Abstract

During the day, serotonin levels in the pineal gland fall in vivo after administration of l-isoproterenol, l-Proprannolol, a beta adrenergic blocking agent, reverses the fall in serotonin caused by isoproterenol. Phentolamine, an alpha adrenergic blocking agent, is without effect under similar circumstances. Inhibition of monoamine oxidase does not cause an increase in the level of serotonin over the course of one hour. l-Propranolol causes a rapid increase the amount of serotonin in the pineal at night. We confirm the finding that serotonin N-acetyltransferase (EC 2.3.1.5) increases in response to beta adrenergic stimulation and that this rise can be prevented by beta adrenrgic blockers. These results suggest that the level of serotonin in the pineal is regulated by a beta adrenergic receptor via control of serotonin N-acetyltransferase activity.