EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON RHYTHMIC MELATONIN SECRETION FROM THE PINEAL ORGAN OF THE WHITE SUCKER (CATOSTOMUS-COMMERSONI) INVITRO

The secretion rate of melatonin from cultured pineal organs of the white sucker was examined for several days under either a 12:12-hr light:dark (LD) cycle or continuous darkness (DD) at either 10° or 20°. The incubation medium was changed at 3-hr intervals and secreted melatonin was measured by RIA. Under a 12:12-hr LD cycle (0800 light on, 2000 light off) melatonin secretion was suppressed during the day and highly active at night, with larger amplitudes at 20 than at 10°. In DD at 10° no circadian rhythmicity in secretion was found in October or January, whereas at 20° a circadian-like pattern was detected in pineals which were derived from animals reared at either 10° or 20° for 1 week prior to the experiment in October or January. The pineals in the DD experiment still responded to an additional 24-hr LD cycle at both temperatures even after 6 or more days. These results clearly reveal the influence of photoperiod and temperature on melatonin secretion of organcultured pineal glands. The existence of a circadian oscillator for melatonin secretion in the pineal gland of the white sucker is suggested. © 1992.