Placental growth, angiogenic gene expression, and vascular development in undernourished adolescent sheep

Limiting maternal nutrient intake during ovine adolescent pregnancy progressively depleted maternal body reserves, impaired fetal nutrient supply, and slowed fetal soft tissue growth. The present study examined placental growth, angiogenic gene expression, and vascular development in this undernourished adolescent model at Days 90 and 130 of gestation. Singleton pregnancies were established, and ewes were offered an optimal control (C; n = 14) or low (L [0.7 x C]; n = 21) dietary intake. Seven ewes receiving L intakes were switched to C intakes on Day 90 of gestation (L-C). Fetal body weight (P < 0.01) and glucose concentrations (P < 0.03) were reduced in L versus C pregnancies by Day 130, whereas L-C group values were intermediate. Placental cellular proliferation, gross morphology, and mass were independent of maternal nutrition at both Day 90 and 130. In contrast, capillary area density in the maternal caruncular portion of the placentome was reduced by 20% (P < 0.001) at both stages of gestation in L compared with C groups. Caruncular capillary area density was equivalent in the L and L-C groups at Day 130. Placental mRNA expression of five key angiogenic ligands or receptors increased (P < 0.001) between Days 90 and 130 of gestation. VEGFA mRNA expression was higher (P < 0.04) in L compared with C and L-C pregnancies at Day 130, but otherwise gene expression of the remaining angiogenic factors and receptors analyzed was unaffected by maternal intake. Undernourishing the pregnant adolescent dam restricts fetal growth independently of changes in placental mass. Alterations in maternal placental vascular development may, however, play a role in mediating the previously reported reduction in maternal and hence fetal nutrient supply.     

Effect of a high maternal dietary intake during mid-gestation on components of the utero-placental insulin-like growth factor (IGF) system in adolescent sheep with retarded placental development

The aim of the present study was to investigate the effects of administering a high plane diet during early to mid-gestation on the uterine and placental insulin-like growth factor (IGF) system and on systemic IGF-I concentrations in pregnant adolescent ewes with restricted placental growth. Embryos recovered from superovulated ewes inseminated by a single sire were transferred in singleton to the uterus of adolescent recipients. After transfer ewes were offered a high (H) or moderate (M) amount of a complete diet calculated to promote rapid or normal maternal growth rates, respectively. Five ewes from each group were switched from either M to H or H to M diets at day 52 of gestation. Maternal and fetal blood samples and placental tissues were collected from all animals at day 104. Ewes on the high plane diet from mid-gestation (HH, MH groups) had restricted placental mass (P < 0.01) and tended to have smaller fetuses. This was associated with increased maternal plasma IGF-I concentrations (P < 0.001). The pattern of expression of components of the IGF system in the uterus and placenta was studied by in situ hybridization. IGF-I mRNA concentrations were below the limit of detection. IGF-II mRNA expression was high in the fetal mesoderm and present in maternal stroma, but was not influenced by nutritional treatment. In contrast, IGF binding protein 1 (IGFBP-1) mRNA expression was higher (P < 0.05) and IGFBP-3 mRNA expression was lower (P < 0.05) in the endometrial glands of ewes in HH and MH groups. In the fetal trophoblast, IGFBP-3 mRNA expression was higher in the MH group. Type 1 IGF receptor expression was increased (P < 0. 01) in the luminal epithelium of the HM group and IGFBP-2 mRNA expression was highest in the placentome capsule of ewes in the HH group. Together, these results indicate that reprogramming of the uterine and placental IGF axis by maternal nutrition could contribute to placental growth retardation in growing adolescent sheep.     

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.     

