Extracellular bicarbonate and non-bicarbonate buffering against lactic acid during and after exercise

Abstract

Defense of extracellular pH constancy against lactic acidosis can be estimated from changes (Delta) in lactic acid ([La]), [HCO(3)(-)], pH and PCO(2) in blood plasma because it is equilibrated with the interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 13 untrained (UT) and 21 endurance-trained (TR) males to find out if acute and chronic exercise influence the defense. During exercise the capacity of non-bicarbonate buffers (beta(nbi) = -Delta[La] . DeltapH(-1) - Delta[HCO(3)(-)] . DeltapH(-1)) available for the extracellular fluid (mainly hemoglobin, dissolved proteins and phosphates) amounted to 32 +/- 2(SEM) and 20 +/- 2 mmol l(-1) in UT and TR, respectively (P < 0.02). During recovery beta(nbi) decreased to 14 (UT) and 12(TR) mmol l(-1) (both P < 0.001) corresponding to values previously found at rest by in vivo CO(2) titration. Bicarbonate buffering (beta(bi)) amounted to 44-48 mmol l(-1) during and after exercise. The large exercise beta(nbi) seems to be mainly caused by an increasing concentration of all buffers due to shrinking of the extracellular volume, exchange of small amounts of HCO(3)(-) or H(+) with cells and delayed HCO(3)(-) equilibration between plasma and interstitial fluid. Increase of [HCO(3)(-)] during titration by these mechanisms augments total beta and thus the calculated beta(nbi) more than beta(bi) because it reduces DeltapH and Delta[HCO(3)(-)] at constant Delta[La]. The smaller rise in exercise beta(nbi) in TR than UT may be caused by an increased extracellular volume and an improved exchange of La(-), HCO(3)(-) and H(+) between trained muscles and blood.

Extracellular pH defense against lactic acid in untrained and trained altitude residents

“…This is in contrast to the traditional view but confirms earlier studies of our group in altitude sojourners after descent (Böning et al 1980(Böning et al , 2001a. b nbi during recovery tends to higher values than in lowlanders (Böning et al 2007b) as well. Differences in pH defense between exercise and rest as well as between UT and TR observed at sea level are also found at altitude.…”

“…increase of [HCO 3 -] by shrinking of the ecf during muscle contractions, see further discussion). The lacking difference between D[La] ecf + ery and -DSBE during recovery after rapid return of the extracellular volume to approximately initial values (Böning et al 2007b) suggests an equal transport of H + and La -across cell membranes. The idea that more H + than La -leave the muscle during or shortly after exercise (e.g.…”

“…6, this seems to be due to the reduction of the b nbi , since b bi behaves rather uniform throughout the entire experiment with little scattering and may be approximated also by one common regression line. In reality the relation is slightly curved because it is determined by the logarithmic Henderson-Hasselbalch equation for constant PCO 2 (Böning et al 2007b), but for the sake of simplicity we have applied only linear regression. This calculation yields the mean b bi for the part of the titration curve under consideration.…”

“…But with interruption of work rapid changes of buffering occur which we have analyzed in recent sea level experiments. Total and bi b during and after exercise were calculated from D[La], D and DpH in plasma (Böning et al 2007b). Whereas b bi remained rather constant, b nbi (b total -b bi ) during recovery corresponded to values previously found by in vivo CO 2 titration at rest (10-17 mmol l -1 ), but increased to 32 mmol l -1 in untrained (UT) and to 20 mmol l -1 in endurance trained (TR) subjects during exercise.…”

Respiratory compensation and blood pH regulation during variable intensity exercise in trained versus untrained subjects

“…However, during VAR HIGH, respiratory compensation was not able to maintain blood acid-base balance and pH blood dropped progressively during exercise. The utilization of [HCO 3 -] blood as well as the magnitude of the respiratory compensation ( _ V E Á _ VCO À1 2 ) were similar between trained and untrained subjects, as previously found during continuous incremental exercise (Böning et al 2007). A limited respiratory compensation in UT subjects (in comparison to T subjects) could have lessened the CO 2 unloading at the lungs, increasing p a CO 2 and blood acidity during exercise.…”