Sympathoinhibitory responses to 2-methylserotonin during changes in sodium intake

Abstract

The vagal-mediated reflex responses elicited by the selective serotonin type 3 receptor agonist 2-methyl- serotontn were examined by administration (6.25, 12.5, 25, and 50 Mg/kg i.v.) of 2-methylserotonin to sinoaortic-denervated rats with either intact or sectioned vagi. To study the influence of dietary sodium intake on 2-methylserotonin-induced vagal reflex responses, we performed experiments in rats fed either a high or low sodium diet. Left ventricular end-diastolic pressure was signiflcantly higher in animals on high than low salt diet. However, mean arterial pressure and heart rate were similar in high and low salt groups. In rats with intact vagi, 2-methylserotonin produced a dose-dependent increase in afferent vagal nerve activity and a dose-dependent decrease in eiferent renal sympathetic nerve activity, mean arterial pressure, and heart rate. The sympathoiuhibitory responses of decreased efferent renal sympathetic nerve activity, mean arterial pressure, and heart rate were abolished by vagotomy and were not affected by changes in dietary sodium intake. We conclude that the sympathoinhibitory effect of 2-methylserotonin is due to stimulation of vagal afferents with inhibitory action on peripheral sympathetic nerve activity and that the sympathoinhibitory responses are unaffected by changes in dietary sodium intake. (Hypertension 1993;21:1000-1004) © 1993 American Heart Association, Inc.