MATERNAL RECOGNITION OF PREGNANCY

Enhanced secretion of PGF(2 alpha) from endometrial explants in vitro in response to oxytocin is associated with augmented activities of phospholipase A(2), phospholipase C and prostaglandin endoperoxide H synthase (PGS). In early pregnancy, maintenance of the corpus luteum is associated with an absence of pulsatile PGF(2 alpha) secretion; an increase in endometrial inhibitors of phospholipase A(2) and PGS contribute to the antiluteolytic alterations of PGF(2 alpha) secretion. Linoleic acid is a competitive inhibitor of arachidonic acid metabolism by PGS, and microsomal concentrations of free linoleic acid are increased in the endometrium of pregnant cattle. The trophoblast produces large quantities of interferon tau (IFN-tau). Inhibition of increases in endometrial oestradiol receptor mRNA and protein are associated with intrauterine administration of recombinant (r) ovine (o) IFN-tau in sheep. Intrauterine injections of rbovine (b) IFN-tau in cattle (days 14-17) altered endometrial function so that secretion of PGF(2 alpha) from cultured endometrial epithelial cells was reduced. Antiluteolytic effects were not expressed in 20% of cows receiving IFN-tau or rbIFN-alpha(I)1 indicating that an inadequate endometrial responsiveness may contribute to embryo mortality. IFN-tau may activate a signal transduction system similar to that induced by other type I IFNs; activation of an intracellular tyrosine kinase ultimately leads to activation of an IFN-stimulated response element to induce gene transcription. Biological responses associated with pregnancy and IFN-tau treatment are integrated into a multifactorial antiluteolytic model. Strategies to enhance embryo survival could include supplementation with rIFN-tau and alterations in endometrial responsiveness to this cytokine through dietary manipulation of lipid metabolism.