Antihypertensive and vasorelaxant effects of ethanol extract of stem barks from Zanthoxylum rhoifolium Lam. in rats.

Administration of ethanol extract of stem bark from Z. rhoifolium (EEtOH-ZR) induced hypotension associated with a dual effect in heart rate in normotensive rats. This response was highlighted in spontaneously hypertensive rats (SHR). In rat superior mesenteric artery rings, the cumulative addition of EEtOH-ZR (0.1-750 microg/mL) on a phenylephrine-induced pre-contraction (10(-5) M) promoted a vasorelaxant effect by a concentration-dependent manner and independent of vascular endothelium. A similar effect was obtained on KCl-induced pre-contractions (80 mM). EEtOH-ZR attenuated contractions induced by cumulative addition of CaCl2 (10(-6)-3 x 10(-2) M) in depolarizing medium without Ca2+ only at 500 or 750 microg/mL. Likewise, on S-(-)-Bay K 8644-induced pre-contractions (10(-7) M), the EEtOH-ZR-induced vasorelaxant effect was attenuated. EEtOH-ZR (27, 81, 243 or 500 microg/mL) inhibited contractions induced by cumulative addition of phenylephrine (10(-9) - 10(-5) M) in endothelium-denuded preparations or by a single concentration (10(-5) M) in a Ca(2+)-free medium. The involvement of K+ channels was evaluated by tetraethylammonium (3 mM); the EEtOH-ZR-induced vasorelaxation was not attenuated. Thus, calcium influx blockade through voltage-operated calcium channels (CavL) and inhibition of calcium release from intracellular stores are probably underlying EEtOH-ZR-induced cardiovascular effects.