MICRO-INJECTION STUDIES OF CAPILLARY PERMEABILITY

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Abstract
By micro-injection methods it has been possible to measure blood pressures in single capillaries of the frog''s mesentery, to inject dyes into capillaries of various diam., and to measure directly the rate of movement of fluid through the capillary wall. Introduction of dye solutions into single capillaries of the frog''s mesentery indicates that the walls of dilated capillaries are not more permeable than those of constricted vessels. Rate of passage of a dye solution through the capillary wall depends upon the level of capillary pressure, not upon capillary diam. At any given pressure various dye solutions differ markedly in the time required for visible passage, due probably to their different colloidal properties. So far as permeability to dyes is concerned, comparison of capillaries made of collodion to the mesenteric capillaries is not justified. Vital red HR introduced into the ventricular blood passes immediately through the walls of those capillaries whose pressure is above 14 cm. of water, but is retained for some min. at pressures below 11 cm. Direct measurement shows the rate of fluid movement through the capillary wall to be directly proportional to the difference between capillary pressure and the osmotic pressure of the plasma proteins, amounting to approximately 0.03 cubic micra per sq. micron of capillary wall per sec. for a difference of 5 cm. water pressure. The osmotic pressure of the plasma proteins against their natural membrane as indicated by this method is 11.5 cm. water. When capillary pressure exceeds this value, filtration occurs; when it falls below it absorption results. Capillaries injured by alcohol and HgCl2 appear to be permeable to the plasma colloids and approximately 7 times more permeable to fluid than the normal capillary wall.

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