Platelet-activating factor (PAF)-like activity, localization of PAF receptor (PAF-R) and PAF-acetylhydrolase (PAF-AH) activity in bovine endometrium at different stages of the estrous cycle and early pregnancy*

PAF-like activity in the endometrium increased from days 2-4 to day 12 and day 20 in both cyclic and pregnant cows. There was an increase in platelet aggregation induced by PAF-like activity in the endometrium of pregnant animals on day 20 as compared to cyclic animals at the same point in time. Two major bands of PAF-R protein at 67 kDa and 97 kDa were detected by Western blot analysis. PAF-R was localized mainly in luminal and glandular epithelium of the endometrium, but the staining was markedly increased in the endometrium of pregnant cows on day 20 compared to cyclic animals on the same day. The purified PAF-AH from the endometrium is similar to in plasma. In cyclic cattle, no changes in PAF-AH activity of endometrium were observed, whereas a decrease in enzyme activity occurred in pregnant cows on day 20 as compared to cyclic animals on the same day. We suggest that the bovine endometrium produces PAF-like activity, expresses the PAF-R and possesses a PAF-AH activity which varies during pregnancy.