4.4. Isolation of Uterus and Measurement of Uterine Contraction

Female ICR mice were pretreated with estradiol benzoate (1 mg/kg/day) by intraperitoneal injection for 3 consecutive days before the ex vivo experiments. After the animals were sacrificed by cervical dislocation, the uteri were collected to a container filled with Locke’s solution (in mmol/L: NaCl 120, KCl 4.6, CaCl₂ 1.5, MgSO₄ 1.2, KH₂PO₄ 1.0, NaHCO₃ 25 and glucose 11). After removal of the adherent fat tissue and mesenteric attachments of uterine strips, the isolated uteri were individually transferred and incubated in 20 mL of Locke’s solution in organ baths at 37 °C bubbled with 95% O₂ and 5% CO₂. Following this, the uterus was preloaded with 1 g tension, before the amplitude of uterine contraction became stable after equilibration for 45 min. Uterine contractions were monitored by a force-displacement transducer connected to a polygraph (Model BL420E+, Tai Meng, Chengdu, China). To evaluate the influence of licorice aqueous extracts on oxytocin-stimulated uterine contractions, oxytocin (0.01 U/mL) was added to the organ bath at 15 min before different concentrations of licorice and nifedipine (positive control) were cumulatively added. The contraction was monitored for about 10 min for each concentration. The data were presented as contraction amplitude and frequency.