The Permeability of Capillaries in Various Organs as Determined by Use of the 'indicator Diffusion' Method.

CRONE, C. The permeability of capillaries in various organs as determined by use of the ‘Indicator Dzffusion’ method. Acta physiol. scand. 1963. 58. 292-305. The theory of a single injection technique, the ‘Indicator Diffusion’ method, for quantitative studies of capillary permeability is developed. It is shown that the permeability of a capillary area can be expressed by three parameters: the initial extraction ( E ) of test substances added in a single injection to the blood flowing to an organ, the blood flow (&) and the surface area ( A ) of the capillaries. The equation relating these figures is: P = ( Q / A ) x logel/(l-E). The permeability coefficients of capillaries in kidney, liver, lung, brain and hind limb to inulin and sucrose are reported. I t is found that the permeability of capillaries varies considerably from organ to organ. It is questioned whether the pore model adequately describes the functional characteristics of the capillaries in the muscles. The existence of pores should result in a pronounced deviation of the ratio between the permeability coefficients for sucrosc and inulin from the ratio between the free diffusion coefficients. This was not found to be the case. One of the most important activities of the vascular system occurs in the capillaries. Yet, ou r knowledge about the membrane across which the exchange between blood and interstitial fluid takes place is scanty. While many biological structures of very small size have been submitted to direct physiological study in later years, the capillaries have not yet yielded to a direct attack. Thus our knowledge of the permeability characteristics of the capillary wall has still to be deduced from experiments on a mass of capillaries. In the part