Inhibitory actions of eugenol on rat isolated ileum

The effects of eugenol (1-2000 muM) on rat isolated ileum were studied. Eugenol relaxed the basal tonus (IC50 83 muM) and the ileum precontracted with 60 mM KCl (IC50 162 muM), an action unaltered by 0.5 muM tetrodotoxin, 0.2 mM N-G-nitro-L-arginine methyl ester, 0.5 mM hexamethonium, and 1 muM 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 IC50 values of approximately 228 and 237 muM, respectively. Eugenol blocked the component of ACh-induced contraction obtained in Ca2+-free solution (0.2 mM EGTA) or in the presence of nifedipine (1 muM). 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 Ca2+ influx.