ABSTRACT
A mechanisms is postulated wherein melatonin can offset the ambient heat-induced suppression of thyroidal support for thermogenesis when less heat production was required due to the higher ambient temperature. Melatonin, an indole synthesized and secreted by the pineal gland, is a hormone whose endogenous secretion maintains a regulatory action on the reproductive system. Body weight may be affected in seasonally changing patterns and part of this is due to the unique coping mechanism developed by mammals to ensure survival of the species under the harshest environmental circumstances. Daily afternoon melatonin injections depressed body weight and phase-advanced the onset and extended the duration of physical activity. Chronic injections of melatonin depress circulating cholesterol levels in young adult rats and hamsters. Several investigators have examined the effects of melatonin after challenging the thyroid axis in various ways in the rat and the hamster.
