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J Appl Physiol (May 16, 2003). doi:10.1152/japplphysiol.00241.2003
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Submitted on March 7, 2003
Accepted on April 27, 2003

Neurohumoral responses during prolonged exercise in humans

Lars Nybo1*, Bodil Nielsen1, Eva Blomstrand2, Kirsten Moller3, and Niels H Secher4

1 Department of Human Physiology, Institute of Exercise Sport Sciences, Copenhagen, Denmark
2 University College of Physical Education and Sports and Department of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden
3 Department of Infection Diseases, Rigshospitalet, Copenhagen, Denmark
4 Department of Anaesthesia, Rigshospitalet, Copenhagen, Denmark

* To whom correspondence should be addressed. E-mail: lnnielsen{at}aki.ku.dk.

This study examined neurohumoral alterations during prolonged exercise with and without hyperthermia. The cerebral oxygen to carbohydrate uptake ratio (O2/CHO = a-vDoxygen divided by avDglucose+lactate/2) and 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, while 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 (a-vD of -1.2 ± 0.3 µmol l-1), 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 ratio was similar across trials, but during recovery from the hyperthermic trial, the ratio decreased to 3.8 ± 0.3 (P<0.05), while it returned to the baseline level of ~ 6 within 5 min after the control trial. The lowering of the O2/CHO ratio was established by an increased a-vDglucose (1.1 ± 0.1 mmol l-1 during recovery from hyperthermia vs. 0.7 ± 0.1 mmol l-1 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.




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