Net lactate uptake during progressive steady-level contractions in canine skeletal muscle.
The purpose of this study was to determine the changes in net lactate uptake (L) by skeletal muscle with a constant elevated blood lactate concentration during steady-level contractions of increasing intensity. The gastrocnemius-plantaris muscle group was isolated in situ in 11 anesthetized dogs. An infusion of lactate/lactic acid at a pH of 3.5-3.7 established a blood lactate concentration of approximately 9 mM while maintaining normal blood gas/pH status. L was measured during three consecutive 30-min periods during which the muscles 1) rested, 2) contracted at 1 Hz, and 3) contracted at 4 Hz. L was always positive, indicating net uptake throughout the lactate/lactic acid infusion. Steady-level O2 uptake averaged 10.9 +/- 2.2 ml.kg-1.min-1 (0.49 +/- 0.10 mmol.kg-1.min-1) at rest, 39.3 +/- 2.1 (1.75 +/- 0.09) at 1 Hz, and 127.8 +/- 9.2 (5.70 +/- 0.41) at 4 Hz. Steady-level L increased with the metabolic rate from 0.113 +/- 0.058 mmol.kg-1.min-1 at rest to 0.329 +/- 0.026 at 1 Hz and 0.715 +/- 0.108 at 4 Hz. The increase in L from rest to 1 Hz was accomplished mainly by an increase in arteriovenous lactate difference, whereas the increase from 1 to 4 Hz was entirely due to a large increase in blood flow. These results support the idea that skeletal muscle is not simply a producer of lactate but can be a significant consumer of lactate even during contractions with a large elevation in metabolic rate.
Department of Health and Human Performance, Auburn University, Alabama 36849.
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Gladden
D000136:Acid-Base Equilibrium / Q000502:physiology; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D004285:Dogs; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007537:Isometric Contraction; D007773:Lactates / Q000097:blood / Q000378:metabolism*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000098:blood supply / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D012039:Regional Blood Flow; D012044:Regression Analysis
D007773:Lactates