Hormonal and Regional Influences of the Oviduct on the Development of Rabbit Embryos

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Abstract
Unicellular rabbit zygotes were transferred from the oviducts of untreated females and placed in the oviducts of rabbits given various hormonal treatments. At the time of zygote transfer, the oviducts of the recipients were left unligated or were ligated at the utero-tubal or the ampullar-isthmic junction; the ligations restricted the embryos to the whole oviduct or to the ampullar region of the oviduct. At the end of a 50 h residence in the oviducts, the embryos were examined for morphological normality of growth, after which the normal embryos were retransferred to the uterine horns of pseudopregnant rabbits for continued development to birth. Region of embryo incubation and hormonal status in the oviduct both influenced embryonic development. Restriction of the oviducts of 1 day pseudopregnant rabbits did not disturb embryonic development. The zygotes cleaved normally and developed to implantation after incubation in the whole unligated oviduct (42% implantations), the oviduct with utero-tubal junction ligation (32%) or with ampullar-isthmic junction ligation (28%). The isthmus of 10 day pseudopregnant animals provided for normal cleavage of zygotes; only 6% of these embryos developed to implantation in uterine recipients. The oviducts of ovariectomized animals provided a milieu for the normal cleavage of rabbit zygotes. Oviductal function was not strictly dependent upon ovarian steroid stimulation. In the ampullae of estrogen-treated, ovariectomized animals, embryonic development was significantly impaired. Few of the zygotes developed to normal morulae; no embryos implanted. The factor which was detrimental to normal embryonic development may be an estrogen-stimulated component in the ampullar fluid.