To determine whether [23H], [33H], and [614C]glucose 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 [614C]glucose during insulin infusion were lower (P < 0.02) than those determined with [23H]glucose and higher (P < 0.01) than those determined with [33H]glucose. In IDDM, glucose turnover rates measured with [614C]glucose during insulin infusion were lower (P < 0.05) than those determined with [23H]glucose, but were not different from those determined with [33H]glucose. All three isotopes indicated the presence of insulin resistance. However, using [33H]glucose led to the erroneous conclusion that glucose utilization was not significantly decreased at high insulin concentrations in the diabetic patients. [614C] and [33H]glucose but not [23H]glucose 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.
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