Chronic pulmonary hypertension in sheep: temporal progression of lesions.

Scant data exist on the evolution of the lesions of pulmonary hypertension. This study establishes a model in sheep in which the left upper lobe (LUL) was rendered hypertensive by a systemic-pulmonary shunt while the rest of the pulmonary circulation remained normotensive. By examining lung tissue at 2 months and 1 1/2 years after shunting, we sought the temporal progression of pulmonary hypertensive lesions. In the hypertensive LULs (n = 5), many vascular lesions were seen in contrast to the absence of lesions in both the contralateral normotensive lungs (n = 5) and the "control" lungs from sheep which underwent thoracotomy without shunting (n = 5). Vascular necrosis and vasculitis were present after 2 months (P < 0.01) but disappeared after 1 1/2 years. In contrast, intimal thickening was present after 1 1/2 years (n = 2, P < 0.01) but not significantly after 2 months. These intimal lesions often demonstrated increased cellularity staining positively for factor VIII. Plexiform lesions were present at 2 months (P < 0.05) but were more profuse after 1 1/2 years (P < 0.01). These findings are consistent with an early vascular injury and a later remodeling or reparative process in hemodynamic pulmonary hypertension.