The effect of carvacrol on muscarinic receptors of guinea‐pig tracheal chains

The effects of three concentrations of carvacrol, the constituent of Zataria multiflora Boiss (a monoterpenoid phenol, C(10) H(14) O) and 10 nm atropine on muscarinic receptors were tested on: non-incubated (n = 7), incubated tracheal chains with propranolol and chlorpheniramine (n = 6) and incubated with propranolol (n = 5). The EC(50) of all three concentrations of carvacrol in incubated tissues with propranolol and chlorpheniramine was significantly greater than those of incubated tissues with propranolol and non-incubated trachea (p < 0.05 to p < 0.001). The EC(50) of two higher concentrations of carvacrol (0.2 and 0.4 µg/mL) in incubated tissues with propranolol was also significantly greater than those of non-incubated trachea (p < 0.01 to p < 0.001). The maximum response in the presence of all concentrations of carvacrol in non-incubated and incubated tissues with propranolol and chlorpheniramine and those of its two higher concentrations (0.2 and 0.4 µg/mL) in incubated tissues with propranolol were lower than saline (p < 0.05 to p < 0.001). There were parallel rightward shifts in the concentration-response curves in the presence of all concentrations of carvacrol in non-incubated and incubated tissues with propranolol and its lower concentration in incubated tissues with propranolol and chlorpheniramine. These results indicated an inhibitory effect of carvacrol on muscarinic receptors. A β-adrenoceptor stimulatory effect was also suggested for carvacrol.