Assessment of insulin action in insulin-dependent diabetes mellitus using 6(14)Cglucose, 3(3)Hglucose, and 2(3)Hglucose. Differences in the apparent pattern of insulin resistance depending on the isotope used.

To determine whether 2(3)H, 3(3)H, and 6(14)Cglucose provide an equivalent assessment of glucose turnover in insulin-dependent diabetes mellitus (IDDM) and nondiabetic man, glucose utilization rates were measured using a simultaneous infusion of these isotopes before and during hyperinsulinemic euglycemic clamps. In the nondiabetic subjects, glucose turnover rates determined with 6(14)Cglucose during insulin infusion were lower (P less than 0.02) than those determined with 2(3)Hglucose and higher (P less than 0.01) than those determined with 3(3)Hglucose. In IDDM, glucose turnover rates measured with 6(14)Cglucose during insulin infusion were lower (P less than 0.05) than those determined with 2(3)Hglucose, but were not different from those determined with 3(3)Hglucose. All three isotopes indicated the presence of insulin resistance. However, using 3(3)Hglucose led to the erroneous conclusion that glucose utilization was not significantly decreased at high insulin concentrations in the diabetic patients. 6(14)C and 3(3)Hglucose but not 2(3)Hglucose indicated impairment in insulin-induced suppression of glucose production. These results indicate that tritiated isotopes do not necessarily equally reflect the pattern of glucose metabolism in diabetic and nondiabetic man.