EFFECTS OF GROWTH-HORMONE ON NEUROENDOCRINE FUNCTION

Although the role of growth hormone (GH) in the control of reproductiv e functions is not well understood, there is considerable evidence tha t the states of both GH deficiency and GH excess are typically associa ted with reproductive deficits. To identify the possible involvement o f functional alterations in the hypothalamic-pituitary system in produ cing these deficits, we are studying neuroendocrine function related t o reproduction in transgenic animals overexpressing GH, in animals wit h congenital GH deficiency, and in animals with selective immunoneutra lization of GH. The results indicate that GH acts on the hypothalamus to alter dopaminergic and noradrenergic control of prolactin and gonad otropin release. Life-long elevation of GH levels outside the physiolo gical range disrupts feedback control of luteinizing hormone (LH) rele ase by gonadal streroids. Plasma LH and follicle-stimulating hormone ( FSH) levels and feedback control of LH release are also abnormal in GH -deficient animals indicating that physiological levels of endogenous GH are normally involved in the control of gonadotropin release. Diffe rences between the effects of bovine vs. human GH in transgenic mice a nd differential effects of GH deficiency in mice and rats should facil itate identification of the mechanisms involved in the actions of GH o n the hypothalamic-pituitary system.