Development of a circadian rhythm in the activity of pineal serotonin N-acetyltransferase.

Abstract

Abstract— Pineal serotonin N‐acetyltransferase (EC 2.3.1.5) is a neurally regulated enzyme. It is detectable in the rat as early as 4 days prior to birth. A circadian rhythm in enzyme activity appears on the fourth day after birth. It develops most rapidly during the second week and achieves an adult magnitude by the end of the third week at which time nocturnal values are more than 30‐fold greater than daytime values. Norepinephrine, which appears to be the neurotransmitter regulating this enzyme, can cause a 2‐ to 3‐fold stimulation of N‐acetyltransferase in organ cultures of pineal glands from 4‐day‐old animals and a 17‐fold increase in the activity of glands from 15‐day‐old animals. Apparently the norepinephrinesensitive system controlling pineal N‐acetyltransferase activity also develops most rapidly during the first few weeks of life. The circadian rhythm in the activity of serotonin N‐acetyltransferase develops in the pineal glands of both male and female rats at the same rate. A similar rhythm for the enzyme was not observed in twelve other tissues of the rat.