Effects of intrauterine infusion of oestradiol-17 beta and prostaglandin E-2 on luteal function in non-pregnant heifers.

Non-pregnant heifers (4/group) received intrauterine infusions of vehicle, oestradiol-17 beta (150 ng), PGE-2 (250 micrograms), or oestradiol + PGE-2 every 6 h from 12:00 h on Day 13 to 06:00 h on the day of subsequent oestrus or 06:00 h on Day 21 (day of oestrus = Day 0). Ten of 12 heifers receiving vehicle, oestradiol or PGE-2 returned to oestrus by Day 21, whereas none of the heifers receiving oestradiol + PGE-2 returned to oestrus by Day 21. Jugular venous progesterone concentrations of vehicle- and PGE-2-treated heifers declined rapidly after Day 15 and were basal (less than 1 ng/ml) by Day 20. For heifers receiving oestradiol infusions, systemic progesterone levels did not decline until after Day 18, but were again basal by Day 20. Heifers treated with oestradiol + PGE-2 maintained elevated systemic progesterone levels until Day 21 after oestrus. In addition, the corpora lutea of the heifers treated with oestradiol + PGE-2 were heavier (P less than 0.01) and contained more (P less than 0.05) progesterone than did corpora lutea of the heifers in the other 3 groups on Day 21 (3.4 g and 19.52 micrograms/g and 1.2 g and 1.65 micrograms/g, respectively). It is concluded that oestradiol-17 beta and PGE-2, both of which are produced by the bovine conceptus and secreted from the gravid uterus, may act synergistically to maintain luteal function during early pregnancy in the cow.