Adaptation de la vitesse de biosynthèse de l'amylase pancréatique et du chymotrypsinogène a des régimes riches en amidon ou en protéines

Abstract

1. 1. Previous investigations in this laboratory have shown that the amounts of amylase in rat pancreas and pancreatic juice are 3–4 time higher, and the amounts of chymotrypsinogen 3 times lower, when the animals receive a starch-rich diet (diet G) rather than a protein-rich diet (diet P). With these variations are associated similar variations in the relative rates of biosynthesis of the enzymes (radioactivity incorporated into the enzymes versu radioactivity incorporated under the same conditions into the total proteins of pancreas). The specific radioactivity of the precursor (labelled valine) has now been evaluated as accurately as possible in order to calculate and to compare the biosynthetic rates themselves in pancreas G and P. 2. 2. Two series of experiments have been carried out, the first using intravenous injection of labelled precursor into rats G and P in vivo, and the second using incubation of slices of pancreas G and P in the presence of precursor. In both cases, the specific radioactivity of the precursor between 2–15 min in the trichloroacetic acid-soluble fraction of the homogenates and the radioactivity incorporated after 5, 10 and 15 min into pure amylase and chymotrypsinogen have been determined. The evaluation of the magnitude of the adaptation effect is greatly facilitated by the fact that the specific radioactivity of the precursor is always about the same in pancreas G and P. 3. 3. Radioactivity measurements on pancreatic juice samples collected from injected animals, and chase experiments with pancreas slices, have shown that no loss of labelled enzymes by secretion and degradation is likely to occur during the assays. 4. 4. As a result, it may be concluded that the ingestion of diet G, as compared with diet P, induces an 8-fold increase in the rate of biosynthesis of amylase and a 2-fold decrease in that of chymotrypsinogen. The fact that the results obtained with pancreas slices are similar to those obtained in vivo suggests that the alimentary stimulus determines a specific modification in the biosynthetic system of pancreas acinar cells. 5. 5. Finally, the experimental values may be used for calculating the number of amylase and chymotrypsinogen molecules synthesized per minute by one acinar cell of rat pancreas.