A low-cost electrically scanned phased array utilizing microstrip patch electrically steerable parasitic array radiator (ESPAR) subarray cells is presented for the first time. Four single-layer ...three-element ESPAR subarray cells at one-wavelength spacing are uniformly illuminated by a corporate feed network consisting of microstrip Wilkinson power dividers and ring hybrids. The array is scanned using a combination of ESPAR capacitive mutual coupling control and microstrip switched delay line phase shifters at the subarray level to achieve a scanning range from Formula Omitted to Formula Omitted while maintaining high return loss. The ESPAR coupling technique allows a 50% reduction in the number of phase shifters used by utilizing a full wavelength subcell spacing, resulting in excellent performance with inexpensive fabrication. The fabricated prototype exhibits boresight gain of 12.1 dBi with low scan loss and 7.0-dB worst case sidelobe level. The array is compared quantitatively to thinned arrays with and without parasitic elements to illustrate this advantageous technique. A functional prototype is fabricated and measured and is aptly predicted by the full-wave model.
A new approach to parasitic phased-array antennas is presented. A symmetric two-layer, single-input inexpensive three-element array at 1-GHz employing varactors as tuning mechanisms are designed, ...fabricated, and measured. The driven element is mutually coupled to two parasitic elements in the H-plane. The varactors are used to control the mutual coupling and beam scanning and to maintain resonance at 1 GHz. A continuous scanning range of -15 + 15° is measured with maintained impedance matching and radiation pattern integrity. The low cost of diode varactors, used in place of expensive phase shifters, allows for more economic fabrication. This is advantageous to applications in point-to-point communication systems, weather, and target tracking radar systems.
The placenta is the organ that transports nutrients, respiratory gases, and wastes between the maternal and fetal systems.
Consequently, placental blood flow and vascular development are essential ...components of normal placental function and are
critical to fetal growth and development. Normal fetal growth and development are important to ensure optimum health of offspring
throughout their subsequent life course. In numerous sheep models of compromised pregnancy, in which fetal or placental growth,
or both, are impaired, utero-placental blood flows are reduced. In the models that have been evaluated, placental vascular
development also is altered. Recent studies found that treatments designed to increase placental blood flow can ârescueâ fetal
growth that was reduced due to low maternal dietary intake. Placental blood flow and vascular development are thus potential
therapeutic targets in compromised pregnancies.
The importance of the placenta and its vascular development to fetal growth and development has been appreciated since ancient times. Based on numerous studies in humans and animal model organisms in ...the last 2-3 decades, normal placental angiogenesis is critically important to ensure adequate blood flow to the placenta and therefore to provide the substrates that support normal fetal growth. Placental angiogenesis is abnormal at term in compromised pregnancies (those in which fetal growth is altered), including those resulting from maternal nutritional or environmental stress, maternal age, increased numbers of fetuses, maternal or fetal genotype, or the use of assisted reproductive technologies (e.g., cloning by somatic cell nuclear transfer). We and others have recently shown that these defects in placental vascular development occur quite early in pregnancy and may therefore presage compromised fetal growth and development. The challenges will be to find biomarkers of abnormal placental angiogenesis and to develop therapeutic strategies to "rescue" placental vascular development and thus fetal growth in compromised pregnancies. Animal models will be essential in meeting these challenges.
Low birthweight is a risk factor for neonatal mortality and adverse metabolic health, both of which are associated with inadequate prenatal adipose tissue development. In the present study, we ...investigated the impact of maternal undernutrition on the expression of genes that regulate fetal perirenal adipose tissue (PAT) development and function at gestation days 89 and 130 (term=145 days). Singleton fetuses were taken from adolescent ewes that were either fed control (C) intake to maintain adiposity throughout pregnancy or were undernourished (UN) to maintain conception weight but deplete maternal reserves (n=7/group). Fetal weight was independent of maternal intake at day 89, but by day 130, fetuses from UN dams were 17% lighter and had lower PAT mass that contained fewer unilocular adipocytes. Relative PAT expression of IGF1, IGF2, IGF2R and peroxisome proliferator-activated receptor gamma (PPARG) mRNA was lower in UN than in controls, predominantly at day 89. Independent of maternal nutrition, PAT gene expression of PPARG, glycerol-3-phosphate dehydrogenase, hormone sensitive lipase, leptin, uncoupling protein 1 and prolactin receptor increased, whereas IGF1, IGF2, IGF1R and IGF2R decreased between days 89 and 130. Fatty acid synthase and lipoprotein lipase (LPL) mRNAs were not influenced by nutrition or stage of pregnancy. Females had greater LPL and leptin mRNA than males, and LPL, leptin and PPARG mRNAs were decreased in UN at day 89 in females only. PAT gene expression correlations with PAT mass were stronger at day 89 than they were at day 130. These data suggest that the key genes that regulate adipose tissue development and function are active beginning in mid-gestation, at which point they are sensitive to maternal undernutrition: this leads to reduced fetal adiposity by late pregnancy.
