title: Evaluation of renal function and fluid homeostasis during recovery from exercise-induced hyponatremia.
abstract: Renal function including fluid and electrolyte balance was studied during recovery in eight subjects who developed symptomatic hyponatremia (HN; plasma sodium concentration less than 130 mM) during an 88-km ultramarathon footrace and compared with results for normonatremic runners [NN; n = 18, mean postrace plasma sodium concentration, 138.2 +/- 1.2 (SE) mM]. Estimated fluid intake during the race for HN was 12.5 +/- 1.6 (SE) liters over 9 h 41 min (+/- 28 min). HN excreted a net fluid excess of 2.95 +/- 0.56 (range 1.2-5.9) liters compared with a fluid deficit of 2.7 +/- 0.3% body weight in NN. The sodium deficit was 153 +/- 35 mmol in HN and 187 +/- 37 mmol in NN. Despite the fluid overload, plasma volume was decreased by 24.1 +/- 5.0% in HN compared with 8.2 +/- 2.6% in NN. Serum renin activity (5.1 +/- 2.0 ng.ml-1.h-1), aldosterone concentrations (410 +/- 34 ng/l), creatinine clearances (174.8 +/- 28.2 ml/min), and urine output (6.4 +/- 1.0 ml/min) were markedly elevated in HN during recovery. Thus the hyponatremia of exercise results from fluid retention in subjects who ingest abnormally large fluid volumes during prolonged exercise.
authors.affiliation: Medical Research Council/University of Cape Town Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School, Observatory, South Africa.
authors.forename: R A
authors.initials: RA
authors.lastname: Irving
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: R
authors.initials: R
authors.lastname: Buck
authors.forename: R
authors.initials: R
authors.lastname: van Zyl Smit
authors.forename: E
authors.initials: E
authors.lastname: Raine
authors.forename: J
authors.initials: J
authors.lastname: Godlonton
authors.forename: R J
authors.initials: RJ
authors.lastname: Norman
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology; D004231:Diuresis / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007010:Hyponatremia / Q000209:etiology* / Q000503:physiopathology; D007668:Kidney / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012084:Renin-Angiotensin System / Q000502:physiology; D012420:Running; D014882:Water-Electrolyte Balance / Q000502:physiology