Studies on the antihypertensive and antidyslipidemic activities of Viola odorata leaves extract

BACKGROUND: This study was undertaken to provide pharmacological basis for the medicinal use of Viola odorata Linn. in hypertension and dyslipidemia using the in vivo and in vitro assays. RESULTS: Viola odorata leaves extract (Vo.Cr), which tested positive for alkaloids, saponins, tannins, phenolics, coumarins and flavonoids, caused a dose-dependent (0.1-1.0 mg/kg) decrease in mean arterial blood pressure in anaesthetized rats. In isolated guinea-pig atria, Vo.Cr equally inhibited force and rate of spontaneous atrial contractions. On the baseline of rat thoracic aortae (endothelium-intact and denuded), the plant extract caused phentolamine-sensitive vasoconstriction. When tested on phenylephrine (PE, 1 μM) and K(+ )(80 mM)-induced vasoconstriction, Vo.Cr caused a concentration-dependent relaxation and also caused a rightward shift of Ca(++ )concentration-response curves as well as suppression of PE (1 μM) control peaks in Ca(++)-free medium, similar to that caused by verapamil. In the presence of L-NAME, the relaxation curve of Vo.Cr was partially inhibited showing involvement of Nitric oxide (NO) mediated pathway. In Tyloxapol-induced dyslipidemia, Vo.Cr caused reduction in total cholesterol and triglyceride levels. In high-fat diet-induced dyslipidemia model, the plant extract caused a significant decrease in total cholesterol, LDL-C, atherogenic index and prevented the increase in average body weights, while it increased HDL-C. CONCLUSIONS: These data indicate that the vasodilator effect of the plant extract is mediated through multiple pathways like inhibition of Ca(++ )influx via membranous Ca(++ )channels, its release from intracellular stores and NO-mediated pathways, which possibly explain the fall in BP. The plant also showed reduction in body weight and antidyslipidemic effect which may be due to the inhibition of synthesis and absorption of lipids and antioxidant activities. Thus, this study provides a pharmacologic rationale to the medicinal use of Viola odorata in hypertension and dyslipidemia.