Auswahl der wissenschaftlichen Literatur zum Thema „Ovine placental lactogen (oPL)“

ABSTRACT Discrepancies exist in the reported purity and biological activity of ovine placental lactogen (oPL), and little structural characterization has been reported. Ovine PL was purified from fetal cotyledonary tissue (day 100 of gestation) by monitoring activity with a recombinant bovine GH (bGH) liver radioreceptor assay. Two hundred grams of tissue yielded 4·2 mg of oPL, with an ∼ 1000-fold purification of oPL specific activity following initial tissue extraction. The oPL was radioiodinated and used in an ovine fetal liver (day 100 of gestation) radioreceptor assay to examine competitive displacement of oPL, ovine GH (oGH) and ovine prolactin (oPRL). The potency of oPL (ED50 = 0·18 nmol/l; ED50 is the quantity of ligand necessary to displace 50% of specifically bound 125I-labelled oPL) was greater than that of oGH (ED50 = 4·1 nmol/l) and oPRL (ED50 = 1·1 μmol/l) in competing for 125I-labelled oPL-binding sites. Attempts to sequence the NH2 terminus of oPL by vapour-phase sequencing indicated that the NH2 terminus was blocked. Purified oPL was subjected to trypsin and CnBr digestion, and two CnBr and six tryptic peptides were sequenced. The peptide sequences were compared with other PLs, oPRL and bGH for sequence similarity, and found to be most similar to bovine PL (bPL; 68% overall identity) and oPRL (47% overall identity). Complementary DNA (cDNA) clones were isolated for oPL by screening a λZAP cDNA library with a cDNA coding for bPL. Three cDNAs were nucleotide sequenced, and their combined sequence included 41 nucleotides of 5'-untranslated region, the complete coding region of pre-oPL (708 nucleotides) and a portion of the 3' untranslated region (158 nucleotides). The predicted amino acid sequence derived from the nucleotide sequence confirmed homology to bPL (67%) and oPRL (48%). Little amino acid sequence existed with other PLs (≤29%) or GH proteins (≤27%). These results suggest that oPL and oGH are more biologically similar in their ability to compete for fetal liver binding sites, but that oPL is structurally more similar to oPRL. Elucidation of exact structure–function relationships for oPL will, however, require further investigation. Journal of Endocrinology (1990) 126, 141–149

Accurate knowledge of placental lactogen localization is fundamental to any hypothesis of its synthesis and secretion. We used locally generated monoclonal and polyclonal antibodies from three separate sources to localize ovine placental lactogen immunoreactivity on light and electron microscope Lowicryl K4M sections of ovine placentomes of 97-145 days of gestation, using immunogold techniques. All antibodies demonstrated that immunoreactivity was exclusively localized in the trophoectoderm binucleate cell Golgi body and granules and in granules in the syncytium derived from binucleate cell migration. No evidence was found to support a recent claim that monoclonal antibodies to oPL that were produced in Canada indicated a predominant localization of ovine placental lactogen to uninucleate trophectodermal cells.

ABSTRACT To determine whether arachidonic acid stimulates the secretion of ovine placental lactogen (oPL), arachidonic acid was infused as an intravenous bolus into pregnant ewes and fetuses. Plasma oPL concentrations were determined in mothers and fetuses before and for 5 h after infusion. The administration of 12·5 mg arachidonic acid (0·15−0·2 mg/kg, n = 11 experiments) to the pregnant ewes caused an increase in maternal plasma oPL concentrations of 73·9±15·6% (s.e.m.) and 60·8±18·1% above the pretreatment concentrations at 4 and 5 h respectively P<0·01 in each instance). The infusion of 25 mg arachidonic acid (n = 8) caused increases of 96·0±19·1% and 100·3±26·4% (P<0·005), and the stimulation was not inhibited by the cyclo-oxygenase inhibitors indomethacin and ibuprofen. In contrast to arachidonic acid, vehicle alone or palmitic acid had no effects on plasma oPL concentrations. Despite the increase in maternal plasma oPL concentrations, plasma oPL concentrations in the fetus remained unchanged after the maternal infusions. The infusion of arachidonic acid (0·5–1·5 mg/kg) directly into six fetuses had no effects on either fetal or maternal oPL concentrations. These studies indicate that (1) arachidonic acid stimulates maternal plasma oPL concentrations but has no effect on fetal oPL concentrations and (2) the stimulation of oPL secretion is not due to the conversion of arachidonic acid to prostaglandins or other cyclo-oxygenase products. J. Endocr. (1985) 106, 43–47

