Persisting Enhanced Proinsulin-insulin and Protein Biosynthesis (³H-Leucine Incorporation) by Pancreatic Islets of the Rat after Glucose Exposure

Pancreatic islets isolated from rats infused with glucose for twenty-four hours incorporated ³H-leucine into protein at higher rates than islets isolated from normoglycemic rats. Incorporation into proinsulin-insulin showed a thirteenfold increase. The effect on other islet proteins was fourfold. Exposure of islets from normoglycemic rats to high glucose in vitro for twenty and ninety minutes and subsequent incubation with ³H-leucine at low glucose showed a twofold and fivefold increase in proinsulin biosynthesis. In the in vitro system pre-exposure of the islets to mannose and dibutyryl-cyclic AMP induced a much smaller increase in proinsulin biosynthesis.