The Role of Growth Hormone in the Control of Gonadotropin Secretion in Adult Male Rats

Although it is known that GH plays an important role in normal growth and development, its influence on the control of gonadotropin secretion is poorly understood. To address this issue, we have treated adult male rats with bovine GH via osmotic pumps (250 μg/day for 2 weeks; Exp design I) or immunized rats against ovine GH (100 μg/month for 6–7 months; Exp design II) and evaluated their neuroendocrine function. Vehicle-treated animals served as controls. Two experiments were conducted to evaluate the gonadotropin responses to: 1) GnRH (in saline) in gonad-intact rats and 2) testosterone propionate (TP; in oil) in castrated rats. Saline- or oil-injected rats served as controls. Circulating GH antibodies, LH, FSH, PRL, testosterone, and insulin-like growth factor I levels were measured by RIAs. Plasma LH levels were decreased (P < 0.025) in rats treated with GH. The plasma LH and FSH responses to GnRH treatment were similar in rats treated with either saline or GH. The suppressive effect of TP on LH secret...