EFFECTS OF BRAIN-SEROTONIN ALTERATIONS ON PROSTAGLANDIN-E1-INDUCED BRADYCARDIA IN RATS

Abstract

The vasodepressor and bradycardia responses of saline control, serotonin-depleted and serotonin-potentiated rats to an i.v. dose of prostaglandin E1 (PGE1) were assessed under the urethane anesthesia. Elevation of serotonin concentration in brain with either 5-hydroxytryptophan (a serotonin precursor) or chlorimipramine (an inhibitor of serotonin reuptake), although causing no changes in vasodepressor response, did enhance the PGE1-induced bradycardia. Depleting serotonin concentration in brain with either p-chlorophenylalanine or 5,7-dihydroxytryptamine greatly reduced the PGE1-induced bradycardia without changes in vasodepressor response. The reduced PGE1 bradycardia induced by p-chlorophenylalanine treatment was readily reversed by the replacement of the depleted brain serotonin with 5-hydroxytryptophan in combination with a peripheral decarboxylase inhibitor Ro4-4602 [benserazide]. Brain serotonergic systems play a role in the elaboration or modulation of the PGE1-induced bradycardia. Specifically, brain serotonin seems to facilitate the PGE1-induced bradycardia since its depletion causes a decrease and its potentiation or elevation causes an increase in the PGE1-induced bradycardia.