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This Article Full Text Full Text (PDF) All Versions of this Article: 107/3/864    most recent 91211.2008v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Stachenfeld, N. S. Articles by Taylor, H. S. PubMed PubMed Citation Articles by Stachenfeld, N. S. Articles by Taylor, H. S.

Sex hormone effects on body fluid and sodium regulation in women with and without exercise-associated hyponatremia

The John B. Pierce Laboratory and Departments of Epidemiology and Public Health, and of Obstetrics, Gynecology and Reproductive Sciences, Yale University School of Medicine, New Haven, Connecticut

Submitted 9 September 2008 ; accepted in final form 19 June 2009

We hypothesized that exercise-associated hyponatremia (EAH) is a function of excess sodium loss combined with high water intake in women at risk for dysnatremias during endurance exercise. We further hypothesized that estradiol and progesterone exposure increases fluid retention and sodium loss during exercise in women at risk for EAH. For 16 days we suppressed estrogens and progesterone with a gonadotropin-releasing hormone antagonist (GnRH ant) in seven women with (Hypo) and nine women without (no Hypo) a history of hyponatremia; we added 17β-estradiol (0.2 mg/day patches) for days 4–16 (E₂) and progesterone (200 mg/day) for days 13–16 (E₂-P₄). Under each hormone condition, subjects cycled in 35°C at 65% peak oxygen consumption (O_2peak) for 60 min, then at 55–60% O_2peak for 120 min. Subjects drank 8 ml/kg of water (and replenished urine volume) every 30 min over the final 120 min of exercise. S_[Na+] fell by 4.3, 3.9, and 3.1 meq/l (P < 0.05) with drinking during GnRH ant, E₂, and E₂-P₄ in Hypo, with little fall in no Hypo. Under all conditions, combined urine and sweat sodium loss were similar between Hypo [–85.6 (SD 36.2), –86.4 (SD 39.2), and –112.0 (SD 30.0) meq] and no Hypo [–98.0 (SD 54.8), –80.9 (SD 57.6), and –105.1 (SD 46.4) meq, for GnRH, E2, and E2-P4], as was mass balance of electrolytes (E_MB) for Hypo [–104.8 (SD 32.8), –103.6 (SD 42.1), and –132.8 (SD 34.9) meq] compared with no Hypo [–128.8 (SD 57.2), –113.5 (SD 61.1), and –143.4 (SD 49.6) meq for GnRH, E2, and E2-P4]. Mass balance of water [V_MB, for Hypo, 0.42 (SD 0.10), 0.62 (SD 0.25), and –0.11 (SD 0.11) liter] compared with no Hypo [0.01 (SD 0.15), 0.03 (SD 17), and –0.16 (SD 0.13) liter for GnRH, E2, and E2-P4, P < 0.05] indicates water retention was the primary contributor to the lower S_[Na+] in Hypo women.

gonadotropin-releasing hormone antagonist; estradiol; progesterone; plasma sodium; exercise; mass balance of water and electrolytes