Differential Increases in Syntheses of Newly Identified Trypsinogen 2 Isoforms by Dietary Protein in Rat Pancreas

Abstract

We have found that dietary protein markedly induced pancreatic serine protease activity via a mechanism independent of luminal trypsin activity in pancreatico-biliary–diverted (PBD) rats. The aim of this study was to examine the effects of dietary protein on the synthesis of trypsinogen isoforms by comparing in vivo incorporation of [³⁵S] l-methionine into isoform proteins in PBD and sham-operated rats. A small duodenal segment including the ampulla of Vater was sectioned and transposed to the upper ileum with end-to-side anastomosis (PBD) or duodenal transection was followed by reanastomosis (sham) in male Sprague-Dawley rats. After recovery, PBD and sham rats were fed a 25% or 60% casein-sucrose–based diet (NC or HC) for 14 days. Rats were then intravenously injected with [³⁵S] l-methionine (15 MBq/kg body weight) 30 mins before being sacrificed for analysis of pancreatic enzymes by two-dimensional SDS-polyacrylamide gel electrophoresis. By using electrophoresis with narrow range of isoelectric focusing (pl 4.5–5.5), five trypsinogen 2 (2-x) isoform spots were identified using both [³⁵S] incorporation and Coomassie brilliant blue (CBB) staining in PBD rats, but not in sham rats. N-terminal sequences of these trypsinogen 2-x spots were identical to known rat trypsinogen 2 with the exception that the third valine was changed to isoleucine in one isoform. In PBD rats, feeding of HC specifically increased the [³⁵S] and CBB intensities of these trypsinogen 2-x isoforms and trypsinogen 3. The degree of induction of the five trypsinogen 2-x molecules by HC varied greatly. Trypsinogen 1 and 4, which are the major trypsinogens in normal rats, showed no changes. We conclude that increases in synthesis of a few newly identified trypsinogen 2-x isoforms mainly contribute to the induction of trypsin activity in the pancreas by HC in PBD rats.