Incorporation of blood lactate and glucose into tissues in rats after short-term strenuous exercise

The purpose of this study was to investigate the main site of removal of blood lactate and glucose and which is the more important substrate for muscle glycogen resynthesis in rats after short-term strenuous exercise, to exhaustion. Male Wistar rats ran to exhaustion at a speed of 70-100m.min-1. Immediately after the exercise the rats received an injection of [U-14C]lactate (LA, 0.025 microCi.g-1, n = 5) or [U-14C]glucose (GL, 0.015 microCi.g-1, n = 5) into the aorta through an indwelling catheter. The rats were sacrificed after 40 min of recovery. During 40 min of recovery, 20.4% +/- 2.0% (mean +/- SE) of 14C injected was recovered as 14CO2 in LA, while 4.1% +/- 0.4% of 14C was recovered as 14CO2 in GL. In LA, the content of 14C incorporated per tissue weight in the vastus lateralis was significantly greater than that in the kidney, heart, and blood, while in GL that in the vastus lateralis was significantly greater than in any other tissues measured. The incorporation of 14C-glucose into muscle glycogen (vastus lateralis) was about five times greater than that of 14C-lactate. Data from this study indicate that lactate and glucose are incorporated from the blood into the skeletal muscle which was active during exercise and that blood glucose is a more preferred substrate for muscle glycogen resynthesis in rats after strenuous exercise to exhaustion.