Effects of aging on glucose-mediated glucose disposal and glucose transport.

To assess the effects of aging on glucose-mediated glucose disposal and glucose transport, glucose disposal rates were measured in 10 nonelderly (32 +/- 4 yr) and 11 elderly (64 +/- 4 yr) subjects at five different plasma glucose concentrations. Glucose disposal was decreased by 30-35% in the elderly at each level of glycemia (100-350 mg/dl) in the presence of similar levels of hyperinsulinemia (approximately 100 microU/ml), and the 50% effective concentration (EC50) was similar in both the nonelderly (100 +/- 9) and elderly (103 +/- 5 mg/dl). The Michaelis constant (Km) of 3-O-methyl glucose transport in adipocytes was unchanged with aging (3.8 +/- 0.5 vs. 3.2 +/- 0.2 mM) while the maximum velocity of insulin stimulated transport was reduced by 34% in the elderly (8.3 +/- 1.3 vs. 12.6 +/- 1.5 pmol/5 X 10(4) cells per s, P less than 0.05). The insulin resistance of aging is therefore due to a reduction in the capacity of the glucose uptake system, while the affinity of glucose utilization (EC50 and Km) is unchanged. This supports the hypothesis that a reduction in the number of glucose transport and metabolic units occurs with aging, but that each unit functions normally.