[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to investigate whether peripheral plasma profiles of pregnancy specific protein B (PSPB) are predictive of pregnancy outcome in adolescent sheep in which growth of the placenta has been compromised by the competing nutrient demands of maternal tissue synthesis. Embryos recovered on day 4 after oestrus from adult ewes inseminated by a single sire were transferred in singleton to prepubertal adolescent recipients. After transfer, the adolescent recipients were individually offered a high or low proportion of a complete diet to promote rapid (RMG) or normal (NMG) maternal growth rates (n = 12 per group). After day 100 of gestation the feed intake of the NMG group was adjusted weekly to meet the nutrient requirements of the gravid uterus. Blood was sampled three times a week throughout gestation and analysed for PSPB and progesterone. Liveweight gain during the first 120 days of gestation was 229 +/- 9.1 and 105 +/- 3.9 g day-1 for the RMG and NMG groups, respectively. For ewes delivering live young, mean placental mass at term was 263 +/- 16.8 and 438 +/- 44.6 g (P < 0.002), while lamb birthweight was 2.74 +/- 0.25 and 4.34 +/- 0.27 kg (P < 0.001) for the RMG (n = 8) and NMG (n = 11) groups, respectively. The biphasic pattern of PSPB secretion during gestation was similar in all ewes delivering live young, but individual concentrations within treatment groups were highly variable. Mean PSPB concentrations were lower in RMG than in NMG ewes throughout gestation (P < 0.05) and the major differences in relative terms were detected between days 50 and 100 of pregnancy. PSPB concentrations during this latter period were correlated (P < 0.05) with placental mass at term but not with lamb birthweight. High dietary intakes, leading to rapid maternal growth rates were associated with low peripheral progesterone concentrations (P < 0.02) throughout gestation. Irrespective of treatment group, progesterone concentrations during the second half of pregnancy were positively associated with both placental mass at term (P < 0.002) and lamb birthweight (P < 0.01). The incidence of non-infectious abortion during late gestation (125 +/- 1.3 days) was higher (P < 0.001) in the RMG (4 of 12) than in the NMG (1 of 12) group and was associated with abnormal PSPB profiles in the former group. The mass of the fetus at the time of abortion was highly correlated (P < 0.01) with mean PSPB concentrations up to day 120 of gestation, but was independent of peripheral progesterone concentrations. These results suggest that sequential measurement of PSPB may provide a reliable indicator of fetal distress and adverse pregnancy outcome in singleton bearing ewes. PSPB and progesterone analysis may also have prognostic value as a biochemical marker of suboptimal placental growth and function in sheep.
[Show abstract][Hide abstract] ABSTRACT: A highly controlled model to investigate nutrient partitioning and the control of fetal growth in the rapidly growing adolescent sheep is described. Embryos recovered from superovulated adult ewes inseminated by a single sire were transferred in singleton to the uterus of prepubertal adolescent recipients induced to ovulate at 21 weeks of age (liveweight 44.4 +/- 0.38 kg). After embryo transfer, the adolescent recipients were individually offered a high (n = 28) or low (n = 20) quantity of a complete diet calculated to achieve rapid (RMG) or normal (NMG) maternal growth rates. After day 100 of gestation the feed intake of the NMG group was adjusted weekly to meet the increasing nutrient demands of the gravid uterus. The proportion of adolescent recipients initially conceiving was significantly (P < 0.01) influenced by maternal nutrient intake and was lower in the RMG (0.57) than in the NMG (0.85) group. For adolescent dams that maintained their pregnancies, liveweight gain during the first 95 days of gestation was significantly (P < 0.001) higher in the RMG compared with the NMG group (234 +/- 9.5 and 75 +/- 5.0 g day-1, respectively). Rapid maternal growth rates were associated with a significant reduction in both fetal and placental weights as determined when the animals were killed on day 95 of gestation (n = 3 per group) or at term. For the RMG (n = 8) and NMG (n = 11) groups, respectively, mean lamb birthweights at term were 2.74 +/- 0.25 and 4.34 +/- 0.27 kg (P < 0.001), while term placental weights were 263 +/- 16.8 and 438 +/- 44.6 g (P < 0.002). The number of fetal cotyledons per placenta and mean fetal cotyledon weight were significantly lower in RMG compared with NMG ewes (P < 0.05). Irrespective of treatment group, lamb birthweight was highly positively correlated with placental weight and both parameters were negatively correlated with maternal liveweight gain during the first 100 days of gestation. The incidence of non-infectious spontaneous abortion at 125 +/- 1.3 days of gestation was higher (P < 0.001) in the RMG (4 of 12) than in the NMG (1 of 12) group. Similarly, duration of gestation for those ewes delivering live young was shorter (P < 0.01) in the RMG compared with the NMG group (140 +/- 0.94 versus 143 +/- 0.28 days). Colostrum yield at parturition was positively related to placental weight and significantly lower (P < 0.001) in the RMG than in the NMG group (35 +/- 12.1 and 247 +/- 36.2 g, respectively). Neonatal survival rates at 72 h after parturition were reduced (P < 0.05) in the RMG (38%) compared with the NMG group (91%). These data suggest that in rapidly growing adolescent ewes, the established anabolic drive to maternal tissue synthesis is maintained at the expense of the gradually evolving nutrient requirements of the gravid uterus. This results in a major restriction in placental growth and a highly significant decrease in birthweight.