Influence of gestational overfeeding on myocardial proinflammatory mediators in fetal sheep heart

Maternal overnutrition is associated with predisposition of offspring to cardiovascular disease in later life. Since maternal overnutrition may promote fetal and placental inflammatory responses, we hypothesized that maternal overnutrition/obesity increases expression of fetal cardiac proinflammatory mediators and alter cardiac morphometry. Multiparous ewes were fed either 150% of National Research Council (NRC) nutrient recommendations (overfed) or 100% of NRC requirement (control) from 60 days prior to mating to gestation Day 75 (D75), when ewes were euthanized. An additional cohort of overfed and control ewes were necropsied on D135. Cardiac morphometry, histology, mRNA and protein expression of toll-like receptor 4, iNOS, IL-1a, IL-1b, IL-6, IL-18, CD-14, CD-68, M-CSF and protein levels of phosphorylated I-κB and nuclear factor κB (NF-κB) were examined. Immunohistochemistry was performed to assess neutrophil and monocyte infiltration. Crown rump length, left and right ventricular free wall weights as well as left and right ventricular wall thickness were significantly increased in D75 fetuses of overfed mothers. Hematoxylin and eosin staining revealed irregular myofiber orientation and increased interstitial space in fetal ventricular tissues born to overfed mothers. Oil red O staining exhibited marked lipid droplet accumulation in the overfed fetuses. Overfeeding significantly enhanced TLR4, IL-1a, IL-1b IL-6 expression, promoted phosphorylation of IκB, decreased cytoplasmic NF-κB levels and increased neutrophil and monocyte infiltration. Collectively, these data suggest that maternal overfeeding prior to and throughout gestation leads to inflammation in the fetal heart and alters fetal cardiac morphometry.     

Switching maternal dietary intake at the end of the first trimester has profound effects on placental development and fetal growth in adolescent ewes carrying singleton fetuses.

The aim was to investigate whether placental growth and hence pregnancy outcome could be altered by switching adolescent dams from a high to a moderate nutrient intake, and vice-versa, at the end of the first trimester. Embryos recovered from adult ewes inseminated by a single sire were transferred in singleton to peripubertal adolescents. After transfer, adolescent ewes were offered a high (H, n = 33) or moderate (M, n = 32) level of a diet calculated to promote rapid or moderate maternal growth rates, respectively. At Day 50 of gestation, half the ewes had their dietary intakes switched, yielding 4 treatment groups: HH, MM, HM, and MH. A subset of ewes were killed at Day 104 of gestation to determine maternal body composition in relation to growth of the products of conception. Maternal body composition measurements revealed that the higher live weight in the high-intake dams was predominantly due to an increase in body fat deposition, with a less pronounced increase in body protein. At Day 104, HH and MH groups (high intake during second trimester) compared with MM and HM groups (moderate intake during second trimester) had a lower (p < 0.002) total fetal cotyledon weight; but fetal weight, conformation, and individual organ weights were not significantly influenced by maternal dietary intake. In ewes delivering live young at term, a high plane of nutrition from the end of the first trimester (HH and MH groups) compared with moderate levels (MM and HM groups) was associated with a reduction in gestation length (p < 0.009), total placental weight (p < 0.002), total fetal cotyledon weight (p < 0.001), and mean fetal cotyledon weight per placenta (p < 0.001). Fetal cotyledon number was dependent on maternal dietary intake during the first trimester only and was lower (p < 0.007) in HH and HM ewes compared to MM and MH ewes. The inhibition of fetal cotyledon growth in HH and MH groups was associated with a major decrease (p < 0.001) in lamb birth weight at term relative to the MM and HM groups. Thus, reducing maternal dietary intake from a high to a moderate level at the end of the first trimester stimulates placental growth and enhances pregnancy outcome, and increasing maternal dietary intake at this time point has a deleterious effect on placental development and fetal growth.     

Placental growth throughout the last two thirds of pregnancy in sheep: vascular development and angiogenic factor expression

