Hyperoxia, mitochondrial redox state, and lactate metabolism of in situ canine muscle.

The effect of hyperoxia on lactate production and release and the mitochondrial NAD+-to-NADH ratio was studied in the in situ canine gastrocnemius to determine whether elevated PO2 altered metabolic regulation. Dogs breathed either air (21% O2) [arterial O2 partial pressure (PaO2) 90 mmHg; n = 8] or hyperoxia (100% O2) (PaO2 546 mmHg; n = 8). The left muscle was stimulated for 10 min at 3 Hz and then both right and left muscles were quick frozen in N2. Hyperoxia did not affect O2 uptake, blood flow, and developed tension. Activity increased glucose 6-phosphate (G-6-P), D-fructose 6-phosphate (F-6-P), NH3, lactate, and F-6-P/F-1,6-P in both treatment groups. No significant differences in arterial or venous lactate, muscle lactate, glucose uptake, or glycogen depletion were noted in hyperoxia. Cytoplasmic NAD+/NADH was in a more oxidized state in hyperoxia at rest but not during activity. The increase in NH3 with stimulation was significantly larger in hyperoxia. Activity decreased alpha-ketoglutarate in hyperoxia but not in air. At stimulation, the estimated mitochondrial NAD+/NADH increased in both groups suggesting that hypoxia was not present. Thus hyperoxia did not affect mitochondrial redox state or lactate production and release in active muscle.