Influence of Prolonged Physical Exercise on Plasma Volume, Plasma Proteins, Electrolytes, and Fluid-Regulating Hormones*

Abstract

Fluid-regulating hormones [arginine vasopressin (AVP) and aldosterone] as well as electrolytes, plasma volume (PV), and plasma proteins were studied in 16 well-trained male amateur runners (mean age 31.8 years) before to), immediately after (t₁), and 60 min (t₂) and 22 h (t₃) after a marathon run. Immediately after the run PV was significantly decreased by 12.1%, whereas the concentration of plasma proteins increased by 13.9%, sodium by 5.8 mMol·^-1, and potassium by 0.58 mMol·^-1, respectively. Aldosterone increased by 1089 pg/ml and AVP by 9.0 pg/ml. PV was significantly increased 22 h after the run by 10.6% (P < 0.001) and plasma proteins were increased by 1.0% (P > 0.05), whereas aldosterone and AVP as well as electrolytes returned to control values. At t₁, and particularly at t₂ and t₃, the total plasma protein concentration increased much more than could have been expected from changes of PV. It is suggested that this phenomenon was caused by an influx of proteins into the vascular space. This might also be the reason for the expanded PV especially in the longer recovery period at t₃. The volume-regulating hormones (AVP and aldosterone) may play an important role during and immediately after the run but not in the longer recovery period (t₂ and t₃).