Differential effects of the charge variants of human follicle-stimulating hormone.

FSH is synthesized and secreted by the anterior pituitary gland in multiple molecular forms; the release of these isoforms depends on the endocrine status of the donor at the time of sample collection. In the present study, we analysed the possibility that the FSH charge isoforms may exert differential effects at the target cell. Seven FSH isoform mixes were isolated from pooled anterior pituitary glycoprotein extracts by high resolution chromatofocusing, followed by affinity chromatography, which removed nearly 90% of the LH that co-eluted with the FSH isoforms during chromatofocusing. The isoforms (isoform I, pH >7.10; II, pH range 6.60-6.20; III, pH 5. 47-5.10; IV, pH 5.03-4.60; V, pH 4.76-4.12; VI, pH 4.05-3.82 and VII, pH <3.80) were then tested for their capacity to stimulate cAMP release, androgen aromatization and tissue-type plasminogen activator (tPA) enzyme activity and cytochrome P450 aromatase, tPA and inhibin alpha-subunit mRNA production by rat granulosa cells in culture. cAMP and oestradiol production were determined by RIA, tPA enzyme activity by SDS-PAGE and zymography and all mRNAs by northern blot hybridization analysis and semiquantitative RT-PCR. All isoforms, with the exception of isoform I, stimulated synthesis and release of cAMP, oestrogen and tPA enzyme activity in a dose-dependent manner; the potency of the less acidic isoforms (pH 6. 60-4.60) was greater than that exhibited by the more acidic/sialylated analogs (pH 4.76 to <3.80; potencies II>III>IV>V>VII>VI). A similar trend was observed in terms of cytochrome P450 aromatase and tPA mRNA production. In contrast, when FSH-stimulated production of alpha-inhibin mRNA was analysed, isoforms V-VII were significantly more potent (two- to threefold) than the less acidic/sialylated counterparts (II-IV). In contrast to isoforms II-VII (which behaved as FSH agonists), isoform I (elution pH >7.10) completely blocked P450 aromatase and tPA mRNA expression, without altering that of a constitutively expressed gene (glyceraldehyde-3-phosphate dehydrogenase). These results show for the first time that the naturally occurring human FSH isoforms may exhibit differential or even unique effects at the target cell level.

Altered luteinizing hormone pulsatility in infertile patients with idiopathic oligoasthenozoospermia.

In a previous study, we demonstrated that oligoasthenozoospermic (OAZ) patients had two types of testosterone response to human chorionic gonadotrophin (HCG) administration: group 1 (OAZ-1) had an altered, monophasic (no first peak) response, and group 2 (OAZ-2) had a normal biphasic response. The objective of the present work was to study the luteinizing hormone (LH) pulsatility in OAZ-1 compared with both OAZ-2 and men of proven fertility (PF), in order partly to determine the possible aetiology of the blunted acute testosterone response to HCG in these patients. LH pulsatility was measured in 10 PF, 10 OAZ-1 and 10 OAZ-2 patients, in blood samples taken every 5 min for 6 h in PF, and for 4 h in OAZ patients. LH values were determined by a time-resolved immunofluorometric assay. Frequency and amplitude of the LH pulses were determined by a computer program. LH pulse frequency, expressed as pulses/4 h, was significantly lower in OAZ-1 (1.5+/-0.97) than in PF (2.4+/-0.63) and OAZ-2 (2.4+/-0.84) patients. In six OAZ-1 and two OAZ-2 patients, LH pulsatility was diminished, as they showed less than two pulses/4 h. No statistically significant differences in LH pulse amplitude were found. These results, together with a higher number of OAZ-1 cases found with decreased LH pulsatility, suggest that, at least in a subset of these men, quantitative and/or qualitative alterations of LH secretion might have occurred.

A naturally occurring basically charged human follicle-stimulating hormone (FSH) variant inhibits FSH-induced androgen aromatization and tissue-type plasminogen activator enzyme activity in vitro.

It is well known that deglycosylation of gonadotropins by enzymatic or chemical procedures or by deletion of sites for N-linked glycosylation produces antagonistic analogs which are able to interact strongly with the receptor and to inhibit binding of the wild-type hormone. In the present study, we analyzed the antagonistic properties of a naturally occurring basic follicle-stimulating hormone (FSH) charge isoform obtained after high-resolution chromatofocusing of human anterior pituitary glycoprotein extracts. Coincubation of increasing amounts of this isoform with a highly purified human pituitary FSH preparation or with recombinant human FSH at doses equivalent to their corresponding ED50 for estradiol and tissue-type plasminogen activator (tPA) production, inhibited FSH-induced estrogen production and tPA enzyme activity by cultured rat granulosa cells in a dose-dependent manner. These inhibitory effects were apparently exerted at steps following 3',5'-cyclic adenosine monophosphate (cAMP) formation and did not involve activation of the protein kinase C pathway since: (a) at low doses, this basic FSH isoform moderately increased FSH-induced cAMP production by cultured rat granulosa cells; (b) coincubation of the antagonist isoform with dibutyryl cAMP completely inhibited the effects of this cAMP analog on estrogen and tPA production; (c) the isoform was able to stimulate production of cAMP in a human fetal cell line expressing the recombinant human FSH receptor, and (d) the inhibitory effects of the isoform were not affected by staurosporine, a protein kinase C inhibitor. The effects of this isoform upon dibutyryl cAMP-induced estrogen and tPA production were blocked by the addition of a highly specific antibody directed against human FSH, further demonstrating that the antagonistic effects observed were due to FSH-like molecules. In contrast to the inhibitory effects exhibited by this basic FSH isoform, a more acidic FSH charge variant consistently acted as an agonist of pituitary and recombinant FSH on both estrogen production and induction of tPA enzyme activity. These results indicate that the anterior pituitary gland normally produces FSH isoforms which act as either agonists or antagonists of FSH at the target cell level.