ENDORPHINS AND NEUROENDOCRINE CONTROL

Abstract

This chapter discusses the role of endogenous opiates in the control of neuroendocrine functions. Opiates morphine and methadone are well known to be potent stimuli of growth hormone and prolactin secretion in the rat. Moreover, morphine stimulates prolactin release in the human. As met-enkephalin and 3-endorphin bind to the opiate receptor and have potent morphine-like activity in various biological assays, the possibility was raised that the endogenous opioid peptides, beside their well-known analgesic potency and activity as behavior modulators, could also be involved in the neuroendocrine control of growth hormone and prolactin secretion. Endorphins and their analogs can stimulate growth hormone and prolactin secretion in experimental animals and man; such data do not prove the physiological role of these peptides in the control of neuroendocrine functions. Advantage can be taken in these studies of the availability of a pure opiate antagonist, naloxone. The finding of a blockage by naloxone of a physiological change of hormone secretion would strongly support the role of endogenous opiate peptides in this process.