Suppression of sham feeding by intraintestinal nutrients is not correlated with plasma cholecystokinin elevation

To test the possibility that blood-borne cholecystokinin (CCK) participates in suppression of sham feeding by intestinal nutrients in rats, we examined the ability of oleate, maltose, L-phenylalanine (L-Phe), and casein to suppress sham ingestion of 15% sucrose solution. Plasma CCK concentrations were measured in parallel experiments in which the same intestinal nutrients were infused in rats that were not feeding. Intraintestinal oleate suppressed sham feeding and elevated plasma CCK concentrations. Casein infusion produced plasma CCK concentrations similar to those produced by oleate but did not suppress sham feeding. Both maltose and L-Phe suppressed sham feeding but failed to significantly elevate plasma CCK. Previously we demonstrated that CCK receptor antagonists attenuate suppression of sham feeding by intestinal infusion of either oleate or maltose, suggesting that endogenous CCK participates in suppression of sham feeding by some intestinal nutrients. The results of the study reported here suggest that plasma CCK levels after nutrient infusion are not correlated with suppression of sham feeding. Therefore, the mechanism of CCK's participation in nutrient-induced suppression of sham feeding may not depend on stimulus-induced elevation of plasma CCK.