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Figure 1 Consequences of pulmonary artery endothelial cell dysfunction on pulmonary artery smooth muscle cell tone and proliferation. Dysfunctional pulmonary artery endothelial cells (blue) have a decreased production of prostacyclin and nitric oxide, with an increased production of endothelin-1-promoting vasoconstriction and proliferation of pulmonary artery smooth muscle cells (red). cAMP = cyclic adenosine monophosphate; cGMP = cyclic guanosine monophosphate; ET = endothelin; ET_A = endothelin receptor A; ET_B = endothelin receptor B; PDE5 = phosphodiesterase type 5.