Dietary Modulation of the mRNA Stability of Trypsin Isozymes and the Two Forms of Secretory Trypsin Inhibitor in the Rat Pancreas

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Abstract
The stability of the mRNAs encoding pancreatic trypsin isozymes, namely the cationic form and the two anionic forms I and II, as well as that of the secretory trypsin inhibitors I and II, were studied in rats fed 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 specific oligonucleotide probes. Under high‐protein dietary conditions, the stability of the mRNAs coding for anionic trypsin II and cationic trypsin 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 contrast with that of trypsin inhibitor I, which decreased. When rats were fed on a protein‐free diet, the stabilities of both anionic trypsin forms and trypsin inhibitor I increased, whereas that of trypsin inhibitor II decreased and that of cationic trypsin remained unchanged. The present results show the existence of differences in the mechanisms whereby gene expression of trypsin isozymes and secretory trypsin inhibitors is regulated, although they are synthesized in parallel in the pancreatic acinar cell and stored in zymogen granules before being secreted into the intestinal lumen.