Plasma nonesterified fatty acid and blood glucose levels in healthy and hypoxemic newborn infants

WNT/β-catenin pathway is a key regulator of cardiac function and energetic metabolism

The WNT/β-catenin pathway is a master regulator of cardiac development and growth, and its activity is low in healthy adult hearts. However, even this low activity is essential for maintaining normal heart function. Acute activation of the WNT/β-catenin signaling cascade is considered to be cardioprotective after infarction through the upregulation of prosurvival genes and reprogramming of metabolism. Chronically high WNT/β-catenin pathway activity causes profibrotic and hypertrophic effects in the adult heart. New data suggest more complex functions of β-catenin in metabolic maturation of the perinatal heart, establishing an adult pattern of glucose and fatty acid utilization. Additionally, low basal activity of the WNT/β-catenin cascade maintains oxidative metabolism in the adult heart, and this pathway is reactivated by physiological or pathological stimuli to meet the higher energy needs of the heart. This review summarizes the current state of knowledge of the organization of canonical WNT signaling and its function in cardiogenesis, heart maturation, adult heart function, and remodeling. We also discuss the role of the WNT/β-catenin pathway in cardiac glucose, lipid metabolism, and mitochondrial physiology.

How type of parturition and health status influence hormonal and metabolic profiles in newborn foals

Thyroid hormones, insulin growth factor I (IGF-I) and non-esterified fatty acids (NEFA) represent important hormonal and metabolic factors associated with perinatal growth and maturation. Their action could be influenced by the type of parturition and the health status of the foal and therefore the aim of this work is to evaluate their plasma concentrations in newborn foals during the first 2 wks of life. Three groups of subjects were enrolled: 15 healthy foals born by spontaneous parturition, 24 healthy foals born by induced parturition and 26 pathologic foals. From each of the healthy foals, blood was collected at 10, 20 and 30 minutes, 3 and 12 hours from birth, daily from Day 1 to Day 7, and at Day 10 and 14 of life. In pathologic foals samples were collected twice a day from the day of admission at the hospital until the day of discharge or death. Thyroid hormones (T3 and T4) and IGF-I were analyzed by radioimmunoassay and NEFA by enzymatic-colorimetric methods. In all the three groups a declining trend of T3 and T4 plasma concentrations was detectable, with lower levels in the pathologic group compared to healthy foals. Spontaneous foals showed higher levels of T3 at 7 d compared to induced foals, while T4 levels were higher in spontaneous vs. induced foals before 6 h of life, at three and seven days. IGF-I showed increasing plasma concentrations in all three considered groups. No differences were found between healthy and pathologic foals. NEFA in spontaneous and induced healthy foals showed a declining trend with higher levels during the first hours of life. Pathologic foals presented higher levels compared to spontaneous foals only at 24 h and 10 d. These data suggest that the type of foaling could influence the reference ranges for thyroid hormones. Moreover, pathologic foals showed some hormonal and metabolic differences related to their health status. Above all changes of thyroid hormones levels, early in postnatal life, could be a cause, and not only a consequence, of the diseased condition of these foals.

Epidermal growth factor and parathyroid hormone-related peptide mRNA in the mammary gland and their concentrations in milk: effects of postpartum hypoxia in lactating rats

The physiological adaptations of the neonatal rat to hypoxia from birth include changes in gastrointestinal function and intermediary metabolism. We hypothesized that the hypoxic lactating dam would exhibit alterations in mammary gland function leading to changes in the concentration of milk peptides that are important in neonatal gastrointestinal development. The present study assessed the effects of chronic hypoxia on peptides produced by the mammary glands and present in milk. Chronic hypoxia decreased the concentration of epidermal growth factor (EGF) in expressed milk and pup stomach contents and decreased maternal mammary gland EGF mRNA. The concentration of parathyroid hormone-related protein (PTHrp) was unchanged in milk and decreased in pup stomach contents; however, mammary PTHLH mRNA was increased by hypoxia. There was a significant increase in adiponectin concentrations in milk from hypoxic dams. Chronic hypoxia decreased maternal body weight, and pair feeding normoxic dams an amount of food equivalent to hypoxic dam food intake decreased body weight to an equivalent degree. Decreased food intake did not affect the expression of EGF, PTHLH, or LEP mRNA in mammary tissue. The results indicated that chronic hypoxia modulated mammary function independently of hypoxia-induced decreases in maternal food intake. Decreased EGF and increased adiponectin concentrations in milk from hypoxic dams likely affect the development of neonatal intestinal function.

