Angiogenic activity of maternal and fetal placental tissues of ewes throughout gestation

In Study 1, explants of caruncular and intercaruncular endometrium and fetal membrane were collected from ewes (5-6/day) on Days 11-13, 16-18 and 21-23 after mating and Days 10-12 after oestrus, and incubated for 24 h. Explant-conditioned media were evaluated for their effects on endothelial cell proliferation. Both caruncular and intercaruncular endometrium secreted factor(s) which stimulated endothelial cell proliferation, and which appeared to be greater than 100 x 10(3) Mr and heat-labile. In Study 2, conditioned media from explant incubations of caruncular and intercaruncular endometrium, cotyledon and intercotyledonary fetal membrane obtained from ewes (6-7/day) on Days 40, 65, 90, 115 and 140 after mating were evaluated for their effects on endothelial cell proliferation. Caruncular and intercaruncular endometrium and intercotyledonary fetal membrane secreted factor(s) which inhibited endothelial cell proliferation. Media from cotyledonary explants tended to stimulate endothelial cell proliferation on Day 115. Conditioned media from cotyledonary explants obtained from 3 additional ewes at Day 120 of gestation stimulated endothelial cell proliferation, and this activity also appeared to be greater than 100 x 10(3) Mr. Placental angiogenesis in ewes therefore appears to be modulated by both maternal and fetal placental tissues via stimulatory and inhibitory factors.     

Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E2 (PGE2) and F2alpha (PGF2alpha) and progesterone in vitro

The objective of this experiment was to determine the effect of AA, LH, or PSPB on secretion of PGE2, PGF2alpha, or progesterone by ovine caruncular endometrium of the estrous cycle or placental tissue of pregnancy in vitro. Ovine caruncular endometrium of the estrous cycle (days 8, 11, 13, and 15) or caruncular/placental tissue on days 8, 11, 13, 15, 20, 30, 40, 50, 60, and 90 postbreeding were incubated in vitro with vehicle, AA, LH, or PSPB in M-199 for 4 and 8 h. Secretion of PGF2alpha by caruncular endometrium of non-bred ewes on days 13 and 15 and by caruncular/placental tissue of bred ewes on days 13, 15, 20, 30, and 40 was increased (P < or = 0.05) when incubated with vehicle and declined (P < or = 0.05) after day-40 in bred ewes. Secretion of PGF2alpha by day-15 caruncular endometrium of non-bred ewes and bred ewes was increased (P < or = 0.05) by AA on days 13 and 15 and by LH on day-15. Secretion of PGF2alpha by caruncular/placental tissue from bred ewes was (P < or = 0.05) by AA on days 13, 15, 20, 30, and 40 and by LH on days 15, 20, 30, and 40, after which the response decreased (P < or = 0.05). Secretion of PGF2alpha by caruncular endometrium of non-bred ewes during the estrous cycle or by caruncular/placental tissue of bred ewes during the first trimester was not affected by PSPB (P > or = 0.05). Secretion of PGE2 by caruncular endometrium of non-bred ewes did not change (P > or = 0.05) and was increased (P < or = 0.05) by caruncular/placental tissue on days 13-90 from bred ewes when incubated with vehicle. Secretion of PGE2 by endometrium from non-bred ewes was not affected (P > or = 0.05) by AA, LH, or PSPB, but was increased (P < or = 0.05) by AA or LH on days 13-50 and by PSPB on days 60 and 90 when incubated with caruncular/placental tissue from bred ewes. Secretion of progesterone by placental tissue of bred ewes increased (P < or = 0.05) on day-50 and continued to increase through day-90. In summary, uterine/placental tissue secretion of PGF2alpha is not reduced until the end of the first trimester of pregnancy in ewes. In addition, LH appears to play a role in luteolysis of non-bred ewes by stimulating caruncular endometrial secretion of PGF2alpha and on day-5 postbreeding to prevent luteolysis during early pregnancy by stimulating caruncular/placental secretion of PGE2 throughout the first trimester of pregnancy in sheep. Secretion of PGE2 by caruncular/placental tissue after day-50 of pregnancy appears to be regulated by PSPB, not LH.     