The placenta may mediate glucocorticoid-induced fetal growth restriction. Previous studies have examined effects of fetal cortisol in sheep, which reduces placental binucleate cell (BNC) number; the source of ovine placental lactogen (oPL). The effects of maternal GC are unknown. Therefore, this study examined the effects of maternal betamethasone (BET) administration on BNC number, distribution, placental oPL protein levels, and maternal and fetal plasma oPL levels. Pregnant ewes were randomized to receive injections of saline or one (104 days of gestation; dG), two (104 and 111 dG), or three (104, 111, and 118 dG) doses of BET (0.5 mg/kg). Placental tissue was collected before, during, and after the period of BET treatment. Fetal (121–146 dG) and placental (121 dG) weights were decreased after BET when compared with controls. In controls, the mean number of BNCs increased until 132 dG and decreased thereafter. Placental oPL protein levels peaked at 109 dG and remained stable thereafter. Maternal plasma oPL levels in controls increased across gestation; fetal plasma oPL levels decreased. BNCs were reduced by 24% to 47% after BET when compared with controls at all ages studied. Placental oPL protein levels, maternal, and fetal plasma oPL levels were also reduced after BET injections, but recovered to values that were not different to controls near term. BET disrupted the normal distribution of BNCs within the placentome. These data may suggest a placental role in growth restrictive effects of prenatal maternal BET exposure through alterations in placental output of oPL, a key metabolic hormone of pregnancy.

To determine whether changes in the relative biological potencies of ovine placental lactogen (oPL) and ovine growth hormone (oGH) during development derive from ontogenetic changes in the binding of these hormones to hepatic receptors, we have compared the binding of 125I-oPL and 125I-oGH to hepatic membranes from fetal lambs and pregnant sheep at mid- and late gestation and from postnatal sheep at 1 day to 7 mo of age. Specific high-affinity 125I-oPL binding sites in ovine fetal liver were detected as early as day 70 of gestation (term = 145 days), and the number of fetal 125I-oPL binding sites increased progressively throughout the latter half of gestation, reaching a maximum (11.2 fmol/mg protein) at 3-7 days before parturition. The potency of oPL (Kd 0.27 nM) in competing for 125I-oPL binding sites was 90 and 1,300 times greater than that of oGH and ovine prolactin, respectively. Although the number of fetal 125I-oPL binding sites increased throughout pregnancy, there was little or no specific binding of 125I-oGH noted in the fetus. Treatment of fetal liver membranes with 4 M MgCl2 did not enhance the subsequent specific binding of 125I-oGH, suggesting that the low specific binding of oGH did not result from occupation of hepatic receptors by endogenous circulating oPL or oGH. In contrast, MgCL2 treatment markedly increased the apparent number of fetal 125I-oPL binding sites, suggesting that oPL receptors in fetal liver are partly saturated in vivo by oPL.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract To clone ovine placental lactogen (oPL) cDNA, total RNA from sheep placental cotyledon was reverse transcribed and the single-stranded cDNA was PCR-amplified with 5′ and 3′ primers containing, respectively, Ncol and PstI sites. The oPL cDNA fragment amplified between these two primers extended from A(−1) to the natural stop codon. The PCR product was gel-purified and subcloned into a Puc vector and the insert was sequenced on both strands, revealing several differences relative to the published sequence: S19N, S69N, D129E and R165Q. We assume that these differences can be accounted for by the high level of individual polymorphism, which has been described in detail for PLs of different species. The insert was subcloned into Ncol/PstI-digested pTrc99A procaryotic expression plasmid and protein expression was induced by isopropyl-1-thio-β-d-galactopyranoside. Because of low expression, oPL's cDNA was further subcloned into pET8 procaryotic expression plasmid. Its expression in E. coli strain BL21 transformed with this vector yielded 30–40 mg/l. The expressed protein, found in the inclusion bodies, was refolded into a monomer and purified on a Q-Sepharose column to homogeneity. Structural analysis using circular dichroism revealed a spectrum similar to that of human GH (hGH) thereby indicating proper refolding. Gel filtration and binding experiments, including real-time kinetic measurements using the surface plasmon resonance method revealed that oPL forms transient homodimeric complexes with extracellular domains of prolactin receptors from rabbit, rat and bovine and with hGH receptor. The purified oPL was biologically active in an Nb2-11C cell proliferation bioassay, in its ability to stimulate β-casein synthesis in explants of ovine and rabbit mammary gland and fat synthesis in explants of bovine mammary gland, and in a proliferation assay using FDC-P1 cells transfected with rabbit or hGH receptors. Journal of Endocrinology (1997) 152, 317–327

