Centrally applied somatostatin influences morphology of pituitary FSH cells but not FSH release

Effects of i.c.v. administered somatostatins on morphology and function of pituitary FSH cells were examined in adult male Wistar rats. The animals were given three 1 microg doses of SRIH-14 or SRIH-28 in 5 microl saline every second day. Controls were given the same volume of saline only. Both SRIH treatments lead to a significant decrease in absolute pituitary weight and volume of FSH cells in comparison with controls. Relative pituitary weight was significantly decreased only after SRIH-28 treatments, while FSH secretion was insignificantly decreased by both SRIH treatments. Our results indicate that i.c.v. applied somatostatins have significant inhibitory effect on absolute pituitary weight and on the volume of FSH cells, without affecting the hormone secretion in male rats.     

Two receptor binding regions of human FSH show sense-antisense similarity to the human FSH receptor

The sequences of two receptor binding regions of the beta-subunit of the human follicle-stimulating hormone (hFSH-beta) were compared with the DNA-derived antisense peptide sequence of the hFSH receptor. A striking sense-antisense similarity was established between these receptor binding regions and the hFSH receptor. Based on this sense-antisense similarity four putative hormone binding regions on the N-terminal extracellular region of the hFSH receptor are identified.     

Can FSH influence longevity?

It was recently reported that the extragonadal actions of follicle‐stimulating hormone (FSH) include regulation of brown and white adipose tissue function and thermogenesis. Based on these findings and on our evidence for reduced FSH levels and enhanced thermogenesis in long‐lived growth hormone (GH)‐deficient mice and GH‐resistant mice, we suggest that FSH may have a role in the control of aging and longevity. We speculate that alterations in FSH secretion may represent one of the mechanisms of trade‐offs between reproduction and aging.     

FSH directly regulates bone mass

Postmenopausal osteoporosis, a global public health problem, has for decades been attributed solely to declining estrogen levels. Although FSH levels rise sharply in parallel, a direct effect of FSH on the skeleton has never been explored. We show that FSH is required for hypogonadal bone loss. Neither FSHbeta nor FSH receptor (FSHR) null mice have bone loss despite severe hypogonadism. Bone mass is increased and osteoclastic resorption is decreased in haploinsufficient FSHbeta+/- mice with normal ovarian function, suggesting that the skeletal action of FSH is estrogen independent. Osteoclasts and their precursors possess G(i2alpha)-coupled FSHRs that activate MEK/Erk, NF-kappaB, and Akt to result in enhanced osteoclast formation and function. We suggest that high circulating FSH causes hypogonadal bone loss.     

Expression of FSH and its co-localization with FSH receptor and GnRH receptor in rat cerebellar cortex

The expression of follicle-stimulating hormone (FSH) and its receptor in extrapituitary and non-HPG axis tissues has been demonstrated and their non-reproductive functions in these tissues have been found. However, there have been no reports concerning the expression and function of FSH and its receptor in the cerebellum. In our study, immunofluorescence staining and in situ hybridization were used to detect the expression of FSH, double-labeled immunofluorescence staining was used to detect co-localization of FSH and its receptor and co-localization of FSH and gonadotropin-releasing hormone (GnRH) receptor in the rat cerebellar cortex. Results showed that some cells of the Purkinje cell layer, granular layer, and molecular layer of the cerebellar cortex showed both FSH immunoreactivity and FSH mRNA positive signals; not only for FSH and FSH receptor, but also for FSH and GnRH receptor co-localized in some cells throughout the Purkinje cell layer, granular layer, and molecular layer of the cerebellar cortex. These suggested that rat cerebellum could express FSH; cerebellum is a target tissue of FSH; FSH may exert certain functions through FSH receptor in a paracrine or autocrine manner; GnRH may regulate FSH positive cells through GnRH receptor in the cerebellum. Our study provides morphological evidence for further functional research on FSH and related hormones in the cerebellum.     

Blocking FSH action attenuates osteoclastogenesis

A direct effect of FSH on bone turnover via stimulation of osteoclast formation has been reported. Here we show that monoclonal or polyclonal antibodies to FSH inhibit osteoclast formation induced by FSH to an extent similar to that noted in FSH receptor (FSHR) knockout cells. Furthermore, we document the amplification of FSHR cDNA from well-characterized human CD14+ osteoclast precursors and osteoclasts, and the direct sequencing of the PCR products to definitively establish the expression of FSHRs. At these sites, the FSHR was expressed predominantly as an isoform that omits exon 9, a linker between the FSH-binding region and a long, invariant signaling domain of the receptor. These data provide compelling evidence for expression of a FSH receptor isoform in osteoclasts and their precursors.     

