Purpose: To evaluate the effects of the methanol extract of Acanthus montanus on guinea pig trachealis muscle.

Methods: Guinea pig tracheae were set up in 10 ml organ baths. The effect of the methanol extract of Acanthus montanus (0.5 - 8 mg/ml) on the spontaneous tone of the trachea and carbachol-precontracted trachea in the absence and presence of propranolol, glibenclamide and procaine was studied.

Results: The extract (0.5 – 8.0 mg/ml) produced a concentration-dependent relaxation of the intrinsic tone in tracheal preparations which was completely blocked by propranolol (3 x 10^-7 M), glibenclamide (10^-7 M) and procaine (10^-3 M). The extract (0.5 - 8 mg/ml) produced a concentration-dependent relaxation of carbachol (10^-5M)-precontracted trachea. This effect of the extract was partially blocked by propranolol (3 x 10^-7M), procaine (10^-3M) and glibenclamide (10^-7M) with a progressive increase in the median effective concentration (EC₅₀) values as follows: control, 0.66mg/ml > propranolol, 1.42mg/ml > glibenclamide, 1.54mg/ml > procaine, 2.04 mg/ml.

Conclusion: The results obtained suggest that the extract produces a non-specific smooth muscle relaxant effect mediated via b-adrenergic receptor mechanism or potassium channels.