Exercise training-induced hypervolemia: role of plasma albumin, renin, and vasopressin.

To investigate the time course and mechanism of the increase in blood volume (BV) during isotonic exercise training, blood hemoglobin, hematocrit, and plasma volume (PV), osmotic, electrolyte, renin activity (PRA), vasopressin (AVP), and protein fractions were measured periodically in eight trained men 20-22 yr (Vo2max = 57 ml . min-1 . kg-1) before, during, and after ergometer exercise training (approximately 160 W, 65% Vo2max) for 2 h/day for 8 days. During training, plasma total osmolar and albumin contents increased to maintain a constant plasma osmolality and protein concentration during PV expansion. After training, BV increased by 457 ml (+8.1% P less than 0.05), due to an increase in PV of 427 ml (+12.1%, P less than 0.05); red cell volume was essentially constant (delta = +30 ml, NS). Plasma hypervolemia during training was associated with two major factors: 1) a ninefold elevation in PRA and AVP during exercise that facilitated Na+ and H2O retention, and 2) a progressive, chronic increase in plasma albumin content that provided increased H2O-binding capacity for the blood. Thus an efficient procedure for increasing PV is the daily performance of high-intensity isotonic leg exercise (65% Vo2max) for 2 h/day.