Capillary Permeability to Macromolecules: Stretched Pore Phenomenon

Abstract

Radioactive iodinated serum albumin and dextran fractions of average molecular weights of 51,000– 255,000 are injected into nembutalized dogs, and concentration changes of these substances are followed in plasma and thoracic and right duct lymphs for 4–6 hours. At this time, when a ‘steady state’ has been established between plasma and lymph, the plasma volumes of the dogs are increased by the infusion of 40 ml/kg of 5% serum albumin in 0.9% saline solution. This results in a significant and striking increase in the concentration of the injected radioactive iodinated albumin and dextrans in right duct and thoracic duct lymph in spite of increased lymph flows. The increase in dextran lymph/plasma concentration ratios occurs with all molecular weight fractions. These results are interpreted as reaffirming our previously formulated concept that infusions producing plasma volume expansion decrease the resistance of the capillary wall to the passage of macromolecules or increase the size of the capillary ‘pores.’ The concept of capillary permeability as a function of ‘pore’ size must, therefore. be modified to include a labile capillary ‘pore’ size, subject to change with variations in plasma volume as well as other factors.