Selective activation of angiotensin AT2 receptors attenuates progression of pulmonary hypertension and inhibits cardiopulmonary fibrosis

Background and Purpose Pulmonary hypertension (PH) is a devastating disease characterized by increased pulmonary arterial pressure, which progressively leads to right-heart failure and death. A dys-regulated renin angiotensin system (RAS) has been implicated in the development and progression of PH. However, the role of the angiotensin AT(2) receptor in PH has not been fully elucidated. We have taken advantage of a recently identified non-peptide AT(2) receptor agonist, Compound 21 (C21), to investigate its effects on the well-established monocrotaline (MCT) rat model of PH. Experimental Approach A single s.c. injection of MCT (50 mg center dot kg(-1)) was used to induce PH in 8-week-old male Sprague Dawley rats. After 2 weeks of MCT administration, a subset of animals began receiving either 0.03 mg center dot kg(-1) C21, 3 mg center dot kg(-1) PD-123319 or 0.5 mg center dot kg(-1) A779 for an additional 2 weeks, after which right ventricular haemodynamic parameters were measured and tissues were collected for gene expression and histological analyses. Key Results Initiation of C21 treatment significantly attenuated much of the pathophysiology associated with MCT-induced PH. Most notably, C21 reversed pulmonary fibrosis and prevented right ventricular fibrosis. These beneficial effects were associated with improvement in right heart function, decreased pulmonary vessel wall thickness, reduced pro-inflammatory cytokines and favourable modulation of the lung RAS. Conversely, co-administration of the AT(2) receptor antagonist, PD-123319, or the Mas antagonist, A779, abolished the protective actions of C21. Conclusions and Implications Taken together, our results suggest that the AT(2) receptor agonist, C21, may hold promise for patients with PH.