Role of Neuropeptides in Regulating the Secretion of Growth Hormone and Prolactin

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The secretion of Growth Hormone (GH) and prolactin (PRL) from the pituitary is regulated by a variety of hypothalamic factors, which are mostly neuropeptides and biogenic amines. We found that GH and PRL secretion induced by serotonin is mediated by hypothalamic GRF and VIP. Galanin stimulates both GH and PRL secretion in the rat. We found that alpha-adrenergic and opioidergic mechanisms are involved in PRL release induced by galanin. Furthermore, the interaction of galanin with serotonin in PRL secretion was also demonstrated. GH secretion induced by galanin is mediated by hypothalamic GRF. On the other hand, PRL and GH secretion is inhibited by endogenous dopamine and somatostatin. GRP stimulates both dopamine and somatostatin release from the hypothalamus. These findings indicate an important and complicated role of neuropeptides in regulating pituitary hormones and suggest a possible therapeutic use of a potent and long-actinf analogue of such neuropeptides in cosistently modulating the function of pituitary tumors.