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1Department of Human Physiology, Institute of Exercise and Sport Sciences, August Krogh Institute, and Departments of 3Infection Diseases and 4Anesthesia, Rigshospitalet, The Copenhagen Muscle Research Center, University of Copenhagen, DK-2100 Copenhagen, Denmark; and 2University College of Physical Education and Sports and Department of Physiology and Pharmacology, Karolinska Institute, SE-171 77 Stockholm, Sweden
Submitted 7 March 2003 ; accepted in final form 27 April 2003
This study examined neurohumoral alterations during prolonged exercise with
and without hyperthermia. The cerebral oxygen-to-carbohydrate uptake ratio
(O2/CHO = arteriovenous oxygen difference divided by arteriovenous
glucose difference plus one-half lactate), the cerebral balances of dopamine,
and the metabolic precursor of serotonin, tryptophan, were evaluated in eight
endurance-trained subjects during exercise randomized to be with or without
hyperthermia. The core temperature stabilized at 37.9 ± 0.1°C (mean
± SE) in the control trial, whereas it increased to 39.7 ±
0.2°C in the hyperthermic trial, with a concomitant increase in perceived
exertion (P < 0.05). At rest, the brain had a small release of
tryptophan (arteriovenous difference of -1.2 ± 0.3 µmol/l), whereas
a net balance was obtained during the two exercise trials. Both the arterial
and jugular venous dopamine levels became elevated during the hyperthermic
trial, but the net release from the brain was unchanged. During exercise, the
O2/CHO was similar across trials, but, during recovery from the
hyperthermic trial, the ratio decreased to 3.8 ± 0.3 (P <
0.05), whereas it returned to the baseline level of 
6 within 5 min after
the control trial. The lowering of O2/CHO was established by an
increased arteriovenous glucose difference (1.1 ± 0.1 mmol/l during
recovery from hyperthermia vs. 0.7 ± 0.1 mmol/l in control; P
< 0.05). The present findings indicate that the brain has an increased need
for carbohydrates during recovery from strenuous exercise, whereas enhanced
perception of effort as observed during exercise with hyperthermia was not
related to alterations in the cerebral balances of dopamine or tryptophan.
brain; dopamine; hyperthermia; tryptophan
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