Relaxant Effects of the Essential Oil of Eucalyptus tereticornis and its Main Constituent 1,8-Cineole on Guinea-Pig Tracheal Smooth Muscle

Abstract

The effects of the essential oil of Eucalyptus tereticornis Sm. (EOET) on guinea-pig tracheal smooth muscle were investigated. EOET (10 - 1000 μg/mL) relaxed the tracheal basal tonus with an EC₅₀ value of 125.3 [52.2 - 300.9] μg/mL. Its maximal relaxation (40 ± 6 %) was significantly lower than that evoked by aminophylline (209 ± 34 %). The K⁺-(60 mM)-induced contractions were significantly reduced by both EOET (200 - 1000 μg/mL) and its main constituent 1,8-cineole (600 - 1000 μg/mL). Acetylcholine (1 μM)-induced contractions were significantly enhanced by 1,8-cineole (10 - 1000 μg/mL). However, they were significantly enhanced and reduced by lower (200 - 400 μg/mL) and higher (800 - 1000 μg/mL) concentrations of EOET, respectively. Electrical field stimulation-induced contractions were significantly increased by EOET (100 - 600 μg/mL). In conclusion, EOET produces myorelaxant effects on guinea-pig isolated trachea, an effect that seems to result from a complex interaction between its monoterpenoid constituents.

References

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