Hormonal, Fluid, and Electrolyte Changes During a 72-h Recovery from a 24-h Endurance Run

Abstract

To examine body fluid regulation over 72 h of recovery from a 24-h endurance race, changes in plasma volume (Δ PV) and plasma aldosterone (A), cortisol (CO), antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP) were studied in nine male runners before (C) and after (1-2 h = D₀; 24 h = D1; 48 h = D₂; 72 h = D₃) the race, 24-h urine collections were made 1 week before (C), during the 24-h race /U₀), and during the 3 days following the end of the race (U₁, U₂, and U₃).

On D₀ ΔPV decreased (2%). A, CO, and ADH increased (380%, 200%, and 133%, respectively, from C values) and ANP decreased (68%). No significant changes were found in sodium, potassium, osmolality in plasma, in 24-h urine volume (UV), and natriuresis (Ṅa⁺). Urinary potassium excretion K̇⁺) increased (256% from C value).

During the 3 days of recovery ΔPV rose markedly with a peak on D₂ (24%) and remained elevated on D₃ (15%). CO, ADH, and ANP returned to baseline on D₁ and A on D₃. Significant inverse effects were observed on ADH (P<0.001) and ANP (P<0.01): from C values, ADH decreased (21% and 29%) and ANP increased (41% and 58%) on D₂ and D₃, respectively. UV and Ṅa⁺ were depressed on D₁ and D₂.

This study shows that the hormonal responses observed immediately after the 24-h run favored a relative fluid conservation. The hypervolemia that occurred during the 3-day recovery was related to renal responses on D₁ and D₂ and appeared to be the primary factor in the hormonal responses on D₂ and D₃.

Key words

atrial natriuretic peptide - aldosterone - antidiuretic hormone - plasma volume change - osmolality