Inhibitory actions of eugenol on rat isolated ileum

Abstract: The effects of eugenol (1-2000 mM) on rat isolated ileum were studied. Eugenol relaxed the basal tonus (IC 50 83 mM) and the ileum precontracted with 60 mM KCl (IC 50 162 mM), an action unaltered by 0.5 mM tetrodotoxin, 0.2 mM N G -nitro-L-arginine methyl ester, 0.5 mM hexamethonium, and 1 mM indomethacin. Eugenol did not alter the resting transmembrane potential (E m ) of the longitudinal muscle layer under normal conditions (5.0 mM K + ) or in depolarised tissues. Eugenol reversibly inhibited contractions induced by submaximal concentrations of acetylcholine (ACh) and K + (40 mM) with IC 50 values of approximately 228 and 237 mM, respectively. Eugenol blocked the component of ACh-induced contraction obtained in Ca 2+ -free solution (0.2 mM EGTA) or in the presence of nifedipine (1 mM). Our results suggest that eugenol induces relaxation of rat ileum by a direct action on smooth muscle via a mechanism largely independent of alterations of E m and extracellular Ca 2+ influx. Key words: essential oil, eugenol, ileum, smooth muscle, antispasmodic. Résumé : On a examiné les effets de l'eugénol (1-2000 mM) sur l'iléon isolé de rat. L'eugénol a provoqué une relaxation du tonus basal (CI 50 83 mM) et de l'iléon précontracté avec 60 mM KCl (CI 50 162 mM); cet effet n'a pas été modifié par 0,5 mM tétrodotoxine, 0,2 mM N G -nitro-L-arginine méthyl ester, 0,5 mM hexaméthonium et 1 mM indométhacine. L'eugénol n'a pas modifié le potentiel transmembranaire (E m ) au repos de la couche musculaire longitudinale dans des conditions normales (5,0 mM K + ) ou dans les tissus dépolarisés. Il a inhibé de manière réversible les contractions induites par des concentrations submaximales d'acétylcholine (ACh) et de K + (40 mM) avec des valeurs de CI 50 d'approximativement 228 et 237 mM respectivement. Il a bloqué la composante de la contraction induite par l'ACh dans une solution sans Ca 2+ (0,2 mM EGTA) ou en présence de nifédipine (1 mM). Nos résultats donnent à penser que l'eugénol provoque une relaxation de l'iléon de rat en agissant directement sur le muscle lisse par l'intermédiaire d'un mécanisme largement indépendant des modifications du potentiel E m et de l'influx de Ca 2+ extracellulaire

Eugenol modifies the excitability of rat sciatic nerve and superior cervical ganglion neurons

Eugenol is a phenylpropene obtained from the essential oils of plants such as clove and basil which has ample use in dentistry. Eugenol possesses analgesic effects that may be related to the inhibition of voltage-dependent Na(+) channels and/or to the activation of TRPV1 receptors or both. In the present study, electrophysiological parameters were taken from the compound action potentials of the isolated rat sciatic nerve and from neurons of the superior cervical ganglion (SCG) impaled with sharp microelectrodes under current-clamp conditions. In the isolated rat sciatic nerve, eugenol inhibited the compound action potential in a concentration-dependent manner. Action potentials recorded from SCG neurons were inhibited by eugenol with an IC(50) of 0.31 mM. At high concentrations (2 mM), during brief applications. eugenol caused significant action potential blockade while it did not interfere with the resting membrane potential or the membrane input resistance. Surprisingly, however, at low eugenol concentrations (0.6 mM), during long time applications, a reversible reduction (by about 50%) in the input membrane resistance was observed, suggesting the possible involvement of a secondary delayed effect of eugenol to reduce neuronal excitability. (C) 2010 Elsevier Ireland Ltd. All rights reserved.CNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPESFundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP)FUNCA