Oxytocin Pretreatment Decreases Oxytocin-induced Myometrial Contractions in Pregnant Rats in a Concentration-dependent But Not Time-dependent Manner

Jan 24, 2009Reproductive sciences (Thousand Oaks, Calif.)

Oxytocin given before reduces oxytocin-triggered uterus contractions in pregnant rats depending on dose but not timing

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Abstract

The area under the curve, frequency, and amplitude of contractions were all significantly suppressed in myometrial strips preexposed to oxytocin 10(-8) mol/L compared to control and lower concentration groups.

Continuous exposure to oxytocin may lead to a desensitization effect on myometrial cells in pregnant rats.
Oxytocin preexposure at 10(-8) mol/L resulted in significant suppression of contractile activity compared to both control and 10(-10) mol/L groups (P < .0001).
The reduction in contractile response was observed as early as 1 hour of preexposure to oxytocin.
Duration of oxytocin exposure, whether for 1 or 4 hours, did not affect the level of contraction suppression.
The contractile inhibition is dependent on the concentration of oxytocin, not on the length of exposure.

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Recent biomolecular studies have shown that continuous exposure of human myometrial cells to oxytocin results in a significant loss of responsiveness to subsequent oxytocin stimulation, perhaps because of desensitization of the oxytocin receptors. However, it is unclear whether this phenomenon results in a reduction of the contractile activity of the uterine muscle in humans or animals. The objective of our study was to investigate the in vitro response of the uterine muscle of pregnant rats to oxytocin, following preexposure to varying concentrations of oxytocin, for varying durations. Longitudinal myometrial strips were isolated from 16 pregnant Wistar rats at 19 to 21 days of gestation and preexposed to oxytocin 10(-10) or 10(-8) mol/L (experimental groups) or physiological salt solution (control groups) for 1- or 4-hour period. All muscle strips were then subjected to a dose-response study with oxytocin 10(-10) to 10(-5) mol/L. The area under the curve, frequency, and amplitude of contractions were recorded and compared between the groups. The area under the curve, frequency, and amplitude of the oxytocin-induced contractions were all significantly suppressed in the groups preexposed to oxytocin 10(-8) mol/L compared to either the control groups (P < .0001) or the groups preexposed to oxytocin 10(-10) mol/L (P < .0001). There was no difference in the oxytocin-induced myometrial contractions between the groups preexposed to oxytocin for either the 1- or 4-hour periods. The inhibition of the oxytocin-induced contractile response of pregnant rat myometrium is observed as early as 1 hour of preexposure to oxytocin and is dependent on the preexposed oxytocin concentration and not on the duration of its exposure.

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Oxytocin Pretreatment Decreases Oxytocin-induced Myometrial Contractions in Pregnant Rats in a Concentration-dependent But Not Time-dependent Manner

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