Glucose- and Tolbutamide-Mediated Insulin Response after Preinfusion with Ethanol

Intravenous glucose tolerance tests (1VGTT) were carried out in five normal subjects after ethanol preinfusion for one, two or four hours. Constant serum level of ethanol was maintained throughout the experiments. Control experiments were performed with saline. Basal levels of serum glucose and insulin were unaffected by ethanol. As regards glucose tolerance a nonsignificant rise in the glucose assimilation constant was seen. During IVGTT peak insulin concentration was unaffected by preinfusion with ethanol for one or two hours, but significantly elevated after four hours. The declining part of the insulin concentration curve was significantly elevated after one or four hours of preinfusion. The insulin increment per glucose increment (the insulinogenic index) rose with the duration of the preinfusion period and, compared to the control experiment, a twofold increment was seen after four hours. When tolbutamide (1 gram) was given intravenously to two of the subjects after preinfusion with ethanol for four hours, the subsequent insulin response followed the same pattern as seen in the four-hour-IVGTT experiment. As the potentiation increases with the duration of the preinfusion period, it might be explained by cummula-tive changes in the beta cell. However, a diminished hepatic degradation rate of insulin cannot be ruled out.