Blastocyst-endometrial interactions in early pregnancy in the sheep

This review analyses the endocrine recognition of pregnancy in the sheep. Particular emphasis is placed on the effect of a blastocyst on prostaglandin and protein metabolism in the endometrium. The preimplantation period is associated with increased prostaglandin content in the endometrium and uterine lumen, increased leucine incorporation into endometrial protein and increased blood flow to the uterus. It is concluded that there are substantial alterations in endometrial function during the protracted preimplantation period and that these alterations constitute an endocrine form of maternal recognition of pregnancy. However, it is not yet possible to attribute these alterations to specific embryonic signals.