title: Causes of differences in exercise-induced changes of base excess and blood lactate.
abstract: It has been concluded from comparisons of base excess (BE) and lactic acid (La) concentration changes in blood during exercise-induced acidosis that more H+ than La- leave the muscle and enter interstitial fluid and blood. To examine this, we performed incremental cycle tests in 13 untrained males and measured acid-base status and [La] in arterialized blood, plasma, and red cells until 21 min after exhaustion. The decrease of actual BE (-deltaABE) was 2.2 +/- 0.5 (SEM) mmol l(-1) larger than the increase of [La]blood at exhaustion, and the difference rose to 4.8 +/- 0.5 mmol l(-1) during the first minutes of recovery. The decrease of standard BE (SBE), a measure of mean BE of interstitial fluid (if) and blood, however, was smaller than the increase of [La] in the corresponding volume (delta[La](if+blood)) during exercise and only slightly larger during recovery. The discrepancy between -deltaABE and delta[La]blood mainly results from the Donnan effect hindering the rise of [La]erythrocyte to equal values like [La]plasma. The changing Donnan effect during acidosis causes that Cl- from the interstitial fluid enter plasma and erythrocytes in exchange for HCO3(-). A corresponding amount of La- remains outside the blood. SBE is not influenced by ion shifts among these compartments and therefore is a rather exact measure of acid movements across tissue cell membranes, but changes have been compared previously to delta[La]blood instead to delta[La](if+blood). When performing correct comparisons and considering Cl-/HCO3(-) exchange between erythrocytes and extracellular fluid, neither the use of deltaABE nor of deltaSBE provides evidence for differences in H+ and La- transport across the tissue cell membranes.
authors.affiliation: Institute of Sports Medicine, Charité, University Medicine Berlin, Arnimallee 22, 14195, Berlin, Germany. dieter.boening@charite.de
authors.forename: Dieter
authors.initials: D
authors.lastname: Böning
authors.forename: Carola
authors.initials: C
authors.lastname: Klarholz
authors.forename: Bärbel
authors.initials: B
authors.lastname: Himmelsbach
authors.forename: Matthias
authors.initials: M
authors.lastname: Hütler
authors.forename: Norbert
authors.initials: N
authors.lastname: Maassen
mesh_terms: D000136:Acid-Base Equilibrium; D000138:Acidosis / Q000097:blood* / Q000378:metabolism / Q000503:physiopathology; D000328:Adult; D001639:Bicarbonates / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D015444:Exercise; D045604:Extracellular Fluid / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000097:blood* / Q000378:metabolism; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D019344:Lactic Acid