Modulation of oviductal transport in mares by local application of prostaglandin E2

Equine embryos enter the uterus 144-156 h after ovulation, before which time the passage of embryos through the oviduct is halted in the region of the ampullary-isthmic junction. It is thought that further onward movement of embryos to the uterus is facilitated by secretion of prostaglandin E2 (PGE2) by the embryos, which relaxes the smooth muscle of the isthmus. In the present study, the effect of a single local application of PGE2 on oviductal transport was examined in 22 Thoroughbred and Pony mares that were inseminated on alternate days during oestrus. On day 4 after ovulation, the ipsilateral ovary, oviduct and tip of the uterine horn were visualized by flank laparoscopy, and either a commercial preparation of PGE2 suspended in a triacetin-based gel or a control gel containing no PGE2 was dripped along the external surface of the oviduct. On day 5, the uterus of each mare was flushed three times with phosphate-buffered saline containing 1% (v/v) fetal bovine serum and, if no embryo was recovered, the flushing procedure was repeated on day 7 or 8. Overall, the embryo recovery rate was similar in PGE2-treated and control mares (65 and 63%, respectively). However, the recovery rate of embryos on day 5 was significantly higher for PGE2-treated mares than for control mares (60 versus 0%; P < 0.01), indicating an increased rate of embryo transport in PGE2-treated mares. Furthermore, unfertilized oocytes were recovered from nine of the PGE2-treated mares on day 5 but from none of the control mares. All of the embryos recovered on day 5 were compacted morulae, whereas all of those recovered on days 7 or 8 were expanding blastocysts. The results of the present study support the role of embryonic PGE2 in oviductal transport in mares. The results also demonstrate that a single local application of PGE2 is a simple and practical method for speeding the passage of embryos through the oviduct for nonsurgical recovery of morulae from the uterus.