Permeability of lymphatic vessels

Abstract

Substances of various molecular sizes were infused through leg or mesenteric lymphatics of anesthetized dogs and their concentrations were followed in thoracic duct lymph and plasma for the subsequent 2 1/2 hr. An isolated in vivo popliteal lymph node preparation was also perfused with some of the same substances. Small molecules were found to diffuse rapidly into the blood stream but hindrance to free exchange between lymph and plasma becomes progressively greater as molecular size increases. Somewhere between molecular weights of 600 and 2,300 it increases significantly so that, at or above the latter level, larger molecules are retained in approximately the same amount, irrespective of molecular size. No evidence of trapping by the popliteal node was seen with the largest substance used, dextran, of average molecular weight of 412,000. Urea in high concentrations exerted a "toxic effect" on the lymphatic vessels and node, rendering them more permeable to albumin. Sodium thiocyanate also exerted a similar action.