The relationship between the embryo and the corpus luteum was investigated by transferring embryos to various isolated portions of the uteri of 115 non-pregnant recipient ewes allocated to four experiments.
Embryos transferred to sheep with intact uteri (Experiment 1) were shown to be capable of maintaining the corpus luteum irrespective of whether they were transferred to the uterine horn adjacent to the corpus luteum (ipsilateral horn) or to the horn on the opposite side of the corpus luteum (contralateral horn.)
Embryos transferred to sheep with one surgically isolated uterine horn (Experiment 2) maintained luteal function only in the ovary adjacent to the gravid horn. Thus, embryos placed in the isolated ipsilateral uterine horn maintained luteal function in 80% of the recipients, while embryos transferred to the isolated contralateral horn had no effect on the life-span of the corpus luteum. However, if the ipsilateral horn was removed, embryos transferred to the contralateral horn regularly maintained the life-span of the corpus luteum during pregnancy.
Embryos transferred to one isolated horn of recipient ewes that had corpora lutea in both ovaries (Experiment 3) further confirmed the existence of a local unilateral relationship between the embryo and the corpus luteum: since only the corpora lutea adjacent to the gravid horn were maintained.
Embryos transferred to the isolated ovarian half of the ipsilateral horn (Experiment 4) maintained luteal function in 30% of the recipients. Embryos placed in the isolated cervical half of the ipsilateral horn or in the ovarian half of the contralateral horn did not prevent regression of the corpus luteum at the 15th day.
These results are interpreted to signify that the embryo overcomes the lytic effect of the uterus in a local manner. It would appear that the life-span of corpora lutea in sheep with ligated uteri is primarily regulated by the relative position of the lytic non-gravid horn and the corpus luteum, and not by the position of the pregnant horn as such.