Expression of Cyclooxygenase‐1 and ‐2 in the Porcine Endometrium during the Oestrous Cycle and Early Pregnancy

Cyclooxygenase (COX) is the rate-limiting enzyme that catalyses the initial step in prostaglandins (PGs) production. In the present studies, endometrial COX-1 and COX-2 expression throughout the oestrous cycle and early pregnancy was analysed in pigs using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry. There were no changes in messenger RNA (mRNA) and protein expression for COX-1 in cyclic pigs. In pregnant animals, mRNA levels of this enzyme increased on days 22-25 (p < 0.001). However, no upregulation of COX-1 protein was detected. Quantification of COX-2 mRNA expression during the oestrous cycle revealed significant increases on days 10-12 and 14 (p < 0.001 and p < 0.01 vs days 2-4, respectively). Protein levels were also increased on day 14 when compared with days 2-12 and 18-20 after oestrus. In pregnant animals, the patterns of both COX-2 mRNA and protein expression were similar. Messenger RNA levels were higher on days 16 and 22-25 (p < 0.01 vs day 10). Moreover, the protein content tended to increase on days 16 and 22-25. COX-1 and COX-2 were localized in the luminal and glandular epithelium as well as in the uterine stroma. In contrast to COX-1, a positive immunostaining reaction for COX-2 was detected only on days 12-16 after ovulation and on days 14-16 of pregnancy. In conclusion, these results indicate specific patterns of COX-1 and COX-2 expression in the porcine endometrium throughout the oestrous cycle and early pregnancy. COX-2 rather than COX-1 seems to be the primary enzyme responsible for modulated PGs production at the time of luteolysis in cyclic and during implantation in pregnant animals.