Human recombinant inhibin A and testosterone act directly at the pituitary to suppress plasma concentrations of FSH in castrated rams

Abstract

The roles of inhibin and testosterone in the negative feedback control of the secretion of FSH were explored in experiments using castrated rams administered human recombinant inhibin A (hr-inhibin) and testosterone propionate (TP). Two experiments were conducted in the non-breeding season. In experiment 1, two groups of long-term castrated rams (wethers) were treated with an i.v. injection of either vehicle or hr-inhibin in two doses (25 and 50 μg) given 2 weeks apart. Plasma concentrations of FSH, measured by radioimmunoassay, were suppressed significantly (P<0.01) and equally by both doses of hr-inhibin with a mean (± S.E.M.) maximal suppression of FSH of 19.9 ± 2.60% occurring 6-10 h aft..