Effects of physical training on pulmonary arterial pressure during exercise under hypobaric hypoxia in rats

In this investigation, we assessed the effects of physical training on exercise-induced systemic and pulmonary hemodynamic changes under hypobaric hypoxia in catheter-implanted rats. We made continuous measurements of pulmonary and systemic arterial pressures during progressive treadmill exercises under hypobaric hypoxia (equivalent to altitudes of 2500 and 5500 m) in 46 control and 41 trained rats. Trained rats were exercised on two running schedules: 4 weeks (4-trained) and 6 weeks (6-trained). Both these groups of trained rats were exercised for the same length of running time each day. The increase in resting mean pulmonary arterial pressure with increasing equivalent altitude was lower in the two trained groups than in the control group. The increase in with progressive intensity of exercise was lower in the 6-trained than in the 4-trained and control groups at 610 and 2500 m. The 6-trained rats showed higher pH,P _{a CO 2} and O₂ saturation in their blood than did the control group, whereas theP _{a O 2} was less. Lung tissue cyclic AMP concentration at rest was higher in the 6-trained than in the control group. Finally, it may be noted that exercise-induced lung tissue vasodilator responses seem to be enhanced in well-trained rats under both normobaric normoxia and hypobaric hypoxia. This study indicates that exercise training may be useful in preventing pulmonary hypertension resulting from both hypoxia and exercise.