Technion - Israel Institute of Technology, Haifa Israel.
n recent years our laboratory has extensively studied the role of the indole derivative hormone - melatonin - in sleep-wake regulation and its interaction with the secretion of gonadotropins and sex-steroid hormones. In the first set of experiments we showed that melatonin exerts hypnotic effects if administered at times when the circulating levels of melatonin are low. Thus, daytime administration of melatonin increased sleep propensity in a time-dependent manner, and administration of melatonin ameliorated insomnia in a child with melatonin deficiency due to a pineal tumor. Similarly, elderly insomniacs were found to have lower nocturnal levels of melatonin and delayed nocturnal peaks in comparison with normal elderly. Replacement therapy with exogenous melatonin ameliorated their sleep disturbances. Further studies have shown that melatonin participates in the regulation of sleep propensity cycles in normals. Investigating the 24-h cycles in sleep propensity concomitantly with melatonin secretion revealed that the onset of nocturnal melatonin secretion preceded the opening of the sleep gate by precisely 2 hours.
In the second set of experiments we investigated the secretion of melatonin in males with gonadotropin-releasing hormone (GnRH) deficiency, and how it was affected by treatment with testosterone. In comparison with same-age normal controls, patients with GnRH deficiency were found to have abnormally high levels of nocturnal melatonin secretion. Treatment with testosterone decreased melatonin levels to normal values. These results suggest that in humans melatonin is functionally involved in the regulation of the pituitary-gonodal axis.
Taken together, our two lines of research indicate that melatonin plays a major role in human sleep and sex physiology. Thus, although treatment with melatonin proved to exert beneficial effects in certain forms of melatonin-deficient insomniacs, more studies are needed in order to determine the long-term effects of melatonin.
