin on FSH-induced progesterone synthesis changes with preovulatory follicular development, from positive regulation in nondifferentiated (immature) granulosa cells to negative regulation in preovulatory (mature) granulosa cells. The aim of the present study was to assess development-related effects of activin on the expression of enzymes crucial to progesterone synthesis: cholesterol side-chain cleavage cytochrome P450 (P450scc) and 3 beta-hydroxysteroid dehydrogenase/delta 5-4-isomerase (3 beta HSD). Nondifferentiated granulosa cells were isolated from the ovaries of estrogen-pretreated immature female rats that received no other treatment; differentiated granulosa cells were obtained from similar animals treated for 48 h with human FSH to induce preovulatory follicular development. Cells were cultured for 48 h in serum-free medium with and without human FSH and/or recombinant activin-A, and medium was collected for measurement of progestagens (progesterone, pregnenolone, and 20 alpha-dihydroprogesterone). In cultures of nondifferentiated granulosa cells, activin augmented the FSH-induced production of all three steroids. In differentiated granulosa cells, activin suppressed the FSH-stimulated production of progesterone and 20 alpha-dihydroprogesterone, but had no effect on pregnenolone. The presence of exogenous pregnenolone increased the overall production of progesterone, but did not alter qualitative steroidogenic responses to activin. To assess the interaction between FSH and activin on 3 beta HSD and P450scc messenger RNA (mRNA) expression, Northern blot analyses were performed on total RNA isolated from cultured granulosa cells. Treatment in vitro with FSH alone markedly enhanced the abundance of both the 3 beta HSD and P450scc mRNA transcripts in nondifferentiated and differentiated granulosa cells. FSH-stimulated expression of P450scc mRNA was further enhanced by cotreatment of nondifferentiated granulosa cells with activin. However, activin had no consistent effect on FSH-stimulated expression of 3 beta HSD mRNA in nondifferentiated cells. In differentiated granulosa cells, both mRNAs were suppressed more than 50% by the presence of activin. We conclude that the in vitro effects of activin on FSH-induced expression of 3 beta HSD and P450scc mRNAs in rat GC are similar: initially stimulatory (P450scc) or without effect (3 beta HSD), then becoming completely inhibitory. The mechanism of this development-dependent change in the granulosa cell response to activin remains to be elucidated.

Cell-specific expression of aromatase and LH receptor mRNAs in rat ovary.

Current understanding of the endocrine and paracrine regulation of follicular oestrogen synthesis predicts that aromatase cytochrome P450 (P450arom) mRNA is inducible by FSH in granulosa cells. LH receptor mRNA is constitutively expressed in thecal/interstitial cells, and is also thought to be induced in granulosa cells in response to joint stimulation by FSH and oestrogen. This study provides direct evidence that FSH induces the ovarian P450arom gene selectively, perhaps exclusively, in the granulosa cells of Graafian follicles. FSH-induction of LH receptor mRNA occurs simultaneously but is independent of oestrogen synthesis per se.

Induced luteal regression: differential effects on follicular and luteal inhibin/activin subunit mRNAs in the marmoset monkey.

During the luteal phase of the primate ovulatory cycle the predominant inhibin/activin subunit mRNAs produced by the corpus luteum and antral follicles are those for the alpha- and beta B-subunits respectively. The control of expression of these mRNAs and the resultant nature of the endocrine and paracrine signals which they may potentially generate has yet to be elucidated. Inhibin/activin subunit mRNAs may have a role in both the paracrine regulation of follicular and luteal function and modulation of FSH secretion. The aim of this study was to investigate the expression of inhibin/activin subunit mRNAs following luteal regression induced by either withdrawal of LH support (GnRH antagonist treatment), or by a direct inhibitory action (prostaglandin administration). Marmoset monkeys with regular ovulatory cycles were treated on day 8 and 9 of the luteal phase with either GnRH antagonist, prostaglandin or vehicle (n = 3 per group). Ovaries were studied 48 h after onset of treatment (on day 10 of the luteal phase) by hybridizing frozen tissue sections with radiolabelled riboprobes specific to the inhibin/activin alpha-, beta A- and beta B-subunit mRNAs. After autoradiographic exposure, grain concentrations were quantified by image analysis. In corpora lutea from control marmosets there was high expression of alpha-mRNA with only marginal expression of beta B-mRNA. Corpora lutea in animals treated with GnRH antagonist or prostaglandin had markedly reduced expression of alpha-mRNA while beta B-mRNA was unchanged. In controls, all healthy antral follicles exhibited a high level of expression of beta B-mRNA in the granulosa cells and low expression of alpha-mRNA in theca cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental regulation of androgen receptor in rat ovary.

