Antihypertensive and vasodilator actions of antioxidants in spontaneously hypertensive rats

This study was designed to determine whether the antioxidants ascorbic acid , aminotriazole, and glutathione acutely reduce blood pressure (BP) by endo thelium-independent or -dependent vasorelaxation in spontaneously hypertens ive rats. Blood pressure of male Wistar-Kyoto (WKY) and spontaneously hyper tensive rats (SHR) was measured before and 4 h after administration of anti oxidants. Thoracic aortic rings with and without endothelium were suspended in organ chambers for isometric tension recordings. Each of the antioxidan ts, administered in vivo, significantly decreased blood pressure in SHR but had no significant effect on BP in WKY rats. The endothelium-dependent imp aired relaxation of SHR aortic rings to acetylcholine (ACh) was improved by prior in vivo administration of each antioxidant, ACh-induced relaxations of aortic rings from WKY was not affected by prior antioxidant treatment. A ddition of each antioxidant directly to the organ chamber containing SHR or WKY aortas produced dose- and endothelium-dependent relaxations. Moreover, antioxidant pretreatment of SHR aortic rings significantly potentiated ACh -induced relaxations in these aortas, suggesting that this effect was endot helium dependent. Relaxations induced by the antioxidants alone or by ACh i n the presence of antioxidants were inhibited by addition of either xanthin e plus xanthine oxidase or nitro-L-arginine. These findings suggest that ei ther excess production of oxidants or a deficiency of antioxidant systems m ay contribute to the high blood pressure and the endothelium-dependent impa irment of vascular relaxation in SHR. (C) 1998 American Journal of Hyperten sion, Ltd.