Oxytocin Pretreatment Attenuates Oxytocin-induced Contractions in Human Myometrium In Vitro

May 17, 2013Anesthesiology

Oxytocin given before reduces oxytocin-triggered contractions in human uterine muscle tissue

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Abstract

Pretreatment with oxytocin 10 and 10 M significantly reduced the motility index by 0.771 and 0.697 square root units, respectively.

Oxytocin pretreatment at concentrations of 10 and 10 M led to a significant reduction in the area under the curve during contractile responses compared to control.
Increasing the duration of oxytocin pretreatment from 2 to 12 hours was associated with a significant decrease in contraction amplitude and motility index.
No significant change in the frequency of contractions was observed despite varying concentrations or durations of oxytocin pretreatment.
The findings suggest that oxytocin receptor desensitization may play a role in decreasing myometrial contractions in response to oxytocin.

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BACKGROUND: Oxytocin receptor desensitization has been shown to occur in humans at biomolecular level and in isolated rat myometrium; however, its effect on human myometrial contractility has not been demonstrated. The objective of this in vitro study was to investigate the contractile response of human pregnant myometrium to oxytocin after pretreatment with different concentrations of oxytocin for variable durations.

METHODS: Myometrial samples were obtained from 62 women undergoing elective cesarean deliveries under regional anesthesia. The strips were pretreated with oxytocin 10, 10, 10 M, or physiological salt solution (control) for 2, 4, 6, or 12 h, followed by a dose-response testing with oxytocin 10 to 10 M. Amplitude and frequency of contractions, motility index, and area under the curve during the dose-response period were recorded, analyzed with linear regression models, and compared among groups.

RESULTS: Pretreatment with oxytocin 10 and 10 M significantly reduced motility index (estimate [standard error]: -0.771 [0.270] square root units, P = 0.005 and -0.697 [0.293], P = 0.02, respectively) and area under the curve (-3.947 [1.909], P = 0.04 and -4.241 [2.189], P = 0.05, respectively) compared with control group, whereas pretreatment with oxytocin 10 M did not significantly attenuate contractions. Increase in duration of oxytocin pretreatment from 2 to 12 h significantly decreased amplitude (type 3 generalized estimating equation analysis: chi-square = 14.0; df = 3; P = 0.003), motility index (chi-square = 9.3; df = 3; P = 0.03), and area under the curve (chi-square = 10.5; df = 3; P = 0.02), but not the frequency of oxytocin-induced contractions.

CONCLUSION: Pretreatment with oxytocin decreases oxytocin-induced myometrial contractions in a concentration and time-dependent manner, likely as a function of the oxytocin receptor desensitization phenomenon.

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Oxytocin Pretreatment Attenuates Oxytocin-induced Contractions in Human Myometrium In Vitro

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