Moringa oleifera leaf extract induces vasorelaxation via endothelium-dependent hyperpolarization and calcium channel blockade in mesenteric arterial beds isolated from L-NAME hypertensive rats

ABSTRACT

Background

An aqueous extract of Moringa oleifera leaves (MOE) is known to cause relaxation of mesenteric resistance arteries of rats in which hypertension has been induced by the administration of L-NAME, but the mechanism(s) of action of MOE remains unclear. The purpose of this study was to investigate these mechanisms in mesenteric arterial beds isolated from L-NAME induced hypertensive rats. Methods: An investigation of vascular reactivity was conducted on isolated mesenteric arterial beds by measuring the changes in perfusion pressure using an in vitro system.

Results

MOE (0.001–3 mg in 0.1 ml injection volume) caused a dose-dependent relaxation in methoxamine (5 µM) pre-contracted arterial beds, which was partially abolished by endothelium removal. The endothelium-dependent component of vasorelaxation was insensitive to both L-NAME (100 µM) and indomethacin (10 µM), while completely inhibited in high KCl (45 mM)-induced contraction. MOE (1 and 3 mg/ml) showed a dose-dependent inhibitory effect on CaCl₂-induced contractions of denuded preparations in Ca²⁺-free medium containing a high KCl (60 mM) or methoxamine (10 µM). In Ca²⁺-free medium, MOE (3 mg/ml) also inhibited phenylephrine-induced contractions of denuded preparations. Conclusion: These findings suggest that MOE relaxes mesenteric arterial beds of L-NAME hypertensive rats via both endothelium-dependent and endothelium-independent mechanisms. The endothelium-dependent action occurred via endothelium-derived hyperpolarizing factor-mediated hyperpolarization. The endothelium-independent action was related to blocking the entry of extracellular Ca²⁺ via voltage-operated and receptor-operated Ca²⁺ channels, and inhibiting mobilization of sarcolemmal Ca²⁺ via inositol trisphosphate receptor Ca²⁺ channels. MOE may be potentially useful as a natural vasodilator against hypertension.

Graphical abstract

KEYWORDS:

• Calcium antagonist
• Hyperpolarization
• Hypertension
• Moringa
• Vasodilator

Acknowledgments

We would like to acknowledge Prof. David Blair for editing the MS via Publication Clinic KKU, Thailand.

Data Availability

The full raw data set is available from the corresponding author upon request.

Declaration of Interest

The authors declare no conflict of interest.

Additional information

Funding

This study was supported by Khon Kaen University [grant number 580033]; and Invitation Research Fund, Faculty of Medicine, Khon Kaen University [grant number IN61132]. Direk Aekthammarat is a PhD candidate and receives a scholarship from Faculty of Medicine, Khon Kaen University, Thailand.