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We rapidly infused 234 +/- 3 mL of 5% human serum albumin in eight men while measuring haematocrit, haemoglobin concentration, plasma volume (PV), albumin concentration, total protein concentration, osmolality, sodium concentration, renin activity, aldosterone concentration, and atrial natriuretic peptide concentration to test the hypotheses that plasma volume expansion and plasma albumin content expansion will not persist for 24 h. Plasma volume and albumin content were expanded for the first 6 h after infusion (44.3 +/- 1.9-47.2 +/- 2.0 mL kg-1 and 1.9 +/- 0.1-2.1 +/- 0.1 g kg-1 at pre-infusion and 1 h, respectively, P < 0.05), but by 24 h plasma volume and albumin content decreased significantly from 1 h post-infusion and were not different from pre-infusion (44.8 +/- 1.9 mL kg-1 and 1.9 +/- 0.1 g kg-1, respectively). Plasma aldosterone concentration showed a significant effect of time over the 24 h after infusion (P < 0.05), and showed a trend to decrease at 2 h after infusion (167.6 +/- 32.5(-1) 06.2 +/- 13.4 pg mL-1, P = 0.07). These data demonstrate that a 6.8% expansion of plasma volume and 10.5% expansion of plasma albumin content by infusion does not remain in the vascular space for 24 h and suggest a redistribution occurs between the intravascular space and interstitial fluid space.

We describe a method for measuring plasma volume (PV) in small animals that allows small sample sizes but does not require the use of radioisotopes and thus is a convenient approach for making repeated measurements. Texas Red covalently bound to albumin (TR-A) was used in a typical indicator-dilution technique to measure PV. The relative fluorescent intensity of TR-A is linear to its concentration (up to 0.15 mg/ml) at an excitation lambda of 590 nm and an emission lambda of 610 nm. Catheters were inserted through the right jugular vein of anesthetized rats and threaded into the vena cava. A 0.5-ml control blood sample was taken, a measured quantity of TR-A was injected, and the catheter was flushed with saline. A 0.5-ml postinjection sample was taken 5 min after TR-A injection. PV was calculated by comparing the difference between the relative fluorescent intensity of control and postinjection plasma samples to a standard. The PV of 22 rats [362 +/- 14 (SE) g] was 14.1 +/- 0.4 ml (39.6 +/- 0.9 ml/kg body wt) measured by the TR-A method and 12.8 +/- 0.4 ml (35.9 +/- 1.0 ml/kg body wt) measured by a standard radioiodinated albumin method. There was a strong correlation between PV measured by both methods in the same rat (r = 0.90, P < 0.01). Infusion experiments indicated that the TR-A method can detect acute changes in PV, and repeated measurements of PV made on a chronically instrumented rat demonstrated that the method can reliably measure PV on consecutive days.

We used intense intermittent exercise to produce a 10% expansion of plasma volume (PV) within 24 h and tested the hypothesis that PV expansion is associated with an increase in plasma albumin content. The protocol consisted of eight 4-min bouts of exercise at 85% maximal O2 uptake with 5-min recovery periods between bouts. PV, plasma concentrations of albumin and total protein (TP), and plasma osmolality were measured before and during exercise and at 1, 2, and 24 h of recovery from exercise. During exercise, PV decreased by 15%, while plasma TP and albumin content remained at control levels. At 1 h of recovery, plasma albumin content was elevated by 0.17 +/- 0.04 g/kg body wt, accounting for the entire increase in plasma TP content. PV returned to control level at 1 h of recovery without fluid intake by the subjects, despite a 820 +/- 120-g reduction in body weight. At 2 h of recovery, plasma TP content remained significantly elevated, and plasma TP and albumin concentration were significantly elevated. At 24 h of recovery, PV was expanded by 4.5 +/- 0.7 ml/kg body wt (10 +/- 1%), estimated from hematocrit and hemoglobin changes, and by 3.8 +/- 1.3 ml/kg body wt (8 +/- 3%), measured by Evans blue dye dilution. Plasma albumin content was increased by 0.19 +/- 0.05 g/kg body wt at 24 h of recovery. If 1 g of albumin holds 18 ml of water, this increase in plasma albumin content can account for a 3.4-ml/kg body wt expansion of the PV. No significant changes in plasma osmolality occurred during recovery, but total plasma osmotic content increased in proportion to PV.(ABSTRACT TRUNCATED AT 250 WORDS)