Increased renal tubular sodium reabsorption during exercise-induced hypervolemia in humans.
Nagashima, Kei, Jauchia Wu, Stavros A. Kavouras, and Gary W. Mack.
The John B. Pierce Laboratory and Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Connecticut 06519
APStracts 8:0317A, 2001.
We tested the hypothesis that renal tubular Na+ reabsorption increased during the first 24-48 h of exercise-induced plasma volume expansion. Renal function was assessed 1 day after no-exercise control (C) or intermittent cycle ergometer exercise (Ex, 85% of peak O2 uptake) for 2 h before and 3 h after saline loading (12.5 ml/kg over 30 min) in seven subjects. Ex reduced renal blood flow (p-aminohippurate clearance) compared with C (0.83 ± 0.12 vs. 1.49 ± 0.24 l/min, P < 0.05) but did not influence glomerular filtration rates (97 ± 10 ml/min, inulin clearance). Fractional tubular reabsorption of Na+ in the proximal tubules was higher in Ex than in C (P < 0.05). Saline loading decreased fractional tubular reabsorption of Na+ from 99.1 ± 0.1 to 98.7 ± 0.1% (P < 0.05) in C but not in Ex (99.3 ± 0.1 to 99.4 ± 0.1%). Saline loading reduced plasma renin activity and plasma arginine vasopressin levels in C and Ex, although the magnitude of decrease was greater in C (P < 0.05). These results indicate that, during the acute phase of exercise-induced plasma volume expansion, increased tubular Na+ reabsorption is directed primarily to the proximal tubules and is associated with a decrease in renal blood flow. In addition, saline infusion caused a smaller reduction in fluid-regulating hormones in Ex. The attenuated volume-regulatory response acts to preserve distal tubular Na+ reabsorption during saline infusion 24 h after exercise.
Received 8 March 2001; accepted in final form 17 April 2001
APS Manuscript Number A223-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001