ABSTRACT The effect of restricting placental growth on maternal glucose, insulin and placental lactogen was investigated in 16 ewes carrying singleton lambs. Uterine caruncles were removed from seven ewes (caruncle ewes) before pregnancy, resulting in reduced placental size and retarded intra-uterine fetal growth. The concentration of insulin in maternal plasma was similar in both control and caruncle ewes. The concentration of glucose was significantly higher in the caruncle than in the control ewes (3·26 ± 0·15 (s.e.m.) mmol/l, number of observations (n) = 9, vs 2·75 ± 0·1, n = 9, P<0·02, and 3·27 ±0·16, n = 7, vs 2·46± 0·11, n = 12, P<0·001, for the carotid artery and utero-ovarian vein respectively). The concentration of ovine placental lactogen (oPL) in the utero-ovarian vein was reduced in the caruncle compared with the control ewes (283± 65 μg/l, n = and 705±106 μg/l, n = 18, P<0·02, respectively). Restriction of placental growth by removal of endometrial caruncles similarly reduced the concentrations of oPL in maternal arterial plasma (231±54 μg/l, n = 9, and 621±96 μg/l, n = 18, P<0·002). Production of oPL by the placenta was also reduced by limiting placental growth to 30±11 μg/min, n = 8, compared with 133±43 μg/min, n = 15, P<0·05, for the controls. Production of oPL per gram of placenta in the caruncle group, although only 34% of the control value, was not reduced significantly. These observations are consistent with the hypothesis that oPL may be involved in the redirection of maternal glucose during pregnancy to maximize the amount available for the fetus. J. Endocr. (1985) 106, 7–11

Abstract The metabolic effects of ovine placental lactogen (oPL) alone and in combination with bovine GH (bGH) were investigated in comparison with the identical dose of bGH alone in the well-fed postnatal lamb. The animals were treated by twice daily intramuscular injection for 5 days with oPL (n=7), bGH (n=7) or bGH+oPL (n=7) at a dose of 0·3 mg/kg per day or saline (n=9). bGH and bGH+oPL treatments, but not oPL treatment, resulted in significantly (P<0·01) higher plasma IGF-I levels than saline treatment. The rate of net protein catabolism (NPC) was significantly (P<0·05) reduced to the same extent by bGH and bGH+oPL treatment compared with saline treatment. In contrast, oPL did not affect the rate of NPC. Blood glucose and insulin:glucose ratio were significantly (P<0·05) elevated in the bGH+oPL group, whereas they were not significantly altered by either bGH or oPL treatment. These results suggest that oPL alone is not somatogenic or anticatabolic in the postnatal lamb despite the earlier evidence that oPL can bind to the oGH receptor (oGHR). However, oPL appeared to augment some of the effects of bGH when administered together, particularly with respect to carbohydrate metabolism. Potentiation of the diabetogenic effect of bGH by oPL may lead to insulin resistance during pregnancy. The lack of any obvious actions by oPL treatment alone may support the hypothesis that oGHR homo-dimerization is required for the full activation of GHR-mediated effects, since oPL binding does not initiate homo-dimerization of the oGHR. Journal of Endocrinology (1995) 145, 87–95

