Human myometrium remains more responsive to subsequent oxytocin after intermittent compared to continuous exposure to oxytocin, most likely due of reduction in oxytocin receptor desensitization, or facilitation of receptor resensitization in the intermittent group. Hence, intermittent oxytocin administration during labor warrants further investigation as a technique to improve uterine oxytocin responsiveness.
The purpose of this study was to investigate myometrial contractility induced by oxytocin in women with advanced maternal age (AMA) and morbid obesity (MO). We hypothesized that both oxytocinpretreated and oxytocin-naïve myometrial tissues from women of AMA and women who are MO would exhibit poor myometrial contractility compared with women that are younger and of normal body mass index (BMI). Methods This prospective in vitro study was conducted using myometrial samples obtained from women undergoing elective Cesarean deliveries. Three groups of patient were studied: control (B 35 yr; BMI, 20-24.9 kgÁm-2), AMA (C 40 yr; BMI, 20-24.9 kgÁm-2), and MO (B 35 yr BMI, C 40 kgÁm-2). Each myometrial strip was
Magnesium sulfate pretreatment does not impair oxytocin-induced myometrial contractility in oxytocin-naïve or desensitized myometrium unless it is continued during oxytocin dose-response testing. These results suggest that its tocolytic effect is likely dependent on an extracellular mechanism. The study was registered with ClinicalTrials.gov, number NCT02647268.
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