Regulation of endometrial prostaglandin F_2α synthesis during luteolysis and early pregnancy in cattle

Luteal regression is caused by a pulsatile release of prostaglandin (PG) F_2α from the uterus in the late luteal phase in most mammals including cattle. Although it has been proposed in ruminants that pulsatile PGF_2α secretion is generated by a positive feedback loop between luteal and/or hypophyseal oxytocin and uterine PGF_2α, the bovine endometrium may possess other mechanisms for initiation of luteolytic PGF_2α secretion. It has been recently demonstrated that tumor necrosis factor-α (TNF-α) stimulates PGF_2α output from bovine endometrial tissue not only during the follicular phase but also during the late luteal phase, suggesting that TNF-α is a factor in the initiation of luteolysis in cattle. Furthermore, our recent study has shown that IFN-τ suppresses the action of TNF-α on PGF_2α synthesis by the bovine endometrium in vitro, suggesting that IFN-τ plays a luteoprotective role by inhibiting TNF-α-induced PGF_2α production in early pregnancy. On the other hand, factors other than oxytocin or TNF-α have also been suggested to be involved in the regulation of PGF_2α synthesis by bovine endometrium. The purpose of this review is to summarize our current understanding of the endocrine mechanisms that regulate the timing and pattern of uterine PGF_2α secretion during the estrous cycle and early pregnancy.