MMC induces pulmonary vascular remodeling in the rat, with pulmonary venous and capillary lesions mimicking capillary hemangiomatosis found in PVOD patients. ((a) and (d)) Control lung. ((b)-(c), (e)–(i)) MMC-exposed lung. (a) Control pulmonary artery (Ar) and vein (V) close to the bronchus (Br). ((b)-(c)) Remodeling of pulmonary arteries and veins close to the bronchi at two levels of distality. (d) Control distal microvessels (arterioles and venules are indistinguishable) (arrows). (e) Remodeled distal pulmonary arteriole delimited by apparent internal and external elastica (blue stained) (arrow). (f) Remodeled distal pulmonary venule delimited by single elastica (blue stained) (arrow). ((g)-(h)) Foci of alveolar-wall thickening suggestive of pulmonary capillary hemangiomatosis (dotted line area). (i) Foci of pulmonary edema (arrow) and capillaritis (arrowhead). ((a)–(i)) Masson’s trichrome stained paraffin-embedded tissue sections: muscle fibers (red), collagen (blue), light red/pink (cytoplasm), and cell nuclei (dark brown/black). Red scale bar = 100 μm. Black scale bar = 50 μm.