Aged garlic extract exerts endothelium-dependent vasorelaxant effect on rat aorta by increasing nitric oxide production

Abstract Background Clinical trials have shown that aged garlic extract (AGE) is effective in reducing blood pressure of hypertensive patients. However, the mechanisms involved remain to be elucidated. Purpose The aim of the present study was to investigate the vasorelaxant effect of AGE on the aorta and its mechanism of action in order to clarify the blood pressure-lowering action of AGE. Methods The vasorelaxant effect was evaluated in isolated rat aortic rings. After aortic rings were contracted by 3 × 10 −6  M norepinephrine (NE) for 30 min, AGE and other test drugs were added to the aortic rings. All results were expressed as percentages of the maximal NE-induced contraction. Results AGE induced the concentration–dependent vasorelaxation of isolated rat aortic rings that had been precontracted with norepinephrine. The effect of AGE was severely impaired in aortic rings lacking endothelium. In addition, the effect of AGE was inhibited by a nitric oxide synthase (NOS) inhibitor and a nitric oxide (NO) scavenger. Moreover, AGE treatment of aorta significantly increased the NO production. When various constituents of AGE were tested, the vasorelaxation of aorta was observed only in the presence of L-arginine, a substrate of NOS. Conclusion AGE causes endothelium-dependent vasorelaxation of aorta via stimulation of NO production and that L-arginine in AGE serves as a key agent for NOS-mediated NO production.