Androgen regulation of immunological and biological activities of pituitary follicle-stimulating hormone isoforms in male rats

Follicle-stimulating hormone (FSH) is involved in the regulation and mainte nance of gametogenesis. It exists in multiple molecular forms with differen t oligosaccharide structures which in turn are influenced by the hormonal m ilieu. Previous studies from our laboratory demonstrated that antiandrogen administration to immature male rats altered the biological activity and th e distribution profile of pituitary FSH isoforms. The aim of this study was to examine possible modifications in pituitary FSH polymorphism throughout sexual development (10-, 32- and 75-day-old rats). In addition, the effect of androgen deprivation by castration (32-day-old rats) and its replacemen t with a nonaromatizable androgen - dihydrotestosterone - on pituitary FSH polymorphism was determined. Concanavalin A affinity chromatography was use d to isolate groups of FSH isoforms according to their carbohydrate inner s tructure. Radioimmunoassay and Sertoli cell bioassay were used to evaluate FSH immuno- and bioactivities. Androgen rise in serum was accompanied by a marked increase in pituitary bio- and immuno-FSH content in 32- and 75-day- old rats. However, FSH pituitary content did not vary despite the significa nt increment observed in serum FSH levels after castration and decrease to control levels after androgen replacement. The distribution profile of immu no- and bioactive FSH changed throughout sexual maturation. The proportion of pituitary FSH isoforms bearing complex oligosaccharide structures (trian tennary, bisecting, complete and truncated biantennary) increased with age, with a concomitant decrease in the proportion of isoforms bearing incomple te carbohydrate chains. The distribution profile observed in castrated 32-d ay-old rats was similar to that determined in 10-day-old animals. Androgen replacement restored the distribution profile to normal. These results sugg est that androgens regulate the incorporation of sugar residues to the carb ohydrate chains of pituitary FSH favoring the biosynthesis of complex-type oligosaccharide structures.