Protein loss and capillary protein permeability in dependent regions upon quiet standing

Seven healthy males were exposed to quiet standing (15 min) after supine rest. Alterations in the total mass of plasma proteins were analysed from changes in plasma volume (PV; determination of control PV and subsequently of induced per cent PV changes using Hb/Hct) and protein concentration as revealed in arterial blood collected after standing. This approach adopted the concept that valid data on overall circulatory haemoconcentrations prevailing on standing can only be reached when blood is sampled on resumption of the recumbent posture, whereas conventional sampling from the standing subject provides erroneous information. The PV reduction on standing averaged 649 +/- 65 mL (16.9 +/- 1.0%). There were very similar net decreases in plasma (serum) total protein (7.6 +/- 0.8 g) and albumin (7.8 +/- 0.9 g). These findings permitted the following main conclusions of physiological and methodological pertinence: (1) Quiet standing leads to a clear-cut net decrease in the plasma protein content predominantly confined to albumin, in all probability via convection secondary to PV loss by filtration in dependent regions. (2) It is suggested that the albumin loss reflects a quite high capillary macromolecular permeability in the dependent limbs on standing preferentially confined to skin/subcutaneous tissues. (3) The albumin loss implies that plasma concentration changes of neither albumin nor of total protein can be used to describe the PV loss on standing. However, concentration changes of the plasma globulin fraction as a whole, expressed by the difference (total protein-albumin), seem to reflect PV alterations approximately.