Overnourishing pregnant adolescent sheep promotes maternal growth but reduces placental mass, lamb birth weight and circulating progesterone. This study aimed to determine whether altered progesterone reflected transcript abundance forStAR(cholesterol transporter) and the steroidogenic enzymes (Cyp11A1,Hsd3bandCyp17). Circulating and placental expression of ovine placental lactogen (oPL) was also investigated. Adolescent ewes with singleton pregnancies were fed high (H) or moderate (M) nutrient intake diets to restrict or support placental growth. Experiment 1: peripheral progesterone and oPL concentrations were measured in H (n=7) and M (n=6) animals across gestation (days 7–140). Experiment 2: progesterone was measured to mid- (day 81; M:n=11, H:n=13) or late gestation (day 130; M:n=21, H:n=22), placental oPL,StARand steroidogenic enzymes were measured by qPCR and oPL protein by immunohistochemistry. Experiment 1: in H vs M animals, term placental (P<0.05), total cotyledon (P<0.01) and foetal size (P<0.05) were reduced. Circulating oPL and progesterone were reduced at mid- (P<0.001,P<0.01) and late gestation (P<0.01,P<0.05) and oPL detection was delayed (P<0.01). Experiment 2: placental oPL was not altered by nutrition. In day 81 H animals, progesterone levels were reduced (P<0.001) but not related to placental or foetal size. Moreover, placental steroidogenic enzymes were unaffected. Day 130 progesterone (P<0.001) andCyp11A1(P<0.05) were reduced in H animals with intrauterine growth restriction (H+IUGR). Reduced mid-gestation peripheral oPL and progesterone may reflect altered placental differentiation and/or increased hepatic clearance respectively. Restricted placental growth and reduced biosynthesis may account for reduced progesterone in day 130 H+IUGR ewes.

Ovine placental lactogen (oPL) is postulated to be involved in the repartitioning of maternal nutrients during pregnancy, through its effect on insulin metabolism. Ovine pancreatic insulin responses to exogenous glucose are depressed during pregnancy and this depression becomes more pronounced as gestation advances. In addition, under the hormonal environment of rising oPL and growth hormone (oGH) concentrations, maternal whole body glucose irreversible loss (GIL) increases. The percentage of GIL accounted for by uterine glucose uptake also increases with advancing gestation and increasing litter size. Regression analysis of oPL concentration with glucose uterine uptake as a percentage of GIL, accounts for 39% of variation. Maternal oPL concentrations which increase with gestational age, were significantly greater in multiple bearing ewes and ewes subjected to reduced metabolisable energy (ME) intakes. It is postulated that through actions on pancreatic sensitivity, oPL plays a major role as a homeorhetic control during pregnancy. Elevated oPL concentrations were strongly associated with continually depressed pancreatic insulin secretory ability. The reduction in pancreatic sensitivity to glucose was not as a result of elevation in GH or non-esterified fatty acid (NEFA) concentrations. Muscle insulin receptor number and affinity were found to increase with increasing litter size, suggesting that pregnancy associated insulin resistance occurs predominantly in adipose tissue. During ovine pregnancy there is a specific stimulation of maternal gluconeogenesis. As gestation advances, an increasingly greater proportion of this glucose is partitioned to the gravid uterus. The development of insulin resistance, together with the suppression of pancreatic activity, ensures the preferential uptake of glucose by non-insulin dependent tissues over insulin dependent tissues. These activities favour uterine glucose uptake, decrease adipose glucose uptake, and also promote adipose mobilisation and hepatic gluconeogenesis, so as to meet the increasing energy requirement of pregnancy. It is postulated that through these effects on insulin secretion and associated adipose tissue mobilisation factors, oPL plays a major role in homeorhesis during pregnancy.
Doctor of Philosophy (PhD)

