Bolus saline infusion induces extracellular fluid-protein redistribution in the upright posture
This study examined the impact of body posture on protein translocation from the extra- to the intravascular space following bolus saline infusion. Subjects (n=5) rested in the upright (UP) or the supine posture (SUP) for 6.5 h. In the middle of experiment, 15 ml/kg body wt of 0.9% saline was infused within 30 min. Plasma volume increased by 3.54 0.59 (mean se) and 4.84 0.54 ml/kg body wt immediately after the infusion in UP and SUP (P<0.05), and remained greater level for next 3 h (P<0.05, 2.75 0.45 and 1.12 0.40 ml/kg body wt). We found an increase in plasma total protein and albumin contents 2 - 3 h after the infusion only in UP (P<0.05, 0.11 0.03 and 0.06 0.02 g/body wt, respectively). Transcapillary escape rate of albumin estimated by the disappearance rate of albumin-bound Evans-Blue was 7.8 1.7 and 7.4 0.7 %/h in UP and SUP. Plasma atrial natriuretic peptide level increased from 45 10 to 56 2 pg/ml (P<0.05) after the infusion in SUP, but, was unchanged (33 3 pg/ml) in UP. The translocation of protein into the vascular space following bolus saline infusion reflects increased lymph return of protein presumably due to decreased central venous pressure and a reduction in the afterload for lymph return in the upright posture.