Effect of Zataria multiflora Bois L. on histamine (H1) receptor of guinea pig tracheal chains.

The effects of three concentrations (2.5, 5 and 10 microg/ml) of aqueous-ethanolic extract of Z. multiflora bois, 10 nM chlorpheniramine, and saline on histamine (H1) receptors were tested on two groups of guinea pig tracheal chains [trachea incubated with indomethacin (Gr. 1), and indomethacin and propranolol (Gr. 2)]. The effective concentration of histamine causing 50% of maximum response (EC50) obtained in presence of chlorpheniramine in both groups, all concentrations of the extract in group 1 and its two higher concentrations in group 2 were significantly greater than those of saline. The values of concentration ratio minus one (CR-1) obtained in presence of all the three concentrations of the extract in group 1 and 10 microg/ml concentration in group 2 were significantly greater than those of chlorpheniramine. The values of EC50 obtained in presence of all the three concentrations of extract and CR-1 obtained in the presence of 2.5 and 5 microg/ml concentrations in group 2 were lower than group 1. There was not significant difference in maximum response obtained in presence of different concentrations of extract between two groups. There were parallel right ward shift in concentration response curves obtained in presence of all concentrations of the extract in both the groups. These results indicated an inhibitory effect of Z. multiflora at histamine H1 receptors.