Ovine placental lactogen (oPL) is postulated to be involved in the repartitioning of maternal nutrients during pregnancy, through its effect on insulin metabolism. Ovine pancreatic insulin responses to exogenous glucose are depressed during pregnancy and this depression becomes more pronounced as gestation advances. In addition, under the hormonal environment of rising oPL and growth hormone (oGH) concentrations, maternal whole body glucose irreversible loss (GIL) increases. The percentage of GIL accounted for by uterine glucose uptake also increases with advancing gestation and increasing litter size. Regression analysis of oPL concentration with glucose uterine uptake as a percentage of GIL, accounts for 39% of variation. Maternal oPL concentrations which increase with gestational age, were significantly greater in multiple bearing ewes and ewes subjected to reduced metabolisable energy (ME) intakes. It is postulated that through actions on pancreatic sensitivity, oPL plays a major role as a homeorhetic control during pregnancy. Elevated oPL concentrations were strongly associated with continually depressed pancreatic insulin secretory ability. The reduction in pancreatic sensitivity to glucose was not as a result of elevation in GH or non-esterified fatty acid (NEFA) concentrations. Muscle insulin receptor number and affinity were found to increase with increasing litter size, suggesting that pregnancy associated insulin resistance occurs predominantly in adipose tissue. During ovine pregnancy there is a specific stimulation of maternal gluconeogenesis. As gestation advances, an increasingly greater proportion of this glucose is partitioned to the gravid uterus. The development of insulin resistance, together with the suppression of pancreatic activity, ensures the preferential uptake of glucose by non-insulin dependent tissues over insulin dependent tissues. These activities favour uterine glucose uptake, decrease adipose glucose uptake, and also promote adipose mobilisation and hepatic gluconeogenesis, so as to meet the increasing energy requirement of pregnancy. It is postulated that through these effects on insulin secretion and associated adipose tissue mobilisation factors, oPL plays a major role in homeorhesis during pregnancy.

