The independency of an intact pineal gland of the inhibition by 5-methoxytryptamine of the reproductive organs in the male hamster.

Subcutaneous injections fo 25 micrograms of 5-methoxytryptamine (5-MT) in oil into intact and pinealectomized male hamsters given between 4.30 p.m. and 5 p.m. (light on from 5 a.m. to 7 p.m.; 14 L/10 D) for 54 consecutive days caused involution of the testes. 5-MT, however, is more effective when the pineal is present. These results indicate that melatonin is not the only pineal factor inducing gonadal atrophy in the hamster. 5-MT seems even more effective than melatonin in so far as it is, contrary to melatonin under the same experimental conditions, also effective in the absence of the pineal. Like melatonin, 5-MT appears to be implicated in the control of the reproductive function.