ROLE FOR 5-HT AND ACH IN SUBMUCOSAL REFLEXES MEDIATING COLONIC SECRETION

Neural reflex pathways activated in response to mucosal stroking were investigated in segments of distal colon from guinea pigs. Stroking th e mucosal surface of whole thickness or muscle-stripped segments with a brush at 1/s evoked an increase in short-circuit current (I-sc) whos e duration and amplitude were dependent on the number of strokes. The increase in I-sc induced by mucosal stroking was virtually abolished b y inhibitors of chloride secretion and by tetrodotoxin. The response w as reduced by atropine, renzapride, and N-acetyl-5-hydroxytryptophyl-5 -hydroxytryptophan amide but not by mecamylamine, ketanserin, tropiset ron, or SDZ-205-557. Mucosal application of 5-hydroxytryptamine and 5- hydroxyindalpine increased I-sc, which was attenuated by tetrodotoxin and renzapride. The results suggest that mucosal stroking evokes chlor ide secretion by activating neural reflex pathways utilizing serotonin ergic receptors, of the 5-HT1P class, as well as muscarinic receptors within the submucosal plexus.