Consistency of cholecystokinin satiety effect across deprivation levels and motivational states

A gastrointestinal hormone, cholecystokinin (CCK), has recently been implicated in the regulation of meal size. The consistency of the CCK satiety effect was examined across deprivation levels and motivational states. In a series of experiments rats were food deprived for varying amounts of time and injected with various doses of the CCK octapeptide before consuming a test meal of a liquid diet. In Experiment 1, 20 rats were deprived for 5 or 19 hr and injected with 0, 15, and 40 Ivy dog units/kg (U/kg) of CCK and in Experiment 2, 18 rats were 48 hr deprived and were injected with 0, 40, or 80 U/kg of CCK. In Experiment 3, 12 rats were deprived for 92 hr and received 80 U/kg of CCK. In all experiments CCK produced a dose-related suppression in food intake. CCK did not appear to become less effective as deprivation increased: 15 U/kg suppressed intake by approximately 30% at 5 and 19 hr deprivation; 40 U/kg suppressed intake by approximately 50% at all three deprivation levels; 40 U/kg suppressed intake by approximately 72% at 48 hr deprivation and 66% at 92 hr deprivation. In Experiment 4, the effects of CCK on food consumed in absence of hunger (0 hr deprivation) were observed by administering hypertonic saline to food-sated rats before presentation of a liquid diet. Under these conditions 40 U/kg of CCK suppressed intake by 76%. An additional experiment indicated that the increased inhibitory effects observed in the latter experiment were not due to the added variable of thirst. Thus under a wide variety of deprivation conditions and under varying motivational states CCK is remarkably consistent in its inhibitory effects on food intake, which are best described by a constant percent of control intake.