Antispasmodic effects of eugenol on rat airway smooth muscle

This study was undertaken to assess the effects of eugenol (EUG) on tracheal muscle (TM) and the putative mechanisms underlying these effects. Cumulatively increasing concentrations (1-1000 μm) of EUG did not affect the resting tonus of TM. However, EUG (1-2000 μm) reduced the contractions induced by electrical field stimulation (IC(50) = 842.3 ± 52.7 μm), an effect that was unaltered by either 10 μm montelukast (IC(50) = 816.1 ± 70.1 μm) or 2 μm indomethacin (IC(50) = 693.1 ± 170.8 μm). EUG also completely relaxed the sustained contractile responses to 80 mM K(+) (IC(50)  = 597.3 ± 60.6 μm) and 1 μm carbamoylcholine (IC(50) = 571.3 ± 148.8 μm), an effect that was unaltered by indomethacin (2 μm). Under Ca(2+) -free conditions, EUG reduced the ACh-induced contractions (IC(50) = 703.4 ± 256.1 μm), the CaCl₂ -induced contractions in preparations pretreated with 60 μm ACh in the presence of nifedipine, and the Ba(2+) -induced contractions in preparations depolarized with K(+) . In tracheal preparations maintained in Ca(2+) -containing solution, EUG (300-2000 μm) relaxed the contractile response to phorbol dibutyrate (1 μm), an activator of protein kinase C. It is concluded that in TM, EUG induces a myogenic antispasmodic effect (not modulated by arachidonic acid derivatives) either through various mechanisms almost with the same pharmacological potency or via an action on a step common to all of them. These mechanisms seem to include blockade of voltage- and receptor-operated Ca(2+) channels, IP₃ -induced Ca(2+) release from sarcoplasmic reticulum and reduction of the sensitivity of contractile proteins to Ca(2+) .