Effects of Angiotensin II Type 1 Receptor Blockade on the Systemic Blood Nitric Oxide Dynamics in N ω -Nitro- L -Arginine Methyl Ester–Treated Rats

We previously succeeded in measuring the nitrosylhemoglobin (HbNO) level as an index of blood nitric oxide (NO) by the electron paramagnetic resonance (EPR) HbNO signal subtraction method. In this study, we examined the effects of olmesartan, an angiotensin II type 1 receptor blocker (ARB), on NO dynamics in Nω-nitro-L-arginine methyl ester (L-NAME)−treated rats by the EPR-subtraction method. Oral administration of L-NAME for 2 weeks induced serious hypertension, and the HbNO concentration was reduced to 37.6% of the level in controls. Coadministration of olmesartan improved hypertension and increased the blood HbNO concentration of L-NAME–treated rats. In contrast, coadministration of hydralazine improved hypertension but did not affect the blood HbNO concentration. In conclusion, our findings suggested that chronic administration of olmesartan ameliorated the endothelial dysfunction in L-NAME–treated rats.