Severe vitamin D (vitD) deficiency is a very common condition in patients with pulmonary arterial hypertension (PAH) and it is predictor of poor prognosis. There is emerging evidence suggesting a connection between the insufficient response to phosphodiesterase-5 inhibitors (PDE5i) and vitD deficiency in patients with PAH. In the present translational study, vitD deficiency was induced in Wistar rats by exposure to vitD free diet for 5 weeks and followed by Su5416 administration and hypoxia (10%) for 3 weeks, a standard experimental model of PAH. Then rats were randomized to either 1) the PDE5i tadalafil and continuing vitD free diet, or 2) tadalafil plus a single dose of vitD and standard diet for four weeks. VitD supplementation improved exercise capacity and right ventricular function and decreased systolic right ventricular pressure, right atrial hypertrophy, right ventricular hypertrophy, and pulmonary arterial remodeling. VitD improved the ex vivo endothelium-dependent response to acetylcholine, indicating an improvement NO bioavailability, which also resulted in an acute ex vivo response to sildenafil. Thus, the restoration of vitD, by rescuing endothelial function and PDE5i effectiveness, significantly improved the histological, hemodynamic, and functional features of rats with PAH. VitD may be especially beneficial for PDE5i treated PAH patients.

Keywords: phosphodiesterase-5 inhibitor; pulmonary arterial hypertension; right ventricle; vascular disease; vitamin D.