Endogenous cholecystokinin's satiating action increases during estrus in female rats.

Food intake and meal size are reduced in female Long-Evans rats during estrus. To investigate the contribution of the satiating action of endogenous cholecystokinin (CCK) to this, rats were injected with 1 mg/kg of the potent, selective CCK(A) receptor antagonist, devazepide, during diestrus, when meal size is maximal, and during estrus, when it is minimal. Devazepide increased spontaneous food intake and meal size during estrus, but not during diestrus. Meal frequency was not affected by devazepide treatment. These results indicate that the potency of the CCK satiety-signaling system increases during estrus.