Morphometric methodologies were developed and applied to investigate the patterns of vascular development in maternal (caruncular; CAR) and fetal (cotyledonary; COT) sheep placentas throughout the last two thirds of gestation. We also examined the expression levels of the major angiogenic factors and their receptors in CAR and COT sheep placentas. Although the vascularity of the CAR tissues increased continuously from Day 50 through Day 140 of pregnancy, those of the COT tissues increased at about twice the instantaneous rate (i.e., the proportionate increase/day) of the CAR. For CAR, vascularity increased 2-fold from Day 50 through Day 140 via relatively small increases in capillary number and 2- to 3-fold increases in capillary diameter. For COT, the increased vascularity resulted from a 12-fold increase in capillary number associated with a concomitant 2-fold decrease in capillary diameter. This large increase in fetal placental capillary number, which was due to increased branching, resulted in 6-fold increases in total capillary cross-sectional area and total capillary surface, per unit of COT tissue. Different patterns of expression of the mRNAs for angiogenic factors and their receptors were observed for CAR and COT. The dilation-like angiogenesis of CAR was correlated with the expression of vascular endothelial growth factor receptor-1 (FLT1), angiopoietin-2 (ANGPT2), and soluble guanylate cyclase (GUCY1B3) mRNAs. The branching-like angiogenesis of COT was correlated with the expression of vascular endothelial growth factor (VEGF), FLT1, angiopoietin-1 (ANGPT1), ANGPT2, and FGF2 mRNAs. Monitoring the expression of angiogenic factors and correlating the levels with quantitative measures of vascularity enable one to model angiogenesis in a spatiotemporal fashion.     

Maternal growth hormone treatment from day 35 to 80 of gestation alters nutrient partitioning in favor of uteroplacental growth in the overnourished adolescent sheep

Overnourishing the pregnant adolescent ewe promotes maternal tissue synthesis at the expense of placental growth and leads to a major reduction in lamb birth weight at term. Growth hormone (GH) secretion is attenuated in these overnourished dams and the maternal somatotrophic axis may play a key role in coordinating nutrient usage in the pregnant adolescent. Thus we investigated whether increasing maternal GH during the period of rapid placental proliferation alters nutrient partitioning between the maternal, placental, and fetal tissues as assessed at Day 81 of gestation. Adolescent recipient ewes were implanted with singleton embryos, derived from superovulated dams and a single sire on Day 4 postestrus. Thereafter, the ewes were offered either a high (H) or moderate intake (M) of the same complete diet. From Day 35 to 80 of gestation, ewes were either injected twice daily (s.c. at 0800 and 1800 h) with recombinant bovine GH (bGH, 0.14 mg/kg live weight/day) or remained untreated (n = 8 ewes per group). Maternal concentrations of GH, insulin, insulin-like growth factor (IGF-1), glucose, and non-esterified fatty acids (NEFAs) were higher, and leptin secretion lower, in bGH-treated dams from both nutritional groups. Maternal body weight gain was higher in H versus M groups and was independent of bGH treatment. Treatment with bGH reduced relative perirenal and carcass fat deposition and increased carcass protein content in both H and M dams. Uteroplacental mass (uterus + placentomes + fetal membranes) averaged 1099, 1069, 1112, and 1754 g in M, H, M+GH, and H+GH groups. This significant increase in uteroplacental development in the H+GH group was associated with higher fetal kidney and liver weights and elevated fetal insulin, glucose, and lactate concentrations. Treatment with bGH also induced polyhydramnios in the H group. The transplacental glucose gradient was increased twofold in the H+GH group but placental GLUT- 1 and GLUT-3 expression was unaffected. In conclusion, administration of GH during the period of rapid placental proliferation alters endocrine status and thus nutrient partitioning in the overnourished adolescent dam in favor of uteroplacental and fetal growth. It remains to be established whether these effects are due wholly to alterations in maternal metabolism or if they also reflect an effect of bGH and/or the IGF system at the level of the uteroplacenta.     

Ontogeny and regulation of ovine placental prostaglandin E2 synthase

Recent evidence suggests that ovine placental output of prostaglandin (PG) E2 rises through late gestation partly because of a direct effect of cortisol on PGH2 synthase 2 (PGHS-2) expression and activity within trophoblast tissue. Synthesis of PGE2 is also dependent, however, on PGE2 synthase (PGES), which converts PGH2 to PGE2. We hypothesized that PGES is expressed in the ovine placenta, and that, similar to PGHS-2, expression increases through gestation and is regulated positively by cortisol. Placental tissues from pregnant ewes in mid and late gestation, at term, and during early and active labor were analyzed to determine the gestational profile of PGES. The regulation of PGES expression was assessed in placental tissues from pregnant ewes in which intrafetal cortisol infusion was administered in late gestation, in the presence or absence of an aromatase inhibitor, to block the cortisol-stimulated rise in estradiol. Expression of PGES was analyzed by in situ hybridization, Western blot analysis, and immunohistochemistry. In the placentome, PGES localized to fetal trophoblast cells and endothelial cells in maternal blood vessels, consistent with its contribution to the rise in placental PGE2 output toward the onset of labor and with a role of PGE2 in the local regulation of uteroplacental blood flow, respectively. Expression of PGES mRNA and protein increased with gestation. However, there was no significant further change with labor or during cortisol infusion in the presence or absence of a rise in fetal plasma estradiol, in contrast to reported changes in PGHS-2. These results suggest that PGES is not coregulated with PGHS-2 in the sheep placenta at term. The progressive increase in PGES, however, likely contributes to the rise in circulating PGE2 in the fetus in late pregnancy.     

