Effect of systemic pH on pHi and lactic acid generation in exhaustive forearm exercise.
To investigate whether changes in systemic pH affect intracellular pH (pHi), energy-rich phosphates, and lactic acid generation in muscle, eight normal volunteers performed exhaustive forearm exercise with arterial blood flow occluded for 2 min on three occasions. Subjects ingested 4 mmol/kg NH4Cl (acidosis; A) or NaHCO3 (alkalosis; B) or nothing (control; C) 3 h before the exercise. Muscle pHi and phosphocreatine (PCr) content were measured with 31P-nuclear magnetic resonance (31P-NMR) spectroscopy during exercise and recovery. Lactate output during 0.5-7 min of recovery was calculated as deep venous-arterial concentration differences times forearm blood flow. Before exercise, blood pH and bicarbonate were lower in acidosis (7.303 +/- 0.009, 18.6 +/- 0.5 meq/l) than alkalosis (7.457 +/- 0.010, 32.2 +/- 0.7 meq/l) and intermediate in control (7.389 +/- 0.007, 25.3 +/- 0.6 meq/l). Lactic acid output during recovery was less with A (245 +/- 39 mumol/100 ml) than B (340 +/- 55 mumol/100 ml) (P less than 0.05) and intermediate in C (293 +/- 31 mumol/100 ml). PCr utilization and resynthesis were not affected by extracellular pH changes. pHi did not differ before exercise (A, 7.04 +/- 0.01; B, 7.09 +/- 0.01; C, 7.06 +/- 0.01) or at its end (A, 6.28 +/- 0.07; B, 6.28 +/- 0.11; C, 6.31 +/- 0.09). Hence systemic acidosis inhibited and alkalosis stimulated lactic acid output. These findings suggest that systemic pH regulates cellular acid production, protecting muscle pH, at the expense of energy availability.
Kantonsspital, University of Basel, Switzerland.
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Hood
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Schubert
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Keller
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Müller
D000328:Adult; D001639:Bicarbonates / Q000097:blood; D005542:Forearm / Q000098:blood supply / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism; D005082:Physical Exertion; D010991:Plethysmography; D012039:Regional Blood Flow
D001639:Bicarbonates; D007773:Lactates; D010725:Phosphocreatine