Developmental Changes in Ovine Myocardial Glucose Transporters and Insulin Signaling Following Hyperthermia-Induced Intrauterine Fetal Growth Restriction

Mitochondrial respiration is lower in the intrauterine growth-restricted fetal sheep heart

Fetuses affected by intrauterine growth restriction have an increased risk of developing heart disease and failure in adulthood. Compared with controls, late gestation intrauterine growth-restricted (IUGR) fetal sheep have fewer binucleated cardiomyocytes, reflecting a more immature heart, which may reduce mitochondrial capacity to oxidize substrates. We hypothesized that the late gestation IUGR fetal heart has a lower capacity for mitochondrial oxidative phosphorylation. Left (LV) and right (RV) ventricles from IUGR and control (CON) fetal sheep at 90% gestation were harvested. Mitochondrial respiration (states 1-3, LeakOmy, and maximal respiration) in response to carbohydrates and lipids, citrate synthase (CS) activity, protein expression levels of mitochondrial oxidative phosphorylation complexes (CI-CV), and mRNA expression levels of mitochondrial biosynthesis regulators were measured. The carbohydrate and lipid state 3 respiration rates were lower in IUGR than CON, and CS activity was lower in IUGR LV than CON LV. However, relative CII and CV protein levels were higher in IUGR than CON; CV expression level was higher in IUGR than CON. Genes involved in lipid metabolism had lower expression in IUGR than CON. In addition, the LV and RV demonstrated distinct differences in oxygen flux and gene expression levels, which were independent from CON and IUGR status. Low mitochondrial respiration and CS activity in the IUGR heart compared with CON are consistent with delayed cardiomyocyte maturation, and CII and CV protein expression levels may be upregulated to support ATP production. These insights will provide a better understanding of fetal heart development in an adverse in utero environment. KEY POINTS: Growth-restricted fetuses have a higher risk of developing and dying from cardiovascular diseases in adulthood. Mitochondria are the main supplier of energy for the heart. As the heart matures, the substrate preference of the mitochondria switches from carbohydrates to lipids. We used a sheep model of intrauterine growth restriction to study the capacity of the mitochondria in the heart to produce energy using either carbohydrate or lipid substrates by measuring how much oxygen was consumed. Our data show that the mitochondria respiration levels in the growth-restricted fetal heart were lower than in the normally growing fetuses, and the expression levels of genes involved in lipid metabolism were also lower. Differences between the right and left ventricles that are independent of the fetal growth restriction condition were identified. These results indicate an impaired metabolic maturation of the growth-restricted fetal heart associated with a decreased capacity to oxidize lipids postnatally.

Cardiac growth and metabolism of the fetal sheep are not vulnerable to a 10 day increase in fetal glucose and insulin concentrations during late gestation

Aims

To evaluate the effects of fetal glucose infusion in late gestation on the mRNA expression and protein abundance of molecules involved in the regulation of cardiac growth and metabolism.

Main methods

Either saline or glucose was infused into fetal sheep from 130 to 140 days (d) gestation (term, 150 d). At 140 d gestation, left ventricle tissue samples were collected. Quantitative real-time RT-PCR and Western blot were used to determine the mRNA expression and protein abundance of key signalling molecules within the left ventricle of the fetal heart.

Key findings

Although intra-fetal glucose infusion increased fetal plasma glucose and insulin concentrations, there was no change in the expression of molecules within the signalling pathways that regulate proliferation, hypertrophy, apoptosis or fibrosis in the fetal heart. Cardiac Solute carrier family 2 member 1 (SLC2A1) mRNA expression was decreased by glucose infusion. Glucose infusion increased cardiac mRNA expression of both Peroxisome proliferator activated receptor alpha (PPARA) and peroxisome proliferator activated receptor gamma (PPARG). However, there was no change in the mRNA expression of PPAR cofactors or molecules with PPAR response elements. Furthermore, glucose infusion did not impact the protein abundance of the 5 oxidative phosphorylation complexes of the electron transport chain.

Significance

Despite a 10-day doubling of fetal plasma glucose and insulin concentrations, the present study suggests that within the fetal left ventricle, the mRNA and protein expression of the signalling molecules involved in cardiac growth, development and metabolism are relatively unaffected.

Long-Term Consequences of Adaptive Fetal Programming in Ruminant Livestock

Environmental perturbations during gestation can alter fetal development and postnatal animal performance. In humans, intrauterine growth restriction (IUGR) resulting from adaptive fetal programming is known as a leading cause of perinatal morbidity and mortality and predisposes offspring to metabolic disease, however, the prevalence and impact in livestock is not characterized as well. Multiple animal models have been developed as a proxy to determine mechanistic changes that underlie the postnatal phenotype resulting from these programming events in humans but have not been utilized as robustly in livestock. While the overall consequences are similar between models, the severity of the conditions appear to be dependent on type, timing, and duration of insult, indicating that some environmental insults are of more relevance to livestock production than others. Thus far, maternofetal stress during gestation has been shown to cause increased death loss, low birth weight, inefficient growth, and aberrant metabolism. A breadth of this data comes from the fetal ruminant collected near term or shortly thereafter, with fewer studies following these animals past weaning. Consequently, even less is known about how adaptive fetal programming impacts subsequent progeny. In this review, we summarize the current knowledge of the postnatal phenotype of livestock resulting from different models of fetal programming, with a focus on growth, metabolism, and reproductive efficiency. We further describe what is currently known about generational impacts of fetal programming in production systems, along with gaps and future directions to consider.

