The endocrinology of the opiates and opioid peptides

Since the isolation of the enkephalins five yr ago, there has been an explosive increase in knowledge concerning the effects of the opiates and opioid peptides. This review deals with the interactions of opiates with the endocrine system in rat and man. The opioid peptides have been demonstrated to exert a variety of effects on pituitary hormone secretion in rat and man. In the rat, opiates stimulate growth hormone, prolactin and ACTH release and inhibit the release of the glycoprotein hormones. In man, the physiologic role of the endogenous opiates appears to be involved predominantly in ACTH and gonadotrophin regulation. Opiate effects are mainly exerted at the level of the hypothalamus but further modulating effects may occur at the pituitary and at end-organs. Opiate-induced hormonal effects appear to be mediated through dopaminergic and/or serotonergic mechanisms. Recent studies have also suggested a possible local neuromodulatory role for the opioid peptides in the control of carbohydrate metabolism and reproductive processes.