Androgen receptor (AR) distribution and developmental regulation in the rat ovary were examined by semiquantitative immunohistochemistry. Ovarian AR mRNA levels were also determined by Northern analysis of total RNA and compared with the levels of cytochrome P450aromatase (P450arom), an established marker of preovulatory follicular maturity. Hypophysectomized immature female rats were treated with recombinant human (rh)-FSH and/or rh-LH, or human menopausal gonadotrophin (HMG). AR was predominantly located in granulosa cells. There was no indication of specific AR immunoreactivity in thecal cells, but scattered stromal cells did stain positively. In control and LH-treated ovaries, only small preantral/early antral follicles were present. Granulosa cells in these follicles showed intense AR immunostaining. Treatment with FSH, FSH and LH or HMG stimulated varying degrees of preovulatory follicular development. In these follicles, the intensity of AR immunostaining progressively declined as follicular development progressed. In intact immature rats treated with FSH, the abundance of ovarian AR mRNA was significantly decreased to 35% of the control value while combined treatment of FSH and LH resulted in further down-regulation of AR mRNA expression to 17% of the control value. A decrease in the abundance of AR mRNA was accompanied by a simultaneous increase in the abundance of P450arom mRNA. Similar results were obtained in hypophysectomized immature rats treated with FSH and LH, suggesting an inverse relationship between AR mRNA expression and granulosa cell maturity. These results suggest that (1) the AR is most abundant in the granulosa cells of rat ovaries and (2) the expression of AR and its mRNA are developmentally regulated, being down-regulated during FSH-stimulated preovulatory follicular development.

Granulated lymphocytes of pregnancy.

In pregnant mammals, the antigenically distinctive conceptus implants and grows in a uterine environment governed by the maternal immune system. The uterus per se is not immunologically privileged and large numbers of lymphocytes accumulate at implantation sites. In mice and humans, many of these lymphocytes have been identified as uterine natural killer (uNK) cells and exhibit a characteristic granulated morphology. In this review we focus on uNK cells and discuss their origin, differentiation and possible roles in the maintenance of healthy pregnancies. In species with less invasive placentation (ruminants, pigs), lymphocytes with similar granular morphology also appear during gestation and their identity and possible functions are examined.

Follicular oestrogen synthesis: the 'two-cell, two-gonadotrophin' model revisited.

The original 'two-cell mechanism' explained the endocrine regulation of follicular oestrogen synthesis and implied paracrine signalling in the follicle wall. It is now known that the CYP17 gene encoding 17-hydroxylase/C17-20-lyase activity crucial to androgen synthesis, is expressed exclusively in thecal cells. 17-Hydroxylase/C17-20-lyase activity is regulated by LH and subject to local modulation by a factor(s) emanating in FSH-stimulated granulosa cells. The FSH receptor gene is expressed exclusively in granulosa cells, where FSH acts directly to induce cytoproliferation and differentiation via cyclic AMP/protein kinase-A mediated post-receptor signalling. Granulosa cells also express androgen receptors, and theca-derived androgen has the potential to modulate locally differentiative responses to FSH. When follicles are recruited to preovulatory development by FSH, their granulosa cells develop LH receptors functionally coupled to aromatase activity and inhibin production. Thereby they simultaneously undertake LH-responsive aromatization and inhibin synthesis. Inhibin has the potential to potently enhance LH-stimulated thecal androgen synthesis. Granulosa-derived inhibin may therefore participate in a paracrine mechanism that locally amplifies androgen synthesis, and hence oestrogen formation, in the preovulatory follicle(s).

Expression of c-myc and c-fos in rat skeletal muscle. Evidence for increased levels of c-myc mRNA during hypertrophy.

