Effect of decreased oxygen availability on NADH and lactate contents in human skeletal muscle during exercise.
Eight men cycled for 5 min at 120 +/- 6 W (mean +/- SE) at which O2 uptake was 50% of its maximal normoxic value, breathing room air (21% O2; normoxia) on one occasion and 11% O2 in N2 (respiratory hypoxia/hypoxic--Resp. Hx.) on the other. Biopsies were taken from the quadriceps femoris muscle. Oxygen uptake during exercise was not significantly different between Resp. Hx (1.59 +/- 0.08 1 min-1) and normoxia (1.55 +/- 0.08 1 min-1). At rest, muscle lactate was the same under both conditions but was four times higher after Resp. Hx (33.2 +/- 5.2 mmol kg-1 dry wt) than normoxic cycling (8.6 +/- 1.0 mmol kg-1 dry wt; P less than 0.01). The muscle lactate/pyruvate (which is proportional to cytosolic NADH/NAD) was significantly higher after Resp. Hx.(76 +/- 19) than after normoxic cycling (26 +/- 2; P less than 0.05). At rest, analytically determined NADH averaged 0.14 +/- 0.02 mmol kg-1 dry wt under both conditions. However, exercise during Resp. Hx. resulted in a significantly higher NADH content (0.17 +/- 0.01) than exercise during normoxia (0.12 +/- 0.01; P less than 0.01). Indirect evidence indicates that the difference in muscle NADH reflects a difference in the mitochondrial redox state (Sahlin & Katz 1986). The increased muscle NADH during Resp. Hx. therefore indicates a relative lack of O2 at the cellular level (muscle hypoxia). It is suggested that the increased lactate production during Resp. Hx. is a consequence of the cellular adaptation to muscle hypoxia (i.e. increases in cytosolic ADP, AMP, Pi and NADH).
Katz
A
A
Department of Clinical Physiology, Karolinska Institute, Huddinge Hospital, Sweden.
Sahlin
K
K
D000328:Adult; D004734:Energy Metabolism; D006439:Hemodynamics; D006801:Humans; D007773:Lactates / Q000378:metabolism*; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D005082:Physical Exertion
D007773:Lactates; D009243:NAD