Ovine placental lactogen (oPL) is secreted by the placenta into both the fetal and maternal compartments. Its biological function(s) during pregnancy and the mechanisms involved are still unclear. A purification procedure was developed for oPL from sheep placental cotyledons of late gestation. Four procedures were attempted to obtain homogeneous oPL. Recoveries of oPL and total protein were measured throughout the several procedures using a specific oPL RIA and the Bradford protein estimation respectively. The third and fourth procedures resulted in homogeneous oPL and a partial amino acid sequence was obtained from the fourth procedure. In the successful procedures, the placental tissue was extracted with 0.1 M ammonium bicarbonate pH 8.5. A pH precipitation of the soluble fraction was performed, followed by 60% saturation with ammonium sulphate. Further separation steps involved chromatogaphic procedures. Carboxymethylcellulose (CM32) cation exchange was performed batchwise at pH 5.6. Subsequently chromatofocusing was performed to elute proteins in order of their isoelectric points. This was carried out using a pH gadient of 0.9 to 6.0. The final chromatographic step was reverse-phase high performance liquid chromatography (RP-HPLC) using a C4 column. To obtain homogeneous oPL in the third procedure, the partially purified oPL was subjected to SDS polyacrylamide gel electrophoresis and the separated proteins were transferred to nitrocellulose membrane. The homogeneous oPL was eluted from the membrane, however, sequencing was unsuccessful. It was assumed that the N terminal of oPL was blocked. Homogeneous oPL was obtained in the fourth procedure by electrophoretic elution from the Hunkapiller gel system performed at 4°C. The oPL was digested with trypsin, the fragments were separated by RP-HPLC chromatography and two peptides were sequenced. Peptide 1: F D E Q Y G Q G I Peptide 2: Y I N C H T Several strategies were attempted to provide more homogeneous oPL to enable more sequencing. The partially purified oPL fractions from each of these attempts were pooled and electrophoresed on an SDS polyacrylamide gel. The section of acrylamide containing the oPL band was homogenised and a trypsin digest was performed. The digested oPL was separated from the gel pieces, filtered through a Sep-Pak filter and the fragments were separated by RP-HPLC. The yield of oPL was low, but sufficient homogeneous oPL was obtained to provide a partial amino acid sequence from tryptic peptides. A further two peptides provided sequences. Peptide 3: (L) A G E M V N R F D E Q Y G Q G I Peptide 4: (L) Q P G K C Q I P L Q S L F Collaborators from Genentech Inc (San Francisco USA) used partially purified oPL produced from the present study and also obtained homogeneous oPL (Colosi et al., 1989). Complementary DNA clones of oPL were isolated and expressed in mammalian cells by recombinant DNA techniques (Colosi et al., 1989). These clones were sequenced, demonstrating that the full sequence of oPL consists of 198 amino acids preceded by a 38 amino acid sequence signal. Recombinant oPL was generated by Colosi et al. (1989) which provided sufficient material to perform physiological studies in vivo. The somatogenic effects of recombinant oPL were investigated in the growth hormone (GH) deficient dwarf rat and compared to identical doses of recombinant bovine GH (bGH) in 3 independent studies. Both oPL and bGH treatments resulted in an increase (p<0.05) in body weight gain compared to that in saline treated controls, with oPL treatment being more potent than bGH (p<0.05). In promoting linear growth, oPL was more potent (p<0.05) than bGH in some instances. Nitrogen content of dry carcass matter was increased with oPL treatment compared to saline (p<0.05), with a nonsignificant increase in bGH treated animals. Carcass fat was similarly reduced by both oPL and bGH treatment (p<0.05) compared to saline. Serum insulin-like growth factor I (IGF-I) concentrations were increased significantly (p<0.05) by both oPL and bGH treatments, with a significantly greater effect of oPL suggested in one study. No increase in hepatic IGF-I mRNA was evident with either treatment, suggesting that the increase in serum IGF-I is due to posttranscriptional mechanisms. The expression of IGF binding protein 3 (IGFBP-3) hepatic mRNA was increased (p<0.05) with bGH treatment compared to that after saline treatment, but was unaffected by opL treatment, indicating regulation by GH at the transcriptional level. The binding of [125I]bGH to hepatic membrane preparations demonstrated no difference in specific binding compared to that in saline controls. However, [125I]oPL specific binding was greater in oPL treated animals (p<0.05). Animals treated with bGH had reduced (p<0.05) hepatic GH receptor mRNA compared to saline controls, but oPL treatment had no effect. Thus, oPL is a potent anabolic and lipolytic agent in the dwarf rat, exerting greater somatogenic effects on some parameters than bGH. The studies in this thesis have described biochemical and biological characterisitics of oPL. The amino acid sequence of oPL is more closely related to prolactin (PRL) than to GH (Colosi et al., 1989). However, oPL has potent somatogenic activities in the GH deficient dwarf rat. Our data suggest differences in receptor binding and effects on GH receptor and IGFBP-3 expression with these two treatments, raising the possibility of actions through different pathways or differential effects at the GH receptor level. These results do not fully resolve whether GH and PRL exert all effects through a single receptor or whether there is a separate PL receptor.

