Role of dietary protein in rat pancreatic enzyme secretory response to a meal.

The role of dietary protein in the pancreatic enzyme secretory response to complete test meals was studied in rats fitted with chronic bile-pancreatic fistulas. Pancreatic enzyme secretory response was observed by collecting combined bile-pancreatic juice and continuously returning it to the intestine by a stream-splitter, which diverted 5% for assay. All rats were fed ad libitum a 24% casein diet during the recovery period. Four days postoperative, rats were infused intragastrically with 5 g of isonitrogenous, complete test meals containing casein (24%), alpha-protein (soy protein), amino acids patterned after casein or alpha-protein, casein + lima bean trypsin inhibitor (LBTI), and a nitrogen-free diet. Pancreatic enzyme secretion under basal conditions and in response to the test meals was determined. The pancreatic response to test meals containing intact casein as nitrogen source was the same as the response to nitrogen-free test meals, and was only slightly greater (not statistically significantly) than the response to test meals containing amino acids. Test meals containing alpha-protein, which was devoid of soybean trypsin inhibitor activity, were much more potent than corresponding amino acid test meals or nitrogen-free test meals. Addition of LBTI greatly increased the pancreatic response to casein test meals. The results indicate that intragastric infusion of diets containing casein as nitrogen source do not stimulate greater pancreatic enzyme secretion than test meals of nitrogen-free or amino acid diets under normal physiological conditions, and it is proposed that this is a consequence of the large reserve capacity of the exocrine pancreas.