Insight into the bronchodilator activity of Vitex negundo

Abstract

Context: Vitex negundo Linn. (Verbenaceae) is traditionally used in hyperactive respiratory disorders.

Objective: This study explored the mechanisms underlying the effectiveness of Vitex negundo in hyperactive respiratory disorders.

Materials and methods: Crude extract of V. negundo leaves was obtained. For in vivo bronchodilatory activity in anesthetized rats, different doses (1, 3, 10, 30, and 50 mg/kg) of the crude extract of V. negundo (Vn.Cr) were tested. The underlying mechanisms were studied in isolated guinea pig tracheal strips, suspended in organ baths at 37 °C.

Results: Intravenous doses of the crude extract of Vn.Cr showed dose-dependent bronchodilatory effect (9–50%) against carbachol (CCh; 100 µg/kg)-induced bronchoconstriction, similar to aminophylline. In isolated guinea-pig tracheal strips, Vn.Crrelaxed CCh (1 µM) and high K⁺ pre-contractions with respective EC₅₀ values of 0.72 (0.48–1.10; n = 5) and 3.38 mg/mL (1.84–6.21; n = 4), similar to papaverine. Diltiazem also relaxed both contractions with more potency against high K⁺ pre-contraction (p < 0.05). Pre-incubation of the tracheal strips with Vn.Cr potentiated the isoprenaline inhibitory concentration response curves (CRCs), similar to papaverine.

Discussion: The inhibitory effect against CCh and high K⁺ suggests involvement of phosphodiesterase (PDE) inhibitory pathway(s), in addition to an inhibitory effect on Ca⁺⁺ entry. This finding was further strengthened when pre-treatment of the tracheal strips potentiated the isoprenaline CRCs.

Conclusion: Results suggest Vn.Cr possesses a combination of papaverine-like PDE inhibitor and diltiazem-like Ca⁺⁺ entry blocking constituents, which partly explain its bronchodilatory effect, thus validating its medicinal importance in asthma.

• Aminophylline
• asthma
• bronchodilatation
• carbachol bronchoconstriction
• crude extract
• diltiazem
• guinea pig trachea
• papaverine
• PDE inhibition

Acknowledgements

The authors are thankful to Miss. Christie Ronge ([email protected]), WI, USA, for reviewing this manuscript for English.

Declaration of interest

The authors report no declarations of interest. This study was supported in part by a grant from Pakistan Science Foundation.