Hyperlipidic diet affects body composition and induces anxiety-like behaviour in intrauterine growth-restricted adult mice

NEW FINDINGS

What is the central question of this study? What is the effect in male and female offspring of a protein-deficient diet producing intrauterine growth restriction (IUGR) in maternal mice on morphometric, metabolic and behavioural parameters before and after a challenge with a fat diet? What is the main finding and its importance? Male and female mice presented different growth trajectories after birth. IUGR favoured increased adiposity in male mice, and high-fat diet-induced anxiety-like behaviour in female mice.

ABSTRACT

As there is sexual dimorphism in the response to maternal manipulations, we aimed to analyse the effects of intrauterine growth restriction (IUGR) in both sexes on morphometric, metabolic and behavioural parameters throughout postnatal development, and after challenge with a hyperlipidic diet. Female Swiss mice (n = 59) were distributed into two groups (SD: standard diet, n = 26; and PDD: isocaloric protein-deficient diet, n = 33), 2 weeks before mating and during the gestational period. After birth, offspring from SD and PDD dams were cross-fostered and nurtured by SD dams until postnatal day (PND) 28. At PND 60 all animals were challenged with a hypercaloric diet for 4 weeks. Offspring birth weight was significantly reduced in the PDD group compared to the SD group (P = 0.0001), but only male offspring presented a rapid catch-up during the first 21 days of development. Although no differences in body weight were observed between groups after the challenge with the hyperlipidic diet, an increase in the relative perigonadal white adipose tissue (P = 0.009) and a decrease in gross gastrocnemius muscle weight (P = 0.010) were observed in the PDD males. In relation to behavioural tests, there was an increase in locomotion in both sexes (P = 0.0001), and a decrease in female grooming (P = 0.006) in the PDD group. Additionally, females from the PDD group showed increased hyperlipidic food intake. In conclusion, IUGR affected both sexes, with females showing prominent behavioural modifications and males presenting altered body composition elicited by a hyperlipidic diet.

Cardiorespiratory consequences of intrauterine growth restriction: Influence of timing, severity and duration of hypoxaemia

At birth, weight of the neonate is used as a marker of the 9-month journey as a fetus. Those neonates born less than the 10th centile for their gestational age are at risk of being intrauterine growth restricted. However, this depends on their genetic potential for growth and the intrauterine environment in which they grew. Alterations in the supply of oxygen and nutrients to the fetus will decrease fetal growth, but these alterations occur due to a range of causes that are maternal, placental or fetal in nature. Consequently, IUGR neonates are a heterogeneous population. For this reason, it is likely that these neonates will respond differently to interventions compared not only to normally grown fetuses, but also to other neonates that are IUGR but have travelled a different path to get there. Thus, a range of models of IUGR should be studied to determine the effects of IUGR on the development and function of the heart and lung and subsequently the impact of interventions to improve development of these organs. Here we focus on a range of models of IUGR caused by manipulation of the maternal, placental or fetal environment on cardiorespiratory outcomes.

Increased pyruvate dehydrogenase activity in skeletal muscle of growth-restricted ovine fetuses

Fetal sheep with placental insufficiency-induced intrauterine growth restriction (IUGR) have lower fractional rates of glucose oxidation and greater gluconeogenesis, indicating lactate shuttling between skeletal muscle and liver. Suppression of pyruvate dehydrogenase (PDH) activity was proposed because of greater pyruvate dehydrogenase kinase (PDK) 4 and PDK1 mRNA concentrations in IUGR muscle. Although PDK1 and PDK4 inhibit PDH activity to reduce pyruvate metabolism, PDH protein concentrations and activity have not been examined in skeletal muscle from IUGR fetuses. Therefore, we evaluated the protein concentrations and activity of PDH and the kinases and phosphatases that regulate PDH phosphorylation status in the semitendinosus muscle from placenta insufficiency-induced IUGR sheep fetuses and control fetuses. Immunoblots were performed for PDH, phosphorylated PDH (E1α), PDK1, PDK4, and pyruvate dehydrogenase phosphatase 1 and 2 (PDP1 and PDP2, respectively). Additionally, the PDH, lactate dehydrogenase (LDH), and citrate synthase (CS) enzymatic activities were measured. Phosphorylated PDH concentrations were 28% lower (P < 0.01) and PDH activity was 67% greater (P < 0.01) in IUGR fetal muscle compared with control. PDK1, PDK4, PDP1, PDP2, and PDH concentrations were not different between groups. CS and LDH activities were also unaffected. Contrary to the previous speculation, PDH activity was greater in skeletal muscle from IUGR fetuses, which parallels lower phosphorylated PDH. Therefore, greater expression of PDK1 and PDK4 mRNA did not translate to greater PDK1 or PDK4 protein concentrations or inhibition of PDH as proposed. Instead, these findings show greater PDH activity in IUGR fetal muscle, which indicates that alternative regulatory mechanisms are responsible for lower pyruvate catabolism.

