Fetal growth restriction: adaptations and consequences

A range of pathophysiological factors can result in a perturbation or restriction of fetal growth, and the cardiovascular, neuroendocrine and metabolic adaptations of the fetus to these stimuli will depend on their nature, timing and intensity. The critical importance of these physiological adaptations for both immediate survival and long-term health outcomes has provided an impetus for experimental studies of the nature and consequences of specific fetal adaptations to a poor intrauterine environment. This review summarizes data from recent studies that have focused on the responses of the fetal cardiovascular, sympathoadrenal, hypothalamo-pituitary-adrenal and renin-angiotensin systems to experimental restriction of placental function in the sheep and discusses the consequences of these adaptations for fetal, neonatal and adult health.

Placental adaptations in growth restriction

The placenta is the primary interface between the fetus and mother and plays an important role in maintaining fetal development and growth by facilitating the transfer of substrates and participating in modulating the maternal immune response to prevent immunological rejection of the conceptus. The major substrates required for fetal growth include oxygen, glucose, amino acids and fatty acids, and their transport processes depend on morphological characteristics of the placenta, such as placental size, morphology, blood flow and vascularity. Other factors including insulin-like growth factors, apoptosis, autophagy and glucocorticoid exposure also affect placental growth and substrate transport capacity. Intrauterine growth restriction (IUGR) is often a consequence of insufficiency, and is associated with a high incidence of perinatal morbidity and mortality, as well as increased risk of cardiovascular and metabolic diseases in later life. Several different experimental methods have been used to induce placental insufficiency and IUGR in animal models and a range of factors that regulate placental growth and substrate transport capacity have been demonstrated. While no model system completely recapitulates human IUGR, these animal models allow us to carefully dissect cellular and molecular mechanisms to improve our understanding and facilitate development of therapeutic interventions.

Increased maternal nutrition alters development of the appetite‐regulating network in the brain

Individuals exposed to an increased nutrient supply before birth have a high risk of becoming obese children and adults. It has been proposed that exposure of the fetus to high maternal nutrient intake results in permanent changes within the central appetite regulatory network. No studies, however, have investigated the impact of increased maternal nutrition on the appetite regulatory network in species in which this network develops before birth, as in the human. In the present study, pregnant ewes were fed a diet which provided 100% (control, n = 8) or approximately 160% (well-fed, n = 8) of metabolizable energy requirements. Ewes were allowed to lamb spontaneously, and lambs were sacrificed at 30 days of postnatal age. All fat depots were dissected and weighed, and expression of the appetite-regulating neuropeptides and the leptin receptor (OBRb) were determined by in situ hybridization. Lambs of well-fed ewes had higher glucose (Glc) concentrations during early postnatal life (F = 5.93, P<0.01) and a higher relative subcutaneous (s.c.) fat mass at 30 days of age (34.9+/-4.7 g/kg vs. 22.8+/-3.3 g/kg; P<0.05). The hypothalamic expression of pro-opiomelanocortin was higher in lambs of well-fed ewes (0.48+/-0.09 vs. 0.28+/-0.04, P<0.05). In lambs of overnourished mothers, but not in controls, the expression of OBRb was inversely related to total relative fat mass (r2 = 0.50, P = 0.05, n = 8), and the direct relationship between the expression of the central appetite inhibitor CART and fat mass was lost. The expression of neuropeptide Y and AGRP was inversely related to total relative fat mass (NPY, r2 = 0.28, P<0.05; agouti-related peptide, r2 = 0.39, P<0.01). These findings suggest that exposure to increased nutrition before birth alters the responses of the central appetite regulatory system to signals of increased adiposity after birth.

