ABSTRACT
ABSTRACT The endogenous luteolysin in ruminants, prostaglandin (PG) F2a, has been shown to have a direct toxic effect on the early embryo in both cattle and sheep. The effect is time/stage specific, occurring during the transition from morula to blastocyst and preventing hatching of the blastocyst. In this chapter, the series of studies in which the embryotoxic effect was discovered in the early-weaned postpartum beef cow is reviewed in detail. The effect could be produced by oxytocin, but it acted through increased secretion of PGF2a. Confirmatory studies were done in sheep, and the effect was shown to be systemic, as opposed to the local nature of luteolytic effects of uterine PGF2a in these species. Applications became apparent when it was shown that inhibition of the secretion of PGF2a at the time of transfer of embryos into recipient cows could improve the pregnancy rate. Subsequently, receptors for PGF2a were demonstrated on the bovine embryos at the morula and blastocyst stages, and an agent that blocks receptors for PGF2a has been shown to improve success of embryo transfers in cattle. These findings have implications for several situations in which uterine secretion of PGF2a may be greater than normal during days 4 through 9 after mating or artificial insemination in cattle and sheep, in addition to the observed effects relative to transferred embryos.
