Summary. Oviduct and uterine cell cultures were prepared from mice at different days of pseudopregnancy and their effects on the development of 1- and 8-cell mouse embryos in co-culture were examined. One-cell mouse embryos in co-culture with oviduct cells from 20 h to 120 h after hCG had a mean (±s.e.) cell number of 70·1 ± 3·6, significantly (P < 0·001) higher compared with those cultured in Whittingham's T6 medium supplemented with 5% fetal calf serum (T6 + 5% FCS) (30·4 ± 1·6). Transfer of embryos, at 96 h after hCG, to synchronous pseudopregnant recipients showed that more embryos in oviduct co-culture formed fetuses than those cultured in T6 + 5% FCS. Co-culture of 1-cell embryos with uterine cells did not confer an advantage in cell numbers over T6 + 5% FCS. However, more 8-cell embryos formed blastocyst outgrowths after 100 h in co-culture with uterine cells prepared from mice at Day 3 of pseudopregnancy than with uterine cultures prepared from mice at Day 1 of pseudopregnancy or oviduct cells. In addition, there was further improvement when the Day 3 uterine co-cultures were supplemented with 1 or 10 ng progesterone/ml.
These results highlight the importance of the oviduct and uterine cells during the different stages of preimplantation embryo development.