Specific response of serine protease mRNA to a protein-free diet in the rat pancreas.

The time course of response of pancreatic chymotrypsin, trypsin and elastase to a protein-free carbohydrate-rich diet was studied in Wistar rats. The levels of serine proteases in pancreatic tissue were markedly decreased for the first two days of diet consumption and further increased up to day 13 without reaching, however, the corresponding levels in control rats. This biphasic pattern of response may be due to some changes in the secretory process and/or the synthesis of enzymes in the acinar cell. The relative rate of synthesis of pancreatic enzymes was found to vary linearly with time and to be regulated in inverse proportion to nutritional substrates. Although the animals were totally deprived of dietary proteins, synthesis of acidic isoenzymic forms of serine proteases was nevertheless increased. The specific response of these proteases to a protein-free diet was mediated, at least partly, by changes in the levels of the corresponding specific mRNAs. As early as day 2 after diet consumption, the level of chymotrypsin mRNA was markedly enhanced in sharp contrast with that of amylase. This difference was further increased up to the fifth day of dietary manipulation. It is suggested that changes in cytoplasmic concentrations of chymotrypsin mRNA most probably resulted from transcriptional control of the corresponding gene although a possible increase in mRNA stability could not be ruled out.