Age and protein restriction followed by balanced refeeding affect pancreatic digestive enzyme outputs and turnover...

Outputs and turnover times of trypsinogen 2, chymotrypsinogen 1, lipase and amylase were determined in pancreatic juice of growing male Wistar rats at various times during protein restriction (5% protein) followed by balanced refeeding (20% protein). In control rats fed a 20% protein diet, trypsinogen 2, chymotrypsinogen 1 and amylase outputs increased progressively with age, those of lipase remained constant and the turnover times of the four hydrolases were shortened. With time, protein restriction induced the most rapid decrease in trypsinogen 2 output, followed by that of amylase, then by those of trypsinogen 1 and lipase. Compared with controls, protein restriction enhanced specific radioactivity in total proteins and each hydrolase and diminished the enzyme turnover times at the beginning of the experiment. Refeeding returned each hydrolase output to control values, but the turnover times remained shortened to the end of experiment. Pancreatic lobules were isolated from control and protein-depleted rat pancreata after 23 d of dietary treatment. After a pulse of [3H]leucine, lobules were incubated in Krebs-Ringer-bicarbonate-HEPES. Basal and stimulated (50 pmol cholecystokinin/L) secretions of total proteins, amylase and radioactive proteins were measured. Protein restriction resulted in a lower response of acinar cells to cholecystokinin. The reduced ability of cholecystokinin to stimulate secretion may be attributable to a lower number and/or to the reduced affinity of cholecystokinin receptors in acinar cells. Therefore, the observed output and turnover changes during protein restriction could be partly due to an impairment of cholecystokinin efficiency.