Late but not early gestational maternal growth hormone treatment increases fetal adiposity in overnourished adolescent sheep

In the overnourished adolescent sheep, maternal tissue synthesis is promoted at the expense of placental growth and leads to a major decrease in lamb birth weight at term. Maternal growth hormone (GH) concentrations are attenuated in these pregnancies, and it was recently demonstrated that exogenous GH administration throughout the period of placental proliferation stimulates uteroplacental and fetal development by Day 81 of gestation. The present study aimed to determine whether these effects persist to term and to establish whether GH affects fetal growth and body composition by increasing placental size or by altering maternal metabolism. Adolescent recipient ewes were implanted with singleton embryos on Day 4 postestrus. Three groups of ewes offered a high dietary intake were injected twice daily with recombinant bovine GH from Days 35 to 65 of gestation (high intake plus early GH) or from Days 95 to 125 of gestation (high intake plus late GH) or remained untreated (high intake only). A fourth moderate-intake group acted as optimally nourished controls. Pregnancies were terminated at Day 130 of gestation (6 per group) or were allowed to progress to term (8-10 per group). GH administration elevated maternal plasma concentrations of GH, insulin, glucose, and nonesterified fatty acids during the defined treatment windows, while urea concentrations were decreased. At Day 130, GH treatment had reduced the maternal adiposity score, percentage of fat in the carcass, and internal fat depots and leptin concentrations, predominantly in the high-intake plus late GH group. Placental weight was lower in high-intake vs. control dams but independent of GH treatment. In contrast, fetal weight was elevated by late GH treatment, and these fetuses had higher relative carcass fat content, perirenal fat mass, and liver glycogen concentrations than all other groups. Expression of leptin mRNA in fetal perirenal fat and fetal plasma leptin concentrations were not significantly altered by maternal nutritional intake or GH. In pregnancies proceeding to term, the duration of gestation, fetal placental mass, and lamb birth weight were reduced in high-intake compared with control dams but were not significantly affected by GH treatment. In conclusion, exogenous GH has profound effects on maternal endocrinology, metabolism, and body composition when administered during early and late pregnancy. Treatment during late pregnancy has a modest effect on fetal growth independent of placental size and a profound effect on fetal adiposity, which may have implications beyond the fetal period.     

Maternal nutrient restriction during placental growth,programming of fetal adiposity and juvenile blood pressure control

Epidemiological and experimental studies have demonstrated that maternal undernutrition during pregnancy is associated with abnormal placental growth. In sheep, maternal nutrient restriction over the period of rapid placental growth (30-80 days) restricts placentome growth. Then following adequate nutrition up to term (147 days), placental mass is greater in association with a higher total abundance of the predominant placental glucose transporter-1. The resulting lambs are larger at birth, have heavier kidneys with an increased expression of the glucocorticoid-responsive type 1 angiotensin II receptor. Near to term, these fetuses possess more adipose tissue, the endocrine sensitivity of which is markedly enhanced. For example, the abundance of mRNA for 11beta-hydroxysteroid dehydrogenase type 1, which catalyses the conversion of cortisone to bio-active cortisol is increased. This is associated with a higher abundance of both leptin and glucocorticoid receptor mRNA. At 6 months of age, the juvenile offspring of nutrient restricted ewes have lower resting blood pressure that was positively correlated with plasma cortisol concentration, suggesting their blood pressure could be more strongly driven by circulating cortisol. These offspring also exhibited a greater pressor response to vasoconstrictor challenges, but showed no difference in vasodilatory response. At this age, the kidney weight was similar between groups, but the abundance of cytochrome c in kidney mitochondria was enhanced in lambs born to nutrient restricted ewes that could indicate increased mitochondrial activity. Reduced maternal nutrition during the period of rapid placental growth may therefore contribute to hypertension in later life through physiological and vascular adaptations during fetal life.     

