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 endotheliumintact 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 endotheliumdenuded 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 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.

Comparative study of the antihypertensive effects of hexane, chloroform and methanol fractions of essential oil of Alpinia zerumbet in rats Wistar

“…Biphasic effect has been identified in other studies with herbal products that evaluated vasodilator activity of natural substances extracted from plants. Regarding this effect, the authors mentioned that it was due to a transient increase in Ca 2+ influx from the extracellular medium (Chiwororo & Ojewole, 2008;Zhang et al, 2010).…”

Health Effects of Psidium guajava L. Leaves: An Overview of the Last Decade

“…The work concluded that the activity may be related to rosmarinic acid, eugenol, carvacrol, catechin, and caffeic acid since they were the major constituents of their extracts. In addition, this activity was supported by the biphasic and contractile effect on rat vascular smooth muscles [119,120]. …”

The prolactin family hormones regulate vascular tone through NO and prostacyclin production in isolated rat aortic rings

“…In that study, the vasodilatory effect exerted On the other hand, successive doses of PRL precipitated a biphasic effect. It has been reported that different molecules [59,60] including hormones [61] , exert dual effects comparable with the effects exerted by PRL; for example, angiotensin II causes transient coronary constriction and exerts positive inotropic effects in some cardiovascular models [62,63] as a result of either progressive endothelial angiotensin I receptor internalization or receptor desensitization [64] , effects associated with tachyphylaxis. In our study, both the effects of the successive doses of PRL and the decreased vasodilation induced by the first PRL dose may be related to an endothelial desensitization process, as cumulative doses of PRL did not exert direct effects on aortic smooth muscle.…”