Transcapillary Escape Rate of Albumin and Plasma Volume in Essential Hypertension

Abstract

The transcapillary escape rate of albumin, the fraction of intravascular mass of albumin that passes to the extravascular space per unit time, was determined from the disappearance of intravenously injected 131 I-labeled human serum albumin during the first 60 minutes after the injection in 10 normotensive and 18 hypertensive male subjects. The investigation was preceded by at least 12 hours of fasting and 30 minutes of rest in the supine position. The transcapillary escape rate of albumin was significantly increased in the hypertensive group: it averaged 7.6±1.2 (SD) %/hour compared with 5.6±1.1%/hour in the normotensive group ( P <0.001). Similar results were obtained for the outflux of albumin, the mass of intravascular albumin that passes to the extravascular space per unit time, when identical intravascular albumin masses were compared ( P <0.001). A highly significant correlation between the transcapillary escape rate of albumin and blood pressure was found in the hypertensive group ( P <0.001). Therefore, the increased transcapillary escape rate and the outflux of albumin probably reflected an increase in arteriolar and capillary permeability to albumin. This increase was probably due to the high intra-arterial pressure, which induces constriction in some arteries and dilatation in others and thus allows the high intraluminal pressure to be transmitted distally with distention of the small vessel walls. Finally, a significant reduction in plasma volume was found in the hypertensive subjects ( P <0.05).