Postnatal Nutrient Repartitioning due to Adaptive Developmental Programming

Fetal stress induces developmental adaptations that result in intrauterine growth restriction (IUGR) and low birthweight. These adaptations reappropriate nutrients to the most essential tissues, which benefits fetal survival. The same adaptations are detrimental to growth efficiency and carcass value in livestock, however, because muscle is disproportionally targeted. IUGR adipocytes, liver tissues, and pancreatic β-cells also exhibit functional adaptations. Identifying mechanisms underlying adaptive changes is fundamental to improving outcomes and value in low birthweight livestock. The article outlines studies that have begun to identify stress-induced fetal adaptations affecting growth, metabolism, and differential nutrient utilization in IUGR-born animals.

Fetal undernutrition, placental insufficiency, and pancreatic β-cell development programming in utero

The prevalence of obesity and type 2 (T2D) diabetes is a major health concern in the United States and around the world. T2D is a complex disease characterized by pancreatic β-cell failure in association with obesity and insulin resistance in peripheral tissues. Although several genes associated with T2D have been identified, it is speculated that genetic variants account for only <10% of the risk for this disease. A strong body of data from both human epidemiological and animal studies shows that fetal nutrient factors in utero confer significant susceptibility to T2D. Numerous studies done in animals have shown that suboptimal maternal environment or placental insufficiency causes intrauterine growth restriction (IUGR) in the fetus, a critical factor known to predispose offspring to obesity and T2D, in part by causing permanent consequences in total functional β-cell mass. This review will focus on the potential contribution of the placenta in fetal programming of obesity and TD and its likely impact on pancreatic β-cell development and growth.

Near to One's Heart: The Intimate Relationship Between the Placenta and Fetal Heart

The development of the fetal heart is exquisitely controlled by a multitude of factors, ranging from humoral to mechanical forces. The gatekeeper regulating many of these factors is the placenta, an external fetal organ. As such, resistance within the placental vascular bed has a direct influence on the fetal circulation and therefore, the developing heart. In addition, the placenta serves as the interface between the mother and fetus, controlling substrate exchange and release of hormones into both circulations. The intricate relationship between the placenta and fetal heart is appreciated in instances of clinical placental pathology. Abnormal umbilical cord insertion is associated with congenital heart defects. Likewise, twin-to-twin transfusion syndrome, where monochorionic twins have unequal sharing of their placenta due to inter-twin vascular anastomoses, can result in cardiac remodeling and dysfunction in both fetuses. Moreover, epidemiological studies have suggested a link between placental phenotypic traits and increased risk of cardiovascular disease in adult life. To date, the mechanistic basis of the relationships between the placenta, fetal heart development and later risk of cardiac dysfunction have not been fully elucidated. However, studies using environmental exposures and gene manipulations in experimental animals are providing insights into the pathways involved. Likewise, surgical instrumentation of the maternal and fetal circulations in large animal species has enabled the manipulation of specific humoral and mechanical factors to investigate their roles in fetal cardiac development. This review will focus on such studies and what is known to date about the link between the placenta and heart development.

Admissions for hypoglycaemia after 35 weeks of gestation: perinatal predictors of cost of stay

BACKGROUND

Hypoglycaemia accounts for approximately one-tenth of term admissions to neonatal units can cause long-term neurodevelopmental impairment and is associated with the significant burden to the affected infants, families and the health system.

OBJECTIVE

To define the prevalence, length and cost of admissions for hypoglycaemia in infants born at greater than 35 weeks gestation and to identify antenatal and perinatal predictors of those outcomes.

MATERIALS AND METHODS

This was a retrospective audit of infants admitted for hypoglycaemia between 1 January 2012 and 31 December 2015, in a level three neonatal intensive care unit at King's College Hospital NHS Foundation Trust, London. The main outcome measures were the prevalence, length and cost of admissions for hypoglycaemia and antenatal and postnatal predictors of the length and cost of the stay.

RESULTS

There were 474 admissions for hypoglycaemia (17.8% of total admissions). Their median (IQR) blood glucose on admission was 2.1 (1.7-2.4) mmol/l, gestation at delivery 38.1 (36.7-39.3) weeks, birthweight percentile 31.4 (5.4-68.9), their length of stay was 3.0 (2.0-5.0). Admissions equated to a total of 2107 hospital days. The total cost of the stay was 1,316,591 Great Britain pound. The antenatal factors associated with admission for hypoglycaemia were maternal hypertension (19.8%), maternal diabetes (24.5%), foetal growth restriction (FGR) (25.9%) and pathological intrapartum cardiotocograph (23.4%). In 13.7% of cases, there was no associated pregnancy complication. Multivariate logistic regression analysis demonstrated lower gestational age, z-score birthweight squared, exclusive breastfeeding and maternal prescribed nifedipine were independently associated with the length and cost of the stay.

CONCLUSION

Hypoglycaemia accounted for approximately one-fifth of admissions after 35-week gestation. Lower gestational age and admission blood glucose, low and high z-score birthweight, maternal nifedipine and exclusive breastfeeding are associated with longer duration of stay.

