Investigating the relaxant effect of aqueous-alcoholic extract of Melissa Officinalis on smooth muscle of isolated rat trachea and its potential mechanisms

Background and Aims: Melissa officinalis (M. officinalis) is a well-known medicinal plant with various therapeutic properties such as, antioxidant and anti-inflammatory effects. Pharmacological effects of this plant is attributed with its main phenolic compounds, rosmarinic acid. This research aimed to study the relaxant effect of the aqueous-alcoholic extract of Melissa officinalis on the isolated tracheal smooth muscle (TSM) of rat. Materials and Methods: The relaxant potential of cumulative concentrations of the aqueous-alcoholic extract of Melissa officinalis (50, 100, 200 µg/ml) was compared with normal saline (1 milliliter of normal saline) as a negative control and three cumulative concentrations of theophylline (0.8, 0.4, 0.2 mM) as a positive control on the TSM of isolated rat. The relaxant effect of M. officinalis extract was examined on non-incubated and incubated TSM with propranolol (1 μM), atropine (1 μM), and chlorpheniramine (1 μM) as different antagonists of beta-2 adrenergic (β2-Adrenergic), muscarinic and H1 histamine receptors respectively. Results: The relaxant effect of M. officinalis extract with all theophylline concentrations on the isolated tracheal smooth muscle exhibited a significant increase compared to saline (P<0.001 in all instances) in non-incubated tissues. The relaxant effect of medium and high dose of M. officinalis extracts (100 and 200 µg/ml) were similar to theophylline and were not significant difference. Conversely, the relaxant effect of M. officinalis exhibited a significant reduction in incubated tissues with chlorpheniramine and atropine compared to the non-incubated tissue. Conclusion: The relaxant effect of aqueous-alcoholic extract of Melissa officinalis on isolated tracheal tissue is possibly be mediated through the inhibition of muscarinic and H1 histamine receptors while having no significant impact on beta-2 adrenergic receptors.