FOOD-INTAKE AND BEHAVIORAL CALORIC COMPENSATION AFTER PROTEIN REPLETION IN THE RAT

The food intake response of rats to intragastrically infused or orally consumed protein was characterized and compared to the response to similarly administered carbohydrate. In Experiment 1, protein hydrolysate loads administered at the beginning of the dark phase via chronic intragastric cannulae led to rapid (complete within 3-4 hr), dose-related suppressions of food intake in comparison to sham loads or to urea loads controlling for volume, concentration and pH. The suppression remained evident in cumulative intake records through 24 hr and represented a greater than caloric compensation for the amount of metabolizeable energy delivered (1.38 and 1.12 kcal/kcal in Experiments 1a and 1b, respectively). In Experiment 2, protein hydrolysate loaded by gavage suppressed food intake significantly more than isocaloric glucose loads (1.32 vs 0.81 kcal/kcal after 24 hr). Water intake in both experiments was elevated by protein loads, although this occurred after the food intake suppression. Differential satiety responses to protein and carbohydrate repletion were shown in Experiment 3 to extend to orally consumed, naturally occurring macronutrients-casein vs starch and disaccharide diets. These data suggest that satiety in the rat is not solely graded with respect to the energy delivered by the preceding meal but rather that repletion with different macronutrients leads to quantitatively (or perhaps qualitatively) different satieties. © 1979.