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Abstract:
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.