Partial reversal of the myometrial progesterone 'block' in the non-pregnant ewe in vivo by oestradiol-17

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Abstract
In ovariectomized non-pregnant ewes myometrial activity, which was suppressed by continued injection of progesterone, showed a significant recovery of spontaneous activity and oxytocin responsiveness by 12 and 24 h after intrauterine administration of estradiol-17.beta.. No such recovery occurred in ewes given vehicle only into the uterus. The estrogen-induced recovery was lost by 60 h after treatment. Infusion of PG[prostaglandin]F-2.alpha. into the uterine lumen instead of estrogen provided no support for the possibility that the estrogen-induced recovery was mediated through PGF-2.alpha. secretion. Apparently, estradiol may participate in the mechanism of parturition in sheep by accelerating myometrial recovery from the effects of progesterone.