Endogenous and exogenous cholecystokinin may reduce food intake by different mechanisms.

To determine whether exogenous cholecystokinin (CCK) and endogenous CCK evoke different gastrointestinal motor responses, we investigated the motility induced by CCK by use of standard manometric methods. Injection (ip) of 500 ng/kg CCK caused immediate profound gastric inhibition and duodenal phasic excitation that did not resemble the postprandial pattern. Similar profound gastric inhibition has been associated with nausea. The contribution of endogenous CCK to the fed pattern of motility was investigated using proglumide; intraperitoneal injection of the antagonist before feeding caused no change, but injection before a second meal induced a decrease (P less than 0.025, n = 6) in gastric pressure with no accompanying duodenal change. This suggests that CCK causes an increase in gastric pressure that could result from a delay in gastric emptying. In support of this hypothesis, we have previously demonstrated, by use of proglumide, that endogenous CCK delays gastric emptying. Therefore exogenous CCK may reduce food intake by evoking an abnormal gastrointestinal motor pattern that may induce malaise, whereas endogenous CCK may decrease food intake by delaying gastric emptying, thus prolonging gastric satiety signals.