In our study, we did not observe altered expression of DHPR or BH4 in aorta of SHR, but if we consider that hypertension and arterial stiffness are associated with reduction of NO bioavailability (induced by RhoA/Rho-kinase pathway activation or increases of ROS), we may hypothesize that increases in NO, due to perindopril treatment (indicated by the plasma nitrite concentration), could be involved in the PWV reduction observed in the present study in treated SHR (SHRP). The gene discussed is RHOA; the disease is hypertensive disorder.