doi: 10.1111/j.1472-8206.2011.00971.x ORIGINAL ARTICLE Inhibitory effect of Zataria multiflora Boiss and carvacrol on histamine (H 1 ) receptors of guinea-pig tracheal chains Mohammad Hossein Boskabady a *, Hengameh Tabanfar a , Zahra Gholamnezhad a , Hamid Reza Sadeghnia b a Department of Physiology and Pharmaceutical Research Centre, Medical School, Mashhad University of Medical Sciences, Mashhad, Iran b Department of Pharmacology and Pharmacology Research Centre of Medicinal Plants, Medical School, Mashhad University of Medical Sciences, Mashhad, Iran INTRODUCTION Zataria multiflora Boiss L is a perennial plant used as food additive and has constituents of classes of terpenes, phenols, aliphatic alcohols, flavonoids, saponins, and tannins. Some of its constituents have been previously identified as bioactive chemicals, particularly terpenes such as thymol and carvacrol. Z. multiflora also con- tains apigenin, luteolin, and 6-hydroxyluteolin glyco- sides, as well as di, tri, and tetramethoxylated forms [1,2]. There is evidence for therapeutic effect of extract of this plant on coughs owing to common cold, bronchitis, and pertussis; laryngitis and tonsillitis (as gargle); the common cold; and disorders of the oral cavity and as an antibacterial agent in oral hygiene in Iranian traditional medicine [3–5]. Both the essential oil and thymol are ingredients of a number of proprietary drugs including antiseptic and healing ointments, syrups for the treat- ment for respiratory disorders, and preparations for inhalation [1]. It has also been used to treat pertussis, stomatitis, and halitosis [2]. Keywords carvacrol, guinea-pig, histamine receptor, inhibitory effect, trachea, Zataria multiflora Boiss Received 18 November 2010; revised 1 June 2011; accepted 4 July 2011 *Correspondence and reprints: boskabadymh@mums.ac.ir; mhboskabady@hotmail.com ABSTRACT The inhibitory effect of aqueous-ethanolic extract of Zataria multiflora Boiss (Labiatae) and carvacrol on histamine (H 1 ) receptors was examined on tracheal chains of guinea-pigs. The effects of three concentrations of aqueous-ethanolic extract, carvacrol, 10 nM chlorpheniramine, and saline on histamine (H 1 ) receptors were tested on three groups of guinea-pig tracheal chains as follows: incubated trachea with (i) indomethacin (n = 9), (ii) indomethacin, propranolol, and atropine (n = 7), and (iii) indomethacin and propranolol (n = 6). The EC 50 (effective concentration of histamine causing 50% of maximum response) obtained in the presence of chlorpheniramine for all concentrations of the extract and carvacrol in all three groups was significantly higher than that of saline (P < 0.001 for all cases). The EC 50 obtained in the presence of all concentrations of extract in groups 2 and 3 was lower than group 1 and in group 3 lower than group 2 (P < 0.01 to P < 0.001). However, EC 50 obtained in the presence of all concentrations of carvacrol in group 3 and two higher concentrations in group 2 was higher than that of group 1 (P < 0.01 to P < 0.001). There was no significant difference in the maximum response obtained in the presence of different concentrations of extract and carvacrol between three groups. There was a parallel rightward shift in concentration–response curves obtained in the presence of all concentrations of the extract and carvacrol in all three groups. These results indicated an inhibitory effect of Z. multiflora and its constituent carvacrol on histamine H 1 receptors. ª 2011 The Authors Fundamental and Clinical Pharmacology ª 2011 Socie ´ te ´ Franc ¸aise de Pharmacologie et de The ´ rapeutique Fundamental & Clinical Pharmacology 1 Fundamental & Clinical Pharmacology