Regulators of steroid secretion and inhibin activity in human ovarian follicular fluid

Elevated inhibin concentration in the follicular fluid of dairy cows with chronic cystic ovarian disease

This study compared serum and follicular fluid inhibin and gonadotropin profiles between chronic cystic ovarian diseased (CCOD) and normal cyclic dairy cows. Blood samples and follicular fluid were collected from CCOD cows (n=15) and cyclic cows in the follicular phase of the estrous cycle (control, n=6) and analyzed for inhibin, follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations. There was a significant increase in inhibin and a decrease in FSH and LH concentrations in the follicular fluid of CCOD cows compared with those of cyclic cows (P < 0.05). Mean serum inhibin, FSH and LH concentrations between CCOD and cyclic cows were not differnt (P > 0.05), however, there was a tendency for serum inhibin to be higher and FSH to be lower in CCOD cows compared to cyclic animals (P < 0.1). The FSH pulse frequency also was lower in CCOD cows than in cyclic cows (P < 0.05). These data suggest that increased production of inhibin from cystic follicles of CCOD cows alters pituitary FSH secretion and subsequently reduces the concentration of FSH in follicular fluid. As a result, decreased FSH stimulation at the ovarian level could ultimately lead to the reduction in follicular LH and FSH receptor concentrations, resulting in abnormal follicular steroidogenesis in CCOD dairy cows.

Isolation of luteinising hormone receptor binding inhibitor from bovine corpus luteum

A luteinising hormone receptor binding inhibitor (LHRBI) has been purified from bovine corpus luteum (CL). Steroid-free extract of the CL was subjected to successive chromatographies on Sephadex G-50, Q-Sepharose, Orange A dye and metal chelate affinity columns followed by high performance-reverse phase and gel filtration columns. Purification was monitored by the ability of the fractions to inhibit the binding of 125I-human chorionic gonadotropin (hCG) to porcine granulosa cells in vitro. The final isolate showed an 8000-fold enrichment of activity. It was also capable of inhibiting porcine granulosa cell secretion of estradiol and progesterone (P) in vitro. Administration of LHRBI into follicle-stimulating hormone (FSH)-stimulated, immature rats strongly inhibited the ovarian ovulatory response to hCG as revealed by decreased P levels and the number of ova released. The M(r) of LHRBI as assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis was ca. 15 kDa and the pI was between 5.0 and 5.5.

Immunocytochemical localization of follicle regulatory-protein (FRP) in testis

Follicle regulatory protein (FRP) can exert paracrine control over follicular development. It is synthesized by the granulosa cells of the developing follicles and was localized in the cytoplasm of the mural cells by immunocytochemistry. When administered to male dogs and rats, FRP causes impairment of spermatogenesis. In the intact male rat, it has been postulated that FRP manifests its effects at a stage prior to the conversion of testosterone to dihydrotestosterone. Sertoli cells of the seminiferous tubules are implicated in testosterone metabolism. Furthermore, Sertoli cells in male gonads are regarded as the counterpart of granulosa cells in ovaries. The exact source of FRP in the male is not known. Therefore, it was of interest to study the localization of FRP in the male gonads. Testicular sections of the pig, dog, cat, rat, mouse, monkey, and man were immunocytochemically stained with monoclonal antibody to porcine FRP of ovarian origin. Sections of pig ovaries were used as controls throughout the study. Specificity of immunocytochemical localization was established by preabsorption. FRP antibody predominantly localized to the interstitial compartment of the pig testis. In the seminiferous tubules, FRP localization was limited to basal spermatogonia and Sertoli cells of tubules at few specific stages of spermatogenesis. The study also showed that the monoclonal antibody against porcine FRP is species-specific. Antibody binding was found only in pig testis, whereas tissues from the cat, dog, mouse, rat, monkey, and man did not display any immunocytochemical reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Activin A increases the number of follicle-stimulating hormone cells in anterior pituitary cultures

The mode of action of activin A on the anterior pituitary gland (AP) was investigated using primary cultured cells. The AP cells were cultured with activin A (1 ng/ml) at various cell densities for 24-96 h, and further incubated for 3 h with activin A-free medium. When the cells were pretreated with activin A for 48 h, follicle-stimulating hormone (FSH) secretion during the following 3-h incubation was increased only at a density of 1 x 10(5) cells/200 mm2, but not at 2 x 10(5) or 4 x 10(5) cells/200 mm2. A longer pretreatment (96 h) was required in order to induce this response at a density of 2 x 10(5) cells/200 mm2. Luteinizing hormone (LH) secretion was not affected by activin A. Thus, the FSH secretory activity of the primary culture of AP was stimulated by activin A in a cell density-dependent manner. Furthermore, it was found that treatment with activin A (10 ng/ml) for 72 h increased the number of immunoreactive FSH cells by 25-41%, and that these newly induced FSH cells were low responders to gonadotropin-releasing hormone stimulation. The proportions of immunoreactive LH, thyroid-stimulating hormone, prolactin or growth hormone cells were not affected. From these results, we conclude that activin A increases FSH secretion by changing the cell population of pituitary gonadotropes.

