The effects of pineal indoles given late in the light period on reproductive organs and pituitary prolactin levels in male golden hamsters

Intact and pinealcctomized adult male hamsters kept in light:dark cycles of 14:10 (in hours) were given daily injections of either 25 Mg melatonin, 5-methoxy-tryptophol, N-acetylserotonin, or 6-hydroxymelatonin at 19.00 hours (13 h after lights on). The injections were continued for 50 consecutive days. The daily melatonin injections significantly elevated body weights and depressed the growth of the testes and accessory sex organs and pituitary prolactin levels in intact hamsters. By comparison, in pinealcctomized animals daily afternoon melatonin injections failed to alter body or testicular weights or pituitary prolactin levels. These findings indicate that for single injections of melatonin to be antigonadotrophic in the male hamster, the pineal must be intact. In intact animals. 5-mcthoxytryptophol and N-acetylscrotonin slightly depressed the growth of the reproductive organs and pituitary prolactin levels, respectively. Again, these effects were negated by removal of the pineal gland. 6-Hydroxy melatonin was without influence on any of the parameters of reproduction that were measured.