Abstract

The relaxant effect of Portulaca oleracea L. (P. oleracea) on tracheal smooth muscles has been shown. The effect of the plant on muscarinic receptors of tracheal smooth muscles as one possible mechanism responsible for its relaxant effect was examined. Concentration response curves to methacholine were performed in the presence of three concentrations of aqueous-ethanol extract from aerial part of the plant (0.25, 0.50 and 1.00 mg/ml), 10 nM atropine, and saline. The values of EC50 (effective concentration causing 50% of maximum response) and CR-1 ((EC50 of test solutions/EC50 of saline)-1) were measured. The study was done using three designs as non-incubated (group 1), incubated tissues with propranolol and chlorpheniramine (group 2) and incubated tissues with propranolol (group 3). Concentration-response curves to methacholine were shifted to the right and EC50 methacholine were higher in the presence of atropine, medium and highest extract concentrations in all groups and its low concentration in group 3 compared to saline (P<0.05 to P<0.001). In addition, EC50 methacholine in the presence of high extract concentration (27.00±2.12) in group 2 was greater than its low (10.33±1.54) and medium (16.83±2.52) concentrations (P<0.001 and P<0.05, respectively). The values of the CR-1 obtained in the presence of all extract concentrations in all groups were lower than that of atropine (P<0.05 to P<0.001). An inhibitory effect for the extract of P. oleracea muscarinic receptors of tracheal smooth muscles was shown and a histamine (H1) receptor blockade was also suggested.