MELATONIN IN NONMAMMALIAN VERTEBRATES - PHYSIOLOGICAL-ROLE IN REPRODUCTION

Although the pineal organ has been clearly implicated in the photoperi odic control of seasonal reproduction in several non-mammalians, the p ossible physiological role for melatonin, the major pineal hormone, is far from clear. In many studies on birds, reptiles, amphibians, fishe s and even some invertebrates, it has been reported that melatonin adm inistration can influence (usually suppress) reproductive parameters. However, in the vast majority of these studies, melatonin has been adm inistered in an unphysiological manner, usually by injection, and/or d ose. It is notable that in most studies where melatonin has been admin istered either using continuous-release implants or by treatments atte mpting to mimick the natural diurnal melatonin rhythm, no or limited e ffects on reproduction were observed. In conclusion, the data availabl e to date do not support the concept that melatonin plays an important physiological role in the photoperiodic control of reproduction in no n mammalians. (C) 1997 Elsevier Science Inc.