[Show abstract][Hide abstract] ABSTRACT: We examined the key events underlying maternal recognition of pregnancy and the prevention of luteolysis in early postpartum ewes by synchronously transferring single expanded blastocysts recovered from control ewes on day 11 of pregnancy into the uterus of either postpartum recipients that had been induced to ovulate 28 days after lambing (n = 12) or control recipients (n = 11). Conceptus development uterine flush interferon (oTP-1) concentrations, endometrial oxytocin receptor concentrations and endometrial prostaglandin F2 alpha (PGF2 alpha) release in vitro were determined 5 days later (corresponding to day 16 of the ovarian cycle). By this stage, both conceptus mass and oTP-1 content of total uterine flush in the eight postpartum recipients that remained pregnant were significantly lower (P < 0.01) than in the eight pregnant control ewes (524 +/- 116.6 versus 959 +/- 80.6 mg and 968 +/- 16.9 versus 1512 +/- 106.2 ng oTP-1 for postpartum and control recipients, respectively). These effects were independent of ovulation rate and daily peripheral progesterone concentrations after blastocyst transfer, which were similar between groups. Endometrial oxytocin receptor density was variable in both groups when they were killed, and was generally higher in pregnant postpartum than in control recipients, and was significantly different (P < 0.05) when the values for the transfer but not the contralateral uterine horns were compared. Similarly, basal and oxytocin-stimulated endometrial PGF2 alpha release during a 4 h incubation were higher (P < 0.01) in pregnant postpartum versus control recipients.(ABSTRACT TRUNCATED AT 250 WORDS)
[Show abstract][Hide abstract] ABSTRACT: Overfeeding during early pregnancy in ewes compromises pregnancy establishment and/or embryo survival. To determine whether high feed intakes after ovulation alter the secretory dialogue between the conceptus and the endometrium, 24 embryos (8-16-cell) from ewes fed maintenance rations were synchronously transferred in singleton on Day 3 of the cycle (oestrus, Day 0) into the uterus of ewes receiving a high or low plane of nutrition from Day 0 (n = 12 ewes per group). Embryo survival and conceptus growth were assessed on Day 16. At this time, pregnancy was maintained in 11 of 12 recipient ewes per group and conceptus mass was not influenced by nutritional plane (637 +/- 48 v. 583 +/- 72 mg for high and low groups respectively). Conceptus and endometrial tissues were cultured separately for a further 24 h in vitro in the presence of [3H]leucine. There was no quantitative difference between nutritional treatments in the incorporation of radiolabel into proteins synthesized and secreted by the conceptus or endometrium. Secretion of ovine trophoblast protein-1 was also similar in both groups. Peripheral progesterone concentrations were significantly (P < 0.05) lower throughout the luteal phase in recipient ewes on high v. low intakes after ovulation. This effect was independent of ovulation rate which was 3.1 +/- 0.40 and 2.6 +/- 0.25 corpora lutea for high and low groups respectively. A high plane of nutrition after ovulation did not influence embryo survival and development in vivo or luteotrophic protein secretion in vitro despite a reduction in peripheral progesterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
No preview · Article · Jan 1994 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: Induction of ovulation early post partum in sheep is associated with a high incidence (30-40%) of premature luteolysis. The present study was designed to characterize oxytocin receptor levels, oxytocin-stimulated inositol phosphate (IP) turnover (second messenger) and oxytocin-stimulated prostaglandin F2 alpha (PGF2 alpha) release in the endometrium of post-partum ewes induced to ovulate 21 days after parturition and expected to exhibit a range of corpus luteal functions subsequently. Ovulation was induced on day 21 post partum using a controlled internal drug release device and pregnant mare serum gonadotrophin, and uterine tissues were collected on days 5, 10 or 15 of the cycle (n = 4/day). A further 12 ewes whose interval from previous parturition exceeded 150 days were similarly treated and acted as controls. Measurement of daily peripheral progesterone concentrations revealed that while all control ewes exhibited normal luteal function, abnormal luteal function was evident in two, two and one post-partum ewes studied on days 5, 10 and 15 of the cycle respectively. Oxytocin receptor binding was detected (by receptor-binding assay and in-vitro autoradiography) in the endometrium and myometrium of post-partum ewes at all three stages of the oestrous cycle but only at day 15 in control ewes. To determine IP turnover, 100 mg caruncular endometrium was incubated in duplicate for 2.5 h with 10 microCi [3H]inositol and treated with 0 or 2 mumol oxytocin/l for 30 min, then [3H]inositol mono-, bis- and trisphosphates were quantified.(ABSTRACT TRUNCATED AT 250 WORDS)
No preview · Article · Feb 1993 · Journal of Endocrinology
[Show abstract][Hide abstract] ABSTRACT: 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 embryos from post-partum donors are transferred to a normal uterine environment 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 during the period of rapid growth coincident with the maternal recognition of pregnancy. In Experiment 1, the efficiency of the blastocyst transfer procedure was determined using control ewes > 150 days post-partum. Eight of nine recipient ewes established pregnancies and 75% of blastocysts survived to term. In Experiment 2, blastocysts were transferred to control (n = 12) or post-partum (n = 10) recipients that had been induced to ovulate 28 days after lambing during the breeding season. Conceptus 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 corresponding control ewes. Conceptus and endometrial tissues were cultured separately for a further 24 h in vitro in the presence of [3H]leucine to determine production of oTP-1 and the pregnancy-specific endometrial 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 trophoblast protein 1 (oTP-1) in vitro. However, despite normal oTP-1 production the conceptus tissue failed to completely suppress endometrial oxytocin receptor binding. The negative correlation between p70 production and oxytocin receptor density implies a possible role for this protein in the suppression of oxytocin receptor synthesis required to prevent luteolysis in pregnant ewes.
