ENZYMATIC AND METABOLIC ANOMALIES IN ISLETS OF DIABETIC RATS - RELATIONSHIP TO B-CELL MASS

A preferential impairment of the pancreatic B cell secretory response to D-glucose occurs in adult rats injected with streptozotocin during the neonatal period. Three possible explanations for such a preferential defect were investigated in the present study. First, the time course for 3-O-methyl-D-glucose uptake by islets suggested that the anomaly in hexose transport was mainly attributable to a decrease in the space accessible to the D-glucose analog commensurate with the decrease in B cell mass, rather than to a delayed equilibration of hexose concentration across the B cell plasma membrane. Second, the activity of glucose-6-phosphatase was found to be equally low in islets from diabetic and control rats, ruling out the futile cycling between D-glucose and D-glucose 6-phosphate as a cause for the preferential alteration of the secretory response to the hexose. Third, the activity of flavine adenine dinucleotide-linked glycerophosphate dehydrogenase was found to be decreased to a greater relative extent than the B cell mass. This coincided with an impaired generation of (HOH)-H-3 from L-[2-H-3] glycerol in intact islets. It is proposed, therefore, that an altered circulation in the glycerol phosphate shuttle may play a major role in the impaired process of glucose-stimulated insulin release in this model of noninsulin-dependent diabetes.