ABSTRACT
In the present study, the effect of tissue incubation with propranolol on functional antagonism of Zataria multiflora Boiss [Z. multiflora] at muscarinic receptors of tracheal smooth muscle was examined. The effects of three concentrations of aqueous-ethanolic extract, 10 nM atropine, and saline on muscarinic receptors were tested on incubated tracheal smooth muscle with propranolol [n=5]. The EC[50] of all concentration of the extract and atropine was significantly higher than that of saline. There was parallel right ward shift in concentration response curves obtained in the presence of all concentrations of the extract. There was not any significant difference in the maximum response and slope obtained in the presence of different concentrations of extract compared to saline. There was significant positive correlation between the concentrations and the values of EC[50] [p<0.001]. The value of [CR-1] obtained in the presence of highest concentration of the extract was significantly higher than that of atropine [p<0.05]. These results indicated that functional antagonism of Z. multiflora at muscarinic receptors of tracheal smooth muscle was mainly due to beta-adrenoceptor stimulatory effect of plant