Baculovirus-insect cell production of bioactive porcine FSH

The in vitro and in vivo bioactivity of recombinant porcine FSH (rpFSH) produced from insect cells through use of a baculovirus expression system were studied and compared with those of natural FSH preparations. Determination of in vitro bioactivity, using the rat Sertoli cell aromatase bioassay, indicated that rpFSH is as active as purified pituitary FSH. Determination of in vivo bioactivity, using the mouse uterine weight bioassay, indicated that rpFSH is as active as purified pituitary FSH. Using the mouse Leydig cell testosterone bioassay, it was demonstrated that the intrinsic LH bioactivity of rpFSH is negligible. The increases in ovarian and uterine weight, and the stimulation in follicular growth in immature hypophysectomized rats induced by rpFSH supplemented with hCG were comparable to those induced by natural FSH preparations. Furthermore, rpFSH alone in hypophysectomized mice stimulated preantral follicular growth to preovulatory stages, and the subsequent injection of hCG caused ovulation. These results demonstrate that in vitro and in vivo biological characteristics of rpFSH produced from baculovirus-insect cells are indistinguishable from those of FSH isolated from natural sources.     

Measurement of human FSH by radioreceptor assay

We established a sensitive RRA system for human FSH, employing PMS-treated immature rat ovary. The dissociation constant of the binding of the receptor preparation to NIAMDD human FSH-2 was 1.15 x 10(-10) M. The standard curve was obtained with 0.2-25.6 ng/tube of NIAMDD hFSH-2. Purified hLH, hTSH, and HCG had no significant effect on the binding. When the anterior pituitary homogenates obtained from humans were assayed by this system, the intra-assay and inter-assay coefficients of variation were 11.9% and 13.4% respectively, and the assay values correlated well with those obtained by RIA. This assay is applicable for the measurement of FSH in serum, when the non-specific inhibitor effects of serum are compensated for by the addition of merthiolate and when FSH-free serum is used instead of the buffer for the standard curve. The intra-assay and inter-assay coefficients of variation were 9.31% and 19.7% respectively. The assay values correlated with those obtained by RIA under the same physiological state. The ratio of the assay values RRA/RIA, was dependent upon the physiological state, e.g. 6.29 in men, 3.84 and 4.18 in women at follicular and luteal phase respectively and 2.40 in menopausal women. During the menstrual cycle, our results showed that the value of RRA/RIA derived from serum did not change significantly.     

FSH bioactivity in commercial preparations of gonadotropins

During the past 2 decades, commercial preparations of FSH have been extensively used to superovulate cattle. The problems that have been encountered in superovulation of cattle include high variability in the ovulation rate and subsequent yield of viable embryos. The lack of predictability in superovulatory trials has been attributed to difficulties in standardizing the potency of commercial FSH preparations. Traditionally, FSH potency has been tested in bioassays that utilize specific responses in whole animals or primary cell cultures. Whole animal bioassays lack sensitivity, while primary cell culture bioassays, which use fresh cells, have inherent variability within each preparation. An FSH bioassay that employed a stable chimeric cell line expressing the human FSH-R was used to provide an accurate measurement of FSH bioactivity. The hormonal potency of 2 commercial preparations of FSH used to superovulate cattle was determined using FSH immuno- and bioassays. Commercial FSH preparations differed in potency. One commercial product, prepared in 4 different years, showed no difference in the immunoactive levels of FSH. In the same product stored under identical conditions, FSH bioactivity varied from year to year. There was variability in FSH bioactivity both between and within commercial products. The lack of correlation between bioactivity and immunoactivity of commercial FSH preparations may explain, in part, the variability observed in superovulation of cattle.     

A synthetic peptide corresponding to human FSH beta-subunit 33-53 binds to FSH receptor, stimulates basal estradiol biosynthesis, and is a partial antagonist of FSH

We have previously shown that hFSH-beta 34-37 (KTCT) and 49-52 (TRDL) inhibit binding of 125I-hFSH to FSH receptor in calf testis membranes and that hFSH-beta 33-53, which encompasses these tetrapeptides, inhibits binding with increased potency. hFSH-beta 33-53 rapidly dimerizes under conditions utilized in the receptor binding assay (pH 7.5) so that the binding inhibition reported earlier was due to the hFSH-beta 33-53 dimer rather than the monomer. At pH 6.5, conversion to dimer does not occur, and binding inhibition could be unequivocally attributed to the monomer. Radioiodinated and alkylated hFSH-beta 33-53 binds to the FSH receptor with a Kd = (5.5 +/- 1.4) X 10(-5) M. The biological activity of hFSH-beta 33-53 was assessed by its ability to affect the conversion of androstenedione to estradiol in rat Sertoli cells cultures. FSH-beta 33-53 behaved as a partial antagonist of the FSH-induced estradiol synthesis. The required incubation medium, however, contains cystine as well as cystine, which rapidly forms a hFSH-beta Cys-(51)-S-S-Cys derivative at the pH of the incubation, 7.4. When hFSH-beta 33-53 was converted either to the hFSH-beta Cys(51)-S-S-Cys or to a carboxymethylated derivative, inhibition of FSH-induced estradiol synthesis still was observed. This result demonstrates that the free R-SH group at Cys51 is not responsible for the inhibition. FSH-beta 33-53 also significantly stimulated basal levels of estradiol synthesis, but not to maximal levels observed with FSH (partial agonist). Neither the carbohydrate content of hFSH-beta nor the alpha subunit of FSH appears to be essential for signal transduction and expression of the hormone effect of FSH-beta 33-53.