To establish the basis for altered placental development and function previously observed at late gestation, fetoplacental growth and placental vascular development were measured at three stages of ...gestation in a nutritional paradigm of compromised pregnancy. Singleton pregnancies to a single sire were established and thereafter adolescent ewes were offered an optimal control (C) or a high (H) dietary intake. At day 50, the H group had elevated maternal insulin and amniotic glucose, whereas mass of the fetus and placenta were unaltered. At day 90, the H group exhibited elevated maternal insulin, IGF1 and glucose; fetal weight and glucose concentrations in H were increased relative to C, but placental weight was independent of nutrition. By day 130, total placentome weight in the H group was reduced by 46% and was associated with lower fetal glucose and a 20% reduction in fetal weight. As pregnancy progressed from day 50 to 130, the parameters of vascular development in the maternal and fetal components of the placenta increased. In the fetal cotyledon, high dietary intakes were associated with impaired vascular development at day 50 and an increase in capillary number at day 90. At day 130, all vascular indices were independent of nutrition. Thus, high dietary intakes to promote rapid maternal growth influence capillary development in the fetal portion of the placenta during early to mid-pregnancy and may underlie the subsequent reduction in placental mass and hence fetal nutrient supply observed during the final third of gestation.
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.
Corpora lutea and blood samples were collected from superovulated ewes 0, 4, 8, 12 and 24 h after prostaglandin F₂α (PGF) analog injection on day 10 of the estrous cycle. Changes in vascular cell and ...fibroblast composition, apoptosis and mRNA expression for several angiogenic factors in the corpus luteum (CL) were determined. While peripheral progesterone concentration decreased at 24 h after PGF injection, CL weight did not change. The area of positive BS-1 lectin staining (endothelial cell marker), smooth muscle cell actin (SMCA; pericyte and SMC marker), collagen type 1 (fibroblast marker), and the rate of cell death changed in luteal tissues after PGF treatment. In association with these cellular changes, mRNA for several angiogenic factors including vascular endothelial growth factor (VEGF) and receptors (Flt and KDR), basic fibroblast growth factor (FGF2) and receptor, angiopoietin (ANGPT) 1 and receptor Tie-2, endothelial nitric oxide synthase (NOS3), and angiotensin II receptor 1 (AT1) were altered. Changes in endothelial cell marker expression were positively correlated with changes in VEGF and NO systems. In addition, changes in mRNA expression for VEGF, Flt and KDR were positively correlated with changes in ANGPT2, Tie-2, and NOS3, indicating a functional relationship. This data demonstrates that after an initial increase, the endothelial component of the vascular bed decreases during PGF-induced luteal regression. However, SMCA expression remained high during luteal regression, potentially indicating a role of pericytes and vascular SMC in luteolysis, likely to regulate tissue remodeling and to maintain the integrity of larger blood vessels. Further, it appears that early regression may increase collagen type 1 production and/or expression by fibroblasts. Expression of angiogenic factors is influenced by PGF-induced luteolysis and may serve to maintain vascular structure in order to aid luteal regression.
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.
For singleton, twin, and triplet pregnancies, uteri were collected on day 140 of pregnancy. For each ewe (
n
= 18), placentomes were fixed by arterial perfusion supplying the fetal (cotyledon) and ...maternal placenta (caruncle). Tissue sections were stained for determination of vascularity by image analysis. Further, protein expression for factor VIII, vascular endothelial growth factor (VEGF) and its receptor, VEGFR1, as well as basic fibroblast growth factor (FGF2) and its receptor, FGFR, in tissue sections was determined by immunohistochemistry and image analyses. Cotyledonary and caruncular samples were analyzed for expression of mRNA for
Vegf
and its two receptors,
Vegfr1
and
Vegfr2
, as well as
Fgf2
and
Fgfr
. Fetal number did not affect placental capillary density or factor VIII expression, whereas increased fetal number reduced total cotyledon and caruncle capillary volume. While expression of
Vegf
,
Vegfr1
,
Vegfr2
, and
Fgfr
mRNA in cotyledonary but not caruncular tissue was greater in twin pregnancies compared to singleton and triplet pregnancies, protein expression of VEGF in the placentome decreased with increasing numbers of fetuses, VEGFR1 did not change, and FGFR was greater in twin versus singleton and triplet pregnancies. Fetal number did not affect the expression of
Fgf2
mRNA in placental tissues, whereas FGF2 protein expression was less in triplet compared to singleton and twin pregnancies. Reduced fetal and placental weights in twins and/or triplet pregnancies are associated with an overall decrease in total placental vascularity, VEGF and FGF2 and/or FGFR protein expression, but not in angiogenic factor mRNA expression or VEGFR1 protein expression in sheep.
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