CONCEPTUS DEVELOPMENT IN-VIVO, ENDOMETRIAL AND CONCEPTUS PROTEIN RELEASE IN-VITRO FOLLOWING BLASTOCYST TRANSFER TO EWES INDUCED TO OVULATE AT 28 DAYS POSTPARTUM

The use of laparoscopic insemination to deposit semen into the tip of the uterine horn ensures fertilization in ewes induced to ovulate at 3 -5 weeks post-partum. Acceptable pregnancy rates are achieved if embry os from post-partum donors are transferred to a normal uterine environ ment yet embryos rarely survive when transferred or returned to a post -partum uterus. Blastocyst transfer procedures were developed to test whether the post-partum uterus can support conceptus development durin g the period of rapid growth coincident with the maternal recognition of pregnancy. In Experiment 1, the efficiency of the blastocyst transf er procedure was determined using control ewes >150 days post-partum. Eight of nine recipient ewes established pregnancies and 75% of blasto cysts survived to term. In Experiment 2, blastocysts were transferred to control (n = 12) or postpartum (n = 10) recipients that had been in duced to ovulate 28 days after lambing during the breeding season. Con ceptus development was assessed 96 h after blastocyst transfer on Day 15 of the cycle. At this time, conceptus mass in the seven post-partum ewes which remained pregnant was generally lower than in the 11 corre sponding control ewes. Conceptus and endometrial tissues were cultured separately for a further 24 h in vitro in the presence of [H-3]leucin e to determine production of oTP-1 and the pregnancy-specific endometr ial protein p70 respectively. Oxytocin binding sites were measured in endometrial tissue. Following 96 h culture in a post-partum uterus the conceptus retained its competence to synthesize and secrete ovine tro phoblast protein 1 (oTP-1) in vitro. However, despite normal oTP-1 pro duction the conceptus tissue failed to completely suppress endometrial oxytocin receptor binding. The negative correlation between p70 produ ction and oxytocin receptor density implies a possible role for this p rotein in the suppression of oxytocin receptor synthesis required to p revent luteolysis in pregnant ewes.