STIMULATORY EFFECTS OF 5-HYDROXYTRYPTAMINE ON FLUID SECRETION AND TRANSMURAL POTENTIAL DIFFERENCE IN RAT SMALL-INTESTINE ARE MEDIATED BY DIFFERENT RECEPTOR SUBTYPES

Abstract— The rise in transmural potential difference (PD) and the fluid secretion induced by 5‐hydroxytryptamine (5‐HT) were measured in rat small intestine in‐vivo. Both cisapride and ketanserin abolished the 5‐HT‐induced rise in systolic blood pressure mediated by 5‐HT2 receptors. Cisapride inhibited the 5‐HT‐induced increases in the transintestinal PD, but over the same dose range it had no effect on the fluid secretion induced by 5‐HT. In contrast, ketanserin caused a dose‐dependent reduction in 5‐HT‐induced fluid secretion at doses that failed to influence the rise in PD. It is concluded that different receptors are responsible for the effects of 5‐HT on fluid secretion and electrical activity in the rat small intestine. 1990 Royal Pharmaceutical Society of Great Britain