A HIGHLY SELECTIVE CARDIORENAL SEROTONERGIC 5-HT3-MEDIATED REFLEX IN RATS

To elucidate whether prolonged stimulation of cardiopulmonary serotone rgic (5-HT3) receptors could play a role in the control of renal sympa thetic nerve activity (RSNA), we compared 15-min intravenous infusions to bolus administrations of the 5-HT3 receptor agonist phenyl biguani de (PBG) and to a 0.9% saline load (5% body wt) in rats. Short-term an d prolonged stimulation of 5-HT3-sensitive cardiopulmonary reflexes ca used dose-related decreases in RSNA but not in lumbar sympathetic nerv e activity (LSNA); only short-term stimulation caused decreases in blo od pressure (BP) and heart rate (HR). Saline loading lowered RSNA but not LSNA, BP, or HR. Baroreceptor denervation did not influence any of these responses. Scopolamine attenuated BP and HR but not RSNA respon ses to bolus PBG. Pretreatment with a 5-HT3 receptor antagonist inhibi ted responses to PBG but not to saline. Vagotomy abolished all respons es to all interventions. Thus 1) the prolonged stimulation of cardiopu lmonary 5-HT3 receptors caused sustained suppression of RSNA, 2) decre ased BP and HR were manifest only during short-term stimulation (3 min ), and 3) blockade of 5-HT3 receptors did not influence responses to c ardiopulmonary mechanoreceptor stimulation.