Evaluation of pancreatic amylase mRNA upon cholinergic stimulation of secretion.
The primary function of the exocrine pancreas consists of the synthesis and secretion of several digestive enzymes. It is well established that amylase secretion by rat pancreatic tissue or by isolated acinar cells in culture can be stimulated by the cholinergic agonist carbachol. However, the effect of this secretagogue on enzyme synthesis remains unclear. Some studies demonstrated increases in rates of synthesis, whereas others reported increases in secretion with or without decreases in synthesis. We have evaluated changes in pancreatic amylase mRNA and total RNA after a single injection of carbachol and under fasting conditions. Two approaches in molecular morphology were applied on rat pancreatic tissue: in situ hybridization and RNase A-gold. Both revealed decreases in RNA labeling at the level of the rough endoplasmic reticulum (RER) 5 min after stimulation of secretion and after fasting. Gradual recovery was registered 15 and 30 min after stimulation of secretion. Northern blotting confirmed drastic decreases in amylase mRNA 5 min after stimulation and after fasting. The combination of such different approaches has demonstrated drastic decreases in RNA at the RER level, reflecting declines in rates of synthesis at the translational level under all conditions tested.