The influence of pregnancy on PGF 2α secretion in cattle. I. Concentrations of 15-keto-13,14-dihydroprostaglandin F 2α and progesterone in peripheral blood of recipients of transferred embryos

Abstract

Three experiments were performed to study the influence of viable or formalin-killed embryos, transferred late in the oestrous cycle, on the maintenance of the corpus luteum and prostaglandin production by the uterus. In Experiment 1, day-12 to day-16 embryos were transferred to synchronous recipients (± 24h) on day 12 to day 17. All five recipients of formalin-killed embryos and nine recipients of viable embryos exhibited a decline in progesterone to baseline levels (0.8 ng/ml) which was followed by oestrus in some of them. In a further nine animals, subsequently shown to be pregnant, luteal phase levels of progesterone were maintained. In six animals (not pregnant at day 42) progesterone levels were maintained for varying periods following transfers between days 13 and 17. In Experiment 2, progesterone and 15-keto-13,14-dihydroprostaglandin F 2α (PGFM) concentrations were determined in plasma samples collected hourly for 15 days from seven animals receiving fresh or formalin-killed embryos on day 16 or 17. Marked hour-to-hour changes in progesterone concentrations were seen in all animals initially and persisted in those in which luteal phase levels were maintained. In three cows progesterone concentrations declined to baseline levels during the period of hourly sampling. Progesterone levels were maintained in the others although they subsequently declined in two cases. In all seven cows a large PGFM peak (189–828 pg/ml) was associated with surgical transfer. The luteolysis in three recipients was associated with a series of PGFM peaks (165–396 pg/ml) whereas only occasional single peaks were observed in those cows in which luteal phase concentrations of progesterone were maintained. In Experiment 3 the cause of the PGFM peak associated with surgery was investigated. While extensive manipulation of the genital tract, at different times in the cycle, or oxytocin injections on day 16 had little effect on PGFM concentrations, a peak (310–1000 pg/ml) was observed immediately after the intravenous injection of sodium thiopentone. It was concluded that the corpus luteum can be maintained by the introduction of a viable embryo as late as day 17 of the cycle and that the decline in progesterone concentration at luteolysis is associated with a series of PGFM peaks which were absent or reduced in animals in which progesterone levels were maintained.