Concentration of oxytocin receptors in the placenta and fetal membranes of cows during pregnancy and labour.

The concentrations of oxytocin receptors were measured in intercaruncular and caruncular endometrium, fetal cotyledons, chorioallantois and amnion during pregnancy and parturition in cows. Tissues were obtained on days 20 (endometrium only), 50, 100, 150, 200, 225, 250, 275, at term (days 280-284), during labour and within 24 h after calving. Receptor concentrations in intercaruncular endometrium were low on day 20 of pregnancy, 39 +/- 11 fmol mg-1 protein. By day 50, receptor concentrations had increased more than tenfold to 572 +/- 52 fmol and rose steadily until day 250 and then levelled off at about 4500 fmol mg-1. Shortly before parturition, on day 282 +/- 1, a further rise to 7300 +/- 1418 fmol mg-1 was observed, these concentrations were maintained throughout labour. By contrast, caruncular endometrial receptor concentrations remained low until term, mean 145 +/- 15 fmol mg-1, and then rose to 720 +/- 163 fmol mg-1 during labour (cervix 17 cm--fully dilated). Fetal cotyledons and membranes had very low oxytocin receptor concentrations during most of pregnancy, on average only 20 fmol mg-1 protein. At term and during labour, receptor concentrations were significantly increased in both tissues. Mean concentrations during labour were 163 +/- 36 fmol mg-1 for cotyledons, 270 +/- 61 fmol mg-1 for chorioallantois and 311 +/- 121 fmol mg-1 for amnion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prostaglandin F and E levels in the conceptus, uterus and plasma during early pregnancy in the ewe

Concentrations of prostaglandins E and F (PGE and PGF) were measured in the embryo or fetus, extra embryonic or fetal membranes (membranes), intercaruncular and caruncular endometrium and plasma collected from uterine and ovarian arterial and venous vessels from separate groups of ewes laparotomized at 5 day intervals from day 10 to day 55 of pregnancy. Our purpose was to investigate the role of prostaglandins E and F in the maternal recognition of pregnancy, implantation and early placental function. Our data suggest that the initial maintenance of the corpus luteum in the pregnant ewe does not involve a reduction in PGF production, compared to pregnant ewes; but a change in the pattern of PGF secretion. This is accompanied by an elevation in PGE production of similar magnitude to that observed in non pregnant ewes. The extra embryonic/fetal membranes appear to be the major source of elevated PGF levels in the maternal circulation prior to day 30 of pregnancy. Between days 35 and 55 of gestation the rising PGF levels in maternal serum probably come from the fetus. Over the same period PGE levels rise in the fetus and intercaruncular endometrium, but PGE secretion into the maternal circulation is not enhanced. A role for PGF and PGE in fetal, placental and uterine growth is suggested; placental and uterine endocrine function may also be targets.     

Prostaglandin F and E levels in the conceptus, uterus and plasma during early pregnancy in the ewe

Concentrations of prostaglandins E and F (PGE and PGF) were measured in the embryo or fetus, extra embryonic or fetal membranes (membranes), intercaruncular and caruncular endometrium and plasma collected from uterine and ovarian arterial and venous vessels from separate groups of ewes laparotomized at 5 day intervals from day 10 to day 55 of pregnancy. Our purpose was to investigate the role of prostaglandins E and F in the maternal recognition of pregnancy, implantation and early placental function. Our data suggest that the initial maintenance of the corpus luteum in the pregnant ewe does not involve a reduction in PGF production, compared to pregnant ewes; but a change in the pattern of PGF secretion. This is accompanied by an elevation in PGE production of similar magnitude to that observed in non pregnant ewes. The extra embryonic/fetal membranes appear to be the major source of elevated PGF levels in the maternal circulation prior to day 30 of pregnancy. Between days 35 and 55 of gestation the rising PGF levels in maternal serum probably come from the fetus. Over the same period PGE levels rise in the fetus and intercaruncular endometrium, but PGE secretion into the maternal circulation is not enhanced. A role for PGF and PGE in fetal, placental and uterine growth is suggested; placental and uterine endocrine function may also be targets.     

