INFLUENCE OF SODIUM-BICARBONATE INGESTION ON PLASMA AMMONIA ACCUMULATION DURING INCREMENTAL EXERCISE IN MAN

This investigation evaluated the influence of metabolic alkalosis on plasma ammonia (NH3) accumulation during incremental exercise. On two occasions separated by at least 6 days, six healthy men cycled at 70, 80, and 90% of maximum oxygen consumption (VO2max) for 5 min; each exercise period was followed by 5 min of seated recovery. Exercise was then performed at 100% VO2max until exhaustion. Beginning 3 h prior to exercise, subjects ingested 3.6 mmol.kg body mass-1 NaHCO3 (test, T) or 3.0 mmol.kg body mass-1 CaCO3 (placebo, P) (both equivalent to 0.3 g.kg-1) over a 2-h period. Trials were performed after an overnight fast and the order of treatments was randomized. Arterialized venous blood samples for the determination of acid-base status, blood lactate and plasma NH3 concentrations were obtained at rest before treatment, 15 s prior to each exercise bout (Pre 70%, Pre 80%, Pre 90%, and Pre 100%), and at 0, 5 (5'Post), and 10 (10'Post) min after exhaustion. Additional samples for blood lactate and plasma NH3 determination were obtained immediately after each exercise bout (Post 70%, Post 80%, Post 90%) and at 15 min after exercise (15'Post). Time to exhaustion at 100% of VO2max was not significantly different between treatments [mean (SE): 173 (42) s and 184 (44) s for T and P respectively]. A significant treatment effect was observed for plasma pH with values being significantly higher on T than on P Pre 70% [7.461 (0.007) vs 7.398 (0.008)], Pre 90% [7.410 (0.010) vs 7.340 (0.016)], and 10'Post [7.317 (0.032) vs 7.242 (0.036)]. The change in plasma pH was significantly greater following the 90% bout (Pre 100% Pre 90%) for T [-0.09 (0.02)] than for P [-0.06 (0.01)]. Blood base excess and plasma bicarbonate concentrations were significantly higher for T than P before each exercise bout but not at the point of exhaustion. During recovery, base excess was higher for T than P at 5'Post and 10'Post while the bicarbonate concentration was higher for T than P at 10'Post. A significant treatment effect was observed for the blood lactate concentration with T on the average being higher than P [7.0 (1.0) and 6.3 (1.1) mmol.l-1 for T and P averaged across the 12 sampling times]. Plasma NH3 accumulation was not different between treatments at any point in time. In addition, no differences were observed between treatments in blood alanine accumulation. The results suggest that under the conditions of the present investigation metabolic alkalosis does not influence plasma NH3 accumulation or endurance capacity during intense incremental exercise.