SEROTONIN CONTRACTS THE ISOLATED RAT PYLORUS VIA A 5-HT2-LIKE RECEPTOR

Serotonin (5-HT) produced concentration-dependent contractions of the isolated rat pylorus in vitro. Serotonergic contractions were antagoni zed by the calcium L-channel blocker, diltiazem, but not by tetrodotox in or atropine. Three drugs that block 5-HT2 receptors, ketanserin, xy lamidine, and methysergide, unsurmountably inhibited contractions to 5 -HT. In contrast, antagonists of 5-HT3, 5-HT1A/1B, beta-adrenergic, or alpha(1)-adrenergic receptors did not alter the response to 5-HT. Dev azepide, an antagonist of cholecystokinin (CCK) type-A receptors, bloc ked contraction produced by CCK-8 but not by 5-HT. Conversely, the 5-H T2 antagonists did not affect CCK-stimulated contraction. These result s suggest that 5-HT contracts the pylorus by a 5-HT2-like receptor on muscle and that this response occurs independently of CCKergic recepto r mechanisms. Furthermore, the parallel between the overall pharmacolo gical profile for serotonergic contraction of the pylorus and that obs erved previously for the anorectic action of peripheral 5-HT makes the pylorus a logical candidate for peripheral serotonergic control of fe eding.