Induction and superinduction of serotonin N-acetyltransferase by adrenergic drugs and denervation in rat pineal organ.

Activity of serotonin N-acetyltransferase (EC 2.3.1.5) in rat pineal organ is rapidly and markedly elevated in vivo after administration of beta-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA), norepinephrine, epinephrine, isoproterenol, monoamine oxidase inhibitors, or theophylline. Serotonin or 5-hydroxytryptophan has no effect on the increase in activity of this enzyme. Inhibitors of protein synthesis or propranolol, a beta-adrenergic blocking agent completely inhibit(s) the increase in activity of serotonin N-acetyltransferase induced by drugs, indicating that new enzyme molecules are formed via stimulation of beta-receptors of pineal cells and adenosine 3':5'-cyclic monophosphate. When rat pineal organ is denervated by ganglionectomy, beta-(3,4-dihydroxyphenyl)-L-alanine induces much more serotonin N-acetyltransferase than in the innervated gland. This superinduction by denervation appears to be due to changes of the postsynaptic site, probably the beta-adrenergic receptor on the pineal cell.