Norepinephrine stimulates serotonin secretion from rat pineal glands, in vitro.

The purpose of this study was to determine if serotonin (5-HT) is secreted by the pineal gland and also to define the parameters of its secretion. After radiolabelling the endogenous 5-HT pool, individual pineal glands were placed within perifusion chambers and stimulated with norepinephrine (NE). [3H]5-HT was rapidly released within 1 min of stimulation and secretion continued throughout the period of exposure to NE. The findings suggest that 5-HT, in addition to melatonin, is a hormone of the pineal gland.