Enhanced insulin secretion and insulin sensitivity in young lambs with placental insufficiency-induced intrauterine growth restriction

Intrauterine growth restriction (IUGR) is associated with persistent metabolic complications, but information is limited for IUGR infants. We determined glucose-stimulated insulin secretion (GSIS) and insulin sensitivity in young lambs with placental insufficiency-induced IUGR. Lambs with hyperthermia-induced IUGR (n = 7) were compared with control lambs (n = 8). GSIS was measured at 8 ± 1 days of age, and at 15 ± 1 days, body weight-specific glucose utilization rates were measured with radiolabeled d-glucose during a hyperinsulinemic-euglycemic clamp (HEC). IUGR lambs weighed 23% less (P < 0.05) than controls at birth. Fasting plasma glucose and insulin concentrations were not different between IUGR and controls for either study. First-phase insulin secretion was enhanced 2.3-fold in IUGR lambs compared with controls. However, second-phase insulin concentrations, glucose-potentiated arginine-stimulated insulin secretion, and β-cell mass were not different, indicating that IUGR β-cells have an intrinsic enhancement in acute GSIS. Compared with controls, IUGR lambs had higher body weight-specific glucose utilization rates and greater insulin sensitivity at fasting (1.6-fold) and hyperinsulinemic periods (2.4-fold). Improved insulin sensitivity for glucose utilization was not due to differences in skeletal muscle insulin receptor and glucose transporters 1 and 4 concentrations. Plasma lactate concentrations during HEC were elevated in IUGR lambs compared with controls, but no differences were found for glycogen content or citrate synthase activity in liver and muscle. Greater insulin sensitivity for glucose utilization and enhanced acute GSIS in young lambs are predicted from fetal studies but may promote conditions that exaggerate glucose disposal and lead to episodes of hypoglycemia in IUGR infants.

Biological features of placental programming

The placenta is a key organ in programming the fetus for later disease. This review outlines nine of many structural and physiological features of the placenta which are associated with adult onset chronic disease. 1) Placental efficiency relates the placental mass to the fetal mass. Ratios at the extremes are related to cardiovascular disease risk later in life. 2) Placental shape predicts a large number of disease outcomes in adults but the regulators of placental shape are not known. 3) Non-human primate studies suggest that at about mid-gestation, the placenta becomes less plastic and less able to compensate for pathological stresses. 4) Recent studies suggest that lipids have an important role in regulating placental metabolism and thus the future health of offspring. 5) Placental inflammation affects nutrient transport to the fetus and programs for later disease. 6) Placental insufficiency leads to inadequate fetal growth and elevated risks for later life disease. 7) Maternal height, fat and muscle mass are important in combination with placental size and shape in predicting adult disease. 8) The placenta makes a host of hormones that influence fetal growth and are related to offspring disease. Unfortunately, our knowledge of placental growth and function lags far behind that of other organs. An investment in understanding placental growth and function will yield enormous benefits to human health because it is a key player in the origins of the most expensive and deadly chronic diseases that humans face.

Increased fetal myocardial sensitivity to insulin-stimulated glucose metabolism during ovine fetal growth restriction

Unlike other visceral organs, myocardial weight is maintained in relation to fetal body weight in intrauterine growth restriction (IUGR) fetal sheep despite hypoinsulinemia and global nutrient restriction. We designed experiments in fetal sheep with placental insufficiency and restricted growth to determine basal and insulin-stimulated myocardial glucose and oxygen metabolism and test the hypothesis that myocardial insulin sensitivity would be increased in the IUGR heart. IUGR was induced by maternal hyperthermia during gestation. Control (C) and IUGR fetal myocardial metabolism were measured at baseline and under acute hyperinsulinemic/euglycemic clamp conditions at 128-132 days gestation using fluorescent microspheres to determine myocardial blood flow. Fetal body and heart weights were reduced by 33% (P = 0.008) and 30% (P = 0.027), respectively. Heart weight to body weight ratios were not different. Basal left ventricular (LV) myocardial blood flow per gram of LV tissue was maintained in IUGR fetuses compared to controls. Insulin increased LV myocardial blood flow by ∼38% (P < 0.01), but insulin-stimulated LV myocardial blood flow in IUGR fetuses was 73% greater than controls. Similar to previous reports testing acute hypoxia, LV blood flow was inversely related to arterial oxygen concentration (r(2 )= 0.71) in both control and IUGR animals. Basal LV myocardial glucose delivery and uptake rates were not different between IUGR and control fetuses. Insulin increased LV myocardial glucose delivery (by 40%) and uptake (by 78%) (P < 0.01), but to a greater extent in the IUGR fetuses compared to controls. During basal and hyperinsulinemic-euglycemic clamp conditions LV myocardial oxygen delivery, oxygen uptake, and oxygen extraction efficiency were not different between groups. These novel results demonstrate that the fetal heart exposed to nutrient and oxygen deprivation from placental insufficiency appears to maintain myocardial energy supply in the IUGR condition via increased glucose uptake and metabolic response to insulin, which support myocardial function and growth.

Programming of glucose-insulin homoeostasis: long-term consequences of pre-natal versus early post-natal nutrition insults. Evidence from a sheep model

AIM

Exposure to adverse intra-uterine conditions can predispose for metabolic disorders later in life. By using a sheep model, we studied (i) how programming of glucose-insulin homoeostasis during late gestation is manifested later in life depending on the early post-natal dietary exposure and (ii) whether dietary alteration in obese individuals can prevent adverse outcomes of early life programming.

METHODS

During late gestation, twin-pregnant sheep were fed 100% (NORM) or 50% (LOW) of energy and protein requirements. After birth, offspring were exposed to a moderate (CONV) or high-carbohydrate-high-fat (HCHF) diet until around puberty. Offspring remaining thereafter (exclusively females) were fed a moderate diet until young adulthood.

