INHIBITION OF ESTROUS CYCLICITY IN GOLDEN-HAMSTERS BY MELATONIN ADMINISTRATION ON THE DAY OF PROESTRUS

Single injections of melatonin (25 micrograms) were administered to female hamsters, 15 minutes before lights‐out (14L:10D), during either the early diestrous (day 1) or proestrous (day 4) phase of the estrous cycle. Hamsters which received melatonin only on the evening of proestrus became anovulatory by three weeks of treatment, while those that were injected with melatonin during diestrus, or administered oil on either day 1 or 4, continued to exhibit normal estrous cycles. These results indicate that quartan injections of melatonin can suppress reproductive function in female hamsters, and that the effectiveness of the injections may be dependent upon the stage of the estrous cycle at which they are administered. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company