Glucose regulates proinsulin and prosomatostatin but not proglucagon messenger ribonucleic acid levels in rat pancreatic islets

Insulin and glucagon are the major hormones involved in the control of fuel metabolism and particularly of glucose homeostasis; in turn, nutrients tightly regulate insulin and glucagon secretion from the islets of Langerhans. Nutrients have clearly been shown to affect insulin secretion, as well as insulin biosynthesis and proinsulin gene expression; by contrast, the effects of nutrients on proglucagon gene expression have not been studied. We have investigated the effect of glucose, arginine, and palmitate on glucagon release, glucagon cell content, and proglucagon messenger RNA (mRNA) levels from isolated rat islets in 24-h incubations. We report here that concentrations of glucose that clearly regulate insulin and somatostatin release as well as proinsulin and prosomatostatin mRNA levels, do not significantly affect glucagon release, glucagon cell content or proglucagon mRNA levels. In addition, though both 10 mM arginine and 1 mM palmitate strongly stimulated glucagon release, they did not affect proglucagon mRNA levels. We conclude that, in contrast to insulin and somatostatin, glucose does not affect glucagon release and proglucagon mRNA levels, and arginine and palmitate do not coordinately regulate glucagon release and proglucagon mRNA levels.