Vascular mechanisms underlying the hypotensive effect of &ITRumex acetosa&IT

Context: Rumex acetosa L. (Polygonaceae) is well known in traditional medicine for its therapeutic efficacy as an antihypertensive. Objective: The study investigates antihypertensive potential of crude methanol extract (Ra.Cr) and fractions of Rumex acetosa in normotensive and hypertensive rat models and probes the underlying vascular mechanisms. Materials and methods: Ra.Cr and its fractions were tested in vivo on normotensive and hypertensive Sprague-Dawley rats under anaesthesia for blood pressure lowering effect. In vitro experiments on rat and Oryctolagus cuniculus rabbit aortae were employed to probe the underlying vasorelaxant mechanism. Results: In normotensive rats under anaesthesia, Ra.Cr caused fall in MAP (40 mmHg) at 50 mg/kg with % fall of 27.88 +/- 4.55. Among the fractions tested, aqueous fraction was more potent at the dose of 50 mg/kg with % fall of 45.63 +/- 2.84. In hypertensive rats under similar conditions, extract and fractions showed antihypertensive effect at same doses while aqueous fraction being more potent, exhibited 68.53 +/- 4.45% fall in MAP (70 mm Hg). In isolated rat aortic rings precontracted with phenylephrine (PE), Ra.Cr and fractions induced endothelium-dependent vasorelaxation, which was partially blocked in presence of L-NAME, indomethacin and atropine. In isolated rabbit aortic rings pre-contracted with PE and K+ -(80 mM), Ra.Cr induced vasorelaxation and shifted Ca2+ concentration-response curves to the right and suppressed PE peak formation, similar to verapamil, in Ca2+-free medium. Discussion and conclusions: The data indicate that L-NAME and atropine-sensitive endothelial-derived NO and COX enzyme inhibitors and Ca2+ entry blocking-mediated vasodilator effect of the extract explain its antihypertensive potential.