Permeability of connective tissue linings isolated from implanted capsules; implications for interstitial pressure measurements.

Quantification of the permeability of connective tissue linings isolated from implanted capsules was achieved by two types of experiments. The objective of the first type was to determine the restriction offered by the lining to diffusion of 125I-labeled human serum albumin. The restricted diffusion coefficient of albumin with respect to the connective tissue lining the luminal capsule surface (internal lining) averaged 3.0 times 10-7 plus or minus 0.4 times 10-7 cm2/sec in ten experiments indicating that the rate if migration of albumin across the structure was 35% of its free diffusion rate in water. In contrast, the albumin diffusion coefficient obtained for the abluminal (external) lining suggested that diffusion of albumin through this structure was 73% of the free diffusion rate in water. The objective of the second type of experiment was to determine solute reflection coefficients for inulin, serum albumin, and gamma-globulin with respect to the internal and external linings. For the internal lining, the reflection coefficients were: inulin 0.07, albumin0.23, and gamma-globulin 0.53. The external lining showed greater leakiness as evidenced by its lower reflection coefficient for a given molecule and its higher hydraulic conductivity. An equivalent pore calculation resulted in a calculated pore radius of 250-350 angstrom for the internal lining and a calculated pore radius of 500-600 angstrom for the external lining. The ineffectiveness of the leaky capsule lining in transmitting oncotic pressure suggests that under normal conditions the capsule measures interstitial hydrostatic pressure rather than oncotic pressure.