RESUMEN
ETHNOPHARMACOLOGICAL RELEVANCE: The twigs and bark of Cinnamomum cassia Presl (Lauraceae) are widely used in traditional Chinese medicine in the treatment of tumor, abdominal pain, dysmenorrhea, digestive system disease and inflammatory diseases. The aim of this study was to determine the inhibitory effect of the essential oil from the twigs of Cinnamomum cassia Presl (EOCC) on uterine contraction in vitro and in vivo. MATERIALS AND METHODS: The Institute of Cancer Research (ICR) mouse uterine contraction was induced by oxytocin (OT) exposure following estradiol benzoate pretreatment. Mice were given the EOCC (60, 30, and 15mg/kg) by gavage. The level of prostaglandin F2α (PGF2α) in uterine tissue were determined according to specification of enzyme linked immunosorbent assay (ELISA) kit. Uterine tissue was collected for histopathological analysis (H&E). Myosin light chain 20 (MLC20), phosphorylation of myosin light chain 20 (p-MLC20) and cyclooxygenase-2 (COX-2) proteins in uterine tissue were assessed by Western Blot. Mouse isolated uterus strips were mounted in tissue organ baths containing Locke's solution. The contractile responses were recorded with Power Lab recording system. The effect of the EOCC on uterine contraction induced by OT, PGF2α, and acetylcholine (Ach) was observed. Myometrial cells were exposed to OT (7µM) to induce Ca2+ release, and the effect of the EOCC (100, 50, and 25µg/ml) on intracellular Ca2+ was analysed with fluorometry imaging. RESULTS: In vivo study demonstrated that the EOCC significantly reduced OT-induced writhing responses with a maximal inhibition of 66.5%. It also decreased the level of PGF2α in OT-induced mice uterine tissue. Moreover, Western blot analysis showed that COX-2 and p-MLC20 expressions in uterine tissue of dysmenorrhea mice were significantly reduced. EOCC inhibited spontaneous uterus contractions in a dose-dependent manner, and the concentration of the EOCC giving 50% of maximal contraction (IC50) value was 61.3µg/ml. The IC50 values of the EOCC on OT, PGF2α, and Ach-induced contractions were 113.0µg/ml, 94.7µg/ml, and 61.5µg/ml, respectively. Further in vitro studies indicated that the EOCC could restrain intracellular Ca2+ levels in favour of uterine relaxation. CONCLUSION: Both in vivo and in vitro results suggest that the EOCC possesses significant spasmolytic effect on uterine contraction. Thus, the EOCC yields a possible therapeutic choice for the prevention and treatment of primary dysmenorrhea.