No preview · Article · Jan 1993 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: Induction of ovulation post partum is associated with a high incidence of prematurely regressing corpora lutea. However, inadequate luteal function is not the sole reason for pregnancy failure, because ewes with normal corpus luteum function and successful fertilization also fail to establish pregnancies. The effects of suckling status and the interval from post partum to rebreeding on corpus luteum and endometrial function were examined in vivo and in vitro. Ewes were weaned early or allowed to lactate, induced to ovulate using a progesterone-impregnated controlled internal drug release device and an intramuscular injection of pregnant mare serum gonadotrophin, and inseminated (intrauterine) at either 21 or 35 days post partum (n = 10 per group). A further 10 standard ewes whose interval from parturition was in excess of 150 days were included for comparative purposes. On Day 10 after insemination the pregnancy rate was determined in four ewes from each of the post-partum groups and five standard ewes. These ewes were then ovariectomized and hysterectomized for studies in vitro. The incidence of premature luteal regression, as assessed by progesterone concentrations in peripheral blood was independent of the suckling stimulus but dependent on stage post partum (21 days post partum, 6 of 19 ewes; 35 days post partum, 0 of 19 ewes; P less than 0.05). Luteal function was normal in all standard ewes. Ovulation rate, corpus luteum weight, corpus luteum progesterone content and basal progesterone production in vitro were significantly less in 21-day than in 35-day post-partum ewes. Pregnancy rates as determined on Day 10 or at term were low in all post-partum groups (7 out of the 38 ewes inseminated) compared with standard ewes (8 of 10). Uterine function was assessed by culturing endometrial tissue from the tip and body of each uterine horn in the presence of [3H]leucine for 30 h at 37 degrees C. Incorporation of radiolabel into non-dialysable proteins synthesized and secreted by the endometrium in vitro was independent of uterine horn location and suckling status but was significantly lower (P less than 0.001) in media from 21-day than from 35-day post-partum ewes. Irrespective of treatment group, incorporation of radiolabel was positively correlated with mean plasma progesterone concentrations on Days 2-10 after insemination and with basal progesterone production in vitro. Secreted proteins were detected by two-dimensional-polyacrylamide-gel electrophoresis and fluorography.(ABSTRACT TRUNCATED AT 400 WORDS)
No preview · Article · Feb 1992 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: The induction of ovulation in early post-partum ewes is associated with a high incidence of premature luteal regression which is independent of the suckling stimulus but dependent on the stage post partum. The aim of the present study was to determine whether oxytocin receptors are present on uterine endometrium early in the luteal phase and hence ascertain whether oxytocin-induced uterine prostaglandin F2 alpha release is a possible mechanism involved in the premature regression of these post-partum corpora lutea. Ovarian and uterine tissues were collected on day 4 of the the cycle in ewes induced to ovulate at either 21 or 35 days post partum (n = 4 per group). A further four cyclic ewes were similarly synchronized to ovulate and acted as controls. Corpora lutea from the 21-day post-partum group were significantly (P less than 0.01) smaller, had a lower progesterone content and a reduced capacity to secrete progesterone in vitro than corpora lutea from 35-day post-partum or control ewes. A highly specific oxytocin receptor ligand 125I-labelled d(CH2)5[Tyr(Me)2, Thr4,Tyr-NH29]-vasotocin was used to localize and characterize high affinity oxytocin receptors in uterine endometrium (dissociation constant 145 pmol/l). Oxytocin receptor concentrations in endometrium from ewes induced to ovulate at 21 days post partum were on average five-fold higher (P less than 0.05) than in 35-day post-partum and control groups.
No preview · Article · Mar 1991 · Journal of Endocrinology