DIFFERENCES IN THE EXPRESSION OF CYTOCHROMES P450-17-ALPHA-HYDROXYLASE AND AROMATASE IN MEISHAN AND YORKSHIRE CONCEPTUSES AT DAYS 10.5-14.0OF GESTATION

The expression of cytochromes P450 17 alpha-hydroxylase (P450c17) and aromatase (P450arom) was compared between preimplantation Chinese Meis han and domestic Yorkshire conceptuses during the period encompassing maternal recognition of pregnancy. Individual conceptuses were recover ed on days 10.5, 11.0, 11.5, 12.0, and 14.0 of gestation. Diameter (sp herical blastocysts), length (elongated blastocysts), DNA, protein and oestradiol content, as well as the amounts of P450c17 and P450arom (w estern analysis) were determined in individual conceptuses. Comparison s were made only between conceptuses of similar diameters on each day which restricted analyses to blastocysts 6 mm or less in diameter on d ays 10.5-12.0. Nonetheless, both DNA and protein content were greater in Yorkshire than in Meishan conceptuses. Oestradiol content also tend ed to be greater in Yorkshire than in Meishan conceptuses across days. A significant effect of breed and breed by day interaction was detect ed for P450c17. Expression of P450c17 in Yorkshire conceptuses increas ed markedly above that in Meishan conceptuses by day II, remained high until day 11.5 and returned to values similar to those of Meishans by day 12. The expression of P450arom was also greater in Yorkshire than in Meishan conceptuses, but no breed by day interaction was detected. These data suggest that differences in development between Meishan an d Yorkshire conceptuses include trophoblastic differentiation during p reattachment stages. The significance and impact of this divergence in development on subsequent growth and survival remains to be determine d.