EFFECT OF INCREASED BLOOD-GLUCOSE AVAILABILITY ON GLUCOSE KINETICS DURING EXERCISE

This study examined the effect of increased blood glucose availability on glucose kinetics during exercise. Five trained men cycled for 40 m in at 77 +/- 1% peak oxygen uptake on two occasions. During the second trial (Glu), glucose was infused at a rate equal to the average hepat ic glucose production (HGP) measured during exercise in the control tr ial (Con). Glucose kinetics were measured by a primed continuous infus ion of D-[3-H-3]glucose. Plasma glucose increased during exercise in b oth trials and was significantly higher in Glu. HGP was similar at res t (Con, 11.4 +/- 1.2; Glu, 10.6 +/- 0.6 mu mol.kg(-1).min(-1)). After 40 min of exercise, HGP reached a peak of 40.2 +/- 5.5 mu mol.kg(-1).m in(-1) in Con; however, in Glu, there was complete inhibition of the i ncrease in HGP during exercise that never rose above the preexercise l evel. The rate of glucose disappearance was greater (P < 0.05) during the last 15 min of exercise in Glu. These results indicate that an inc rease in glucose availability inhibits the rise in HGP during exercise , suggesting that metabolic feedback signals can override feed-forward activation of HGP during strenuous exercise.