EFFECTS OF MELATONIN ON THE SYNTHESIS OF PROTEINS BY THE RAT HYPOTHALAMUS, HYPOPHYSIS AND PINEAL ORGAN

Abstract

After decades of contradictory results it has become apparent that the mammalian pineal exerts an inhibitory influence on several neuroendocrine functions, namely the hypophysial-gonadal system, the adrenal cortex and the thyroid gland (Wurtman, Axelrod & Kelly, 1968). Among pineal secretory products the best characterized is melatonin (5-methoxy-N-acetyltryptamine), which reverses many of the endocrine changes that follow pinealectomy and mimics the effect of injecting pineal extracts into experimental animals. In the last 15 years considerable information has been accumulated on the mechanisms involved in the regulation of pineal melatonin synthesis; very little is known, however, about the biochemical processes evoked by melatonin in its target organs. Exogenous melatonin has been shown to become concentrated within the hypothalamus (Antón-Tay & Wurtman, 1969; Cardinali, Hyyppä & Wurtman, 1973). Implants of melatonin in the hypothalamus decrease pituitary gonadotrophin levels (Fraschini, 1969); moreover, melatonin perfusions of the third ventricle decrease plasma levels of