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Ethnopharmacological Relevance: Achillea millefolium L. (Asteraceae), known as yarrow (milenrama), is a plant used in Mexican traditional medicine for the treatment of hypertension, diabetes, and related diseases., Aim: To determine the vasorelaxant and antihypertensive effect of A. millefollium and to isolate the main bioactive antihypertensive agents., Materials and Methods: Organic (hexane, dichloromethane and methanol) and hydro-alcohol (Ethanol-H 2 O: 70:30) extracts obtained from flowers, leaves and stems were evaluated on isolated aorta rat rings with and without endothelium to determine their vasorelaxant effect. Hexane extract from flowers (HEAmF) was studied to evaluate its antihypertensive effect on spontaneously hypertensive rats (SHR). From HEAmF, bioactive compounds were obtained by bio-guided phytochemical separation through chromatography., Results: Organic extracts showed the best vasorelaxant activity. Hexane extract from flowers was the most potent and efficient ex vivo vasorelaxant agent, showing significant decrease of systolic and diastolic blood pressure in SHR (p < 0.05). Phytochemical separation of HEAmF yielded two epimeric sesquiterpene lactones: leucodin (1) and achillin (2), the major components of the extract. Both 1 and 2 showed similar vasorelaxant action ex vivo (p < 0.05), and their effects where modified by L-NAME (10 μM, nitric oxide synthase inhibitor), by ODQ (1 μM, soluble guanylyl cyclase inhibitor), and also relaxed the contraction induced by KCl (80 mM). Finally, 1 and 2 intragastric administration (50 mg/kg) decreased systolic and diastolic blood pressure in SHR., Conclusions: Achillea millefolium showed antihypertensive and vasorelaxant effects, due mainly to leucodin and achillin (epimers). Both compounds showed antihypertensive activity by vasorelaxation putatively by endothelium-dependent NO release and cGMP increase, as well as by calcium channels blockade., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Ethnopharmacological Importance: Achillea millefolium L. (Asteraceae) is used for the treatment of respiratory diseases, diabetes, and hypertension., Aim: to explore its tracheal relaxant properties and clarify its functional mechanism of action on smooth muscle cells, which allow us to propose it as a potential anti-asthmatic drug., Material and Methods: organic and hydro-alcoholic extracts from A. millefolium were obtained by macerations, then their relaxing effect on ex vivo isolated rat trachea rings was determined. Most active extract (hexanic extract, EHAm) was studied to determine its functional mechanism of action using synergic, antagonist and inhibitor agents related with the contraction/relaxation process of the smooth muscle. Also, EHAm was subjected to bio-guided fractionation by open-column chromatography (on silica gel) using cyclohexane-EtOAc (80:20) in an isocratic way to isolate main bioactive compounds., Results: organic and hydro-alcoholic extracts showed relaxant effect in a concentration-response dependent manner, being EHAm the most active. The functional mechanism of action indicates that EHAm induced a non-competitive antagonism to the muscarinic receptors ; in addition, the NO/cGMP pathway is involved in the relaxation process of the tracheal smooth muscle. However, the most important mechanism of action showed by EHAm was related with the calcium channel blockade influx into the smooth muscle cells. On the other hand, epimeric sesquiterpene lactones leucodin (1) and achillin (2) were isolated and purified, which are responsible for the observed smooth muscle relaxant activity of the extract., Conclusion: hexanic extract of A. millefollium induced a significant relaxant effect on tracheal rat rings by calcium channel blockade and NO release., Competing Interests: Declaration of competing interest The authors declare no conflict of interest. Author contributions to the paper were as follows: Extracts preparation, and leucodin and achillin isolation: L. A-D., M. H-M, F. Ch-S. Structural elucidation: G. N–V., I. L-R. Pharmacological evaluation: R. V-M., M. I–B., L. A-D., S. E-S. Identification and recollection of plant material: I. P-A. Study design: S. E-S. Manuscript preparation: all authors. Notes: The authors declare no competing financial interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)