Dietary effects on (pro)insulin biosynthesis and insulin-degrading activity in islets from sand rats

Sand rats were fed either a vegetable (vegetable group) or a standard pellet diet. After 14-16 weeks, the normoglycemic subgroup selected (pellet group) from the animals that had been maintained on the standard diet showed a modest increase in body weight. Plasma immunoreactive insulin levels were not significantly increased, but glucose-stimulated insulin release was elevated from islets isolated from sand rats of the pellet group. Insulin biosynthesis was estimated in vitro by measuring [3H]leucine incorporation into (pro)insulin at 1.5 or 15 mmol/l glucose. The rate of (pro)insulin biosynthesis was elevated only at 15 mmol/l glucose in islets from those normoglycemic sand rats fed the pellet diet when compared with islets from the vegetable group. Specific insulin-degrading activity, as determined by measuring degradation of 125I-labeled insulin, was also increased for islets from the pellet group. The metabolic state of these sand rats is thus associated with normoglycemia in vivo, and increased stimulated rates of insulin biosynthesis and degradation in pancreatic islets in vitro.