The possible counteracting effect of angiotensin (Ang)-converting enzyme (ACE)2/Ang-(1-7)/Mas axis against the ACE/Ang II/Ang II type 1 (AT1) receptor axis in blood pressure control has been previously described. We examined the possibility that this pathway might be involved in the anti-hypertensive effect of a newly developed AT1 receptor blocker (ARB), azilsartan, and compared azilsartan's effects with those of another ARB, olmesartan. Transgenic mice carrying the human renin and angiotensinogen genes (hRN/hANG-Tg) were given azilsartan or olmesartan. Systolic and diastolic blood pressure, as determined by radiotelemetry, were significantly higher in hRN/hANG-Tg mice than in wild-type (WT) mice. Treatment with azilsartan or olmesartan (1 or 5 mg kg(-1) per day) significantly decreased systolic and diastolic blood pressure, and the blood pressure-lowering effect of azilsartan was more marked than that of olmesartan. The urinary Na concentration decreased in an age-dependent manner in hRN/hANG-Tg mice. Administration of azilsartan or olmesartan increased urinary Na concentration, and this effect was weaker with olmesartan than with azilsartan. Azilsartan decreased ENaC-α mRNA expression in the kidney and decreased the ratio of heart to body weight. Olmesartan had a similar but less-marked effect. ACE2 mRNA expression was lower in the kidneys and hearts of hRN/hANG-Tg mice than in WT mice. This decrease in ACE2 mRNA expression was attenuated by azilsartan, but not by olmesartan. These results suggest that the hypotensive and anti-hypertrophic effects of azilsartan may involve activation of the ACE2/Ang-(1-7)/Mas axis with AT1 receptor blockade.