EFFECTS INVITRO OF ALLOXAN ON THE GLUCOSE-METABOLISM OF MOUSE PANCREATIC B-CELLS

To facilitate detailed studies of the B-cytotoxic action of alloxan we developed a model using isolated pancreatic islets of normal mice. An essential feature of this model is the low temperature employed during exposure to alloxan, which minimizes the degradation of the drug. The islets were incubated with alloxan for 30 min at 4°C and subsequently various aspects of their metabolism were studied. The O2 consumption was measured by the Cartesian-diver technique. Islets exposed to 2mM-alloxan and control islets had the same endogenous respiration, whereas the O2 uptake of the alloxan-treated islets was inhibited and that of the control islets stimulated when they were incubated with 28 mM-glucose as an exogenous substrate. The islet glucose oxidation was estimated by measurement of the formation of 14CO2 from [U-14C]glucose at 37°C. Compared with the controls, alloxan-treated islets showed a decrease in the glucose-oxidation rate in a dose-dependent manner. Pretreatment of the islets with 28 mM-glucose for 30 min at 37°C completely protected against this effect, whereas preincubations at glucose concentrations below 16.7 mM failed to exert any protective effect. The glucose utilization was estimated as the formation of 3H2O form [5-3H]glucose. Alloxan (2 mM) failed to affect islet glucose-utilization rate in the presence of either 2.8 or 28 mM-glucose. In contrast, islets exposed to 5 or 10 mM-alloxan exhibited lowered utilization. It is concluded that in vitro alloxan has an acute inhibitory effect on the islet glucose metabolism, and that this action can be prevented by previous exposure to a high glucose concentration. The results are consistent with the idea that the B-cytotoxicity of alloxan reflects an interaction with intracellular sites involved in the oxidative metabolism of the B-cell.