Central problems in sheep and dairy cattle production are reproductive failure due to embryonic/fetal mortality and low birth weights, especially in prolific breeds, and reduced milk yields which adversely affect neonatal survival and economy of production. The sheep placenta expresses lactogenic (ovine placental lactogen, oPL) and somatogenic (ovine placental growth hormone, oGH) hormones. Our research has focused on the biological roles of oPL and oGH in function of the uterine endometrium during gestation and the mammary gland during pregnancy and lactation. Major conclusions were that: ( 1 ) immunization of prepubertal ewes against oPL resulted in increased birth weights of their lambs and their milk production during lactation; (2) neither oPL nor oGH had an antiluteolytic effect on uterine endometrium to affect lifespan of the corpus luteum; (3) only sequential exposure of the progesterone stimulated uterus to oIFNt and oPL or oGH increased endometrial gland proliferation and secretory protein gene expression; (4) oPL signals through a homodimer of ovine prolactin receptor (PRL-R) and heterodimer of oPRL-R and growth hormone receptor (GH-R); (5) exogenous recombinant oPL and oGH stimulated mammogenesis and milk yield during lactation; and (6) mutation of oPL and oGH was used to define specific biological effects and a rational basis for design of a specific receptor agonists or antagonists. This project was very productive in elucidating basic biological effects of oPL and oGH on intracellular signal transduction pathways, uterine development and secretory function, as well as mammogenesis and lactogenesis. We determined that immunization of prepubertal ewes against roPL increased birth weights of their lambs, especially those born as twins and triplets, as well as enhanced lactational performance. These studies significantly extended our knowledge of uterine and fetal-placental physiology and provided a foundation for new strategies to enhance reproductive and lactation efficiency. Based on these results, the major achievements were: 1) creation of a practical and cost effective management tool for producers to increase reproductive performance, neonatal survival, and milk yield of ewes in commercial flocks; and 2) define, for the first time, biological effects of oPL on endometrial functions and gene expression by uterine gland epithelium.

The key objectives of this BARD project were to: (1) study long-term effects of immunization of prepubertal ewes against recombinant ovine placental lactogen (roPL) on subsequent birth weights of their lambs and their milk production; (2) optimize the anti-roPL immunization protocol using adjuvant preparations acceptable to producers and regulatory agencies; and (3) determine the physiological mechanism(s) whereby immunization against oPL increases fetal growth and development and mammogenesis. These objectives were based on key findings from a previous BARD project that: (a) immunization of ewes against roPL increased lamb birth weight and ewe milk production during lactation; (b) roPL and recombinant ovine growth hormone (roGH) increased the proliferation and differentiated function of endometrial glands that, in turn, would enhance uterine secretions necessary for fetal and placental growth; and (c) exogenous roPL and roGH stimulated mammogenesis and milk production during lactation. The BARD projects address central problems in sheep production, including reproductive failure due to embryonic/fetal mortality, low birth weight of lambs especially in prolific breeds, and reduced milk yields which affect neonatal survival. The sheep placenta secretes both lactogenic (oPL) and somatogenic (oGH) hormones. The receptors for those hormones are present in the fetus and placenta as well as maternal uterus, and mammary gland. Our research has focused on determining the biological role of these placental hormones in development and differentiation of the uterus during gestation and the mammary gland during pregnancy and lactation. Studies conducted in the current BARD project indicated that the effects of anti-roPL immunization were variable in ewes and that commercially available and widely acceptable adjuvant preparations were not effective to produce high anti-roPL titers in pre-pubertal ewes. In the non-prolific Rambouillet ewe in Texas and in the Awassi and the Assaf in Israel, anti-roPL immunization increased lamb birth weight; however, the magnitude of this effect and the inherent variability precluded our ability to determine the physiological mechanism of how the immunization increases fetal growth. Collectively, our findings suggest that anti-roPL immunization is not currently feasible as an easy and efficacious tool for the producer to increase flock reproductive and production efficiency. The variability in response of individual ewes to anti-roPL immunization likely includes modifying the recombinant hormone and the type of adjuvant used for the immunization. In particular, the oPL may need to be modified to ensure maximum antigenicity in a broad range of breed types. Nonetheless, the investigators continue to collaborate on identifying fundamental mechanisms that can be improved by genetics or management to enhance the efficiency of uteroplacental function and, in turn, fetal growth and development. High prolificacy is a desirable trait in intensive sheep production systems. One of the main limitations of using prolific breeds of sheep is that increased litter size is associated with low birth weights and increased mortality of lambs. Further, low birth weight is associated with an increased propensity for adult diseases and decreased production efficiency. Indeed, our recent studies find that the birth weights of lambs born in large litters can be improved by both genetics and management. Future cooperative research will continue to focus on reproductive efficiency of sheep that have broader implications for improving production efficiency in all types of ruminant livestock.