DO 5-HT4 RECEPTORS MEDIATE THE INTESTINAL SECRETORY RESPONSE TO 5-HT IN RAT IN-VIVO

The involvement of the recently characterized 5-HT4 receptor in the ac tions of 5-hydroxytryptamine (5-HT) on jejunal, ileal and colonic elec trogenic ion secretion was investigated in the rat in-vivo. 5-HT and t he 5-HT1-, 5-HT2- and 5-HT4-receptor agonist 5-methoxytryptamine (5-Me OT), induced a rise in transintestinal PD in all regions of the gut. H owever, the 5-HT4-receptor agonists renzapride and cisapride had no ef fect. Furthermore, the 5-HT4-receptor antagonists SDZ 205-557 (2-dieth ylaminoethyl-[2-methoxy-4-amino-5-chloro] benzoate), tropisetron and S B 204070 ([1-butyl-4-piperidinylmethyl]-8-amino-7-chloro-1 ,4-benzodio xan-5-carboxylate hydrochloride) did not affect the secretory response to either 5-HT or 5-MeOT in the jejunum, but did cause a small inhibi tion in the ileum and colon. It is concluded that 5-HT4 receptors do n ot make a contribution to the electrically monitored 5-HT intestinal s ecretory response in the rat jejunum in-vivo, but may play a small rol e in the ileum and colon.