title: Increased renal tubular sodium reabsorption during exercise-induced hypervolemia in humans.
abstract: We tested the hypothesis that renal tubular Na(+) reabsorption increased during the first 24 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 O(2) 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.
authors.affiliation: The John B. Pierce Laboratory, New Haven, Connecticut 06519, USA.
authors.forename: K
authors.initials: K
authors.lastname: Nagashima
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: S A
authors.initials: SA
authors.lastname: Kavouras
authors.forename: G W
authors.initials: GW
authors.lastname: Mack
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008094:Lithium / Q000493:pharmacokinetics; D008297:Male; D009997:Osmotic Pressure; D012079:Renal Circulation / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D014556:Urine
chemical_list: D008094:Lithium; D012964:Sodium