Myoendothelial Junctional Complexes in Postobstructive Pulmonary Vasculopathy: A Quantitative Electron Microscopic Study

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Abstract
Postobstructive pulmonary vasculopathy (POPV), produced by chronic unilateral ligation of one pulmonary artery, is characterized by (1) marked proliferation of bronchial collateral vessels, (2) increased pulmonary vascular resistance, and (3) hyperreactivity of arteries to serotonin and of veins to histamine. Electron microscopic examination of the vessels in POPV suggested an increase in myoendothelial junctional complexes (MEJC). To quantitate this change, the number of MEJC in the vessel walls of the left lung was compared with that of the right lung in 16 dogs after ligation of the left main pulmonary artery for 8.4 ±1.6 (SE) months. The lungs were fixed by airway instillation of 3% glutaraldehyde. Electron micrographs were taken of pulmonary arteries, capillaries, and veins and of bronchial vessels, and their external diameter and length of endothelial basal lamina were measured. The MEJC were counted and expressed as number per length of basal lamina and typed: Type I consisted of endothelial processes, type II of smooth muscle or pericyte processes, and type III of processes from each cell type. The results demonstrated that the vasculature from the control lung had the smallest number of MEJC and the majority were type I. With ligation, there was a significant increase (p < .01) in the number of MEJC for each type of vessel examined, but no significant change in the distribution of the type. In addition, no correlation was found between the number of MEJC and vascular diameter. It can be concluded that MEJC are increased in each region of the lung's vasculature in POPV and that they may play a role in the proliferative response of the bronchial vasculature, the remodeling of the pulmonary vasculature, and the pulmonary vascular hyperreactivity of this model.