SARKAR, Soma; MCCALL, R. Dale; KINSEY, Stephen T.; Univ. of North Carolina at Wilmington; Univ. of North Carolina at Wilmington; Univ. of North Carolina at Wilmington: Oxygen consumption in mice with inherited hypoxic exercise tolerance

Oxygen consumption (VO₂) was determined during hypoxic exercise after acclimation to normoxia or hypoxia in three inbred strains of mice. BALB/cBy (C) and C57BL/6J (B6) parental strains and their F1 hybrid had similar hypoxic exercise tolerances (HET), defined as the duration of hypoxic treadmill exercise (1/2 atm, 40 cm/s, 15° incline), following exposure to normoxia. However, following acclimation to hypobaric hypoxia the 3 strains had dramatic differences in HET. Hypoxia acclimation induced little improvement of HET in C mice, while B6 mice doubled their HET and the F1 hybrid had an endurance capacity that far exceeded that of either parental strain. Previous work has demonstrated that two genes are principally responsible for the large differences in HET. VO₂ at rest, at the test speed of 40 cm/s, and at the maximal belt velocity that each strain could accomodate (VO_2max) was elevated in all strains following hypoxia acclimation. At the test speed of 40 cm/s, all of the mice were exercising at about 95% of VO_2max, despite the fact that the duration of exercise in some individuals exceeds 80 min. The best performing F1 mice had the highest values of VO_2max, suggesting that this variable may be important in promoting HET in this strain. However, B6 mice had the lowest VO_2max values but their HET is far superior to C mice. VO_2max is therefore not a general indicator of hypoxic endurance among the 3 strains.