Inhibin production by Sertoli cells during testicular regression in the golden hamster

The objective of this study was to determine if testicular regression in the hamster results in changes in Sertoli cell function that reflect altered pituitary function. Inhibin-like activity was measured in spent media from Sertoli cells cultured from adult control and optically enucleated hamsters with regressed testes using a homologous hamster Sertoli cell/hamster pituitary cell bioassay. The inhibin activity resulted in a dose-related decrease in FSH release from both normal and "regressed" pituitary cultures but maximal inhibition occurred at a 3- to 4-fold lower dose with media from Sertoli cells obtained from regressed hamsters. When pituitary cells from control adult or adult hamsters with regressed testes were incubated with Sertoli cell spent media, pituitary cells from regressed hamsters were more sensitive than normal pituitary cells to both normal and "regressed" inhibin. This greater production of inhibin-like activity and/or an enhanced sensitivity to inhibin in the regressed hamster may contribute to the decline in FSH levels during testicular regression. This data lends further support to a physiologic role for inhibin.

Reduction of fertility in the male rat by systemic treatment with follicle regulatory protein

Forty-five-day-old rats received daily injections of follicle regulatory protein (FRP). After 15, 30, 45, and 70 days of therapy, serum was measured for testosterone, androstenedione, estradiol, and follicle-stimulating hormone levels. Testes were evaluated for sperm head counts, plasminogen activator activity, weight, and length of seminiferous epithelial stages. In no case was serum follicle-stimulating hormone concentration reduced in FRP-treated rats. After 75 days of treatment, there was a significant decrease in the number of the sperm head counts. After 60 days of treatment, the length of the dark zone of the tubule was longer than that of control. Pregnancy rates for FRP-treated rats were reduced after 45 and 60 days of treatment. In conclusion, systemic injection of FRP alters seminiferous epithelial function by reducing development of mature sperm.

A postulated role for naturally occurring aromatase inhibitors in follicle selection

The studies reviewed here indicate that follicle regulatory protein (FRP) alters aromatase and 3B-hydroxysteroid dehydrogenase activity in porcine, human, and rat granulosa cells. The inhibitory effect of FRP on granulosal aromatase activity depend upon the response of the cell to FSH: large amounts of FSH can partially overcome FRP inhibition while relatively small amounts of FSH sensitize the granulosal aromatase system to FRP. Although androgens potentiate FSH-mediated granulosal functions, they also sensitize granulosa cell steroidogenic enzymes to inhibition by FRP. The demonstration that FRP acts primarily on granulosa cells of less mature antral follicles to inhibit aromatase supports the hypothesis that FRP may facilitate follicle selection and suggests a role for FRP in atresia. Most of the effects of FRP on granulosal activities reflect an interplay between the systemic endocrine and local paracrine systems. That FRP functions, at least in part, by modulating follicular response to FSH is consistent with the hypothesis that paracrine effectors are important mediators of folliculogenesis in the presence of gonadotropins.

Comparison of isoelectric focusing in Sephadex vs immobiline flatbeds for the recovery of follicle regulatory protein from porcine follicular fluid

We describe and compare the use of isoelectric focusing (IEF) in a granulated Sephadex matrix and in polyacrylamide immobilized pH gradients to separate an aromatase inhibitor (follicle regulatory protein: FRP) in preparative amounts from porcine follicular fluid (PFF). The starting material for IEF was derived from pFF after passage through agarose immobilized textile dye Orange A (0.5 KC1 eluent). Before IEF, some Orange A bound (OAB) material was further purified on a FPLC employing a Mono-Q anion exchange column. Previous use of chromatofocusing indicated that aromatase inhibitory activity is largely concentrated in OAB fractions with a pI in the ranges of pH approximately 4.5 and approximately 6.5. The current study revises these findings to provide a more precise measure of the isoelectric points in question to pH 4.73 +/- 0.05 and pH 6.41 +/- 0.06. The use of Sephadex was limited by gradient instability and the selection of pH ranges available. IEF using immobilized pH gradients had several advantages over Sephadex: 1) broader selection of gradients from 0.1 to 7.0 pH units; greater resolving power, and enhanced stability. The principal disadvantage of the immobiline system was the recovery of focused material from the gel matrix. The use of isoelectric focusing with immobilized pH gradients on a preparative scale to purify FRP from OAB resulted in a greater than 50% recovery with a substantial increase in specific activity (from ID50 approximately 300 micrograms/ml to 20 ng/ml).

Porcine follicular fluid protein(s) inhibit rat ovary granulosa cell steroidogenesis

We examined the effect of an isolated fraction of follicular fluid, termed follicle regulatory protein, on the production of estrogen, progesterone, and 20 alpha-dihydroprogesterone by cultured rat ovarian granulosa cells. We found a stepwise decrease in estrogen production with an increasing concentration of follicle regulatory protein (9 to 300 micrograms/ml) when the cells were stimulated by 6.25 ng/ml of ovine follicle-stimulating hormone, but the addition of a saturating dose of ovine follicle-stimulating hormone (50 ng/ml) prevented the inhibitory effect of follicle regulatory protein on estrogen production. Follicle regulatory protein inhibited progesterone production at both low and saturating levels of ovine follicle-stimulating hormone. We examined whether cholesterol substrate in the form of high-density lipoprotein or low-density lipoprotein could overcome the follicle regulatory protein inhibition of progesterone and 20 alpha-dihydroprogesterone production stimulated by follicle-stimulating hormone. At all concentrations of high-density and low-density lipoprotein, 75 micrograms/ml of follicle regulatory protein inhibited progesterone production by 80% to 90%. In the case of 20 alpha-dihydroprogesterone, the presence of high-density and low-density lipoprotein accentuated the inhibitory effect of follicle regulatory protein. These results demonstrate that the effects of follicle regulatory protein on ovarian steroidogenesis depend on: the concentration of gonadotropin, the concentration of follicle regulatory protein, and the availability of cholesterol substrate.