Dose-response relationship of insulin to glucose fluxes in the awake and unrestrained mouse.

The purpose of the study was to use the hyperinsulinemic-euglycemic clamp technique to generate insulin dose-response curves for insulin suppression of endogenous glucose output (EGO) and stimulation of the glucose disposal rate (GDR) in conscious unstressed mice. Five groups of male ICR (Institute for Cancer Research) mice were studied (N = 43). The animals underwent surgery for implantation of a jugular vein catheter 2 to 3 days before the clamp and were fasted 6 hours before the study. Each group was clamped at a different insulin infusion rate of 0, 2.5, 10, or 20 mU/kg/min. 3H-3-glucose was infused for measurement of the glucose turnover rate (rate of appearance [Ra]). Blood samples were collected by milking a severed tail-tip. EGO was calculated as the difference between the Ra and glucose infusion rate (GIR), and the glucose clearance rate (GCR) as the GDR divided by the plasma glucose concentration. From the curves generated, half-maximal EGO and GCR were obtained at a plasma insulin concentration of 20 to 30 microU/mL, which was achieved at an insulin infusion rate of about 4 to 5 mU/kg/min. Maximal suppression of EGO and stimulation of the GCR occurred at an insulin infusion rate of 10 mU/kg/min. The establishment of normative curves for insulin-stimulated glucose metabolism in conscious mice facilitates the evaluation of glucose metabolism in a variety of mouse models of insulin resistance.