DIETARY MODULATION OF THE MESSENGER-RNA STABILITY OF TRYPSIN ISOZYMESAND THE 2 FORMS OF SECRETORY TRYPSIN-INHIBITOR IN THE RAT PANCREAS

The stability of the mRNAs encoding pancreatic trypsin isozymes, namel y the cationic form and the two anionic forms I and II, as well as tha t of the secretory trypsin inhibitors I and II, were studied in rats f ed on either a high-protein diet, or a protein-free diet compared with a standard diet for a 10-day period. Either immediately or 3 h and 6 h after injecting the transcription inhibitor, actinomycin D, the mRNA levels were quantified by performing dot-blot hybridization with spec ific oligonucleotide probes. Under high-protein dietary conditions, th e stability of the mRNAs coding for anionic trypsin II and cationic tr ypsin showed no change, whereas that of anionic trypsin I and the two forms of secretory trypsin inhibitor were affected. The mRNA half-life of anionic trypsin I and trypsin inhibitor II increased, in sharp con trast with that of trypsin inhibitor I, which decreased. When rats wer e fed on a protein-free diet, the stabilities of both anionic trypsin forms and trypsin inhibitor I increased, whereas that of trypsin inhib itor II decreased and that of cationic trypsin remained unchanged. The present results show the existence of differences in the mechanisms w hereby gene expression of trypsin isozymes and secretory trypsin inhib itors is regulated, although they are synthesized in parallel in the p ancreatic acinar cell and stored in zymogen granules before being secr eted into the intestinal lumen.