Interaction between Purified Ovine Inhibin and Steroids on the Release of Gonadotropins from Cultured Rat Pituitary Cells*

Primary pituitary cell cultures derived from adult male rats were used to explore the interaction between purified 32K ovine inhibin and gonadal steroids on the modulation of basal and GnRH-stimulated secretion of FSH and LH. Purified o-inhibin was a potent inhibitor of basal FSH secretion (IC50 = 3.4 pM) and 10 nM GnRH-stimulated FSH and LH secretion (IC50 = 8.8 and 18.4 pM, respectively). Purified o-inhibin had no effect on basal LH secretion. In this system, the androgens testosterone, 5 alpha-dihydrotestosterone, and androstenedione slightly stimulated basal FSH secretion, and o-inhibin could reverse this stimulatory effect. By contrast, androgens suppress GnRH-stimulated FSH and LH secretion. In combination, androgens and o-inhibin provided greater inhibition of GnRH-mediated gonadotropin secretion than either did alone.