Microarray and real-time PCR analysis of adrenal gland gene expression in the 7-day-old rat: effects of hypoxia from birth

We hypothesize that changes in adrenal gene expression mediate the increased plasma corticosterone and steroidogenesis in rat pups exposed to hypoxia from birth. In the current study, rat pups (with their dams) were exposed to hypoxia from birth and compared with pups from normoxic dams fed ad libitum or pair fed to match the decreased maternal food intake that occurs during hypoxia. Microarray analysis was performed, followed by verification with real-time PCR. Furthermore, the expression of selected genes involved in adrenal function was analyzed by real-time PCR, regardless of microarray results. Hypoxia increased plasma ACTH and corticosterone, while food restriction had no effect. Microarray revealed that many of the genes affected by hypoxia encode proteins that require molecular oxygen (monooxygenases, oxidoreductases, and electron transport), whereas only a few genes known to be involved in adrenal steroidogenesis were affected. Interestingly, the expression of genes involved in mitochondrial function and intermediary metabolism was increased by hypoxia. Real-time PCR detected a small but significant increase in the expression of Cyp21a1 mRNA in the hypoxic adrenal. When decreased maternal food intake was controlled for, the effects of hypoxia were more pronounced, in that real-time PCR detected significant increases in the expression of Star (244%), Cyp21a1 (208%), and Ldlr (233%). The present study revealed that increased plasma corticosterone in rat pups was due to hypoxia per se, and not as a result of decreased food intake by the hypoxic dam. Furthermore, hypoxia induced changes in gene expression that account for more productive and efficient steroidogenesis.

Metabolomic analysis of adrenal lipids during hypoxia in the neonatal rat: implications in steroidogenesis

The nursing rat pup exposed to hypoxia from birth exhibits ACTH-independent increases in corticosterone and renin/ANG II-independent increases in aldosterone. These increases are accompanied by significant elevation of plasma lipid concentrations in the hypoxic neonates. The purpose of the present study was to compare changes in the concentrations of specific fatty acid metabolites and lipid classes in serum and adrenal tissue from normoxic and hypoxic rat pups. We hypothesized that lipid alterations resulting from hypoxia may partly explain increases in steroidogenesis. Rats were exposed to normoxia or hypoxia from birth, and pooled serum and adrenal tissue from 7-day-old pups were subjected to metabolomic analyses. Hypoxia resulted in specific and significant changes in a number of fatty acid metabolites in both serum and the adrenal. Hypoxia increased the concentrations of oleic (18:1 n-9), eicosapentaenoic (EPA; 20:5 n-3), and arachidonic (20:4 n-6) acids in the triacylglyceride fraction of serum and decreased oleic and EPA concentrations in the cholesterol ester fraction. In the adrenal, hypoxia caused an increase in several n-6 fatty acids in the triacylglyceride fraction, including linoleic (18:2 n-6) and arachidonic acid. There was also an increase in the concentration of alpha-linolenic acid (18:3 n-3) in the triacylglyceride fraction of the hypoxic adrenal, along with an increase in linoleic acid concentration in the diacylglyceride fraction. We propose that specific changes in lipid metabolism in the adrenal, as a result of hypoxia, may partly explain the increased steroidogenesis previously observed. The mechanism responsible may involve alterations in cellular signaling and/or mitochondrial function. These cellular changes may be a mechanism by which the neonate can increase circulating adrenal steroids necessary for survival, therefore bypassing a relative insensitivity to normal stimuli.