Angiogenesis in the placenta

The mammalian placenta is the organ through which respiratory gases, nutrients, and wastes are exchanged between the maternal and fetal systems. Thus, transplacental exchange provides for all the metabolic demands of fetal growth and development. The rate of transplacental exchange depends primarily on the rates of uterine (maternal placental) and umbilical (fetal placental) blood flows. In fact, increased uterine vascular resistance and reduced uterine blood flow can be used as predictors of high risk pregnancies and are associated with fetal growth retardation. The rates of placental blood flow, in turn, are dependent on placental vascularization, and placental angiogenesis is therefore critical for the successful development of viable, healthy offspring. Recent studies, including gene knockouts in mice, indicate that the vascular endothelial growth factors represent a major class of placental angiogenic factors. Other angiogenic factors, such as the fibroblast growth factors or perhaps the angiopoietins, also may play important roles in placental vascularization. In addition, recent observations suggest that these angiogenic factors interact with the local vasodilator nitric oxide to coordinate placental angiogenesis and blood flow. In the future, regulators of angiogenesis that are currently being developed may provide novel and powerful methods to ensure positive outcomes for most pregnancies.     

Insulin-like growth factor-I and binding proteins 1, 2, and 3 in bovine nuclear transfer pregnancies

In cloned pregnancies, placental deficiencies, including increased placentome size, reduced placentome number, and increased accumulation of allantoic fluid, have been associated with low cloning efficiency. To assess differences in paracrine and endocrine growth regulation in cloned versus normal bovine placentomes and pregnancies, we have examined the expression of insulin-like growth factor (IGF)-I and -II and their binding proteins (IGFBP)-1 through -3 in placentomes of artificially inseminated (AI), in vitro-produced (IVP), and nuclear transfer (NT) pregnancies at Days 50, 100, and 150 of gestation. Fetal, maternal, and binucleate cell counts in representative placentomes were performed on Days 50-150 of gestation in all three groups. Increased numbers of fetal, maternal, and binucleate cells were present in NT placentomes at all stages of gestation examined. Immunolocalization studies showed that spatial and temporal patterns of expression of IGFBP-2 and -3 were markedly altered in the placentomes of NT pregnancies compared to AI/IVP controls. Concentrations of IGF-I in fetal plasma, as determined by RIA, were significantly higher (P = 0.001) in NT pregnancies (mean +/- SEM, 30.3 +/- 2.3 ng/ml) compared with AI (19.1 +/- 5.5 ng/ml) or IVP (24.2 +/- 2.5 ng/ml) pregnancies on Day 150 of gestation. Allantoic fluid levels of IGFBP-1 were also increased in NT pregnancies. These findings suggest that endocrine and paracrine perturbations of the IGF axis may modulate placental dysfunction in NT pregnancies. Furthermore, increased cell numbers in NT placentomes likely have significant implications for fetomaternal communication and may contribute to the placental overgrowth observed in the NT placentomes.     

Maternal and fetal growth, body composition, endocrinology, and metabolic status in undernourished adolescent sheep

