title: Gynura procumbens Merr. decreases blood pressure in rats by vasodilatation via inhibition of calcium channels.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia. hoesz@ummc.edu.my
authors: See-Ziau
authors: SZ
authors: Hoe
authors: Chen-Neng
authors: CN
authors: Lee
authors: Shiueh-Lian
authors: SL
authors: Mok
authors: Mohd Yusoff
authors: MY
authors: Kamaruddin
authors: Sau-Kuen
authors: SK
authors: Lam
mesh_terms: D000818:Animals; D019659:Asteraceae / Q000737:chemistry*; D001794:Blood Pressure / Q000187:drug effects*; D000440:Butanols / Q000494:pharmacology*; D002118:Calcium / Q000032:analysis; D002121:Calcium Channel Blockers / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves; D011188:Potassium / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D000440:Butanols; D002121:Calcium Channel Blockers; D010936:Plant Extracts; D014665:Vasodilator Agents; D011188:Potassium; D002118:Calcium