Permeability of pulmonary vascular endothelium

Three aspects of transendothelial exchange in the lungs are considered: stretching of interendothelial junctions of pulmonary microvessels by increase in pulmonary capillary pressures; selective stretching of interendothelial junctions of bronchial venules in response to histamine, bradykinin and endotoxin; active transport of peptides across the body of the endothelial cell after enzymic action at or near the luminal surface of the endothelial cell. Stretching of interendothelial junctions between the cells lining the pulmonary capillaries was demonstrated using a variety of macromolecular tracers under controlled haemodynamic conditions. Selective leakage of bronchial venules, the systemic venules of the lungs, was shown using colloidal carbon as a tracer. Transendothelial transport of peptides across the pulmonary capillary lining involved the use of electron microscopic autoradiography after intravenous administration of radioactively-labelled lipoproteins. Different mechanisms appear to provide routes of entry into the perivascular interstitial spaces of the lungs.