Ontogeny of phenylalanine (endogenous cholecystokinin) induced modulation of food intake in normal and undernourished rats.

1. The development of endogenous cholecystokinin (CCK) effects on food intake was studied in normal and undernourished growing rats of postnatal day 1-22. 2. Food intake was estimated by recording the gain in body weight before weaning. 3. l-phenylalanine, a potent stimulant of endogenous CCK release, suppressed 30 min food intake in normally nourished pups of day 7-15 or more but not of day 1-6 rats. 4. However, l-phenylalanine did not affect 24 hr gain in body weight day 1-6 or more, rat pups. 5. l-phenylalanine neither suppressed 30 min food intake nor affected 24 hr body weight in day 16-19 or 20-22 undernourished rat pups. 6. The study suggests that the endogenous CCK satiety effects appear early in the second week of postnatal life in normally nourished rats, whereas in undernourished rat pups it does not appear till day 20-22.