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Recovery time of oxytocin induced desensitization in human myometrium in-vitro
Abstract Number: GM-03
Abstract Type: Original Research
Introduction: Postpartum hemorrhage secondary to uterine atony is a leading cause of maternal morbidity. Prolonged exposure to oxytocin for labor augmentation can result in the ‘desensitization’ phenomenon, a decrease in the responsiveness of the myometrium to further oxytocin. It is not known if following cessation of oxytocin, waiting for a specific period would allow the oxytocin receptors to ‘resensitize’ and recover, thereby improving oxytocin induced myometrial contractility. We aimed to investigate the effect of a rest-time of 30, 60 and 90 min, on the recovery of desensitized myometrium in vitro.
Methods: Patients undergoing elective cesarean deliveries were recruited in this in-vitro study. Myometrial tissue was dissected into four strips. Each strip was mounted in a single organ bath with physiological salt solution (PSS) under homeostatic conditions and then pretreated for 2h with 10-5M oxytocin (myometrial desensitization model ). Following pretreatment, each strip was washed with PSS, and allowed to ‘rest’ in PSS solution for either 30, 60 or 90 min. At the end of the ‘rest’ period, a dose-response to oxytocin 10-10M to 10-5M was performed. A control group consisted of an oxytocin dose-response without any pretreatment to oxytocin. Contractile parameters were measured. The primary outcome was motility index (amplitude x frequency) of myometrial contractions. Data were analyzed using mixed linear model using baseline contractions and tone as covariates.
Results: A total of 20 women were recruited and 55 successful experiments were performed: control (n=14); 30 min (n=14); 60 min (n=13); 90 min (n=14). The motility index of contractions (square root g.contractions/10min) was significantly higher in control group [mean (SE)] [2.91 (0.36)] as compared to 30 min [2.60 (0.24), adjusted p=0.02]; 60 min [2.58 (0.26), adjusted p=0.002] and 90 min [2.16 (0.31), adjusted p<0.001] (Fig 1).
Discussion: We found that even after a rest-period from 30-90 min, recovery of oxytocin responsiveness does not take place if the myometrium is previously desensitized with oxytocin. This implies that stopping oxytocin infusion prior to cesarean section in women with augmented labor is unlikely to improve oxytocin induced contractility after delivery.
References: 1) Am J Obstet Gynecol 2003;188:497-502
2) Anesthesiology 2013; 119: 552-561