Vasodilating effect of Hypericum revolutum (Vahl) (Clusiaceae) methanol extract in rats

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Purpose: To investigate the vasodilating effect of Hypericum revolutum Vahl (Clusiaceae) in rats. Methods: H. revolutum aerial parts were extracted with methanol. The total methanol extract was fractionated with chloroform to yield fraction I. The remaining aqueous solution was chromatographed on Diaion HP-20 using water, 50 % methanol, and methanol to yield three fractions (II- IV). Total methanol extract and fractions I-IV were applied to phenylephrine-pre-contracted (10 μM) rat aortic rings at doses of 1, 3, and 10 μg/mL. Subsequent decreases in aortic tension were recorded by an isometric force transducer to evaluate the vasodilation. Column chromatography was utilized to separate the active components of the bioactive fraction. Results: Remarkable decreases in aortic tension (p<0.05) revealed that fraction I (3 and 10 μg/mL) produced a vasodilating effect, whereas fractions III and IV did not possess any substantial effect. Vasodilation induced by fraction I was endothelial-dependent because it was significantly (p<0.05) blocked by endothelial denudation. Phytochemical inspection of fraction I led to the isolation of β- sitosterol (1), 1,7-dihydroxyxanthone (euxanthone) (2), and 2,3,4-tirmethoxy xanthone (3). Conclusion: Fraction I of the H. revolutum extract was responsible for its vasodilating effect. This fraction may be used as a possible anti-hypertensive preparation after in vivo testing and successful clinical trials.

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