Mechanism of Endothelium-Dependent Vasodilation Induced by a Proanthocyanidin-Rich Fraction from Ouratea semiserrata

Abstract

The vasodilator effects of Ouratea semiserrata stem hydroethanolic extract (OSE) and its ethyl acetate fraction (OSR) were evaluated in endothelium-intact aortic rings. OSR produced a more potent vasodilatation (IC₅₀ = 3.5 ± 0.8 μg/ml) than OSE (IC₅₀ > 30 μg/ml). OSR also presented a higher content of total proanthocyanidins (21.8 ± 1.5 %) in comparison to OSE (6.5 ± 0.4 %), suggesting that compounds of this class play a role in the vasorelaxing activity. The vasodilatation mechanism of OSR was further investigated. In endothelium-intact aortic rings, its vasorelaxing effect was completely abolished by L-NAME (300 μM), a nitric oxide (NO) synthase inhibitor, but not by a muscarinic antagonist (atropine, 1 μM) nor by a cyclo-oxygenase inhibitor (indomethacin, 10 μM). The OSR vasodilator effect was completely abolished in endothelium-denuded vessels. Furthermore, OSR did not change the vasodilatation produced by SIN-1, an NO donor, in endothelium-denuded vessels. These findings led us to conclude that OSR, a proanthocyanidin rich fraction of O. semiserrata, induces vasodilatation by a mechanism dependent on endothelium-derived factors, likely NO.

Key words

Ouratea semiserrata - Ochnaceae - proanthocyanidin-rich fraction - vasodilator effects - rat aorta - nitric oxide

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