The effect of alpha human atrial natriuretic peptide on plasma volume and vascular permeability in normotensive subjects.

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.