Sympathetic Regulation of Circadian Rhythm of Serotonin N‐Acetyltransferase Activity in Pineal Gland of Infant Rat

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Abstract
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.