Cholecystokinin inhibits gastric emptying and contracts the pyloric sphincter in rats by interacting with low affinity CCK receptor sites

The aim of these experiments was to characterize the receptor affinity state through which CCK produces pyloric contraction and inhibits gastric emptying in the rat using the novel CCK heptapeptide analog CCK-JMV-180. CCK-JMV-180 has been demonstrated to act as a functional agonist at high affinity pancreatic CCKA receptors but as a functional antagonist at CCKA low affinity receptors. CCK-8 (1, 3.2 and 10 nM) induced dose dependent tension increases in isolated pyloric segments. CCK-JMV-180 (3.2 microM) or vehicle failed to mimic this action when administered alone but blocked the ability of CCK-8 (3.2 nM) to induce tension increases. CCK-8 (2 micrograms/kg) also inhibited the gastric emptying of physiological saline. CCK-JMV-180 (320 and 1000 micrograms/kg) failed to inhibit emptying when administered alone but dose dependently antagonized CCK induced inhibition of gastric emptying. Thus, in both preparations CCK-JMV-180 acted as a functional CCK antagonist. This profile is consistent with the interpretation that the actions of CCK in pyloric contraction and the inhibition of gastric emptying are mediated through CCK's interactions with receptors functionally similar to pancreatic low affinity sites.