Induction of cyclooxygenase type-2 (COX-2) in rat endometrium at the peak of serum estradiol during the estrus cycle.

We investigated the induction of cyclooxygenase (COX) in rat endometrium during the estrus cycle. The estrus cycle was divided into five stages (proestrus, estrus, diestrus-1, diestrus-2, diestrus-3) by cytological observation of vaginal smears. COX-1 was detected in the endometrium during all five stages of the estrus cycle. In contrast, COX-2 in the endometrium was detectable only in three stages (diestrus-3, proestrus, estrus) and showed a peak at diestrus-3, coinciding with the peak in serum estradiol level, suggesting the estradiol-dependent induction of COX-2.