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

To determine whether I23LI, 133H1, and [6'4Cjglucose 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 ofthese isotopes before and during hyperinsulinemic euglycemic clamps. In the nondiabetic subjects, glucose turnover rates determined with [614Cjglucose during insulin infusion were lower (P< 0.02) than those determined with [23Hjglucose and higher (P < 0.01) than those determined with 133Higlucose. In IDDM, glucose turnover rates measured with 1614Cjglucose during insulin infusion were lower (P< 0.05) than those determined with [23Hjglucose, but were not different from those determined with 133Hhglucose. All three isotopes indicated the presence of insulin resistance. However, using 133Hjglucose led to the erroneous conclusion that glucose utilization was not significantly decreased at high insulin concentrations in the diabetic patients. [6'4qC and 133Hjglucose but not [23Hjglucose 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.