A local signal from the gravid horn to the ovary for the onset of parturition in rats

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Abstract
Rats were unilaterally ovariectomized on day 17 of pregnancy and the times of onset of parturition were recorded. Unilateral ovariectomy did not delay the onset of parturition in bilaterally pregnant rats. In rats which were unilaterally pregnant (spontaneously or after ligation of 1 uterine horn), removal of the ovary on the side of the gravid horn led to delayed or partial parturitions. When fetuses and placentas were removed from 1 uterine horn on day 13 and the ovary from the opposite side on day 17, or when the uterine artery and/or vein were ligated on 1 side and the ovary removed from the other, about half of the parturitions were abnormal. A substance produced by the gravid uterine horn apparently is transmitted to the ovary primarily by a local circulatory system which initiates the onset of parturition.