Vasorelaxant properties of Vernonia amygdalina ethanol extract and its possible mechanism

Abstract

Context: Vernonia amygdalina Del. (VA) (Asteraceae) is commonly used to treat hypertension in Malaysia.

Objective: This study investigates the vasorelaxant mechanism of VA ethanol extract (VAE) and analyzes its tri-step FTIR spectroscopy fingerprint.

Materials and methods: Dried VA leaves were extracted with ethanol through maceration and concentrated using rotary evaporator before freeze-dried. The vasorelaxant activity and the underlying mechanisms of VAE using the cumulative concentration (0.01–2.55 mg/mL at 20-min intervals) were evaluated on aortic rings isolated from Sprague Dawley rats in the presence of antagonists.

Results: The tri-step FTIR spectroscopy showed that VAE contains alkaloids, flavonoids, and saponins. VAE caused the relaxation of pre-contracted aortic rings in the presence and absence of endothelium with EC₅₀ of 0.057 ± 0.006 and 0.430 ± 0.196 mg/mL, respectively. In the presence of Nω-nitro-l-arginine methyl ester (EC₅₀ 0.971 ± 0.459 mg/mL), methylene blue (EC₅₀ 1.203 ± 0.426 mg/mL), indomethacin (EC₅₀ 2.128 ± 1.218 mg/mL), atropine (EC₅₀ 0.470 ± 0.325 mg/mL), and propranolol (EC₅₀ 0.314 ± 0.032 mg/mL), relaxation stimulated by VAE was significantly reduced. VAE acted on potassium channels, with its vasorelaxation effects significantly reduced by tetraethylammonium, 4-aminopyridine, barium chloride, and glibenclamide (EC₅₀ 0.548 ± 0.184, 0.158 ± 0.012, 0.847 ± 0.342, and 0.304 ± 0.075 mg/mL, respectively). VAE was also found to be active in reducing Ca²⁺ released from the sarcoplasmic reticulum and blocking calcium channels.

Conclusions: The vasorelaxation effect of VAE involves upregulation of NO/cGMP and PGI₂ signalling pathways, and modulation of calcium/potassium channels, and muscarinic and β₂-adrenergic receptor levels.

Keywords:

• Tri-step FTIR
• calcium channel
• potassium channel
• NO/cGMP pathway
• prostacyclin

Acknowledgements

The authors sincerely thank the Institute of Postgraduate Studies (IPS) at Universiti Sains Malaysia (USM) for providing USM Fellowship Award to the first author.

Disclosure statement

We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

Additional information

Funding

This study was supported by the Universiti Sains Malaysia Research University grant [1001/Pbiologi/870039].