Effect of neonatal hypoxia on the development of hepatic lipase in the rat

Increases in plasma lipids occur during hypoxia in suckling but not in weaned rats and may result from altered hepatic enzyme activity. We exposed rats to 7 days of hypoxia from birth to 7 days of age (suckling) or from 28 to 35 days of age (weaned at day 21). Hypoxia led to an increase in hepatic lipid content in the suckling rat only. Hepatic lipase was decreased to approximately 45% of control in 7-day-old rats exposed to hypoxia but not in hypoxic 35-day-old rats. Hypoxic suckling rats also had a 50% reduction in lactate dehydrogenase activity, whereas transaminase activity and CYP1A and CYP3A protein content were not different between hypoxic and normoxic groups. Additional rats were studied 7 and 14 days after recovery from hypoxic exposure from birth to 7 days of age; hepatic lipase activity had recovered to 85% by 7 days and to 100% by 14 days in the rats previously exposed to hypoxia. Administration of dexamethasone to neonatal rats to simulate the hyperglucocorticoid state found in hypoxic 7-day-old rats led to a moderate decrease ( approximately 75% of control) in hepatic lipases. Developmentally, in the normoxic state, hepatic lipases increased rapidly after birth and reached levels more than twofold that of the newborn by 7 days of age. Hypoxia delays the maturation of hepatic lipases. We suggest that the decrease in hepatic lipase activity contributes to hyperlipemia in the hypoxic newborn rats.

Neonatal hypoxic hyperlipidemia in the rat: effects on aldosterone and corticosterone synthesis in vitro

Neonatal hypoxia increases aldosterone production and plasma lipids. Because fatty acids can inhibit aldosterone synthesis, we hypothesized that increases in plasma lipids restrain aldosteronogenesis in the hypoxic neonate. We exposed rats to 7 days of hypoxia from birth to 7 days of age (suckling) or from 28 to 35 days of age (weaned at day 21). Plasma was analyzed for lipid content, and steroidogenesis was studied in dispersed whole adrenal glands untreated and treated to wash away lipids. Hypoxia increased plasma cholesterol, triglycerides, and nonesterified fatty acids in the suckling neonatal rat only. Washing away lipids increased aldosterone production in cells from 7-day-old rats exposed to hypoxia, but not in cells from normoxic 7-day-old rats or from normoxic or hypoxic 35-day-old rats. Addition of oleic or linolenic acid to washed cells inhibited both aldosterone and corticosterone production, although cells from hypoxic 7-day-old rats were less sensitive. We conclude that hypoxia induces hyperlipidemia in the suckling neonate and that elevated nonesterified fatty acids inhibit aldosteronogenesis.

Effect of oral lipid administration on glucose homeostasis in small-for-gestational-age infants

The metabolic effect of feeding with 1.3 g/kg bw lipids (67% medium chain triglycerides) was studied in 15 small-for-gestational age (SGA) term infants. It was compared to a control group of 7 SGA term infants, to 7 term infants with an appropriate birth weight (AGA) and to 7 AGA preterm infants. Plasma glucose concentration rose from (M +/- SE) 3.6 +/- 0.2 to 4.4 +/- 0.3 mmol/l at 30 min in SGA term infants (p less than 0.01). A similar increase was observed in AGA term and preterm infants. The lipid load produced no change in plasma glucagon concentration but a significant increase in insulin/glucagon molar ratio was observed in AGA term infants only. In term SGA infants, the disappearance rate of glucose in plasma after the lipid load was similar to the control: 1.24% per min. The evolution of blood pyruvate and lactate concentration was not modified by the lipid load. Despite lower concentrations of free fatty acids and ketone bodies (KB) in SGA infants than in AGA term infants, the lipid load induced a 120% increase of ketone bodies in SGA infants and a 40% increase only in AGA infants. These data show that these lipids produce a hyperglycemic response in SGA infants as in AGA infants without any change of the disappearance rate of glucose. They suggest that these lipids can stimulate gluconeogenesis and ketogenesis in SGA infants.

Free fatty acids, glycerol and triglycerides during the first 24 hours in infants with a birth weight less than or equal to 2700 grams

The influence of birth weight and gestational age on the concentrations of free fatty acids, glycerol and triglycerides during the first 24 hours of life were studied in 86 healthy newborn infants with BW less than or equal to 2700 g. Very low FFA values were found in the first 6 hours in infants with GA less than or equal to 34 weeks, whereas FFA increased from the second hour in infants with higher GA. All infants had peak values at 12 h. Significant correlations were found between FFA and GA, most pronounced in the second hour after birth. No differences were seen between AGA and SGA infants of similar GA. High glycerol concentrations were found from the second hour in all infants irrespective of GA and BW. Triglyceride concentrations 24 hours after birth were not influenced by GA or BW. Triglyceride concentrations 24 hours after birth were not influenced by GA or BW. The finding of intact lipolysis but low FFA releases in the first hours in infants with GA less than or equal to 34 weeks could not be explained by differences in rectal temperature, blood glucose or caloric intake.

