Submitted on January 21, 2003
Accepted on March 3, 2003
EXERCISE DELAYS THE HYPOXIC THERMAL RESPONSE IN RATS
Andrew D Ray1, Andrew J Roberts2, Shin-da Lee1, Gaspar A Farkas1, Charles Michlin1, Daniel I Rifkin3, Peter T Ostrow4, and John A Krasney2*
1 Exercise Science and Nutrition, University at Buffalo School of Medicine and Biomedical Sciences, Buffalo, New York, USA
2 Physiology and Biophysics, University at Buffalo School of Medicine and Biomedical Sciences, Buffalo, New York, USA
3 Neurology, University at Buffalo School of Medicine and Biomedical Sciences, Buffalo, New York, USA
4 Pathology and Anatomical Sciences & Center for Sleep Disorder Research, University at Buffalo School of Health Related Professions, Buffalo, New York, USA
* To whom correspondence should be addressed. E-mail: krasney{at}buffalo.edu.
Exercise exacerbates acute mountain sickness. In infants and small mammals hypoxia elicits a decrease in body temperature (Tb) (hypoxic thermal response, HTR) which may protect against hypoxic tissue damage. We postulated that exercise would counteract the HTR and promote hypoxic tissue damage. Tb was measured by telemetry in rats (n=28) exercising or sedentary in either normoxia or hypoxia (10% O2, 24hrs) at 25°C ambient temperature (Ta). After 24 h of normoxia, rats walked at 10 m.min-1 on a treadmill (30 min exercise/ 30 min rest) for 6 h followed by 18 h of rest in either hypoxia or normoxia in either hypoxia or normoxia. Exercising normoxic rats increased Tb (°C) vs baseline (39.68 ± 0.99 (1SD) vs 38.90 ± 0.95, p<0.05) and vs sedentary normoxic rats (38.0 ± 0.09, p<0.05). Sedentary hypoxic rats decreased Tb (36.15 ± 0.97 vs 38.0 ± 0.36, p<0.05) whereas Tb was maintained in the exercising hypoxic rats during the initial 6 hours of exercise (37.61 [[plusmn] 0.55 vs 37.72 ± 1.25,ns). After exercise in hypoxic rats, Tb reached a nadir similar to sedentary hypoxic rats (35.05 ± 1.69 vs 35.03 ± 1.32, respectively). Tb reached its nadir significantly later in exercising hypoxic vs sedentary hypoxic rats (10.51 ± 1.61 vs 5.36 ± 1.83 hours, respectively p=0.002). Significantly greater histopathological damage and water contents were observed in brain and lungs in the exercising hypoxic vs sedentary hypoxic and normoxic rats. Thus, exercise early in hypoxia delays but does not prevent the HTR. Counteracting the HTR early in hypoxia by exercise exacerbates brain and lung damage and edema in the absence of ischemia.
