Evaluation of antioxidant, ACE inhibitory and vasorelaxant activities of Murraya siamensis leaf extract

Murraya siamensis Craib (Rutaceae) is a small shrub found in Asia, and its leaves have long been used for the treatment of various ailments.Nevertheless, the pharmacological activity of this plant is less documented.This study aimed to elucidate the antioxidant and angiotensin-converting enzyme (ACE) inhibitory properties of the ethanolic extract of M. siamensis leaves (MSE) and to explore the vasorelaxant effect of MSE and its underlying mechanisms.The antioxidant activity of MSE was evaluated by DPPH and ABTS radical scavenging assays, and its ACE-inhibitory activity was measured by the spectrophotometric method.Additionally, the vasorelaxant activity of MSE was determined on thoracic aortic segments isolated from Sprague Dawley rats.Results showed that MSE exhibited DPPH and ABTS scavenging activity with IC50 values of 710±10 and 488±20 µg/mL, respectively.MSE also showed ACE inhibitory activity with IC50 values of 1.01±0.02mg/mL.Additionally, MSE (0.1-1 mg/mL) elicited a concentration-dependent relaxation in both endothelium-intact and -denuded aortic rings.The relaxant response to MSE was partially inhibited by pretreatment with tetraethylammonium or 4-aminopyridine but not in the presence of barium chloride or glibenclamide.Additionally, MSE (1 mg/mL) completely inhibited phenylephrine (PE)-induced transient contraction and abolished CaCl2-induced contraction in the aortic rings pretreated with PE or 60 mM KCl.These results suggest that MSE has antioxidant and ACE inhibitory activities.Additionally, MSE exerts endothelium-independent vasorelaxant effects in the rat aorta through inhibiting intracellular Ca 2+ release and extracellular Ca 2+ influx via voltage-dependent and receptor-operated Ca 2+ channels and opening KCa and KV channels.