THE INDEPENDENCY OF AN INTACT PINEAL-GLAND OF THE INHIBITION BY 5-METHOXYTRYPTAMINE OF THE REPRODUCTIVE-ORGANS IN THE MALE HAMSTER

5-Methoxytryptamine (5-MT) injections, 25 .mu.g, s.c., into intact and pinealectomized male hamsters given between 1630 h and 1700 h (light on from 0500-1900 h; 14 L/10 D) for 54 consecutive days caused involution of the testes. 5-MT, however, is more effective when the pineal gland is present. Apparently 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 gland. Like melatonin, 5-MT appears to be implicated in the control of the reproductive function.