Effect of heat stress on glucose kinetics during exercise.
Hargreaves, Mark, Damien Angus, Kirsten Howlett, Nelly Marmy Conus,
and Mark Febbraio.
Department of Physiology, The University of Melbourne, Parkville,
3052 and Department of Human Movement Science, Royal Melbourne
Institute of Technology, Bundoora, 3083, Australia
APStracts 3:0285A, 1996.
To identify the mechanism underlying the exaggerated hyperglycemia
during exercise in the heat, six trained men were studied during 40
min of cycling exercise at a workload requiring 65% VO2 peak on two
occasions, at least one week apart. One one occasion, the ambient
temperature was 20C (CON), while on the other it was 40C (HT). Rates
of glucose appearance (Ra) and disappearance (Rd) were measured using
a primed, continuous infusion of 6,6-[2H]glucose. No differences in
oxygen uptake during exercise were observed between trials. After 40
min of exercise, heart rate, rectal temperature, RER and plasma
lactate were all higher (P<0.05) in HT compared with CON. Plasma
glucose levels were similar at rest (CON: 4.54 +/- 0.19 mmol.L-1; HT:
4.81 +/- 0.19), but increased to a greater (P<0.05) extent
during exercise in HT (6.96 +/- 0.16) compared with CON (5.45 +/-
0.18). This was the result of a higher glucose Ra in HT during the
last 30 min of exercise. In contrast, glucose Rd and metabolic
clearance rate were not different at any time point during exercise.
Plasma catecholamines were higher (P<0.05) after 10 and 40 min
of exercise in HT compared with CON, while plasma glucagon, cortisol
and growth hormone were higher in HT after 40 min. These results
indicate that the hyperglycemia observed during exercise in the heat
is caused by an increase in liver glucose output, without any change
in whole-body glucose utilization.
Received 26 December 1995; accepted in final form 5 June 1996.
APS Manuscript Number A1343-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96