Abstract: The aim of this study was to investigate the antioxidant and vasodilatative effects of Hyssopus officinalis essential oil (HEO) on thoracic aorta rings in vitro and to elucidate the possible mechanism.The antioxidant properties of HEO were evaluated by different antioxidant tests,including 2,2 diphenyl-2-bitter hydrazo (DPPH) scavenging ability and pyrogallol autoxidation.The thoracic aorta was isolated from male Sprague-Dawley (SD) rats,the isometric tension of aortic rings with or without endothelium was measured.The recording changes in vascular tone were measured by BL-420 bio-functional experiment system.HEO had a certain ability to scavenge free radicals,the maximum scavenging rates on DPPH radical and pyrogallol radical were 19.24% and 11.44%,respectively.HEO (100-1100 mg/L) produced concentration-dependent,endothelium-independent relaxations in phenylephrine (PE)-contracted aortic rings.As a result,the maximum relaxation by HEO was 96.34%±5.13% in endothelium intact rings and 94.39%±8.95% in endothelium removed rings.HEO pre-treatment significantly inhibited vasoconstrictions to Dopamine (Dopa),potassium ions (K⁺) and PE by 74.38% ,89.91% and 95.81%,respectively (P<0.01).Compared with the control group,HEO markedly inhibited potassium-stimulated Ca²⁺-dependent contraction which mainly due to Ca²⁺ influx (P<0.01).In conclusion,HEO had partly antioxidant activities and relaxed the isometric tension of aortic rings in an endothelium-independent manner,mainly through interfering intracellular calcium homeostasis by blocking Ca²⁺ influx and intracellular Ca²⁺ release,as well as inhibiting the vascular contraction by partial of the vasoconstrictor.

Key words: Hyssopus officinalis, antioxidant, vasodilation, calcium channel, pyrogallol self-oxidation