Potentiation of colonic contractility to cholecystokinin and other peptides.

Changes in colonic contractility were studied in anesthetized cats following the intravenous injection of several peptides. Increases in contractile activity were observed after the octapeptide of cholecystokinin (CCK-8), pentagastrin, substance P or neurotensin. On the other hand, vasoactive intestinal peptide (VIP) caused an inhibition which, in some cases, was followed by an excitatory response. The responses produced by pentagastrin, substance P or neurotensin, but not by CCK-8, were partially inhibited by atropine. Following bethanechol pretreatment, the stimulation in contractile activity elicited by CCK-8, substance P, neurotensin or pentagastrin was markedly enhanced. Responses were also increased by pretreatment with eserine, hexamethonium or mecamylamine. This potentiation was blocked by atropine. It is concluded that, following treatments which cause an increase in the level of cholinergic input to the colon, an exaggerated motor response to some peptides can develop.