Cholecystokinin-induced anorexia depends on serotoninergic function

The existence of a relationship between cholecystokinin (CCK)-induced satiety and the serotoninergic system was evaluated. The food intake of 3-h-fasted male rats was studied after treatment with the COOH-terminal octapeptide of CCK (CCK-8) alone or in combination with one of two blockers of serotonin (5-HT) receptors, metergoline (MET; 1.0 or 0.06 mg/kg), active in both the periphery and brain, or xylamidine tosylate (XYL; 1.5 mg/kg), active only in the periphery. CCK-8 reduced food intake in the 30 min after food presentation by 37% at 2 micrograms/kg, 68% at 4 micrograms/kg, and 80% at 8 micrograms/kg compared with controls. Both doses of MET attenuated CCK-8-induced satiety, increasing food intake of rats treated with all doses of CCK-8 to control values. Food intake was significantly increased over base line by the 1.0-mg/kg dose of MET alone but unaffected by the 0.06-mg/kg dose of MET alone. XYL had no effect either given alone or in combination with CCK-8. These results indicate that the inhibitory action of CCK-8 on food intake is dependent on intact functioning of the serotoninergic system, probably at central sites.