Effects of training on blood glucose kinetics during glucose challenge in rats.

We hypothesized that endurance training would alter blood glucose kinetics in rats given an exogenous glucose challenge. Primed-continuous infusion of H14CO3- and [3-3H]glucose were given to fasted rats during an intravenous glucose load of approximately 150% of the normal endogenous appearance rate for 3 h. In all rats blood glucose concentrations increased with loading, but in trained animals glucose stabilized at significantly lower levels. Trained animals had lower blood glucose turnover rates than the controls (75 +/- 2.3 vs. 120 +/- 6.3 mumoles/kg x min, respectively). Glucose metabolic clearance rates in trained rats (11.5 +/- 1.7) were not different from those in controls (11.6 +/- 1.2 ml/kg x min). Gluconeogenic rates estimated from incorporation of 14C into blood glucose did not differ between trained and untrained groups. However, the rate of hepatic glucose release estimated from the difference between tracer measured and exogenous appearance rate was lower in the trained group. These findings support the concept that when resting trained animals are challenged with an exogenous load, more glucose is diverted to anabolic processes as opposed to increased turnover.