RESULTS

LOW lambs had increased insulin secretory responses during intravenous glucose tolerance tests indicative of reduced insulin sensitivity. HCHF lambs were hypertriglyceridaemic, 75% had mild pancreatic collagen infiltration, and their acute insulin secretory response and insulin clearance during intravenous glucose and insulin tolerance tests, respectively, were reduced. However, NORM-HCHF in contrast to LOW-HCHF lambs had normal glucose tolerance, indicating that later health outcomes are highly influenced by pre-natal nutrition. Dietary alteration normalized glucose-insulin homoeostasis in adult HCHF females, whereas late-gestation undernutrition (LOW) permanently depressed insulin sensitivity.

CONCLUSION

Maintenance of glucose tolerance in sheep exposed to pre-natal undernutrition relied on pancreatic hypersecretion of insulin to compensate for reduced insulin sensitivity. A mismatching high-fat diet in early post-natal life interfered with this pancreatic hypersecretion resulting in reduced glucose tolerance. Early post-natal, but not late pre-natal, impacts on glucose-insulin homoeostasis could be reversed by dietary correction later in life.

Down-regulation of placental mTOR, insulin/IGF-I signaling, and nutrient transporters in response to maternal nutrient restriction in the baboon

The mechanisms by which maternal nutrient restriction (MNR) causes reduced fetal growth are poorly understood. We hypothesized that MNR inhibits placental mechanistic target of rapamycin (mTOR) and insulin/IGF-I signaling, down-regulates placental nutrient transporters, and decreases fetal amino acid levels. Pregnant baboons were fed control (ad libitum, n=11) or an MNR diet (70% of controls, n=11) from gestational day (GD) 30. Placenta and umbilical blood were collected at GD 165. Western blot was used to determine the phosphorylation of proteins in the mTOR, insulin/IGF-I, ERK1/2, and GSK-3 signaling pathways in placental homogenates and expression of glucose transporter 1 (GLUT-1), taurine transporter (TAUT), sodium-dependent neutral amino acid transporter (SNAT), and large neutral amino acid transporter (LAT) isoforms in syncytiotrophoblast microvillous membranes (MVMs). MNR reduced fetal weights by 13%, lowered fetal plasma concentrations of essential amino acids, and decreased the phosphorylation of placental S6K, S6 ribosomal protein, 4E-BP1, IRS-1, Akt, ERK-1/2, and GSK-3. MVM protein expression of GLUT-1, TAUT, SNAT-2 and LAT-1/2 was reduced in MNR. This is the first study in primates exploring placental responses to maternal undernutrition. Inhibition of placental mTOR and insulin/IGF-I signaling resulting in down-regulation of placental nutrient transporters may link maternal undernutrition to restricted fetal growth.

Fetoplacental biometry and umbilical artery Doppler velocimetry in the overnourished adolescent model of fetal growth restriction

OBJECTIVE

The purpose of this study was to evaluate ultrasonographically fetal growth trajectories, placental biometry, and umbilical artery (UA) Doppler indices in growth-restricted pregnancies of overnourished adolescent ewes and normally developing pregnancies of control-fed ewes.

STUDY DESIGN

Singleton pregnancies were established using embryo transfer in 42 adolescent ewes that were overnourished (n = 27) or control-fed (n = 15) and were scanned at weekly intervals from 83-126 days' gestation and necropsied at 131 days' gestation (term = 145 days).

RESULTS

Ultrasonographic placental measurements were reduced and UA Doppler indices were increased from 83 days' gestation; measurements of fetal abdominal circumference and femur length, renal volume and tibia length, and biparietal diameter were reduced from 98, 105, and 112 days' gestation, respectively, in overnourished vs control-intake pregnancies.

CONCLUSION

Overnourishment of adolescent sheep dams produced late-onset asymmetric fetal growth restriction that was commensurate with brain sparing. Ultrasonographic placental biometry was already reduced and UA Doppler indices increased by mid gestation in overnourished pregnancies, preceding reduced fetal growth velocity and indicating an early nutritionally mediated insult on placental development.

Intrauterine growth restriction decreases pulmonary alveolar and vessel growth and causes pulmonary artery endothelial cell dysfunction in vitro in fetal sheep

Intrauterine growth restriction (IUGR) increases the risk for bronchopulmonary dysplasia (BPD). Abnormal lung structure has been noted in animal models of IUGR, but whether IUGR adversely impacts fetal pulmonary vascular development and pulmonary artery endothelial cell (PAEC) function is unknown. We hypothesized that IUGR would decrease fetal pulmonary alveolarization, vascular growth, and in vitro PAEC function. Studies were performed in an established model of severe placental insufficiency and IUGR induced by exposing pregnant sheep to elevated temperatures. Alveolarization, quantified by radial alveolar counts, was decreased 20% (P < 0.005) in IUGR fetuses. Pulmonary vessel density was decreased 44% (P < 0.01) in IUGR fetuses. In vitro, insulin increased control PAEC migration, tube formation, and nitric oxide (NO) production. This response was absent in IUGR PAECs. VEGFA stimulated tube formation, and NO production also was absent. In control PAECs, insulin increased cell growth by 68% (P < 0.0001). Cell growth was reduced in IUGR PAECs by 29% at baseline (P < 0.01), and the response to insulin was attenuated (P < 0.005). Despite increased basal and insulin-stimulated Akt phosphorylation in IUGR PAECs, endothelial NO synthase (eNOS) protein expression as well as basal and insulin-stimulated eNOS phosphorylation were decreased in IUGR PAECs. Both VEGFA and VEGFR2 also were decreased in IUGR PAECs. We conclude that fetuses with IUGR are characterized by decreased alveolar and vascular growth and PAEC dysfunction in vitro. This may contribute to the increased risk for adverse respiratory outcomes and BPD in infants with IUGR.

