Vasodilator Effect of Phlomis bracteosa Constituents Is Mediated through Dual Endothelium-Dependent and Endothelium-Independent Pathways

Abstract

This study describes the vasorelaxant potential of some pure compounds isolated from Phlomis bracteosa L.: marrubiin, phlomeoic acid, and two new constituents labeled as RA and RB. In rat thoracic aortic rings denuded of endothelium, marrubiin, phlomeoic acid, RA, and RB caused relaxation of high K⁺ (80 mM) and phenylephrine (1 μM)-induced contractions at the concentration range of 1.0–1000 μg/mL. Marrubiin, phlomeoic acid, RA, and RB concentration dependently (3.0–10 μg/mL) shifted the Ca⁺⁺ curves to the right obtained in Ca⁺⁺-free medium. The vasodilator effect of marrubiin, phlomeoic acid, RA, and RB was partially blocked by N_ω-nitro-L-arginine methyl ester in endothelium-intact aorta preparations. These results reveal that P. bracteosa constituents: marrubiin, phlomeoic acid, RA, and RB exhibit vasodilator action occurred via a combination of endothelium-independent Ca⁺⁺ antagonism and endothelium-dependent N_ω-nitro-L-arginine methyl ester-sensitive nitric oxide-modulating mechanism.

• Phlomis bracteosa compounds
• vasodilatation
• Ca⁺⁺ channel inhibition
• nitric oxide modulation

ACKNOWLEDGMENTS

This study was carried out with partial financial support from the University of Malaya (RG140/2009HTM). The author, Arif-ullah Khan, is on leave from Kohat University of Science and Technology, Kohat, Pakistan, and is a recipient of Post-Doctoral Research Fellowship at the University of Malaya.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.