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To examine body fluid regulation over 72 h of recovery from a 24-h endurance race, changes in plasma volume (delta 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 delta PV 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 (Na+). Urinary potassium excretion (K+) increased (256% from C value). During the 3 days of recovery delta PV 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 less than 0.001) and ANP (P less than 0.01): from C values, ADH decreased (21% and 29%) and ANP increased (41% and 58%) on D2 and D3, respectively. UV and Na+ 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.
Fellmann et al. (Fri,) studied this question.