Serum melatonin and pineal indoleamine metabolism in a species with a small day/night N-acetyltransferase rhythm

1. 1. Ovine serum and pineal melatonin levels are low during the day, increase five to ten-fold at night, decrease during a light pulse at night, and rapidly increase to night levels following the light-dark transition. 2. 2. N-Acetyltransferase activity increases three-fold at night, falls significantly in response to the light pulse, but does not increase following the light pulse. No significant change in N-acetylserotonin occurs under these conditions. 3. 3. These results suggest that the biochemical mechanisms controlling pineal melatonin synthesis in the sheep pineal gland may be different from those in the rat.