The intrauterine growth restriction phenotype: fetal adaptations and potential implications for later life insulin resistance and diabetes

The intrauterine growth restricted (IUGR) fetus develops unique metabolic adaptations in response to exposure to reduced nutrient supply. These adaptations provide survival value for the fetus by enhancing the capacity of the fetus to take up and use nutrients, thereby reducing the need for nutrient supply. Each organ and tissue in the fetus adapts differently, with the brain showing the greatest capacity for maintaining nutrient supply and growth. Such adaptations, if persistent, also have the potential in later life to promote nutrient uptake and storage, which directly lead to complications of obesity, insulin resistance, reduced insulin production, and type 2 diabetes.

Catecholamines mediate multiple fetal adaptations during placental insufficiency that contribute to intrauterine growth restriction: lessons from hyperthermic sheep

Placental insufficiency (PI) prevents adequate delivery of nutrients to the developing fetus and creates a chronic state of hypoxemia and hypoglycemia. In response, the malnourished fetus develops a series of stress hormone-mediated metabolic adaptations to preserve glucose for vital tissues at the expense of somatic growth. Catecholamines suppress insulin secretion to promote glucose sparing for insulin-independent tissues (brain, nerves) over insulin-dependent tissues (skeletal muscle, liver, and adipose). Likewise, premature induction of hepatic gluconeogenesis helps maintain fetal glucose and appears to be stimulated by both norepinephrine and glucagon. Reduced glucose oxidation rate in PI fetuses creates a surplus of glycolysis-derived lactate that serves as substrate for hepatic gluconeogenesis. These adrenergically influenced adaptive responses promote in utero survival but also cause asymmetric intrauterine growth restriction and small-for-gestational-age infants that are at greater risk for serious metabolic disorders throughout postnatal life, including obesity and type II diabetes.

The tissue and plasma concentration of polyols and sugars in sheep intrauterine growth retardation

In an ovine model of placental insufficiency-induced intrauterine growth retardation (PI-IUGR), characterized by hypoxia, hypoglycemia and a significant reduction in fetal weight, we assessed alterations in fetal and placental polyols. Arterial maternal–fetal concentration differences of glucose and mannose were greater in the PI-IUGR fetus; glucose: C ( n = 7), 2.68 ± 0.14 mmol/L versus PI-IUGR ( n = 9), 3.18 ± 0.16 mmol/L ( P < 0.02) and mannose: C, 42.9 ± 8.1 μmol/L versus PI-IUGR, 68.5 ± 19.1 μmol/L ( P < 0.001). For PI-IUGR fetuses, fetal arterial plasma myo-inositol concentrations were significantly increased ( P < 0.001). The concentrations of sorbitol, glucose and fructose were significantly reduced ( P < 0.03, 0.01, 0.02, respectively). The cotyledons of IUGR placentas had a significantly increased concentration of myo-inositol ( P < 0.003) and decreased concentrations of sorbitol, fructose and glycerol ( P < 0.01, 0.02, 0.01, respectively). Fetal hepatic concentrations of sorbitol ( P < 0.001) and fructose ( P < 0.03) were also significantly reduced. These profound changes in both placental and fetal concentrations of polyols and sugars in sheep PI-IUGR pregnancies support the conclusion that within the PI-IUGR placenta there is an increased flux through the glucose 6-P:inositol 1-P cyclase system and decreased flux through the polyol dehydrogenase system, leading to increased placental myo-inositol production and decreased sorbitol production. The decreased placental supply of sorbitol to the fetal liver may lead to decreased fetal hepatic fructose production. These observations highlight that, in association with hypoxic and hypoglycemic PI-IUGR fetuses, there are major placental and fetal alterations in polyol production. The manner in which these alterations in fetoplacental carbohydrate metabolism contribute to the pathophysiology of PI-IUGR is currently unknown.

Effects of chronic hypoglycemia and euglycemic correction on lysine metabolism in fetal sheep

In this study, we determined rates of lysine metabolism in fetal sheep during chronic hypoglycemia and following euglycemic recovery and compared results with normal, age-matched euglycemic control fetuses to explain the adaptive response of protein metabolism to low glucose concentrations. Restriction of the maternal glucose supply to the fetus lowered the net rates of fetal (umbilical) glucose (42%) and lactate (36%) uptake, causing compensatory alterations in fetal lysine metabolism. The plasma lysine concentration was 1.9-fold greater in hypoglycemic compared with control fetuses, but the rate of fetal (umbilical) lysine uptake was not different. In the hypoglycemic fetuses, the lysine disposal rate also was higher than in control fetuses due to greater rates of lysine flux back into the placenta and into fetal tissue. The rate of CO2 excretion from lysine decarboxylation was 2.4-fold higher in hypoglycemic than control fetuses, indicating greater rates of lysine oxidative metabolism during chronic hypoglycemia. No differences were detected for rates of fetal protein accretion or synthesis between hypoglycemic and control groups, although there was a significant increase in the rate of protein breakdown (P<0.05) in the hypoglycemic fetuses, indicating small changes in each rate. This was supported by elevated muscle specific ubiquitin ligases and greater concentrations of 4E-BP1. Euglycemic recovery after chronic hypoglycemia normalized all fluxes and actually lowered the rate of lysine decarboxylation compared with control fetuses (P<0.05). These results indicate that chronic hypoglycemia increases net protein breakdown and lysine oxidative metabolism, both of which contribute to slower rates of fetal growth over time. Furthermore, euglycemic correction for 5 days returns lysine fluxes to normal and causes an overcorrection of lysine oxidation.