The influence of relative maternal undernutrition on growth, endocrinology, and metabolic status in the adolescent ewe and her fetus were investigated at Days 90 and 130 of gestation. Singleton pregnancies to a single sire were established, and thereafter ewes were offered an optimal control (C; n = 14) or low (L [0.7 x C]; n = 21) dietary intake. Seven ewes receiving the L intake were switched to the C intake on Day 90 of gestation (L-C). At Day 90, live weight and adiposity score were reduced (P < 0.001) in L versus C dams. Plasma insulin and IGF1 concentrations were decreased (P < 0.02), whereas glucose concentrations were preserved in L relative to C intake dams. Fetal and placental mass was independent of maternal nutrition at this stage. By Day 130 of gestation, when compared to C and L-C dams, maternal adiposity was further depleted in L intake dams; concentrations of insulin, IGF1, and glucose were reduced; and nonesterified fatty acids increased. At Day 130, placental mass remained independent of maternal nutrition, but body weight was reduced (P < 0.01) in L compared with C fetuses (3555 g vs. 4273 g). Body weight was intermediate (3836 g) in L-C fetuses. Plasma glucose (P < 0.03), insulin (P < 0.07), and total liver glycogen content (P < 0.04) were attenuated in L fetuses. Fetal carcass analyses revealed absolute reductions (P < 0.05) in dry matter, crude protein, and fat, and a relative (g/kg) increase in carcass ash (P < 0.01) in L compared with C fetuses. Thus, limiting maternal intake during adolescent pregnancy gradually depleted maternal body reserves, impaired fetal nutrient supply, and slowed fetal soft tissue growth.     

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.     

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.     

Chronic alterations in ovine maternal corticosteroid levels influence uterine blood flow and placental and fetal growth

Previous work from this laboratory demonstrated that the elevation of maternal plasma corticosteroid concentrations during pregnancy is important for the support of fetal development. Reducing ovine maternal plasma cortisol concentrations to nonpregnant levels stimulates homeostatic responses that defend fetal blood volume. The present study was designed to test the hypothesis that chronic decreases or increases in maternal plasma cortisol concentration alter uterine and placental blood flow and morphology. Three groups of pregnant ewes and their fetuses were chronically catheterized and studied: ewes infused with cortisol (1 mg.kg(-1).day(-1); high cortisol), ewes adrenalectomized and underreplaced with cortisol (0.5 mg.kg(-1).day(-1); low cortisol), and control ewes. The normal increment in uterine blood flow between 120 and 130 days was eliminated in the low-cortisol ewes; conversely, uterine blood flow was increased in the high-cortisol group compared with the control group. Fetal arterial blood pressure was increased in the high-cortisol group compared with controls, but there was no increase in fetal arterial pressure from 120 to 130 days of gestation in the low-cortisol group. The fetuses of both low-cortisol and high-cortisol groups had altered placental morphology, with increased proportions of type B placentomes, and overall reduced fetal placental blood flow. The rate of fetal somatic growth was impaired in both low-cortisol and high-cortisol groups compared with the fetuses in the intact group. The results of this study demonstrate that maternal plasma cortisol during pregnancy is an important contributor to the maternal environment supporting optimal conditions for fetal homeostasis and somatic growth.     

Melatonin supplementation alters uteroplacental hemodynamics and fetal development in an ovine model of intrauterine growth restriction

Using a mid- to late-gestation ovine model of intrauterine growth restriction (IUGR), we examined uteroplacental blood flow and fetal growth during melatonin supplementation as a 2 × 2 factorial design. At day 50 of gestation, 32 ewes were supplemented with 5 mg of melatonin (MEL) or no melatonin (CON) and were allocated to receive 100% [adequate; (ADQ)] or 60% [restricted (RES)] of nutrient requirements until day 130 of gestation. Umbilical artery blood flow was increased from day 60 to day 110 of gestation in MEL vs. CON dams, while umbilical artery blood flow was decreased from day 80 to day 110 of gestation in RES vs. ADQ dams. At day 130 of gestation, uteroplacental hemodynamics, measured under general anesthesia, and fetal growth were evaluated. Uterine artery blood flow was decreased in RES vs. ADQ dams, while melatonin supplementation did not affect uterine artery blood flow. Total placentome weight and placentome number were not different between treatment groups. Fetal weight was decreased by nutrient restriction. Abdominal girth and ponderal index were increased in fetuses from MEL-ADQ dams vs. all other groups. Fetal biparietal distance was decreased in CON-RES vs. CON-ADQ dams, while melatonin supplementation rescued fetal biparietal distance. Fetal kidney length and width were increased by maternal melatonin treatment. Fetal cardiomyocyte area was altered by both maternal melatonin treatment and nutritional plane. In summary, melatonin may negate the consequences of IUGR during specific abnormalities in umbilical blood flow as long as sufficient uterine blood perfusion is maintained during pregnancy.