EFFECT OF LOCAL COOLING ON FLUID MOVEMENT, EFFECTIVE OSMOTIC PRESSURE AND CAPILLARY PERMEABILITY IN THE FROG'S MESENTERY

Abstract

During local cooling of the frog''s mesentery no microscopic signs of injury or of protein leakage from capillaries appeared until after the tissue had been frozen. Capillary stasis always developed as soon as blood flow was resumed after thawing but was often reversible, particularly after very brief periods of freezing. Micromanipulative studies of the relation between filtration or absorption of fluid and blood pressure in single capillaries indicated that at tissue temps, between [long dash]2 and +2[degree][degree]C (slightly above the freezing point), the filtration constant of the capillary wall was decreased 73% and the effective osmotic pressure of the blood within the cooled capillaries was increased at least 31%. The significant increase in total effective osmotic pressure cannot be attributed to an increase in colloid osmotic pressure, either absolute or relative. On theoretical grounds, it might be explained by either (a) decreased permeability of the capillary wall to certain non-protein constituents of plasma or (b) thermosmosis; neither explanation can be excluded at present. The changes observed during cooling were the reverse of those previously found to result from injury (chemical) to mesenteric capillaries (increased filtration constant and decreased effective osmotic pressure).