In the ewe, endometrial expression of cOx-2 is limited to the LE and SG and is detectable only at peak expression between Day 12 and Day 17 of the cycle or pregnancy. In the cow, staining for COX-2 is observed at all stages, even in the stroma and in DG. Nonetheless, four major resemblances remain between the two species regarding the expression of COXs: first, COX-1 is undetectable in the conceptus; second, COX-2 expression in the conceptus decreases with time; third, endometrial COX-2 is high in the late phase of the estrous cycle; and fourth, endometrial COX-2 is stimulated during early pregnancy. Thus, in both species, COX-2 is high in the endometrium at the time of onset of luteolysis and maximal at the ma-terno-fetal interface during establishment of pregnancy. COX-2 null female mice have reproduction failures at multiple levels.
In accordance, the current study supports the assertion that COX-2 is responsible for the regulation of PG synthesis in the endometrium and conceptus. However, the physiological role of COX-1-positive cells in the bovine stroma remains to be determined. Their exact identity is unknown at this time, although they are presumed to be leukocytes based on their pattern of distribution.