The developmental regulation of amylolytic and proteolytic enzymes in the embryonic rat pancreas.

During the period of morphogenesis of the rat pancreas, the specific exocrine enzymes accumulation pattern from Day 13 through Day 14 to as late as Day 15 is a low and constant basal level of each specific protein (the protodifferentiated level). Subsequently, the levels of the exocrine enzymes increase dramatically. The specific activities of chymotrypsin(ogen), trypsin(ogen), (pro)carboxypeptidase A and B, and amylase increase approximately lOOO-fold (differentiated stage). The inflection point of the typically sigmoid accumulation (plotted logarithmically) of the different enzymes occurs between 16% and 18% days. The initiation of these increases is not temporally coincident for all the proteins nor do the changes in specific activity of the enzymes appear to be coordinate. The levels of the enzymes in the adult pancreas average from several fold less to several fold more than those present in that of the newborn animal. Addition of agents implicated in altering the quantity of chymotrypsin and amylase in the adult animal have no effect on the in vitro embryonic accretion of these enzymes. Thus the levels appear to be independently modulated by unknown factors. Determinations in embryonic and adult tissues other than pancreas indicate that (pro)carboxypeptidase A activity is present in significant quantity only in the pancreas. In all cases, specific activities are considerably less than that of the pancreatic protodifferentiated level. This substantiates the existence of a protodifferentiated stage in pancreatic development. Enzyme assay of explants following organ culture of 13day pancreatic rudiments yields a profile of specific protein accumulation coincident with that observed in vivo. Measurements of rates of biosynthesis of exocrine enzymes in uifro demonstrate a 30to 60-fold increase during the developmental period studied (13 to 19 days). Inclusion of