Endothelium mediated vasorelaxant response of garlic in isolated rat aorta: role of nitric oxide.

The vasorelaxant effect of garlic (Alium sativum L.) has been suggested to be partially mediated through endothelium. The present study was designed to evaluate the role of various endothelium-mediated mechanisms in vasorelaxant response of garlic on isolated aortic rings of rats. In tissues precontracted with phenylephrine (PE) 10(-6)M, concentration-response curve for different concentrations of garlic (1, 5, 10, 20 and 50 microg/ml) was examined. In all the preparations garlic showed a concentration-dependent vasorelaxant response. There was a significant attenuation of vasorelaxation in tissues pretreated with K(+) channel blocker, glybenclamide (10(-6)M). Indomethacin (10(-5)M) enhanced the relaxant response of garlic. N(G)-Monomethyl-L-arginine (L-NMMA) 30 microM, a potent inhibitor of nitric oxide synthase, did not produce any significant effect on the response of garlic. However, cGMP blocker methylene blue (10(-5)M) showed a strong vasoconstriction and inhibited the vasorelaxant response of garlic. The results indicate that endothelium modulated vasorelaxation of garlic is partly mediated through EDHFs and cycloxygenase pathways. However, relaxing factor(s) other than NO, mediated through cGMP has a major role in the vasorelaxant response of garlic.