Time course of changes in rat pancreatic synthesis rates and retention thresholds of four hydrolases during consumption of a low-protein followed by a balanced diet.

Synthesis rates of pancreatic amylase, trypsinogen 2 (Tg2), chymotrypsinogen 1 (Chtg1), and lipase, were measured in control rats fed a 20% protein diet for 46 days and in malnourished rats fed a 5% protein diet for 23 days (protein malnutrition) followed by refeeding a balanced diet for 23 days. In the control group, a progressive pancreatic maturation (namely an increase in hydrolase synthesis per gram of tissue) appeared with age. In the malnourished group, pancreas maturation of the four hydrolases was inhibited. Synthesis rates of the four hydrolases were reduced to a lesser extent from day 2 of protein malnutrition. With continued protein malnutrition, Tg2 synthesis rates remained steady, whereas the lipase synthesis rate continued to decrease and Chtg1 and amylase rates started to increase. As soon as refeeding was initiated, an important enhancement in synthesis was observed. The synthesis rates of Tg2, Chtg1, and amylase actually showed a rebound effect, then decreased with the refeeding time to reach control values, except for Chtg1, which remained higher than control values throughout the refeeding phase. Lipase synthesis rate rose more slowly and reached the control values only after 9 days of refeeding. The retention threshold (pancreas tissue versus pancreatic secretion) values showed that the storage levels were different from one hydrolase to the other and were variable with age in the control group, and with protein malnutrition and refeeding times in the malnourished group. In the control group, a preferential secretion of newly synthesized enzymes was observed in young rats, whereas with age, the proportion of newly synthesized hydrolases excreted decreased slowly.(ABSTRACT TRUNCATED AT 250 WORDS)