Effect of insulin administration on contents, secretion, and synthesis of pancreatic lipase and colipase in rats.
After insulin administration in vivo, changes in pancreatic lipase, colipase and amylase contents and outputs were assayed and quantitatively compared. The incorporation of [35S]cysteine into individual enzymes was measured. The mRNA coding for lipase and amylase were determined by dot-blot hybridization. It was found that insulin dose-dependently decreased lipase and colipase contents, but only slightly decreased amylase content. Four hours after insulin administration (0.5 U/100 g), the contents of lipase and colipase decreased 80 and 72%, respectively, while amylase content decreased only about 25%. The decrease in amylase content was accompanied by a 21% increase in its output. The outputs of lipase and colipase only increased transiently and then sharply decreased to a level much lower than control. Total outputs of lipase and colipase could not quantitatively explain the great loss of lipase and colipase contents caused by insulin administration. After insulin injection, the incorporation of [35S]cysteine into amylase increased by 21%, whereas incorporation into lipase and colipase decreased by 18 and 25%, respectively. Dot-blot hybridization with cDNA probes revealed that lipase mRNA decreased by 50% 4 h after insulin administration, whereas mRNA for amylase did not significantly change. The results indicate an inhibitory effect of insulin administration on synthesis of pancreatic lipase and colipase, with the inhibition of lipase synthesis being at pretranslational level.