Ontogeny of cholecystokinin satiety in rats.

The development of cholecystokinin satiety effects was studied in newborn rats. Weight gain during tests was the measure of intake in the sucklings, until the rats were weaned at 20 days of age. Thereafter food intake was measured directly. Intraperitoneal injection of cholecystokinin (CCK-OP) suppressed feeding in 1-7 day old rat pups. Gastric loads of 0.9% NaCl, 2.5% D-phenylalanine, and L-phenylalanine suppressed subsequent intake in 1-10 day old rats, but not in 10-20 day old rats. The early satiety effect of the intragastric loads was attributed to gastric distension. At 21-25 days of age, rats showed a suppression of intake following gastric loads of L-phenylalanine but not D-phenylalanine. This is tentative evidence that releasers of endogenous CCK do not induce satiety until immediately after weaning.