Hypotensive and endothelium-independent vasorelaxant effects of methanolic extract from Curcuma longa L. in rats

Ethnopharmacological relevanceCurcuma longa L. (CL) is a yellow rhizome that is used in African traditional medicine to treat palpitation, hypertension or other related blood circulation disorders.Aim of the studyTo justify the use of CL in ethnomedicine, we investigated the vasorelaxant effect of methanolic extract of CL (CLME) and its underlying mechanisms in isolated rat mesenteric artery.Materials and methodsThe effect of CLME on the mean arterial pressure (MAP) and heart rate (HR) (pulse interval) were determined in vivo in non-anaesthetized rats. Superior mesenteric rings were isolated, suspended in organ baths containing Tyrode solution at 37 °C and gassed with 95% O2 + 5% CO2, under a resting tension of 0.75 g. The vasorelaxant effects of CLME were studied by means of isometric tension recording experiments.ResultsIn normotensive rats, CLME (10, 20 and 30 mg/kg, i.v.) induced dose-dependent hypotension (2.0 ± 0.5%; 27.1 ± 5.0% and 26.7 ± 4.6%, respectively), and pronounced bradycardia (5.8 ± 1.2%, 19.3 ± 3.2% and 22.9 ± 4.6%, respectively). CLME (1–1000 μg/mL) induced concentration-dependent relaxation of tonic contractions evoked by phenylephrine (Phe) (10 μM) and KCl (80 mM) in rings with intact-endothelium (Emax = 82.3 ± 3.2% and 97.7 ± 0.7%) or denuded-endothelium (Emax = 91.4 ± 1.0% and 97.8 ± 1.1%). Also, in a depolarized, Ca2+ free medium, CLME inhibited CaCl2 (1 μM–30 mM)-induced contractions and caused a concentration-dependent rightward shift of the response curves, indicating that CLME inhibited the contractile mechanisms involving extracellular Ca2+ influx. In addition, in Ca2+ free media containing EGTA (1 mM), CLME inhibited the transient contraction of denuded rings constricted with Phe, but not those evoked by caffeine (20 mM). In contrast, neither glibenclamide, BaCl2, tetraethylammonium nor 4-aminopyridine affected CLME-induced relaxation.ConclusionsThese results demonstrate the hypotensive and bradycardic effects of CLME, as well as its potent vasodilation of rat mesenteric arteries. These effects, may in part, be due to the inhibition of extracellular Ca2+ influx and/or inhibition of intracellular Ca2+ mobilization from Phe-sensitive stores.