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 angiotensinconverting 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 × 10⁻²M) 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.