Phospholipase A activity in human and ovine uterine tissues

Phospholipase A was assayed in crude lysosomal fractions of human decidua, amnion, chorion and myometrium. Activity was present in all the tissues and was highest in decidua and amnion which contained enzymes with pH optima of 6.5 – 8.0 and 7.2 respectively. Comparison of the activities in tissues obtained before labor with others obtained during labor showed no differences. In sheep, the fetal membranes contained a greater activity of phospholipase A than placenta and myometrium. Stimulation of the fetal adrenals with corticotrophin caused a marked increase in activity in both amnion and chorioallantois. It is concluded that the human amnion and the ovine amnion and chorioallantois could participate in the biosynthesis of prostaglandins by releasing stored arachidonic acid.     

Phospholipase A activity in human and ovine uterine tissues.

Phospholipase A was assayed in crude lysosomal fractions of human decidua, amnion, chorion and myometrium. Activity was present in all the tissues and was highest in decidua and amnion which contained enzymes with pH optima of 6.5-8.0 and 7.2 respectively. Comparison of the activities in tissues obtained before labor with others obtained during labor showed no differences. In sheep, the fetal membranes contained a greater activity of phospholipase A than placenta and myometrium. Stimulation of the fetal adrenals with corticotrophin caused a marked increase in activity in both amnion and chorioallantois. It is concluded that the human amnion and the ovine amnion and chorioallantois could participate in the biosynthesis of prostaglandins by releasing stored arachidonic acid.     

Uterine prostaglandin concentrations following fetal death in sheep

Concentrations of prostaglandin E (PGE), PGF and 6-oxo-PGF_1α (the hydrolytic product of PGI₂) were measured by radioimmunoassay (RIA) in myometrium, endometrium, cotyledons, amnion and chorioallantois taken from different uterine areas from chronically catheterized sheep bearing fetuses which had died 12–26 h previously (n=4) or 34–72 h previously (n=4). These two groups of animals were designated fetuses dead <30 h and >30 h respectively. The time of fetal death was assessed on the basis of fetal heart rate and blood gases. At the time of the tissue collection the ewes were between 123 and 130 days after mating. For comparative purposes, tissues also were collected from four sheep bearing live chronically catheterized fetuses at 130 days of gestation.For myometrium, concentration of PGF, PGE and 6-oxo-PGF_1α were significantly higher in sheep bearing dead fetuses, compared to those bearing live fetuses. Analysis of variance also showed a significant effect of uterine area on myometrial PGE concentrations, concentrations being higher in tubal areas than elsewhere. Concentrations of PGE, PGF and 6-oxo-PGF_1α were higher in endometrium taken from uteri containing dead fetuses. In cotyledons, concentrations of PGF and 6-oxo-PGF_1α but not PGE, were significant elevated following fetal death. Concentrations of 6-oxo-PGF_1α, but not PGE or PGF, were elevated in both chorioallantois and amnion of sheep bearing dead fetuses, compared to those bearing live fetuses. In association with elevated PG concentrations, there was a progressive increase in the frequency and maximum amplitude of uterine contractions. These results show that PG concetrations are elevated following fetal death in sheep, and suggest an association between elevated PG concentrations and delivery of the dead fetus.     

