THE 2,3-DPG LEVELS OF HUMAN RED-BLOOD-CELLS DURING AN INCREMENTAL EXERCISE TEST - RELATIONSHIP TO THE BLOOD ACID-BASE-BALANCE

The aim of this study was to evaluate the influence of exercise with t he intensity progressively increasing from rest until maximal oxygen u ptake (VO2max) on 2,3-DPG levels in red blood cells (RBC) in relation to the changes in the acid-base balance and plasma lactate concentrati on. Six healthy young men (age 22.5+/-1.5 years, VO2max 3.48+/-0.20 l/ min) participated in this study. The subjects performed an incremental exercise test on a cycloergometer until exhaustion. Blood samples wer e tested for acid-base balance indices (pH, HCO3-, BE), plasma lactate and RBC 2,3-DPG concentration. Gas exchange variables were measured c ontinuously breath-by-breath. In this paper we present data concerning 2,3-DPG, plasma lactate, pH, HCO3- and BE measured at rest, at the po wer output corresponding to the lactate threshold (PO LT), at the powe r output at maximal oxygen uptake (PO VO2max), as well as 5, 15 and 30 min after finishing the incremental test. Increase of power output ab ove the lactate threshold to the PO VO2max was accompanied by a signif icant (p<0.01) increase of plasma lactate from 2.58+/-0.78 mmol/l to 1 0.22+/-3.04 mmol/l. This was also accompanied by a significant drop (p <0.01) in blood pH value from 7.352+/-0.025 at the PO LT to 7.294+/-0. 041 at the PO VO2max. No significant changes of the RBC 2,3-DPG level were observed at any of the analysed stages of the exercise. The RBC 2 ,3-DPG level expressed in relation to the changes of haematocrit showe d only minor changes during the exercise period and after 15 min of re covery vs. resting value (3.21+/-1.19). However, after 30 min of recov ery, RBC 2,3-DPG decreased to the value of 2.32+/-1.19 mu mol/ml. We c onclude that, during an incremental test, no increase in RBC 2,3-DPG c oncentration is required to reach the maximal oxygen uptake level. Mor eover, a rapid decrease in blood pH, developing during a single bout o f exercise, is not a stimulus powerful enough to cause significant cha nges in the RBC 2,3-DPG level during short-term exercise.