Role of interstitial fibroblasts and intermediate cells in microvascular wall remodelling in pulmonary hypertension

The cellular basis of the development of new contractile cells in lung microvessels in hyperoxic pulmonary hypertension is reviewed. Extensive remodelling of the walls of the nonmuscular segments of these vessels was induced in rats breathing 87% oxygen for 1-28 days and the cellular changes followed at the ultrastructural level. In certain segments it is the interstitial fibroblast that forms a new layer of contractile cells within the vessel wall. In other segments intermediate cells, a population of cells within the vessel intima, are the basis of new contractile cell development. Tropoelastin secretion and elastic lamina(e) formation are critical events in the development of these contractile cells into a medial layer. In general, the interstitial fibroblast and intermediate cells remodel different vascular segments, although each can remodel the same segment. By these alternate pathways, thick-walled microvessels with a medial layer of contractile cells form adjacent to capillaries in the hypertensive lung.