UTERINE CELLULAR-CHANGES IN 2',5'-OLIGOADENYLATE SYNTHETASE DURING THE BOVINE ESTROUS-CYCLE AND EARLY-PREGNANCY

The signal for maternal recognition of pregnancy in cattle is bovine t rophoblast protein-1 (bTP-1), a Type I trophoblast interferon. One of the many functions of interferons is the induction of the 2',5'-oligoa denylate (2-5[A]) system, which is involved in cell division and selec tive degradation of mRNA. The present study focused on the cellular ch anges of 2-5(A) synthetase in bovine endometrium during the estrous cy cle and early pregnancy. Ability of recombinant bTP-1 to stimulate act ivity of the enzyme in uterine cells throughout the estrous cycle was also evaluated in vitro. Surface epithelium, glandular epithelium, and stroma were enzymatically separated in cows on Day 5, 10, 15, or 18 p ostestrus and on Day 1 5 or 18 of pregnancy. Cell samples were lysed a nd frozen for determination of the endogenous cellular content of 2-5( A) synthetase. Additional cells obtained during the estrous cycle were cultured and treated with increasing doses of recombinant bovine inte rferon alpha (rbIFN-alpha) or recombinant bTP-1 (rbTP-1). During the e strous cycle, 2-5(A) synthetase was greatest on Day 5 and declined app roximately 10-fold by Day 15 (p < 0.01). Cellular content of 2-5(A) sy nthetase was similar among all three endometrial cell types. In the gr avid horn of pregnant animals, presence of a conceptus significantly i ncreased (p < 0.01) 2-5(A) synthetase in all endometrial cell types co mpared to levels on Days 15 and 18 of the estrous cycle. On Day 18, le vels of 2-5(A) synthetase were 30-fold greater (p < 0.01) in epitheliu m (surface and glandular) from pregnant cows compared to that from cyc lic cows. Stromal content of 2-5(A) synthetase increased 10-fold (p < 0.01) in pregnant compared to cyclic cows. In cultured uterine cells, between 1 and 10 U/ml of rbTP-1 or rbIFN-alpha stimulated 2-5(A) synth etase in all endometrial cell types from Day 5, 10, and 15 cyclic cows . Endometrial cells cultured from Day 18 of the estrous cycle had high er 2-5(A) synthetase levels than native cells, indicating that these c ells differentiated during the 7-10 days of culture. These results ind icate that the conceptus directly stimulates the endometrium to increa se the activity of 2-5(A) synthetase at the time of maternal recogniti on of pregnancy (Day 15), and that the observed increase in 2-5(A) syn thetase is more pronounced in the epithelium than in the stroma.