EFFECT OF ALKALOSIS ON MAXIMUM OXYGEN-UPTAKE IN RATS ACCLIMATED TO SIMULATED ALTITUDE

The objective of the present experiments was to determine whether prevention or moderation of exercise acidosis would influence arterial blood oxygenation and exercise capacity in hypoxia. The effect of administration of 0.3 M NaHCO3 (3 ml/100 g) on maximum O2 uptake (VO2 max) and arterial blood oxygenation was determined in rats acclimated to simulated altitude (370-380 Torr barometric pressure) for 3 wk (HxBic) and in normoxic littermates (NxBic). Controls were simulated-altitude (HxNaCl) and normoxic rats (NxNaCl) given 0.3 M NaCl. Inspiratory PO2 during treadmill exercise was approximately 70 Torr for hypoxic rats and 140-145 Torr for normoxic rats. VO2max was 18% higher in HxBic than in HxNaCl (62.8 + 1.6 vs. 53.1 + 1.0 ml STPD . min-1 . kg-1, respectively, P < 0.05) and only 8% higher in NxBic than in NxNaCl (74.0 + 1.1 vs. 68.7 + 1.5 ml STPD . min-1 . kg-1, respectively, P < 0.05). Exercise in HxNaCl resulted in a decrease in arterial O2 concentration (Ca(O2)), which was largely due to a pH-induced decrease in O2 saturation of arterial blood, and occurred despite an increase in arterial PO2. NaHCO3 moderated the acidosis of exercise and largely attenuated the decrease in Ca(O2). The effects of acidosis and bicarbonate on Ca(O2) were much less evident in the normoxic controls. There was an almost linear relationship between VO2 max and the corresponding Ca(O2) for all four groups, suggesting that the effect of NaHCO3 on VO2 max may be related to moderation of the decrease in Ca(O2).