title: Interaction of gastrin I, secretin, and cholecystokinin on gallbladder smooth muscle.
abstract: The effect of cholecystokinin (CCK), the octapeptide of cholecystokinin (CCK-OP), gastrin I, and secretin was studied on guinea pig gallbladder smooth muscle in vitro. Both CCK and CCK-OP stimulated gallbladder contraction, with CCK-OP being more potent. Gastrin I, over a wide dose range, had no effect on gallbladder contractility. Secretin alone also showed no effect on gallbladder smooth muscle but in combination with CCK-OP it produced a noncompetitive type of inhibition. Michaelis-Menten kinetics showed the calculated maximum response of the secretin plus CCK-OP interaction to be less than with CCK-OP alone. There was no change in the dose required to achieve half-maximal response, D50. These studies indicate that: a) CCK-OP has a greater effect on gallbladder contractility than CCK, b) gastrin I has no effect on gallbladder muscle tone, and c) secretin acts as a noncompetitive antagonist of CCK-OP. These findings suggest that gallbladder motor function may be determined in part by the interaction of secretin and CCK rather than solely in response to CCK.
mesh_terms: D000818:Animals; D002766:Cholecystokinin / Q000031:analogs & derivatives / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005704:Gallbladder / Q000187:drug effects*; D005755:Gastrins / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D012633:Secretin / Q000494:pharmacology*
chemical_list: D005755:Gastrins; D012633:Secretin; D002766:Cholecystokinin