[Role of endogenous opioids in the modulation of hypophyseal hormone secretion]

The aim of the present study is to review current knowledge of the endogenous opiates in order to identify both their basic features and their receptors' properties, including the biological effects of their stimulation, and finally their endocrine actions. Since the identification of methionine-enkephalin and leucin-enkephalin, many opioid peptides with higher molecular weight have been characterized, and their origin from specific precursor has been recognized: proopiomelanocortin, preproenkephalin A, preproenkephalin B. In particular we have analyzed the pharmacological properties and the biological effects of beta-endorphin and met -and leu-enkephalins, the most diffuse of opioids. The use of naloxone has permitted the study of endogenous opioid tone and its effects on the release of the pituitary hormones. The present study reports a summary of data in the literature and personal observation indicating that the peripheral sexual steroids are the most important modulators of naloxone effects on endogenous opioid tone. Finally, the paper reports preliminary observations indicating that during naloxone infusion, females with hypothalamic amenorrhoea show a hormonal profile which differs from normal subjects.