[In vivo insulin sensitivity in adrenodemedullated rats]

Insulin sensitivity and responsiveness were determined in adrenal demedullated rats (ADMX) with euglycemic insulin clamp technique. Adrenal medulla was extirpated bilaterally a week before the study. Catheters were placed at right atrium via right jugular vein for sampling blood and at inferior vena cava via femoral vein for the infusion of insulin and glucose solution. Insulin was infused at rates of 4.4, 8.8, 14.7, 29.3, 88.0, 293.0 mU/kg/min. Blood was collected every five min. during the clamp and glucose infusion rate was modulated to control the blood glucose concentrations at fasting levels. Glucose metabolism was calculated from the amount of glucose infused from 60th to 120th min. during the euglycemic clamp. The results obtained were as follows: 1. Glucose metabolisms of ADMX in each infusion rate of insulin, 4.4, 8.8, 14.7, 29.3, 88.0, 293.0 mU/kg/min were 5.2 +/- 0.5, 12.5 +/- 0.5, 17.6 +/- 1.2, 19.8 +/- 2.3, 29.0 +/- 1.5, and 25.2 +/- 1.9 mg/kg/min, respectively. 2. Glucose metabolisms of control group in each dose were 6.6 +/- 0.4, 9.0 +/- 0.9, 18.5 +/- 1.2, 23.4 +/- 2.4, 24.6 +/- 1.1, and 27.0 +/- 1.3 mg/kg/min, respectively. 3. Significant difference (p less than 0.01) in glucose metabolism between ADMX and control was observed at the insulin infusion rate of 8.8 mU/kg/min which might be equivalent to physiological hyperinsulinemia. 4. There were not any differences in insulin responsiveness between both groups. These results suggest that epinephrine regulates insulin sensitivity under physiological hyperinsulinemic condition via defects of insulin receptors.