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Levels of chymotrypsin mRNA in the pancreatic tissue of preruminant calves were significantly decreased on d 28 and to a lesser extent on d 119 as compared to those of newborns. Enzymic activity regularly increased during the same period. By contrast, both chymotrypsin-specific activity and the mRNA level in the ruminant animals were enhanced on d 119 (1.4- and 2.3-fold, respectively), suggesting that some pretranslational regulation of the chymotrypsin gene was induced by weaning.

The levels of digestive enzymes are known for a long time to be modulated by dietary manipulations as well as genetic and hormonal factors. Adaptation of both types of enzymes, secretory pancreatic hydrolases and intestinal membrane-bound enzymes, to changes in diet has been shown to result from specific variations in the rate of their biosynthesis. As a first step towards the elucidation of the mechanism underlying adaptation of pancreatic enzymes to nutritional substrates we have measured the levels of translatable mRNAs coding for amylase, lipase, serine proteases and procarboxypeptidases. Our results indicate that dietary regulation occurs at a transcriptional level but also involves in some cases changes in mRNA stability. With respect to intestinal enzymes, reliable quantitative data were obtained by activity determination and monodimensional immunoelectrophoresis in response to changes in diet.

Translation of total pancreatic RNA using the rabbit reticulocyte lysate system allowed us to estimate the relative levels of active mRNA coding for a number of secretory proteins in Rats fed high-carbohydrate or high-protein diets. Quantitative synthesis of secretory proteins in isolated pancreatic lobules was also achieved. Protein synthesis in lobules or as the result of active mRNA translation in a cell-free system was found to give similar results either on a qualitative or quantitative standpoint. We were also able to show that the levels of specific mRNA for pancreatic amylase and serine protease zymogens could directly be related to the amount of carbohydrate or protein in the diet. These findings indicate that nutritional regulation of pancreatic enzyme synthesis occurs through the modulation of levels of specific mRNAs in the acinar cell.