Embryonic suppression of oxytocin--associated neurophysin release in early pregnant sheep.

Pulsatile release of the oxytocin-neurophysin (OT-N) occurs during luteal regression in non-pregnant sheep. The effect on this neurophysin release by the presence of a conceptus was investigated. It was found that the transfer of an embryo, on either Day 12 or 13, to the uterus of a non-pregnant sheep inhibited the pulsatile release of OT-N. This result suggests that in the early pregnant sheep, the embryo may prevent corpus luteum regression by suppressing the pulsatile release of maternal oxytocin which is considered to induce the release of uterine prostaglandin F2 alpha.