Studies on Bronchodilator Activity of Salvia officinalis (Sage): Possible Involvement of K⁺ Channel Activation and Phosphodiesterase Inhibition

The aqueous methanolic extract of the aerial parts of Salvia officinalis (So.Cr) was studied to provide possible underlying mechanism(s) for its medicinal use in asthma using the in vivo bronchodilatory assay and isolated tracheal preparations. S. officinalis (1-10 mg/kg) dose-dependently inhibited carbachol (CCh)-induced bronchospasm in anesthetized rats with three-fold greater potency than the positive control, aminophylline. In tracheal preparations, So.Cr inhibited the low K+ (25 mM)-induced contractions. Pretreatment of the tissues with 4-aminopyridine reversed the inhibitory effect of the plant extract against low K+, whereas glibenclamide did not show any effect, thus showing the involvement of voltage-sensitive K+ channels. When tested against the CCh-induced pre-contractions for the involvement of any additional mechanism, interestingly, the extract showed a dose-dependent (0.03-0.1 mg/mL) inhibitory effect and shifted the inhibitory concentration response curves of isoprenaline to the left, thus showing phosphodiesterase enzyme inhibitory-like action, similar to that of papaverine. These results indicate that the crude extract of S. officinalis possesses bronchodilatory activity mediated predominantly via activation of voltage-dependent K+ channels and inhibition of phosphodiesterase enzyme; thus, this study provides sound pharmacological basis for its medicinal use in hyperactive airways disorders such as asthma and cough.