An animal model of placental insufficiency-induced intrauterine growth restriction

Intrauterine growth restriction (IUGR), often associated with functional placental insufficiency, results in increased perinatal mortality and morbidity. For obvious reasons, many questions regarding the progression of IUGR pregnancies cannot be addressed experimentally in humans, predicating the use of animal models. Although no animal model fully recapitulates human pregnancy, the pregnant sheep has been used extensively to investigate maternal-fetal interactions. In sheep, surgical placement of catheters in both the maternal and fetal vasculature allows repeated sampling from nonanesthetized pregnancies. Considerable insight has been gained on placental oxygen and nutrient transfer and utilization from use of pregnant sheep, often confirmed in the human once appropriate technologies became available. This review will focus on one sheep model, used to examine the impact of placental insufficiency-induced IUGR on oxygen and nutrient transport and utilization.

Adult sequelae of intrauterine growth restriction

Fetal intrauterine growth restriction has been associated with adult disease in both human epidemiologic studies and in animal models. In some cases, intrauterine deprivation programs the fetus to develop increased appetite and obesity, hypertension, and diabetes as an adult. Although the mechanisms responsible for fetal programming remain poorly understood, both anatomic and functional (cell signaling) changes have been described in affected individuals. In some animal models, aspects of fetal programming can be reversed postnatally; however, at the present time, the best strategy for avoiding the adult consequences of fetal growth restriction is prevention.

Resistin modulates glucose uptake and glucose transporter-1 (GLUT-1) expression in trophoblast cells

The adipocytokine resistin impairs glucose tolerance and insulin sensitivity. Here, we examine the effect of resistin on glucose uptake in human trophoblast cells and we demonstrate that transplacental glucose transport is mediated by glucose transporter (GLUT)-1. Furthermore, we evaluate the type of signal transduction induced by resistin in GLUT-1 regulation. BeWo choriocarcinoma cells and primary cytotrophoblast cells were cultured with increasing resistin concentrations for 24 hrs. The main outcome measures include glucose transport assay using [³H]-2-deoxy glucose, GLUT-1 protein expression by Western blot analysis and GLUT-1 mRNA detection by quantitative real-time RT-PCR. Quantitative determination of phospho(p)-ERK1/2 in cell lysates was performed by an Enzyme Immunometric Assay and Western blot analysis. Our data demonstrate a direct effect of resistin on normal cytotrophoblastic and on BeWo cells: resistin modulates glucose uptake, GLUT-1 messenger ribonucleic acid (mRNA) and protein expression in placental cells. We suggest that ERK1/2 phosphorylation is involved in the GLUT-1 regulation induced by resistin. In conclusion, resistin causes activation of both the ERK1 and 2 pathway in trophoblast cells. ERK1 and 2 activation stimulated GLUT-1 synthesis and resulted in increase of placental glucose uptake. High resistin levels (50–100 ng/ml) seem able to affect glucose-uptake, presumably by decreasing the cell surface glucose transporter.

Chronic late-gestation hypoglycemia upregulates hepatic PEPCK associated with increased PGC1alpha mRNA and phosphorylated CREB in fetal sheep

Hepatic glucose production is normally activated at birth but has been observed in response to experimental hypoglycemia in fetal sheep. The cellular basis for this process remains unknown. We determined the impact of 2 wk of fetal hypoglycemia during late gestation on enzymes responsible for hepatic gluconeogenesis, focusing on the insulin-signaling pathway, transcription factors, and coactivators that regulate gluconeogenesis. Hepatic phosphoenolpyruvate carboxykinase and glucose-6-phosphatase mRNA increased 12-fold and 7-fold, respectively, following chronic hypoglycemia with no change in hepatic glycogen. Chronic hypoglycemia decreased fetal plasma insulin with no change in glucagon but increased plasma cortisol 3.5-fold. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha mRNA and phosphorylation of cAMP response element binding protein at Ser(133) were both increased, with no change in Akt, forkhead transcription factor FoxO1, hepatocyte nuclear factor-4alpha, or CCAAT enhancer binding protein-beta. These results demonstrate that chronic fetal hypoglycemia triggers signals that can activate gluconeogenesis in the fetal liver.

