Monocrotaline (MCT) is a pyrolizidine alkaloid isolated from the plant Crotalaria spectabilis. In addition to the multi-organ toxicity associated with MCT ingestion by humans and livestock, a single subcutaneous injection of the alkaloid in intact rats produces a spectrum of pulmonary vascular lesions remainiscent of idiopathic pulmorary hypertension in humans. Although the mechanisms of MCT-induced pneumotoxicity are unknown, extensive studies in our laboratories demonstrate that the polyamines play a central pathogenetic role. The research proposed herein explores the specific mechanisms by which polyamines participate in the lung injury and hypertensive pulmonary vascular disease observed in MCT-treated rats. To test the hypothesis that polyamines mediate MCT-induced pulmonary endothelial dysfunction, (1) autoradiographic and immunocytochemical techniques will be used to determine if endothelial cells in the lungs of MCT-treated rats exhibit enhanced ODC activity and if the increased endothelial ODC activity is temporally related to perivascular edema formation; (2) Cultured endothelial cells will be used to determine if MCT-derived pyrroles, in the absence of blood-borne elements, directly provoke polyamine dependent endothelial injury accompanied by increased endothelial permability; and (3) Perfused lungs isolated from MCT-treated rats will be employed to determine if MCT-induced depression of endothelial serotonin uptake is polyamine-dependent. To assess the mechanism by which polyamines mediate MCT-induced hypertentensive pulmonary vascular remodeling, autoradiographic and immunocytochemical techniques will be used to determine; (5) if MCT enhances polyamine biosynthetic activity in specific vascular cells that are functionally related to vascular remodeling, and (6) if DNA and protein synthesis is enhanced. Finally, studies with potential clinical relevance will be conducted to determine if and when inhibition of polyamine synthesis can arrest or reverse progression of MCT-induced hypertensive pulmonary vascular disease. Viewed collectively, results of the proposed studies will shed light on an important biochemical mechanism governing the response of the pulmonary vasculature to chemically-mediated injury. Additionally, these studies may point to pharmacology interventions capable of forestalling progression of hypertensive pulmonary vascular disease.