Patterns of expression of Bax, Bcl-2 and Bcl-x(L) in the implantation site in rat during pregnancy.

The uterine endometrium responds to blastocyst implantation with extensive proliferation and differentiation of stromal cells into decidual cells, forming the antimesometrial and mesometrial decidua. These undergo regression by apoptosis but as this process occurs at different time periods suggest that there is spatially dependent temporal control of apoptosis in these specific regions. To elucidate the role of the mitochondrion-dependent signalling pathway in tissue regression, we investigated the spatial and temporal pattern of expression of the Bcl-2 family members in uterine tissues of the implantation site, from the post-implantation period to parturition. Furthermore, the activities of the initiator caspases-8 and -9, and of the executioner caspase-3 were determined. Overall Bax and Bcl-2 were expressed from day 8 till day 19, whilst Bcl-x(L) was extinguished by day 16. In the antimesometrial and in the mesometrial decidua both Bcl-2 and Bax declined from days 10 to 12. In the latter Bcl-2 immunoreactivity decreased till the end of pregnancy, whilst for Bax a constant level remained thereafter. The pattern of variation of enzymatic activities throughout pregnancy for all the enzymes was similar, increasing from days 10 to 14 and decreasing towards the end of pregnancy. The increased levels of active caspase-9 correlated with Bax/Bcl-2 and Bcl-x(L) expression suggesting that the apoptotic mitochondrion-dependent pathway is involved in decidual regression during pregnancy progression.