Regulation of pancreatic amylase and lipase gene expression by diet and insulin in diabetic rats

Abstract

Although insulin has been proposed to mediate the dietary regulation of pancreatic amylase, its interaction with diet in the regulation of amylase and lipase is not well understood and was examined in diabetic rats fed diets high in carbohydrate (HC), protein (HP), or fat (HF) and treated with insulin. Diabetes, independent of diet, decreased amylase content (97%; P < 0.0001) and mRNA (90%; P < 0.0001), but insulin only restored amylase content and mRNA to respective dietary control values. Diabetes, independent of diet, also increased lipase mRNA 1.6-fold (P < 0.004) but interacted (P < 0.0003) with diet on lipase content, resulting in opposite effects in HC- (increased 202%) and HF-diabetic rats (decreased 40%). Insulin partially restored lipase content and mRNA to respective dietary control values. Diet, independent of diabetes, regulated amylase content (P < 0.0001) and mRNA (P < 0.0003), which were three- to fourfold greater in HC- than in HF-fed rats, and lipase content (P < 0.001) and mRNA [rat pancreatic lipase 1 (rPL-1), P < 0.04; rPL-3, P < 0.0001], which were 1.8-fold greater in HF- than in HC- or HP-fed rats. Insulin failed to stimulate maximal amylase gene expression in HP- or HF-fed diabetic rats, suggesting that it is necessary, but not sufficient, for this dietary regulation. Differential regulation of lipase activity and mRNA by diet and insulin raises the possibility that lipase gene expression is regulated by a complex interaction of diet and insulin.