The levels of c-myc and c-fos mRNA were investigated in rat skeletal muscle by Northern hybridization. During post-natal development in the rat, c-myc mRNA levels were similar at birth and at 7 and 21 days of age, but then declined at 90 days and were barely detectable at 1 year. c-fos mRNA levels followed this pattern of expression until 90 days, but showed a large increase at 1 year. Hypertrophy of soleus and plantaris muscles was induced either by severance of the tendon to the synergistic gastrocnemius (tenotomy) or by administration of the beta-adrenoceptor agonist clenbuterol. In both cases hypertrophy was associated with a rapid increase in c-myc mRNA levels. Following tenotomy the increase was both greater (8-fold) and more rapid (3 h) in soleus than in plantaris (2-3 fold, 12 h). Similar effects were observed during clenbuterol administration. Neither treatment caused any alteration in c-fos mRNA levels in the plantaris muscle. The results show that increased c-myc mRNA levels are an early event in the response of skeletal muscle to hypertrophic stimuli; it is argued that this occurs within the differentiated skeletal muscle fibres.

c-myc mRNA in cytoskeletal-bound polysomes in fibroblasts.

3T3 fibroblasts were treated sequentially with 25 mM-KCl/0.05% Nonidet P40, 130 mM-KCl/0.05% Nonidet P40 and finally with 1% Nonidet P40/1% deoxycholate in order to release free, cytoskeletal-bound and membrane-bound polysomes respectively. The membrane-bound fraction was enriched in the mRNA for the membrane protein beta 2-microglobulin, whereas the cytoskeletal-bound polysomes were enriched in c-myc mRNA. Actin mRNA was present in both free and cytoskeletal-bound polysomes. The results suggest that cytoskeletal-bound polysomes are involved in the translation of specific mRNA species.

Gonadotrophin control of follicular function.

It has been known for over 50 years that both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are required to stimulate both follicular development and oestradiol synthesis. However, previous experiments employing FSH and LH preparations (whether of pituitary or urinary origin) have not been able to answer unequivocally, whether an observed response was solely due to either FSH or LH because they were not pure preparations. In view of the recent availability of both 100% pure recombinant human FSH and recombinant human LH, we now have a unique opportunity to test their contribution in the regulation of ovarian function. Such experiments may have important clinical implications as they offer a means to interpret the effect of 'pure' FSH preparations when used to stimulate ovarian function in women undergoing different therapeutic regimens. To test the contribution of LH to optimize ovarian responsiveness to FSH, 21-day-old hypophysectomized, immature, female rats were treated for a 2-day period with varying total doses of rec-FSH (30-72 IU and/or rec-LH at 12-hourly intervals. At 48 h after the first injection, ovaries were removed, weighed and used to isolate granulosa and thecal interstitial cells for assessment of basal and gonadotrophin-responsive steroidogenesis in vitro; homogenized to extract total RNA for Northern analysis of 17-hydroxylase/C17-20-lyase (cytochrome P-450C17); mRMA; or examined using in situ hybridization to determine the expression of P-450C17 in the rat graafian follicle. The experiments demonstrated the potential for rec-FSH to influence LH-responsive androgen synthesis (via a paracrine mechanism) which involves an up-regulation of thecal P-450C17 mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

The cyclo-oxygenase inhibitors indomethacin and ibuprofen inhibit the insulin-induced stimulation of ribosomal RNA synthesis in L6 myoblasts.

Insulin stimulated total RNA accretion and the incorporation of [3H]uridine into RNA in L6 skeletal-muscle myoblasts. Incorporation of uridine into the rRNA was measured after either separation of 18 S and 28 S rRNA species by agarose-gel electrophoresis or separation of dissociated 40 S and 60 S ribosomal subunits on sucrose density gradients. Both methods showed a stimulation by insulin of uridine incorporation into the RNA of the two subunits. Two non-steroidal anti-inflammatory drugs, indomethacin and ibuprofen, which inhibit the metabolism of arachidonic acid by the cyclo-oxygenase pathway, inhibited the insulin-induced accretion of total cellular RNA and the incorporation of uridine into the RNA of both ribosomal subunits. The effect of insulin was observed both by using a tracer dose of [3H]uridine (5 microM) and in the presence of a high concentration (1 mM) of uridine to minimize possible changes in intracellular precursor pools. Neither insulin nor indomethacin was found to affect the incorporation of uridine into the total intracellular nucleotide pool, or the conversion of uridine into UTP. The ability of inhibitors of arachidonic acid metabolism to prevent insulin-induced increases in RNA metabolism suggests that a prostaglandin or other eicosanoid is involved in the signal mechanism whereby insulin stimulates RNA synthesis.