Detection of PrPres in genetically susceptible fetuses from sheep with natural scrapie

Scrapie is a transmissible spongiform encephalopathy with a wide PrPres dissemination in many non-neural tissues and with high levels of transmissibility within susceptible populations. Mechanisms of transmission are incompletely understood. It is generally assumed that it is horizontally transmitted by direct contact between animals or indirectly through the environment, where scrapie can remain infectious for years. In contrast, in utero vertical transmission has never been demonstrated and has rarely been studied. Recently, the use of the protein misfolding cyclic amplification technique (PMCA) has allowed prion detection in various tissues and excretions in which PrPres levels have been undetectable by traditional assays. The main goal of this study was to detect PrPres in fetal tissues and the amniotic fluid from natural scrapie infected ewes using the PMCA technique. Six fetuses from three infected pregnant ewes in an advanced clinical stage of the disease were included in the study. From each fetus, amniotic fluid, brain, spleen, ileo-cecal valve and retropharyngeal lymph node samples were collected and analyzed using Western blotting and PMCA. Although all samples were negative using Western blotting, PrPres was detected after in vitro amplification. Our results represent the first time the biochemical detection of prions in fetal tissues, suggesting that the in utero transmission of scrapie in natural infected sheep might be possible.     

Secretion of angiogenic activity by placental tissues of cows at several stages of gestation

Samples of maternal and fetal placental tissues were obtained from cows on Days 100 (N = 4), 150 (N = 5), 200 (N = 6) and 250 (N = 6) of gestation and incubated for 24 h. Conditioned media from caruncular explants were mitogenic for bovine aortic endothelial cells (BAEC) on all days of gestation. Media from intercaruncular endometrium were stimulatory for proliferation of BAEC on Day 100 but inhibitory on Days 150, 200 and 250. Media from cotyledonary and intercotyledonary tissues inhibited proliferation of BAEC on all days. Caruncular-conditioned media stimulated migration of BAEC on Days 150, 200 and 250. Cotyledonary-conditioned media inhibited migration of BAEC on all days. Effects of media from intercaruncular and intercotyledonary tissues on migration of BAEC varied with stage of gestation. Angiogenic activity of media from caruncular (all stages) and intercaruncular (Day 100) tissues appeared to have an Mr greater than 100,000. In cows, therefore, the maternal placentome (caruncle) appears to be the primary source of placental angiogenic activity throughout gestation. The fetal placentome (cotyledon) secretes activity which inhibits two major components of angiogenesis (proliferation and migration of endothelial cells) throughout gestation. Intercaruncular and intercotyledonary tissues may modulate placental angiogenesis throughout gestation. Placental vascular development in the cow is therefore probably controlled by an interaction between stimulatory and inhibitory factors produced by the placenta itself.     

Developmental changes in polyamine levels and synthesis in the ovine conceptus

Polyamines (putrescine, spermidine, and spermine) are essential for placental growth and angiogenesis. However, little is known about changes in polyamine synthesis associated with development of the ovine conceptus (embryo/fetus and associated placental membranes). We hypothesized that rates of placental polyamine synthesis were maximal during the rapid placental growth that occurs in the first half of pregnancy. This hypothesis was tested using ewes between Days 30 and 140 of gestation. Columbia cross-bred ewes were hysterectomized on Days 30, 40, 60, 80, 100, 120, or 140 of gestation (Day 0 = mating; n = 4 ewes/day) to obtain placentomes, intercotyledonary placenta, intercaruncular endometrium, and allantoic as well as amniotic fluids. The tissues were analyzed for ornithine decarboxylase (ODC) and arginase activities; arginine, ornithine, and polyamine concentrations; and polyamine synthesis using radiochemical and chromatographic methods. Maximal ODC and arginase activities and the highest rates of polyamine synthesis were observed in all tissues on Day 40 of gestation. Concentrations of ornithine and polyamines in placentomes and intercaruncular endometrium also peaked on Day 40 of gestation. In ovine allantoic and amniotic fluids, polyamines were most abundant during early (Days 40-60) and late (Days 100-140) gestation, respectively. Amniotic fluid spermine increased progressively with advancing gestation. Results of the present study indicate metabolic coordination among the several integrated pathways that support high rates of polyamine synthesis in the placenta and endometrium during early pregnancy. Our findings may have important implications for both intrauterine growth retardation and fetal origins of diseases in adults.     

