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

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Abstract
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.