How blocking oxytocin and stress hormone receptors affects oxytocin receptors in the uterus during labor in rats

In vivo infusion of the beta2-adrenoceptor antagonist ICI-118.551 in late pregnant rats prevented the rise in myometrial oxytocin receptor binding normally seen during delivery.

• A reduced responsiveness of uterine strips to oxytocin was observed during labor after beta2AR blockade.
• Treatment with the OTR antagonist atosiban down-regulated OTR binding sites in myometrium and impaired contractile response to oxytocin, without affecting gestational length.
• Neither atosiban nor ICI-118.551 alone changed fetal mortality rates, but the combination significantly increased the incidence of fetal deaths.
• The combination treatment also resulted in down-regulation of myometrial OTR and weakened contractile responses to oxytocin.
• The findings suggest that the rise in OTR may not be essential for normal parturition outcomes, although it could play a role in preterm labor.

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