Control of ingestion in 6-day-old rat pups: termination of intake by gastric fill alone?

Six-day-old rat pups, tested away from the dam, vigorously ingested orally infused milk for up to 90 min when the ingested milk was allowed to drain through a gastric fistula. Total intake in pups with unplugged fistulas was more than double that consumed by littermates with plugged fistulas. This persistent feeding could not be due to the absence of postgastric cues because blocking movement of the milk into the intestine with a closed pyloric noose resulted in less intake than when the noose was open. Furthermore, a 5% body weight gastric preload of milk or nonnutritive saline suppressed intake in pups with either open or closed pyloric nooses by an amount equal to the preload. Regardless of noose or preload condition, ingestion stopped when stomach content reached approximately 6.5% of body weight. Thus level of gastric fill appeared critical for intake control. When gastric fistulas were unplugged after pups had ingested milk until they stopped, vigorous ingestion followed, with total intakes of up to 20% body weight. Intake termination in young rat pups thus appears to be controlled exclusively by gastric fill level; pregastric signals alone appear insufficient, and postgastric signals appear unnecessary for termination of intake.