Pre-exercise glucose ingestion and glucose kinetics during
exercise.
Conus, Nelly Marmy, Suzanne Fabris, Joseph Proietto, and Mark
Hargreaves.
Department of Physiology and Department of Medicine (Royal
Melbourne Hospital), The University of Melbourne, Parkville, 3052,
Australia
APStracts 3:0187A, 1996.
The present study was undertaken to examine the effects of glucose
ingestion before exercise on liver glucose output and muscle glucose
uptake during exercise. On two occasions, at least one week apart,
six trained men (VO2 peak = 5.11 +/- 0.17 L.min-1) ingested 400 ml of
a solution, containing either 75 g glucose (CHO) or a sweet placebo
(CON), 30 min prior to 60 min of exercise at 71 +/- 1 % VO2 peak.
Glucose kinetics (Ra and Rd) were measured by a primed continuous
infusion of 6,6-2H2 glucose. Liver glucose output was derived from
total glucose appearance and the appearance of ingested glucose from
the gut. Following glucose ingestion, plasma glucose increased to 6.4
+/- 0.4 mmol.L-1 immediately prior to exercise, fell to 4.2 +/- 0.5
mmol.L-1 after 20 min of exercise, then increased to a higher value
than in CON (5.4 +/- 0.3 vs. 4.7 +/- 0.1 mmol. L-1, P<0.05)
after 60 min of exercise. In CHO, plasma insulin was higher
(P<0.05) immediately prior to exercise and despite falling
during exercise, remained higher than in CON after 60 min of exercise
(57.0 +/- 11.4 vs. 24.8 +/- 1.7 pmol.L-1, P<0.05). The rapid
fall in plasma glucose in CHO was the result of a higher
(P<0.05) muscle glucose uptake with the onset of exercise, which
could not be matched by glucose Ra. Liver glucose output was
decreased by glucose ingestion and although increasing during the
early stages of exercise in CHO, it did not rise above the basal
values and was reduced by 62 % over the 60 min of exercise compared
with CON. In summary, pre-exercise glucose ingestion results in
increased muscle glucose uptake and reduced liver glucose output
during exercise.
Received 28 December 1995; accepted in final form 25 March 1996.
APS Manuscript Number A1354-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96