Abnormal insulin secretion and glucose metabolism in pancreatic islets from the spontaneously diabetic GK rat

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Abstract
Insulin secretion and islet glucose metabolism were compared in pancreatic islets isolated from GK/Wistar (GK) rats with spontaneous Type 2 (non-insulin-dependent) diabetes mellitus and control Wistar rats. Islet insulin content was 24.5±3.1 μU/ng islet DNA in GK rats and 28.8±2.5 μU/ng islet DNA in control rats, with a mean (±SEM) islet DNA content of 17.3±1.7 and 26.5±3.4 ng (p < 0.05), respectively. Basal insulin secretion at 3.3 mmol/l glucose was 0.19±0.03 μ · ng islet DNA−1· h−1 in GK rat islets and 0.40±0.07 in control islets. Glucose (16.7 mmol/l) stimulated insulin release in GK rat islets only two-fold while in control islets five-fold. Glucose utilization at 16.7 mmol/l glucose, as measured by the formation of 3H2O from [5-3 H]glucose, was 2.4 times higher in GK rat islets (3.1±0.7 pmol · ng islet DNA−1 · h−1) than in control islets (1.3±0.1 pmol · ng islet DNA−1 · h−1; p14CO2 from [U-14C]glucose, was similar in both types of islets and corresponded to 15±2 and 30±3 % (p3H2O) was 16.4±3.4% in GK rat and 6.4±1.0% in control islets, respectively (p<0.01). We conclude that insulin secretion stimulated by glucose is markedly impaired in GK rat islets. Glucose metabolism is also altered in GK rat islets, with diminished ratio between oxidation and utilization of glucose, and increased glucose cycling, suggesting links between impaired glucose-induced insulin release and abnormal glucose metabolism.