Olmesartan reduces oxidative stress in the brain of stroke-prone spontaneously hypertensive rats assessed by an in vivo ESR method

We previously showed that oxidative stress in the brain is involved in the neural mechanisms of hypertension. Therefore, olmesartan, an angiotensin type 1 receptor blocker, might affect oxidative stress in the brains of stroke-prone spontaneously hypertensive rats (SHRSP). Here, we evaluated the effects of olmesartan treatment using an in vivo electron spin resonance (ESR)/spin probe technique. Two groups of SHRSP were treated with either olmesartan (10 mg kg(-1) day(-1)) or hydralazine (Hyd, 20 mg kg(-1) day(-1))/hydrochlorothiazide (HCT, 4.5 mg(-1) kg day(-1)) for 30 days (n=5 for each). Systolic blood pressure decreased similarly in both groups after treatment. Heart rate and urinary norepinephrine (NE) excretion increased in rats treated with Hyd/HCT, but not in those treated with olmesartan. The in vivo ESR signal decay rates of the blood-brain barrier-permeable spin probe methoxycarbonyl-PROXYL were significantly higher in SHRSP brains than in age-matched normotensive Wistar-Kyoto rat brains (P<0.01; n=6 for each). Olmesartan attenuated the ESR signal decay rates in SHRSP brains, but Hyd/HCT did not. Intracerebroventricular infusion of active form of olmesartan, RNH-6270, reduced blood pressure and NE excretion, and the ESR signal decay rate was reduced in SHRSP brains. These findings indicate that olmesartan has anti-oxidative property in the brain without stimulating reflex-mediated sympathetic activity in SHRSP. Hypertension Research (2009) 32, 1091-1096; doi: 10.1038/hr.2009.160; published online 18 September 2009