Expression of the amylase gene in the rat exocrine pancreas during postnatal development: effect of dexamethasone.

Pancreatic amylase enzyme activity starts to increase rapidly around weaning (17-21 days) and reaches the adult level during postnatal development in the rat. To see whether the maturation of amylase involves changes in amylase gene expression, total pancreatic RNA was prepared from rats of various ages (term-fetus, 5, 10, 15, 20, 28 days and adult). Northern blots of these RNAs were probed with amylase cDNA. Levels of amylase mRNA peaked around 10 days i.e., about 1 week prior to peak amylase enzyme activity. The role of glucocorticoid in pancreatic amylase development was studied by giving rat pups at ages 5, 10 and 30 days a single injection (i.p.) of dexamethasone (DX). They and their littermates (controls) were killed 24 and 48 h after the injection. Increases in amylase mRNA levels were seen in the DX treated 5- and 10-day-old groups with corresponding increases in amylase enzyme activities. A slight decrease in amylase mRNA level was, however, observed in the DX treated 30-day-old pups which also had a slight decrease in amylase enzyme activity suggesting an age dependent differential responsiveness to DX. A time sequence study with 10-day-old pups killed after a single injection of DX at 6, 12, 24 and 48 h showed a rapid increase in mRNA levels which peaked around 12 h. Amylase enzyme activity, however, did not peak until 24 h after DX injection. These results suggest that pancreatic amylase is regulated at the level of gene expression in both normal- and DX-induced maturation. Regulation appears to occur at the transcription level as both increases to amylase activity and mRNA were blocked by actinomycin D.