Differential Transport of Fertilized and Unfertilized Ova in the Rat

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Abstract
A possible role of the quality of eggs in the regulation of ovum transport was investigated in pseudopregnant rats. Pseudopregnancy was induced by mechanical stimulation of the cervix at 2200 h on the day of proestrus. This was immediately followed by artificial insemination with fertile or infertile epididymal spermatozoa. The following day was designated as day 1 of pseudopregnancy. Spermatozoa were rendered infertile by freezing and thawing. Insemination with fertile spermatozoa yielded between 80% and 100% of normally developing embryos, as judged by their microscopic appearance and by the implantation rate on day 10 of pseudopregnancy. Insemination with infertile spermatozoa yielded only cytolyzed or fragmented ova. Animals were randomly assigned to either 1 or 3 groups: In Group 1 they were inseminated in both uterine horns with fertile spermatozoa. Females in Group 2 were inseminated in both uterine horns with infertile spermatozoa and those in Group 3 were inseminated with fertile spermatozoa in one uterine horn and with infertile spermatozoa in the contralateral horn. Animals in a subgroup of Group 2 had the uterine horns ligated on day 4. The females were sacrificed at different intervals between days 2 and 5 of pseudopregnancy, to determine the number, condition and distribution of ova in the genital tract and to determine plasma progesterone concentrations in blood obtained from the aorta. The number and distribution of ova in Groups 1 and 2 and in both sides of Group 3 was similar until morning of day 4, but after their passage to the uterus there was a significant loss of unfertilized ova which was prevented by placement of a ligature in the uterine horns. The differential transport of embryos and unfertilized ova was not associated with different plasma progesterone levels. Differential transport was observed in animals transporting the 2 types of eggs at the same time but in different uterine horns. Evidently, ova can exert a local influence upon the uterine phase of transport which is associated with fertilization and/or development.

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