Exercise alters the distribution of ammonia and lactate in blood

Six subjects (3 males, 3 females) worked for 4 min on a cycle ergometer at 115% of peak O2 uptake (VO2). Venous samples drawn before, directly after, and 15 min after exercise were analyzed for ammonia (NH3) and lactate concentrations of plasma, whole blood, and erythrocytes (RBCs) to examine the effect of exercise on blood NH3 and lactate distribution. Exercise increased (P less than 0.05) the [NH3] of plasma and RBCs, with the larger (P less than 0.05) change in plasma (1.8- vs. 0.7-fold). This reduced (P less than 0.05) the RBC-to-plasma [NH3] ratio of 2.4 at rest to 1.3. The plasma-to-RBC [lactate] gradient (P less than 0.05) at rest (0.5 mmol/l) increased (P less than 0.05) 16-fold immediately after exercise (8.7 mmol/l), reflecting the greater increase (P less than 0.05) in plasma than RBCs [lactate] (15.5 vs. 7.5 mmol/l). [Lactate] and [NH3] did not decrease (P greater than 0.05) immediately after to 15 min after exercise. Plasma and whole blood [NH3] or [lactate] were correlated (r greater than 0.93, P less than 0.01) at all sample times, but the slopes of the relations for [NH3] (immediately after vs. 15 min after exercise) or for [lactate] (before and immediately after vs. 15 min after exercise) differed (P less than 0.05). The results indicate that supramaximal exercise alters the distribution of NH3 and lactate between plasma and RBC, thus changing the relations between plasma and whole-blood concentrations of these metabolites. The alteration of NH3 distribution may reflect changes in the pH gradient between plasma and RBCs.