Increased insulin sensitivity and maintenance of glucose utilization rates in fetal sheep with placental insufficiency and intrauterine growth restriction

In this study we determined body weight-specific fetal (umbilical) glucose uptake (UGU), utilization (GUR), and production rates (GPR) and insulin action in intrauterine growth-restricted (IUGR) fetal sheep. During basal conditions, UGU from the placenta was 33% lower in IUGR fetuses, but GUR was not different between IUGR and control fetuses. The difference between glucose utilization and UGU rates in the IUGR fetuses demonstrated the presence and rate of fetal GPR (41% of GUR). The mRNA concentrations of the gluconeogenic enzymes glucose-6-phophatase and PEPCK were higher in the livers of IUGR fetuses, perhaps in response to CREB activation, as phosphorylated CREB/total CREB was increased 4.2-fold. A hyperglycemic clamp resulted in similar rates of glucose uptake and utilization in IUGR and control fetuses. The nearly identical GURs in IUGR and control fetuses at both basal and high glucose concentrations occurred at mean plasma insulin concentrations in the IUGR fetuses that were approximately 70% lower than controls, indicating increased insulin sensitivity. Furthermore, under basal conditions, hepatic glycogen content was similar, skeletal muscle glycogen was increased 2.2-fold, the fraction of fetal GUR that was oxidized was 32% lower, and GLUT1 and GLUT4 concentrations in liver and skeletal muscle were the same in IUGR fetuses compared with controls. These results indicate that insulin-responsive fetal tissues (liver and skeletal muscle) adapt to the hypoglycemic-hypoinsulinemic IUGR environment with mechanisms that promote glucose utilization, particularly for glucose storage, including increased insulin action, glucose production, shunting of glucose utilization to glycogen production, and maintenance of glucose transporter concentrations.

The pregnant sheep as a model for human pregnancy

Successful outcome of human pregnancy not only impacts the quality of infant life and well-being, but considerable evidence now suggests that what happens during fetal development may well impact health and well-being into adulthood. Consequently, a thorough understanding of the developmental events that occur between conception and delivery is needed. For obvious ethical reasons, many of the questions remaining about the progression of human pregnancy cannot be answered directly, necessitating the use of appropriate animal models. A variety of animal models exist for the study of both normal and compromised pregnancies, including laboratory rodents, non-human primates and domestic ruminants. While all of these animal models have merit, most suffer from the inability to repetitively sample from both the maternal and fetal side of the placenta, limiting their usefulness in the study of placental or fetal physiology under non-stressed in vivo conditions. No animal model truly recapitulates human pregnancy, yet the pregnant sheep has been used extensively to investigate maternal-fetal interactions. This is due in part to the ability to surgically place and maintain catheters in both the maternal and fetal vasculature, allowing repeated sampling from non-anesthetized pregnancies. Considerable insight has been gained on placental oxygen and nutrient transfer and utilization from use of pregnant sheep. These findings were often confirmed in human pregnancies once appropriate technologies became available. The purpose of this review is to provide an overview of human and sheep pregnancy, with emphasis placed on placental development and function as an organ of nutrient transfer.

Sensitivity to metabolic signals in late-gestation growth-restricted fetuses from rapidly growing adolescent sheep

Fetal sensitivity to insulin and glucose was investigated during fetal hyperinsulinemic-euglycemic (HI-euG, n = 18) and hyperglycemic-euinsulinemic (HG-euI, n = 12) clamps. Singleton bearing adolescent ewes were fed high (H) or control (C) nutrient intakes to induce compromised or normal placental/fetal size, respectively. Catheters were inserted in the umbilical vein (v), fetal artery, (a) and veins, and studies were conducted between day 126 and 133 of gestation. Umbilical blood flow (UmBF) was determined by the steady-state transplacental diffusion technique using (3)H(2)O, and glucose fluxes were quantified by the Fick principle. For the HI-euG study, fetal glucose utilization was measured at spontaneously occurring fetal insulin concentrations and two additional higher levels, whereas fetal glucose was clamped at the initial baseline level. For the HG-euI study, fetal insulin was suppressed by somatostatin infusion, and fetal glucose utilization was determined at baseline (before somatostatin) glucose concentrations, and at 150 and 200% of this value. Placentome weight (219 vs. 395 g), fetal weight (2,965 vs. 4,373 g), and UmBF (519 vs. 794 ml/min) were lower (P < 0.001) in H than in C groups. Relative to control fetuses, glucose extraction (G[v - a]/G[v] x 100) in the nonperturbed state was higher (21.7 vs. 15.9%) in growth-restricted fetuses despite lower glucose (0.78 vs. 1.05 micromol/ml) and insulin (8.5 vs. 16.9 microU/ml) concentrations (all P < 0.001). During the HI-euG study, total fetal glucose utilization rate increased in response to higher insulin concentrations (65 and 64% in H and C groups). Similarly during the HG-euI study, a twofold increase in glucose supply increased fetal glucose utilization by 41 and 44% in H and C groups, respectively. Throughout both studies, absolute total fetal glucose utilization rates were reduced in H vs. C groups (P < 0.01) but were similar when expressed per kilogram fetus (HI-euG: 34.7, 49.5, and 57.5 in H vs. 34.7, 51.2, and 56.1 micromol.min(-1).kg(-1) in C, HG-euI: 28.7, 35.7, and 40.8 in H vs. 32.9, 34.5, and 43.8 micromol.min(-1).kg(-1) in C). These normal body weight-specific metabolic responses to short-term experimental increases in plasma insulin and glucose in response to chronic IUGR indicate maintained mechanisms of insulin action and glucose uptake/utilization capacity, which, if persistent, might predispose such IUGR offspring to excessive energy deposition in later life.