Hypotensive effect of the water extract of the leaves of Pseuderanthemum palatiferum

The cardiovascular effects of the water extract from fresh leaves of P. palatiferum (PP) were evaluated in rats in both in vivo and in vitro models. The PP extract consisted of alkaloids, coumarins and sterols. The extract (5–25 mg/kg, I.V.) decreased both the mean arterial blood pressure and heart rate of normotensive and l-N-(ω)-nitro-arginine methyl ester (l-NAME)-induced hypertensive anesthetized rats. The extract caused relaxation of the norepinephrine-contracted endothelium-intact aorta ring (EC₅₀ = 81.0 μg/mL). Functional removal of the endothelium attenuated the vasodilatation effect of the extract (EC₅₀ = 136.4 μg/mL). Pretreatment with l-NAME or atropine did not alter the vasodilation effect of the extract. Pre-incubation with atropine did not alter bradycardic effect of the extract on isolated rat atrium. The effects of isoproterenol on isolated atrium were attenuated by the extract (2.5–5 mg/mL). In conclusion, the water extract from fresh leaves of P. palatiferum possessed hypotensive and bradycardic effects. The vasorelaxant effect of the extract was dependent partly on the vascular endothelium but was not dependent on the synthesis of nitric oxide and did not act through activation of the muscarinic receptor.