Endothelial nitric oxide synthase‐enhancing G‐protein coupled receptor antagonist inhibits pulmonary artery hypertension by endothelin‐1‐dependent and endothelin‐1‐independent pathways in a monocrotaline model

This study investigates whether endothelin-1 (ET-1) mediates monocrotaline (MCT)-induced pulmonary artery hypertension (PAH) and right ventricular hypertrophy (RVH), and if so, whether the G-protein coupled receptor antagonist KMUP-1 (7-{2-[4-(2-chlorobenzene)piperazinyl]ethyl}-1,3-dimethylxanthine) inhibits ET-1-mediated PA constriction and the aforementioned pathological changes. In a chronic rat model, intraperitoneal MCT (60 mg/kg) induced PAH and increased PA medial wall thickening and RV/left ventricle + septum weight ratio on Day 21 after MCT injection. Treatment with sublingual KMUP-1 (2.5 mg/kg/day) for 21 days prevented these changes and restored vascular endothelial nitric oxide synthase (eNOS) immunohistochemical staining of lung tissues. Western blotting analysis demonstrated that KMUP-1 enhanced eNOS, soluble guanylate cyclase, and protein kinase G levels, and reduced ET-1 expression and inactivated Rho kinase II (ROCKII) in MCT-treated lung tissue over long-term administration. In MCT-treated rats, KMUP-1 decreased plasma ET-1 on Day 21. KMUP-1 (3.6 mg/kg) maximally appeared at 0.25 hours in the plasma and declined to basal levels within 24 hours after sublingual administration. In isolated PA of MCT-treated rats, compared with control and pretreatment with l-NG-nitroarginine methyl ester (100 μM), KMUP-1 (0.1-100 μM) inhibited ET-1 (0.01 μM)-induced vasoconstriction. Endothelium-denuded PA sustained higher contractility in the presence of KMUP-1. In a 24-hour culture of smooth muscle cells (i.e., PA smooth muscle cells or PASMCs), KMUP-1 (0.1-10 μM) inhibited RhoA- and ET-1-induced RhoA activation. KMUP-1 prevented MCT-induced PAH, PA wall thickening, and RVH by enhancing eNOS and suppressing ET-1/ROCKII expression. In vitro, KMUP-1 inhibited ET-1-induced PA constriction and ET-1-dependent/independent RhoA activation of PASMCs. In summary, KMUP-1 attenuates ET-1-induced/ET-1-mediated PA constriction, and could thus aid in the treatment of PAH caused by MCT.