Oscillations enhance the efficiency and stability of glucose disposal

Oscillations in plasma concentrations of glucose and insulin as well as the rates of glucose disposal by liver and periphery have been observed in dogs during states of net glucose anabolism. To examine whether the existence of oscillations is important for efficient disposal of nutrients, we compared constant glucose infusion (with plasma glucose and insulin oscillations) to experiments in which glucose oscillations were suppressed using the glucose clamp. Mean glucose levels attained were the same for the two protocols (142 +/- 2 for constant glucose infusion at 10.8 +/- 0.4 mg X kg-1 X min-1, 144 +/- 1 mg/dl for clamps, P = 0.35). Despite matched mean glucose, integrated plasma insulin was 36.3 +/- 3.2 mU X ml-1 X 600 min in controls but higher in clamps (53.8 +/- 9.1 mU X ml-1 X 600 min, P = 0.017). Despite 48% higher insulin, total glucose disposed during the 10-h clamps was not greater than during constant glucose infusion (clamps, 162.1 +/- 10.7 g/600 min; infusions, 154.4 +/- 7.5 g/600 min; P = 0.19). These studies demonstrate that the presence of coordinated oscillations in glucose and insulin, during glucose infusion, are associated with more efficient disposal of glucose than when oscillations are suppressed. The results suggest that oscillations may play an important role in the efficient disposal of administered nutrient and may be an important component of normal glucose tolerance.