Kinetics of 13CO2 elimination after ingestion of 13C bicarbonate: the effects of exercise and acid base balance

• Published in: European journal of clinical investigation Vol. 24; no. 12; p. 818
• Main Authors: Leese, G P, Nicoll, A E, Varnier, M, Thompson, J, Scrimgeour, C M, Rennie, M J
• Format: Journal Article
• Language: English
• Published: England 01-12-1994
• Subjects: Acid-Base Equilibrium; Adult; Bicarbonates - metabolism; Carbon Dioxide - metabolism; Energy Metabolism; Exercise; Female; Humans; Hydrogen-Ion Concentration; Lactates - metabolism; Lactic Acid; Male
• ISSN: 0014-2972
• DOI: 10.1111/j.1365-2362.1994.tb02025.x

In order to investigate the effects of muscular work and preceding exercise on the retention of exogenous labelled bicarbonate, we studied the effects of oral administration of [13C]bicarbonate (0.1 mg kg-1) in five subjects at rest before exercise and during and after 1 h of treadmill walking at 73% VO2max on three separate occasions. Elimination of CO2 from labelled bicarbonate was 62.6 +/- 8.1% at rest, 103.6 +/- 11.3% during exercise (P < 0.01) and 43.0 +/- 4.7% during recovery from exercise (P = 0.01). During exercise mean residence time (MRT) was shorter than at rest (35 +/- 7 min vs. 54 +/- 9 min, P < 0.02) and CO2 pool size was larger (998 +/- 160 ml CO2 kg-1, vs. 194 +/- 28 ml CO2 kg-1, P < 0.001). Compared to values obtained at rest, during recovery from exercise, MRT and CO2 pool size were reduced (34 +/- 5 min, P < 0.05; 116 +/- 19 ml CO2 kg-1, P < 0.02, respectively). In an additional five subjects acidosis and alkalosis were induced prior to administration of oral [13C]bicarbonate at rest. Elimination of bicarbonate was lower during acidosis (46.1 +/- 5.6%, P < 0.01) but was unaltered (50.9 +/- 5.6%, NS) during alkalosis, compared to the values obtained at resting pH. During acidosis MRT and CO2 pool size decreased (37 +/- 3 min, P < 0.01 and 123 +/- 10 ml CO2 kg-1, P < 0.01, respectively) whereas in alkalosis MRT was unchanged (65 +/- 8 min NS) but CO2 pool size was increased (230 +/- 23 ml CO2 kg-1, P < 0.05).