Daily rhythms of serotonin and N-acetyltransferase in chicks

1. In chickens, the pineal gland has a daily change in the synthesis of melatonin. 2. This daily change has been attributed to the daily change in N-acetyltransferase activity, the first of the two enzymes responsible for the conversion of serotonin to melatonin. 3. When serotonin was measured under the same condition as N-acetyltransferase activity, the serotonin showed a 7-fold daily change. 4. Peaks of serotonin were found in the light-time near dawn and dusk when the N-acetyltransferase level was low; nadir serotonin values were obtained in the dark-time when the N-acetyltransferase activity was high. 5. However, the serotonin daily change does not seem to be a simple consequence of N-acetyltransferase activity in the pineal gland. © 1979