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Vol. 84, Issue 4, 1413-1417, April 1998
Departments of 1 Physiology and of 2 Medicine (Royal Melbourne Hospital), The University of Melbourne, Parkville 3052, Australia
This study
examined the effect of increased blood glucose availability on glucose
kinetics during exercise. Five trained men cycled for 40 min at 77 ± 1% peak oxygen uptake on two occasions. During the second trial
(Glu), glucose was infused at a rate equal to the average hepatic
glucose production (HGP) measured during exercise in the control trial
(Con). Glucose kinetics were measured by a primed continuous infusion
of
D-[3-3H]glucose.
Plasma glucose increased during exercise in both trials and was
significantly higher in Glu. HGP was similar at rest (Con, 11.4 ± 1.2; Glu, 10.6 ± 0.6
µmol · kg
1 · min
1).
After 40 min of exercise, HGP reached a peak of 40.2 ± 5.5 µmol · kg
1 · min
1
in Con; however, in Glu, there was complete inhibition of the increase
in HGP during exercise that never rose above the preexercise level. The
rate of glucose disappearance was greater
(P < 0.05) during the last 15 min of
exercise in Glu. These results indicate that an increase 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.
liver glucose output; muscle glucose uptake; hyperglycemia
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