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Myometrial contractility with different uterotonic agents in laboring and non-laboring women
Abstract Number: 128
Abstract Type: Original Research
Introduction: Oxytocin is the uterotonic drug of choice to prevent and treat post partum hemorrhage, although ergonovine, carboprost, and misoprostol are also used. Laboring and nonlaboring women may exhibit different responses to uterotonic agents as a result of oxytocin receptor desensitization during labor. The objective of this study was to compare the in-vitro myometrial contractions in response to these four uterotonic drugs in laboring and non-laboring women.
Methods: After REB approval and informed consent, the study was conducted in 20 term pregnant women undergoing Cesarean sections (CS) under regional anesthesia. The study population consisted of laboring women (either oxytocin augmented or non-augmented) who required CS for labor arrest (n=8), and non-laboring women who underwent elective CS (n=12). Myometrial sample from each patient, retrieved from the uterine incision during CS, was dissected into 4 strips (2x2x10mm each), and mounted in 4 tissue bath chambers. The strips were allowed to equilibrate in physiological salt solution at 1g tension before being subjected to a dose-response testing with oxytocin, ergonovine, carboprost or misoprostol (10-10 to 10-5M). The amplitude (amp), frequency (freq) and motility index (MI=amp x freq) of contractions during the dose-response period were analyzed using mixed linear modeling and compared among the groups.
Results: There was no statistically significant difference in the amp, freq and MI of myometrial contractions during the dose-response testing with any of the uterotonic drugs in the augmented or non-augmented labouring and non-laboring women (Fig 1). The MI was significantly higher in oxytocin as compared to carboprost (p<0.0001), ergonovine (p=0.049), and misoprostol (p<0.0001) groups.
Conclusions: Our study demonstrates that in the in-vitro preparation, the contractile responses to various uterotonic agents do not differ between laboring and non-laboring women. This implies that oxytocin-induced desensitization may not always be observed after exposure to oxytocin in the clinical settings. Among all the uterotonic drugs, oxytocin still produces superior contractions, and this reinforces its importance as the primary drug in treating PPH. Further studies with combinations of uterotonic agents are warranted to understand the synergistic effects of the drugs.
References: Am J Obstet Gynecol 2003, 188: 497-502; Reprod Sci 2009, 16: 501-8.