Effects of Melatonin on Changes Induced by Castration and Testosterone in Sexual Structures of Male Rats

The effect of parenteral administration of melatonin on the levels of pituitary LH activity of castrated and castrated, testosterone- treated male rats was studied. The possible direct effect of melatonin on the accessory sex glands, structures well recognized to be under the control of androgenic hormones, was also investigated. Melatonin caused a significant decrease in the weight of the adenohypophyses in castrated rats and also in 1 of the 2 groups of castrated, testosterone-treated male rats. Melatonin also induced significant decreases in ventral prostate weights in both groups of castrated, testosterone-treated rats. Pituitary LH concentration was not significantly affected in any group. Pituitary LH content appeared lower in all groups treated with melatonin. These results suggest a possible direct effect of melatonin on the ventral prostates, which in some way modifies the stimulatory effect of testosterone on these structures.