Analysis of prion protein genotypes in relation to reproduction traits in local and cosmopolitan German sheep breeds

Due to the genetic determination of susceptibility to scrapie and other forms of transmissible spongiform encephalopathy (TSE) in sheep breeding to the less susceptible prion protein (PrP) genotype ARR/ARR was advanced within EU. In 4961 ewes of nine German sheep breeds (Coburg Fox sheep, Gray Horned Heath sheep, Merinoland sheep, Rhoen sheep, German Blackheaded Mutton sheep, Shropshire, Suffolk, Texel and White East Friesian Milk sheep) representing local and cosmopolitan breeds the reproductive traits number of lambs born, dead (including abortion at the end of pregnancy, stillbirth and death during the first 56 days post natum), weaned and rearing rate at each lambing were recorded and in 1641 of these ewes the PrP genotype was determined. A linear model was used to evaluate associations between PrP genotype and reproduction traits including the effects of PrP genotype (four classes: ewes with two, one and no copy of the ARR allele and with unknown PrP genotype), breed, interaction of PrP genotype and breed, number of lambing, lambing season and stock. Significant associations were only observed between the PrP genotype and the number of dead lambs at each lambing in Shropshire and Merinoland sheep and the rearing rate at each lambing in Shropshire. These significant associations were mainly caused by differences between animals with unknown PrP genotype and animals of the other PrP classes. In conclusion, breeding for TSE resistant sheep will not lead to a reduction in economically important reproduction traits.     

Characterization of endometrial receptors for ovine trophoblast protein-1 during the estrous cycle and early pregnancy in sheep

Scatchard analysis was used to determine the distribution, number, and affinity of unoccupied receptors for ovine trophoblast protein-1 (oTP-1) in endometrium of sheep throughout the estrous cycle and early pregnancy. In Experiment I, oTP-1 receptor characteristics were determined in membrane preparations of caruncular and intercaruncular regions of endometrium collected from uterine horns ipsilateral and contralateral to the ovary bearing the corpus luteum. Receptor concentrations and affinity constants for oTP-1 were not different (p greater than 0.1) between the four endometrial regions examined, suggesting that the expression of receptors for oTP-1 occurs uniformly throughout the endometrium. Endometrial receptor characteristics for oTP-1, luteal wet weights, and progesterone contents were determined throughout the estrous cycle and early pregnancy in Experiment II. Concentration of receptors and affinity constants for oTP-1 varied throughout the estrous cycle and early pregnancy (p less than 0.01), with the pattern of change differing between cyclic and pregnant ewes (p less than 0.01). Numbers of receptors for oTP-1 were maximal on Day 4 of the estrous cycle and declined progressively to Day 12 (p less than 0.05) in both cyclic and pregnant ewes. After Day 12, the quantity of unoccupied receptors for oTP-1 increased (p less than 0.05) gradually to Day 16 in cyclic ewes, but declined (p less than 0.05) further in the endometrium of pregnant ewes. The affinity constants of endometrial receptors for oTP-1 were similar in cyclic and pregnant ewes prior to Day 12, increasing threefold from Days 4 to 12 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Preventing experimental vertical transmission of scrapie by embryo transfer

This study investigated whether the transmission of naturally occurring scrapie in sheep can be prevented using embryo transfer. Embryos were collected from 38 donor ewes in a Suffolk sheep flock with a high incidence of naturally occurring scrapie, treated with a sanitary procedure (embryo washing) recommended by the International Embryo Transfer Society and then transferred to 58 scrapie-free recipient ewes. Ninety-four offspring were produced. None of the offspring or the recipient ewes developed scrapie. Furthermore, offspring derived from embryos collected from donor ewes bred to the immunohistochemically positive ram did not develop scrapie. We conclude that scrapie was not transmitted to offspring via the embryo nor was the infective agent transmitted to recipient ewes during embryo transfer procedures.     

