Tissue to plasma capillary permeability of 131I-albumin in the perfused rabbit ear

Abstract

The tissue to plasma transfer of 131I-albumin was recorded in perfused rabbit ears ( n = 6) following equilibration for 24 hr. 125I-fibrinogen served as the plasma marker, and was introduced intravenously 15 min before clamping. The ears were rollerpump perfused with isotonic diluted plasma at a constant rate of (mean ± SD) 5.1 ± 1.5 ml (min · 100 g) −1. The mean extravascular albumin distribution volume was 12.4 ± 1.1 ml · 100 g −1, and the fibrinogen volume (plasma volume in tissue) was 3.1 ± 0.4 ml · 100 g −1 as determined from biopsies of the contralateral ear. The initial transfer of albumin was marked, and occurred at rates corresponding to a unidirectional clearance (Cl(0)) of 0.068 ± 0.012 ml (min · 100 g) −1. However, with a reduction of mean interstitial albumin tracer content of no more than 4%, net transport decreased to reach slowly declining levels 5 to 10 times lower within 10 min of continued perfusion. The decrease was considered due to rapid exhaustion of a small interstitial pool of tracer immediately adjacent to the exchange vessel membrane, followed by an increasingly retarded outwash from more distant areas. The results suggest a bimodal structural resistance to albumin movement: a relatively low resistance in the capillary membrane, and a considerable restriction to albumin transport located within the interstitial space.