Circadian rhythms of indoleamines and serotonin N-acetyltransferase activity in the pineal gland

Conclusion The circadian rhythm of melatonin synthesis in the pineal glands of various species has been summarized. The night-time elevation of melatonin content is in most if not all cases regulated by the change of N-acetyltransferase activity. In mammals, the N-acetyltransferase rhythm is controlled by the central nervous system, presumably by suprachiasmatic nuclei in hypothalamus through the superior cervical ganglion. In birds, the circadian oscillator that regulates the N-acetyltransferase rhythm is located in the pineal glands. The avian pineal gland may play a biological clock function to control the circadian rhythms in physiological, endocrinological and biochemical processes via pineal hormone melatonin.