Steroid production by dispersed cells from fetal membranes and intrauterine tissues of sheep

The hypothesis was examined that the fetal membranes and the endometrium and myometrium of pregnant sheep have the ability to produce oestrogens and progesterone from exogenous precursors, and that this capacity might change during the course of pregnancy, and in relation to the onset of parturition. Cells were dispersed from samples of myometrium, endometrium, allantois, chorion and amnion from sheep at Day 50, Days 130-135 of pregnancy, and at term, in labour, and were incubated in the presence of pregnenolone and 20 alpha-dihydroprogesterone as potential precursors for progesterone production, and oestrone sulphate and androstenedione as potential precursors for oestrogen production. In addition, the metabolism of radioactive progesterone and oestrone sulphate by the dispersed cells was examined. Pregnenolone was converted to progesterone in significant amounts by dispersed cells from chorion and endometrium only. At Day 130 and at term this conversion was blocked by the addition of trilostane, an inhibitor of 3 beta-hydroxysteroid dehydrogenase activity. There was no significant change in the net production of progesterone from exogenous pregnenolone with gestation. 20 alpha-Dihydroprogesterone was converted to progesterone by all tissues, and at each stage of gestation. Formation of progesterone from 20 alpha-dihydroprogesterone was invariably greater than that from pregnenolone, but did not change with pregnancy. Oestrone sulphate was converted to oestrone and oestradiol by all tissues. In the myometrium and chorion this conversion was lower at term than at Day 50 of pregnancy. In contrast, there was very little conversion of androstenedione to unconjugated oestrogen, minimal activity being demonstrable only in dispersed cells from the chorion in some preparations. Radioactive progesterone was converted to radiochemically pure 17 alpha-hydroxyprogesterone by chorion, and to radiochemically pure 20 alpha-dihydroprogesterone by amnion, chorion, allantois and endometrium obtained at term pregnancy. At term [3H]oestrone sulphate was converted to radiochemically pure oestrone by all tissues. We conclude that there is a tissue-specific distribution of different steroid metabolizing enzyme activities in the fetal membranes and intrauterine tissues of pregnant sheep. Of the substrates examined, 20 alpha-dihydroprogesterone and oestrone sulphate were preferred for progesterone and oestrogen production, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cotyledonary responses to maternal selenium and dietary restriction may influence alterations in fetal weight and fetal liver glycogen in sheep

To examine the effects of maternal supranutritional selenium (Se) and nutrient restriction during mid and late gestation on placental characteristics and fetal liver glycogen, ewes received either adequate Se (ASe) or high Se (HSe) prior to breeding. On d 64 of gestation, ASe and HSe ewes remained at 100% of requirements (controls; CON) or were restricted (RES; 60% of requirements). On d 135 of gestation, fetal weight (P ≤ 0.08) was greatest in both HSe and CON ewes. Placentome number, mass, and caruncular and cotyledonary weight were not different (P ≥ 0.17) among treatments. Fetal mass:placental mass ratio was less (P = 0.06) in RES compared to CON ewes. Compared to ASe, HSe exhibited increased (P ≤ 0.08) cellular proliferation and DNA concentration and decreased (P = 0.07) cellular size in cotyledonary tissue. Nutritional restriction decreased (P ≤ 0.08) cotyledonary protein concentration and cellular size. VEGF receptor 1 (Flt) mRNA in cotyledonary tissue was greater in HSe compared with ASe ewes (P = 0.06) and in RES compared with CON ewes (P = 0.08). There was no effect of diet on caruncular growth variables (P ≥ 0.13) or on placental vascularity (P ≥ 0.11). Progesterone was greater (P ≤ 0.08) in ASe–RES ewes compared to all groups at d 90 and ASe–CON and HSe–CON at d 104. Although fetal glucose and cortisol concentrations were not affected by diet, fetal liver glycogen was greater (P = 0.04) in ASe–RES compared to ASe–CON and HSe–RES ewes with HSe–CON being intermediate. Both Se and nutritional plane may impact placental function and fetal growth, as fetal weight and liver glycogen are altered despite similar placental vascularity measurements.     

