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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 (EC(50) = 81.0 μg/mL). Functional removal of the endothelium attenuated the vasodilatation effect of the extract (EC(50) = 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.

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The objectives of this study were to assess acute and ninety-day oral toxicity of the water extract from the fresh leaf of P. palatiferum in rats. Acute oral toxicity study was conducted by a single administration 2,000 mg/kg of the water extract to female rats. The clinical signs related to toxic effects and the mortality of the rats were observed for a 14-day further. Repeated dose oral toxicity study was performed in both sexes of rats by giving 1,000 mg/kg of the extract once daily for 90 days. The toxic signs and health of the animals were monitored. At the end of the study, blood and the internal organs were collected for chemistry assay and the histopathological examination, respectively. The results revealed no significant difference between the control and treated rats in the acute oral toxicity study. There was no death of animals during 90-day orally given the water extract. All assessed parameters were similar to those of the control rats and were within the normal range. No significant pathologic feature and no difference between the groups of the animals were observed. In conclusion, the water extract of the fresh leaf of P. palatiferum at the single oral dose of 2,000 mg/kg produces neither any acute toxicity signs nor mortality in female rats. The daily dose of 1,000 mg/kg of the extract repeated administration for 90 days reveals well tolerance and safety profile in both sexes of rats.