title: Biphasic effect of Psidium guajava Linn. (Myrtaceae) leaf aqueous extract on rat isolated vascular smooth muscles.
abstract: In this study, we examined the effects of Psidium guajava 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 (P<0.05) rises of the basal tones and amplitudes of pendular, rhythmic contractions, followed by secondary pronounced, longer-lasting and significant (P<0.05-0.001) 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, 10(-7)M)-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 N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM), 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.
authors.affiliation: Department of Pharmacology, University of KwaZulu-Natal, Durban, South Africa.
authors.forename: Witness D H
authors.initials: WD
authors.lastname: Chiwororo
authors.forename: John A O
authors.initials: JA
authors.lastname: Ojewole
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D045462:Endothelium-Dependent Relaxing Factors / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves; D011169:Portal Vein / Q000187:drug effects / Q000502:physiology; D031647:Psidium; D051381:Rats; D017208:Rats, Wistar
chemical_list: D045462:Endothelium-Dependent Relaxing Factors; D004791:Enzyme Inhibitors; D010936:Plant Extracts; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine