Correlation between insulin clearance and insulin responsiveness: studies in normal, obese, hyperthyroid, and Cushing's syndrome patients.

Insulin clearance and secretion determine the plasma insulin concentration. To elucidate the significance of these parameters in man, we employed the euglycemic insulin clamp technique to measure insulin sensitivity, insulin responsiveness, and insulin clearance, and we calculated the basal insulin delivery rate. In 27 patients (six normal, six obese, ten hyperthyroid, and five with Cushing's syndrome), insulin was infused at rates of 0.3, 1, 3, or 10 mU/Kg/min, and insulin concentration and glucose utilization were measured. C-peptide concentrations were measured before and during insulin infusion and decreased significantly, indicating a reduction of endogenous insulin secretion to 62% of basal in normals and a similar reduction in the other groups. Maximal responsiveness to insulin was a glucose utilization rate of 450 +/- 20 mg/min/m2 in normals, unchanged in obese, 42% increased in hyperthyroid, and 34% decreased in Cushing's syndrome patients. Sensitivity to insulin was decreased in all three abnormal groups. Insulin clearance rates were 1,050 +/- 80 mL/min/m2 for normals, not significantly changed in obese, 45% increased in hyperthyroid, and 33% decreased in Cushing's syndrome patients. All three abnormal groups showed hyperinsulinemia compared to normal. The basal insulin delivery rates were calculated as 7.0 +/- 0.3 mU/min/m2, with a threefold increase in obese and in hyperthyroid and no significant change in Cushing's syndrome patients. Insulin clearance correlated well with insulin responsiveness (r = .65, P less than 0.001), but poorly with insulin sensitivity (r = .36).(ABSTRACT TRUNCATED AT 250 WORDS)