The hypothesis that pregnancy success could be improved in early postpartum ewes by prolonging the lifespan of the corpus luteum via active immunization against prostaglandin F2α (PGF2α) was tested. Further experiments in ewes immunized against PGF2α investigated the effects of exogenous PGF2α on the preovulatory follicle and the effects of PGF2α and oestradiol benzoate on corpus luteum function. Four weeks prepartum, 39 ewes bred to lamb during seasonal anoestrus received either 5 mg PGF2α–ovalbumin conjugate (n = 20; immunized) or ovalbumin (n = 19; control) in Freund's complete adjuvant. Treatments were repeated on day 5 post partum with reagents emulsified in Freund's incomplete adjuvant. On day 17 post partum, ewes received 500 iu pregnant mares' serum gonadotrophin (PMSG) and 48 h later 50 μg gonadotrophin-releasing hormone (GnRH). Laparoscopy was performed 36 h after GnRH to assess ovarian activity and ewes with recent ovulations were inseminated into the uterus. No immunized ewes had ovulated, but ten had follicles that luteinized and secreted progesterone during the 8 weeks studied. Eighteen of 19 control ewes ovulated and 15 of 18 had increased progesterone concentration for at least 21 days. By day 70 post partum, progesterone had returned to basal values in all control ewes. In a second study, 24 immunized ewes bearing persistent corpora lutea, and for which the interval from the previous parturition was greater than 90 days, received 15 mg PGF2α and 500 iu PMSG followed 48 h later by 50 μg GnRH. PGF2α induced corpus luteum regression in all ewes. PMSG and GnRH treatments resulted in oestrus in 21 of 24 ewes. Sixteen hours after GnRH, 10 ewes received a second injection of 15 mg PGF2α. PGF2α induced follicular rupture in eight of ten immunized ewes, whereas only two of 14 ewes not receiving PGF2α ovulated (P < 0.01). All anovular ewes had large cystic follicles that luteinized. In a third study, 22 ewes immunized against PGF2α, and having persistent corpora lutea, received, on two consecutive days, either oestradiol benzoate (750 μg; n = 11) in oil or oil (n = 11). Laparoscopy was performed on all ewes immediately before injections and four of the 11 ewes in each group possessed uterine horns that were filled with fluid. No fluid was judged to be in the horns of the remaining seven ewes in each group. On the basis of serum concentrations of progesterone and laparoscopies, oestradiol benzoate induced luteal regression in those ewes with uterine fluid and failed to induce luteal regression in those ewes lacking uterine fluid. Luteal function was unaffected in ewes that received the oil vehicle. These data suggest that premature luteal regression was not the reason for failure of occurrence of pregnancy. Immunization against PGF2α was effective in blocking ovulation, but not in inhibiting oestrous behaviour or the formation of persistent luteal tissue. Treatment of immunized ewes with exogenous PGF2α restored the ability of ewes to ovulate, providing further evidence for the involvement of PGF2α in ovulation. The ability of oestradiol to induce luteolysis in immunized ewes was associated with the presence of uterine fluid.
C. M. V. Bettencourt, R. J. Moffatt and D. H. Keisler
J. D. Godkin, F. W. Bazer, J. Moffatt, F. Sessions and R. M. Roberts
Summary. Sheep blastocysts (Day 13–21) incubated in a modified Minimum Essential Medium released proteins into the medium at an approximately linear rate over a 24-h period. Single Day-16 blastocysts converted 2–8% of the radioactivity supplied (100 μCi L-[3H]leucine) into non-dialysable macromolecules which were released into the medium. Two-dimensional polyacrylamide gel electrophoresis revealed that at Day 13 there was only one major product (Protein X), consisting of three closely similar isoelectric species (pI of denatured polypeptides about 5·5), each with molecular weights of 17 000. Between Days 14 and 21 additional proteins were detected. One of these was of high molecular weight (>660 000) and did not appear on the two-dimensional gels, but Protein X continued to predominate until Day 23 when it could not be detected. Explants of chorion from Day 30 of pregnancy failed to secrete Protein X. Protein X was released in significant quantities (50–100 μg per 24 h) by the trophoblast but not the yolk sac of Day-14 and Day-16 conceptuses, but was present in very low amounts in the tissues. Protein X from the incubation medium of Day-14 and Day-16 conceptuses was purified by successive DEAE ion exchange and Sephacryl S-200 gel chromatography. Because Protein X and some of the other proteins are produced transiently between Days 13 and 21, it is possible that they may play a role in maternal recognition of pregnancy in sheep.
D. Caton, F. W. Bazer, P. S. Kalra and R. J. Moffatt
Summary. On Day 5 of pregnancy, before the blastocyst migrates to the uterus, one uterine horn was ligated to restrict the trophoblast to the lumen ipsilateral to the corpus luteum. The numbers of placentomes (caruncles and cotyledons) were reduced by half, but neither at 120 nor at 140 days of pregnancy (term 147 days) did the weights of placentae and fetuses of treated ewes differ significantly from those of control ewes. Amongst uterus-ligated animals prepared for chronic study, the rate of uterine blood flow (electromagnetic flow transducer, ml/min) to the pregnant horn was higher than in control ewes, as was the concentration of progestagens in maternal peripheral blood. There may be a compensatory response that causes hypertrophy of placentomes and that increases blood flow to the uterine horn containing placental tissue.
W. G. Zollers Jr, H. A. Garverick, M. F. Smith, R. J. Moffatt, B. E. Salfen and R. S. Youngquist
Luteal lifespan is short after first postpartum ovulation in early-weaned beef cows unless cows are pretreated with a progestogen. Regression of the short-lived corpus luteum in the postpartum beef cow is due to a premature release of prostaglandin F2α (PGF2α) from the uterus. The premature release of PGF2α may be mediated through lower concentrations of receptors for progesterone, higher concentrations of oxytocin receptors, or both, in the endometrium. Thirty-one beef cows were randomly assigned to four groups at parturition. Calves from cows assigned to the short cycle group (n = 6; control) and the short cycle/endometrium group (n = 10) were weaned at 30–32 days post partum. Cows in the normal cycle group (n = 5; control) and the normal cycle/endometrium group (n = 10) received norgestomet implants for 9 days beginning 21–23 days post partum and calves were weaned at implant insertion. Duration of oestrous cycle (x ± sem; P < 0.01) following first postpartum ovulation for the short cycle group was 11.5 ± 1.9 days compared with 18.8 ± 0.6 days for the normal cycle group. On day 5 following first postpartum ovulation, cows in the short cycle/endometrium and the normal cycle/endometrium groups were hysterectomized and endometrial tissue collected for measurement of progesterone and oxytocin receptors. Mean number of total progesterone receptors per cell was lower (P < 0.05) in the short cycle/endometrium group than in the normal cycle/endometrium group. Mean concentration of oxytocin receptors (fmol mg−1 protein) in the short cycle/endometrium group was higher (P < 0.05) than that in the normal cycle/endometrium group. In conclusion, uterine receptor populations for progesterone and oxytocin may influence the timing of PGF2α secretion during short oestrous cycles.