Growth and in-vitro metabolism of placental tissues of cows from day 100 to day 250 of gestation.

Weight of placental tissues of cows increased exponentially from Day 100 to Day 250 of gestation, but at much slower relative and absolute rates than fetal weight. In addition, growth rate of fetal placental tissues was less than that of maternal placental tissues. Concentrations of DNA, RNA and protein, however, increased in fetal placental but not in maternal placental tissues. Fetal placental tissues therefore exhibited hyperplasia, which probably contributes to increased functional capacity of the placenta during late gestation. The rate of O2 uptake in vitro was greatest for maternal placental tissues, suggesting that the maternal portion of the placenta accounts for most of the large rate of placental O2 utilization in vivo. Compared with other placental tissues, rate of secretion of macromolecules by intercaruncular endometrium was high, but decreased from Day 100 to 250, suggesting that uterine glandular secretory activity may decrease as gestation advances. Rate of secretion of macromolecules also was high for intercotyledonary tissues and increased with day of gestation, suggesting a role for secretory products of chorioallantois in gravid uterine function.     

Analysis of prion protein mRNA by in situ hybridization in brain and placenta of sheep

In this study, prion protein (PrP) mRNA was focally detected in brain and placenta of pregnant sheep by Northern blot analysis. In addition, host-encoded cellular prion protein (PrP(C)) was observed in brain and placenta of the ruminant by Western blot analysis as well. Localization of PrP mRNA in pregnant sheep tissues was rendered possible with in situ hybridization. In sheep brain, PrP mRNA was predominantly localized within large neocortical neurons in the cerebrum, Purkinje cells and neurons of the molecular and granule cell layers in the cerebellum. In the placenta, signals were observed in the myometrium, including stratum longitudinale tunicae muscles and circular layers of muscular tunics. In the caruncle and placentome, signals were stronger by in situ hybridization. Since accumulation of the scrapie isoform PrP (PrP(Sc)) is required to PrP(C), these results suggest that brain and placenta of sheep may be important organs and sites for the conversion of PrP(C) to PrP(Sc).     

The effect of dietary supplementation with linoleic acid to late gestation ewes on the fatty acid composition of maternal and fetal plasma and tissues and the synthetic capacity of the placenta for 2-series prostaglandins

Linoleic acid (18:2n-6) is metabolised to arachidonic acid (20:4n-6), the precursor for 2-series prostaglandins (PGs). Increased consumption of 18:2n-6 during pregnancy may thus modify PG synthesis during labour. We have investigated whether increased 18:2n-6 composition during gestation altered the fatty acid consumption and PG synthesis of maternal and fetal tissues in the sheep. Ewes were fed a control diet or a diet providing 40% more 18:2n-6 from 96 days gestation. Half of each group received dexamethasone on day 136 to up-regulate the PG synthetic pathways promoting parturition. Maternal and fetal tissues were collected at 138 days. The 18:2n-6 diet significantly increased the 20:4n-6 content of maternal plasma, fetal plasma and allantochorion (51-81%) phosphatidylcholine, and fetal liver (40%) and maternal caruncular endometrium (57%) phosphatidylethanolamine. Increased 18:2n-6 intake increased production of PGF(2alpha) and PGE(2) in all placental tissues (maternal caruncular and intercaruncular endometrium and fetal allantochorion) by 23-98%, whereas dexamethasone increased it by 32-142%. This suggests that consumption of an 18:2n-6-enriched diet in late pregnancy enhanced placental PG production by increasing the supply of 20:4n-6. Variations in the extent to which the diet altered the polyunsaturated fatty acid (PUFA) content of the different tissues indicated complex interactions between nutrient availability and metabolic adaptation.