Microvascular exchange of albumin.

The transcapillary exchange of albumin was examined in seven rabbits using plasma disappearance curves and black box kinetic analysis. From the experimental data and the Renkin and Kedem-Katchalsky equations it was found that the average whole body diffusional capillary permeability coefficient for albumin was 24 X 10(-8) cm/sec as the total whole body capillary permeability-surface area product was 0.0739 ml/100 g X min (surface area estimate 50 cm2/g). The convective components of the net albumin tracer flux was found to be 15%, and the pure permeation ratio of influx to outflux (R = 0.61) of systemic albumin was reduced to 0.57. The solvent drag component of either unidirectional flux relative to the permeative component was 0.037. The Casley-Smith hypothesis of solvent drag convection up a gradient across the capillary membrane could not be verified as possible. It is emphasized that the so-called transcapillary escape rate is an arbitrary rate constant which cannot be attributed to reflect any physiological process, especially not the transcapillary exchange of albumin.