Insulin Response to an Intravenous Glucose Load During Development of Obesity in Gold Thioglucose-Injected Mice

The insulin secretory response to an intravenous glucose load was examined in chronically catheterized, conscious mice 2, 5, and 10 wk after induction of obesity by a single injection of gold thioglucose. At 2 wk after administration of gold thioglucose, a significant increase in both the insulinemia and incremental area under the curve of insulin release after intravenous glucose were observed (incremental area under the curve for 2-wk control mice, 852 ± 54 min/pM; incremental area under the curve for 2-wk GTG-injected mice, 1140 ± 114 min/pM; P < 0.05). At this stage, no significant difference existed in the glucose tolerance or body weight of control and gold thioglucose-injected mice. By 5 wk, the gold thioglucose-injected mice were ∼33% heavier than their lean controls and showed a marked glucose intolerance. This was accompanied by overt hyperinsulinemia in both the basal state and also in response to an intravenous glucose bolus as indicated by the increase in the incremental area under the curve of insulin (5-wk control mice, 816 ± 114 min/pM; 5-wk gold thioglucose-injected mice, 1374 ± 156 min/pM; P < 0.05). At 10 wk after gold thioglucose administration, body weight and the degree of glucose intolerance were increased. Although 10-wk gold thioglucose-injected mice showed basal hyperinsulinemia, an intravenous glucose bolus elicited a smaller insulin secretory response than that observed in the age-matched lean control animals (10-wk control mice, 672 ± 54 min/pM; 10-wk gold-thioglucose-injected mice 186 ± 42 min/pM; P < 0.05). Thus, during the early stages of gold thioglucose-induced obesity, a marked increase in insulin secretion in response to an intravenous glucose load occurs, but as the animals become chronically hyperinsulinemic and hyperglycemic, the insulin secretory response to intravenous glucose decreases, possibly indicating glucose toxicity of the pancreas. The increase in insulin secretion observed in 2-wk gold thioglucose-injected animals may be an important abnormality in the initiation of obesity responsible for the onset of the hyperlipogenesis and insulin resistance in this animal model.