Intercellular junctions in "shock lung". A freeze-fracture study.

Intercellular junctions in the alveolar epithelium and in the capillary endothelium in lung from five dogs after hemorrhagic shock (mean blood pressure, 40 mm. Hg for 3 hours) and from five control dogs were observed in the electron microscope using the freeze-fracture technique. Following shock zonulae occludentes (tight junctions) in the alveolar epithelium showed alterations in substructure that were not present in control animals. These changes were morphologically similar to those reported in junctions altered after exposure to osmotic gradients with marked degradation and disappearance of junctional strands. The appearance of tight junctions in the capillary endothelium, which were of a rather poorly organized "leaky" type in control animals, was generally unaltered after shock. Disintegration and disappearance of junctional strands in "focal" regions, however, were occasionally observed. The increased pulmonary capillary permeability observed physiologically after hemorrhagic shock could be explained by such alterations of endothelial zonulae occludentes.