Biphasic effect of Psidium guajava Linn. (Myrtaceae) leaf aqueous extract on rat isolated vascular smooth muscles

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概要

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• In this study, we examined the effects of iPsidium guajava/i Linn. leaf aqueous extract (PGE) on isolated, spontaneously-contracting portal veins, as well as on endothelium-intact and endothelium-denuded descending thoracic aortic ring preparations of healthy, normotensive rats. Graded concentrations of PGE (0.25-4.0 mg/ml) caused concentration-dependent, initial brief but significant (iP/i0.05) rises of the basal tones and amplitudes of pendular, rhythmic contractions, followed by secondary pronounced, longer-lasting and significant (iP/i0.05-0.001) inhibitions of contractile amplitudes of the isolated portal veins. Relatively low concentrations of PGE (1.0 mg/ml) always contracted freshly-mounted, naïve, endothelium-intact aortic ring preparations. However, relatively high concentrations of PGE (1.0-4.0 mg/ml) always produced initial brief contractions/augmentations of noradrenaline (NA, 10sup-7/supM)-induced contractions of endothelium-intact and endothelium-denuded aortic ring preparations, followed by secondary, pronounced relaxations of the aortic ring muscles. Moreover, relatively high concentrations of PGE (1.0-4.0 mg/kg) always relaxed NA-induced contractions of the aortic ring preparations in a concentration-related manner. The arterial-relaxing effects of PGE were more pronounced in endothelium-intact aortic rings than in endothelium-denuded aortic ring preparations. The relaxant effects of PGE on endothelium-intact aortic rings were only partially inhibited by NsupG/sup-nitro-L-arginine methyl ester (L-NAME, 100 μM), a nitric oxide synthase inhibitor, suggesting that the vasorelaxant effect of PGE on aortic rings is probably mediated via both endothelium-derived relaxing factor (EDRF)-dependent and EDRF-independent mechanisms. Taken together, the findings of this study indicate that PGE possesses a biphasic effect on rat isolated vascular smooth muscles.br

著者

• Ojewole John

  Department Of Pharmacology Faculty Of Health Sciences University Of Kwazulu-natal

• Chiwororo Witness

  Department of Pharmacology, School of Pharmacy & Pharmacology, Faculty of Health Sciences, University of KwaZulu-Natal

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