Rat serum stimulates serotoninN-acetyltransferase activity in pineal monolayer cultures

Summary The effect of rat serum on serotoninN-acetyltransferase (NAT) activity and indole synthesis in monolayer cultures of neonatal rat pineal glands was examined. The addition of 5% rat serum to these cultures resulted in stimulation of NAT activity equal to that obtained with optimal concentrations of the adrenergic agonist norepinephrine (NE). Rat serum also increased the synthesis of bothN-acetylserotonin and melatonin from tryptophan. Stimulation of NAT activity by rat serum was partially blocked by metoprolol and propranolol, but not by phentolamine or butoxamine. The serum factor responsible for the stimulation was stable to both freezing and boiling. No significant amounts of epinephrine, norepinephrine, or dopamine were detected in the serum. This research was supported by NIH Grant HD12904, by a Basil O’Connor starter grant from the March of Dimes Birth Defects Foundation, and by the Veterans Administration. Vernon Rowe is the recipient of Teacher Investigator Award NS00439.