Evidence for fatty acid transfer across the human placenta

Lipid analysis of blood from umbilical artery and vein, experiments on artificially perfused human placentas, measurements of fetal blood triglyceride concentrations and the relative percentage of essential fatty acids in fetal adipose tissue are all consistent with the view that fatty acids cross the human placenta and that the flow to the fetus is influenced by maternal blood concentrations of free fatty acids and triglycerides.

Perinatal plasma lipid concentrations

The effect of the maternal environment on umbilical cord plasma lipid concentrations was studied in a group of mothers and babies. Changes in neonatal plasma concentrations during the first week of life were followed in a small group of infants. The lipoprotein distribution of the cholesterol and triglyceride content of umbilical cord plasma was similar to that seen in maternal plasma at delivery. Neonatal plasma cholesterol was significantly correlated with the cholesterol content of maternal low density lipoprotein. Neonatal plasma triglyceride concentration was related to maternal parity, duration of labour and the existence of maternal hypertension and to the occurrence of foetal distress and dysmaturity.

Concentrations of triglycerides, free fatty acids and glycerol in cord blood of newborn infants with a birth weight of less than or equal to 2700 grams

Concentrations of triglycerides, free fatty acids (FFA) and glycerol were measured in umbilical venous blood from 99 infants with a birth weight of between 1100-2700 g and a gestational age of 27-41 weeks. Thirty infants were small for gestational age (SGA), 58 were appropriate (AGA) and 11 were of uncertain gestational age. In AGA infants with a gestational age of less than or equal to 35 weeks. FFA values were lower than in those with a gestational age of less than 35 weeks; otherwise concentrations of triglycerides, FFA and glycerol were independent of birth weight and gestational age in AGA infants. In SGA infants, higher FFA values were found compared with both AGA and term infants of normal birth weight. Triglyceride values were higher in SGA than in AGA infants. In SGA infants, a significant positive correlation was found between gestational age and concentrations of both FFA and triglycerides. No differences in FFA, glycerol and triglyceride concentrations were seen between asphyxiated and non-asphyxiated AGA infants.

Substrate mobilization: a new hypothesis for the aetiology of the idiopathic respiratory distress syndrome

This hypothesis for the aetiology of the idiopathic respiratory distress syndrome of the newborn (IRDS) proposes that, although the aetiology is multifactorial, the factor of prime importance is the mobilization of substrate for surfactant synthesis. All factors known to influence the incidence, treatment, and prognosis of the IRDS can be shown to be associated with the mobilization of substrate and thereafter its continued availability for the synthesis of adequate surfactant. Thus factors which promote an antenatal increase in the breakdown of energy stores will be associated with a reduced incidence of the IRDS. On the other hand, despite adequate mobilization, factors associated with a lack of substrate secondary to poor transport of substrate, a reduction in pulmonary circulation or an alteration in fetal or neonatal metabolism which involves an increased utilization of substrate to provide energy, will be associated with an increased incidence of the IRDS.

Neonatal hypertriglyceridemia: a new index of antepartum-intrapartum fetal stress?

The 95th percentile value of cord serum triglyceride concentration in 82 consecutively live born infants was found to be 0.79 mmol/l. This level was arbitrarily used to define neonatal hypertriglyceridemia. A comparison between 78 normotriglyceridemic and 61 hypertriglyceridemic newborn infants showed a significant association between elevated cord serum triglyceride concentration and insufficiency of the placenta, fetal bradycardia, meconium-stained amniotic fluid and one-minute Apgar score less than or equal to 7. A significantly (p less than 0.001) greater number of infants with one or several of these four factors, indicating antepartum and/or intrapartum fetal stress were found to be hypertriglyceridemic at birth. This finding suggests that estimation of cord serum triglyceride which is easy and inexpensive might be of value for a more complete evaluation of the newborn infant, and can serve as a supplement to the Apgar Score system.