Low dose infusion of alpha human atrial natriuretic peptide (ANP) has been shown 
to cause a shift of intravascular fluid to the interstitial space. No studies 
have been reported on the effect of ANP on capillary permeability to plasma 
proteins. We studied the effect of low dose ANP (2.5 pmol/kg.min) or equal 
volume of saline control when infused over 90 min, on plasma volume, 
transcapillary escape rate of intravascular albumin, and the rate of reentry of 
albumin to the vascular space in eight normal subjects. Intravenous injection of 
125I-human serum albumin was used for measurement of plasma volume and 
intravascular albumin escape rate. A significant ANP-induced fall in plasma 
volume (P < 0.01) was observed. Transcapillary escape rate of intravascular 
albumin when corrected for concurrent plasma volume changes showed a 
significantly greater escape during ANP infusion than during saline control (P < 
0.05). The mean +/- SEM changes in plasma albumin concentration were +0.36 +/- 
0.22 g/L.h during ANP infusion and -0.46 +/- 0.50 g/L.h during placebo. Plasma 
sodium, red cell volume, and urinary albumin and radioactivity remained 
unchanged. The mass of albumin reentering the circulation per hour showed no 
significant difference between the 2 days. In summary, low dose ANP infusion in 
healthy subjects caused a shift of plasma water and electrolytes from the 
circulation, with albumin escape as a secondary phenomenon.