Serum levels of mu-opioid receptor according to menstrual cycle phases are associated with postoperative pain and opioid consumption in laparoscopic gynecological surgeries: a prospective observational study.

ABSTRACT

AIMS: In this prospective observational clinical study, we aimed to evaluate the relationship between serum mu-opioid receptor (MOR) levels according to menstrual cycle phases on postoperative pain scores and analgesic requirements. METHODS: A total of 80 female patients undergoing laparoscopic surgery were divided into two groups according to the phases of the menstrual cycle as follicular and luteal. Postoperative pain scores, total tramadol consumptions, and numbers of demands on patient-controlled analgesia (PCA) of the patients were recorded at 5 time points (T0 in the recovery room, T1 1st hour in the ward, T2 6th hour in the ward, T3 12th hour in the ward, T4 24th hour in the ward). Serum MOR concentrations were measured by enzyme-linked immunosorbent assay. RESULTS: The mean serum MOR levels were significantly higher in the follicular group (275 ± 32 pg/ml) compared to the luteal group (254 ± 28 pg/ml) (p = 0.003). Total tramadol consumption (T0, T2, and T3) was significantly higher in the luteal group (p = 0.031, p = 0.012, p = 0.017, respectively). Postoperative pain scores did not differ significantly between the groups. With the exception of T4 (p = 0.057), the number of demands on PCA was significantly higher in the luteal group. However, multivariate logistic regression analysis showed that serum MOR levels were affected by the menstrual cycle phase (follicular) (ß = 0.361) (p = 0.001). CONCLUSIONS: Our study revealed that patients during the follicular phase with higher serum MOR levels consumed less opioid analgesic postoperatively. More comprehensive studies are needed to determine the relationship between serum MOR levels and menstrual cycle phases as well as postoperative pain. (Trial registration number NCT04690491 www. CLINICALTRIALS gov ).