Effects of Agonists and Antagonists of Cholecystokinin on Contractile and Myoelectric Activity of Isolated Muscle of Colon and Ileum in the Dog and Guinea Pig

This study evaluates the effects of agonists and antagonists of cholecystokinin (CCK) on contractile and myoelectrical activity in isolated longitudinal muscle strips from colon or ileum of guinea pigs or beagle dogs. Caerulein and CCK-8 caused a dose-dependent increase of contractile and myoelectrical spike activity in both species with maximal effects seen between 10⁻⁸ and 3 × 10⁻⁸ M. The dose responses were identical for both CCK agonists and species. The dose-related effects of CCK compounds on colonic muscle were slightly shifted to the right when compared to ileum in both species. All antagonists, the proglumide-derivatives CR1409, CR1392, and CR1505, as well as the nonpeptide substances asperlicin and L-364,718, caused a parallel rightward shift of CCK's dose-dependent motor activity response, indicating the competitive nature of inhibition. The antagonists displayed a rank order of potency in antagonizing CCK's action on intestinal motility similar to their ability to antagonize CCK's action on pancreas and gallbladder. L-364,718 was the most potent antagonist, followed by CR1409, CR1505, CR1392, asperlicin, and proglumide. The antagonists did not affect contractile or myoelectrical responses to acetylcholine, histamine, motilin, or substance P. Thus compounds that have been described as CCK antagonists for pancreas and gallbladder also act as specific and competitive antagonists of CCK's action on contractile and myoelectrical activity of Heal and colonie muscle.