REGULATION OF MELATONIN SECRETION BY LIGHT IN THE ISOLATED PINEAL ORGAN OF THE WHITE SUCKER (CATOSTOMUS-COMMERSONI)

The effects of different lighting conditions and physical parameters o f light were investigated in the isolated pineal organ of the white su cker kept under static or superfusion culture. The secretion of pineal melatonin is directly controlled by the photoperiod and completely su ppressed under constant illumination. When pineal organs are exposed t o unexpected light at night, the secretion of melatonin is significant ly reduced within 15 min and reaches basal value after 30-35 min of li ght treatment. The inhibition of melatonin secretion by unexpected lig ht at night depends on the irradiance, duration, timing of the treatme nt and the lighting history of the pineal organ.