Permeability of rabbit heart capillaries to nonelectrolytes

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Abstract
Isolated perfused rabbit hearts were used to study the permeability characteristics of their capillaries with respect to inulin, raffinose, sucrose, and urea. The method used involved a continuous weighing of the isolated perfused heart. Each heart was isolated and was initially perfused with a Ringer solution containing no test molecule. Then a sudden switch was made to a Ringer solution that differed from the original only by containing a small amount of test material. Since each substance was osmotically active the heart lost weight as a function of time. Analysis of these osmotically induced weight transients was done in order to estimate capillary permeability coefficients. A theory thought to be approximately valid for this system is based on the integration over the capillary length of equations giving the concentration of the test substance in the plasma and extracellular space. Values for the permeability coefficients obtained from this approach are: inulin 0.54 x 10-5 cm sec.-l; raffinose 3.9 x 10-5 cm sec.-l; sucrose 5.9 x 10-5 cm sec.-l; urea 9.7 x 10-5 cm sec.-l. In the discussion section of the paper validification of the approach is attempted by analyzing some of the assumptions made.

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