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Altered Pulmonary Vascular Reactivity in Mice with Excessive Erythrocytosis

Department of Anesthesiology and Critical Care Medicine; Department of Physiology, University of Lübeck, Lübeck; Department of Physiology, University of Essen, Essen; and Division of Pulmonary Pharmacology, Research Center Borstel, Borstel, Germany

Correspondence and requests for reprints should be addressed to Stefan Uhlig, Ph.D., Division of Pulmonary Pharmacology, Research Center Borstel, Center for Medicine and Biosciences, Parkallee 22, D-23845 Borstel, Germany. E-mail: suhlig{at}fz-borstel.de

Pulmonary vascular remodeling during chronic hypoxia may be the result of either oxygen deprivation or erythrocytosis. To separate experimentally the effects of hypoxia and erythrocytosis, we analyzed transgenic mice that constitutively overexpress the human erythropoietin gene in an oxygen-independent manner. These mice are characterized by polycythemia but have normal blood pressure, heart rate, and cardiac output. In transgenic mice, pulmonary artery pressure (PAP) was increased in vivo but was reduced in blood-free perfused lungs. The thromboxane receptor agonist U46619 caused a smaller rise in PAP in isolated transgenic lungs than in lungs from wild-type mice. The transgenic pulmonary vasculature was characterized by elevated prostacyclin production, stronger endothelial nitric oxide synthase expression, and reduced pulmonary vascular smooth muscle thickness. The fact that transgenic polycythemic mice have marked pulmonary hypertension in vivo but not in vitro suggests that their pulmonary hypertension is due to the increased blood viscosity, thus supporting an independent role of polycythemia in the development of pulmonary hypertension. In addition, our findings indicate that the lungs of transgenic animals adapt to the high PAP by elevated synthesis of vasodilators and reduced vascular smooth muscle thickness that tend to reduce vascular tone and vascular responsiveness.

Key Words: pulmonary hypertension • erythropoietin • isolated mouse lung • vascular remodeling

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