Effects of the oral angiotensin II type 2 receptor agonist C21 in Sugen-hypoxia induced pulmonary hypertension in rats

Substantial evidence supports involvement of the renin-angiotensin system
in pulmonary hypertension (PH), and the angiotensin II type 2 receptor
(AT2R) is known to exert tissue-protective actions. The effect of the
selective AT2R agonist C21 (also known as Compound 21 or buloxibutid) was
evaluated in the rat Sugen-hypoxia PH model. After a single injection of
Sugen 5416 and hypoxia for 21 days, C21 (2 or 20 mg/kg) or vehicle was
administered perorally twice daily from Day 21 to Day 55. On Day 56,
hemodynamic assessments were performed, and lung and heart tissue were
prepared for quantification of cardiac and vascular remodeling and
fibrosis. Treatment with C21 20 mg/kg improved cardiac output and stroke
volume and decreased right ventricular hypertrophy (all p<0.05).
Treatment with C21 2 mg/kg significantly decreased vessel wall and
muscular layer thickness and increased the luminal opening in vessels
>100 μm (all p<0.05). There were no significant differences
between the two C21 doses on any parameter, and post hoc analyses
comparing the merged C21 groups with the vehicle group showed that C21
treatment reduced vascular remodeling (reduced endothelial proliferation
and thickening of the vascular wall) in vessels of all sizes; moreover,
the diastolic pulmonary artery pressure and right ventricular pressure
were reduced along with reduction of right ventricular hypertrophy. Sugen
5416 and hypoxia increased pulmonary collagen deposition, which was
counteracted by C21 20 mg/kg. In conclusion, the effects of C21 on
vascular remodeling, hemodynamic alterations, and fibrosis suggest that
AT2R agonists may have a role in Group 1 and 3 PH treatment.