Sympathetic regulation of circadian rhythm of serotonin N-acetyltransferase activity in pineal gland of infant rat.

The circadian rhythms of serotonin N-acetyltransferase activity in the pineal glands of infant and adult rats were compared. The nighttime increase of N-acetyltransferase activity in the pineals of infant rats was blocked by removal of superior cervical ganglion or by pretreatment with reserpine, l-propranolol, and cycloheximide. Injection of isoproterenol to infant rats markedly elevated pineal N-acetyltransferase activity. When the pineal glands of infant rats were organ-cultured, N-acetyltransferase activity spontaneously increased 7--12 h after the rats were killed. When infant rats were previously denervated or pretreated with reserpine and their pineals were cultured, this spontaneous elevation of N-acetyltransferase activity was abolished, indicating that the transient increase of the enzyme activity in organ culture was due to a liberation of catecholamine from degenerating nerve endings. Additional illumination until midnight prevented the nighttime increase of N-acetyltransferase activity in intact infant rats but not in blinded infant rats. These observations are taken to indicate that N-acetyltransferase rhythm in immature rat pineals is regulated by the sympathetic nerves in the same manner as in adult rat pineals, that the immature rat pineal does not contain a time-keeping system, and that there is no extraretinal light perception in infant rats as far as N-acetyltransferase rhythm is concerned.