A COMPARATIVE-STUDY OF MELATONIN PRODUCTION IN THE RETINA, PINEAL-GLAND AND HARDERIAN-GLAND OF BUFO-VIRIDIS AND RANA-ESCULENTA

1. The circadian patterns of melatonin and of its synthesizing enzyme N-acetyltransferase (NAT) were investigated in the serum, retina, pine al gland and Harderian gland (HG) of two amphibian species, Bufo virid is and Rana esculenta. 2. Serum melatonin levels showed no diurnal flu ctuations in Bufo viridis, whereas, in Rana esculenta, they exhibited a circadian rhythm, with the highest values occurring during the night . Retina melatonin exhibited characteristic circadian patterns in both species, with the highest values occurring during the day, in Bufo, a nd the highest concentrations occurring at night in Rana. 3. In the re tina, NAT activity peaked at night in both amphibians, but in Bufo the levels were up to 30 times higher than in Rana. In the HG and in the pineal gland, NAT activity showed different patterns in the two specie s with no diurnal variations in Bufo, and characteristic circadian rhy thms in Rana. 4. In the HG and pineal gland of both species, melatonin was only occasionally detectable over the 24-hr period. 5. This is th e first report exploring melatonin production in Bufo viridis and Rana esculenta. In our experimental conditions, marked differences emerged between the two species.