A previous experiment showed that total protein extract from pig conceptuses did not affect CL activity when injected in utero to cyclic gilts during Days 12-15. In this experiment, 4-mg doses of secretory proteins, collected from supematants of conceptus cultures (30 h), were injected twice daily to gilts that had been primed with small doses of estrogen. The amount of IFN contained in the 4mg daily samples raises questions. In the study of Harney and Bazer, no antiviral assay was performed, as the finding of antiviral activity in the pregnant pig uterus was published at the time or after the completion of their experiment. Present results confirm and substantiate these data, at least as far as IFNs are concerned. buy flovent inhaler
Another result of Harney and Bazer’s work was that conceptus secretory proteins had no effect on cyclic CL activity even in the presence of a “priming dose” of estra-diol-17£ administered on Day 11 to mimic the peak of estrogen secreted by Day 11 conceptuses. This would suggest an absence of synergistic effect between estrogen at low doses on the one hand, and secretory proteins, including IFNs, on the other. The most probable hypothesis for maternal recognition of pregnancy in pigs would be that of estrogen-driven alteration of PGF2c, secretion, as previously described, and also tested in vitro using cyclic uterus fragments in a perifusion device. Such a system could be used to re-assay a possible synergistic effect (on PGF2a secretion) between IFNs and estradiol, using sub-effective doses of the steroid. It indeed remains possible that IFNs could synergize with the second estrogen release by the conceptus, which occurs on Days 15-18 and which seems to be necessary for prolonged extension of the CL lifespan. If estrogens appeared to be the main or only effector of maternal recognition of pregnancy in pigs, then the biological role of trophoblastic IFNs in this species would remain to be determined.