Gynura procumbens Merr. decreases blood pressure in rats by vasodilatation via inhibition of calcium channels

INTRODUCTION: Gynura procumbens has been shown to decrease blood pressure via inhibition of the angiotensin‐converting enzyme. However, other mechanisms that may contribute to the hypotensive effect have not been studied. OBJECTIVES: To investigate the cardiovascular effects of a butanolic fraction of Gynura procumbens in rats. METHODS: Anaesthetized rats were given intravenous bolus injections of butanolic fraction at doses of 2.5–20 mg/kg in vivo. The effect of butanolic fraction on vascular reactivity was recorded in isolated rat aortic rings in vitro. RESULTS: Intravenous administrations of butanolic fraction elicited significant (p<0.001) and dose‐dependent decreases in the mean arterial pressure. However, a significant (p<0.05) decrease in the heart rate was observed only at the higher doses (10 and 20 mg/kg). In isolated preparations of rat aortic rings, phenylephrine (1×10(‐6) M)‐ or potassium chloride (8×10(‐2) M)‐precontracted endothelium‐intact and ‐denuded tissue; butanolic fraction (1×10(‐6)–1×10(‐1) g/ml) induced similar concentration‐dependent relaxation of the vessels. In the presence of 2.5×10(‐3) and 5.0×10(‐3) g/ml butanolic fraction, the contractions induced by phenylephrine (1×10(‐9)–3×10(‐5) M) and potassium chloride (1×10(‐2)–8×10(‐2) M) were significantly antagonized. The calcium‐induced vasocontractions (1×10(‐4)–1×10(‐2) M) were antagonized by butanolic fraction concentration‐dependently in calcium‐free and high potassium (6×10(‐2) M) medium, as well as in calcium‐ and potassium‐free medium containing 1×10(‐6) M phenylephrine. However, the contractions induced by noradrenaline (1×10(‐6) M) and caffeine (4.5×10(‐2) M) were not affected by butanolic fraction. CONCLUSION: Butanolic fraction contains putative hypotensive compounds that appear to inhibit calcium influx via receptor‐operated and/or voltage‐dependent calcium channels to cause vasodilation and a consequent fall in blood pressure.