Restriction of placental function alters heart development in the sheep fetus

Placental insufficiency, resulting in restriction of fetal substrate supply, is a major cause of intrauterine growth restriction (IUGR) and increased neonatal morbidity. Fetal adaptations to placental restriction maintain the growth of key organs, including the heart, but the impact of these adaptations on individual cardiomyocytes is unknown. Placental and hence fetal growth restriction was induced in fetal sheep by removing the majority of caruncles in the ewe before mating (placental restriction, PR). Vascular surgery was performed on 13 control and 11 PR fetuses at 110-125 days of gestation (term: 150 +/- 3 days). PR fetuses with a mean gestational Po(2) < 17 mmHg were defined as hypoxic. At postmortem (<135 or >135 days), fetal hearts were collected, and cardiomyocytes were isolated and fixed. Proliferating cardiomyocytes were counted by immunohistochemistry of Ki67 protein. Cardiomyocytes were stained with methylene blue to visualize the nuclei, and the proportion of mononucleated cells and length and width of cardiomyocytes were measured. PR resulted in chronic fetal hypoxia, IUGR, and elevated plasma cortisol concentrations. Although there was no difference in relative heart weights between control and PR fetuses, there was an increase in the proportion of mononucleated cardiomyocytes in PR fetuses. Whereas mononucleated and binucleated cardiomyocytes were smaller, the relative size of cardiomyocytes when expressed relative to heart weight was larger in PR compared with control fetuses. The increase in the relative proportion of mononucleated cardiomyocytes and the relative sparing of the growth of individual cardiomyocytes in the growth-restricted fetus are adaptations that may have long-term consequences for heart development in postnatal life.

Fetal growth restriction, catch-up growth and the early origins of insulin resistance and visceral obesity

There is an association between growing slowly before birth, accelerated growth in early postnatal life and the emergence of insulin resistance, visceral obesity and glucose intolerance in adult life. In this review we consider the pathway through which intrauterine growth restriction (IUGR) leads to the initial increase in insulin sensitivity and to catch-up growth. We also discuss the importance of the early insulin environment in determining later visceral adiposity and the intrahepatic mechanisms that may result in the emergence of glucose intolerance in a subset of IUGR infants. We present evidence that a key fetal adaptation to poor fetal nutrition is an upregulation of the abundance of the insulin receptor in the absence of an upregulation of insulin signalling in fetal skeletal muscle. After birth, however, there is an upregulation in the abundance of the insulin receptor and the insulin signalling pathway in the IUGR offspring. Thus, the origins of the accelerated postnatal growth rate experienced by IUGR infants lie in the fetal adaptations to a poor nutrient supply. We also discuss how the intracellular availability of free fatty acids and glucose within the visceral adipocyte and hepatocyte in fetal and neonatal life are critical in determining the subsequent metabolic phenotype of the IUGR offspring. It is clear that a better understanding of the relative contributions of the fetal and neonatal nutrient environment to the regulation of key insulin signalling pathways in muscle, visceral adipose tissue and the liver is required to support the development of evidence-based intervention strategies and better outcomes for the IUGR infant.

The correlation between serum and salivary melatonin concentrations and urinary 6-hydroxymelatonin sulphate excretion rates: two non-invasive techniques for monitoring human circadian rhythmicity

Although there is a circadian rhythm in blood melatonin concentrations in humans, the problems associated with frequent blood collection limit the use of this rhythm in the investigation of the circadian system and in the diagnosis and treatment of chronobiological disorders. Therefore, to establish a convenient, non-invasive technique for monitoring melatonin circadian rhythmicity, we compared the melatonin concentrations in blood samples collected from five subjects every 2-4 h over a 26 h period, with the melatonin concentrations in saliva samples and with the total amount of 6-hydroxymelatonin sulphate excreted in the urine during 2-h periods. There was significant correlation between serum and salivary melatonin concentrations (r = 0.81, P less than 0.001), and between serum melatonin concentrations and 6-hydroxymelatonin sulphate excretion rates (r = 0.72, P less than 0.001). The results demonstrate that both salivary melatonin concentrations and urinary 6-hydroxymelatonin sulphate excretion rates are reliable indices of serum melatonin concentrations. These measurements, in combination with frequent sample collection, provide two convenient, non-invasive techniques for monitoring melatonin circadian rhythmicity.

Increased maternal nutrition stimulates peroxisome proliferator activated receptor-gamma, adiponectin, and leptin messenger ribonucleic acid expression in adipose tissue before birth

During fetal life, adipose tissue is predominantly comprised of brown or thermogenic adipocytes and there is a transition to white, lipid-storing adipocytes after birth concomitant with the onset of suckling. In pregnancies complicated by gestational diabetes, the fetus is hyperglycemic, has an increased fat mass, and is at increased risk of obesity in later life. In the present study, we have investigated the hypothesis that exposure to increased maternal nutrition during late gestation results in increased expression of genes that regulate adipogenesis and lipogenesis in perirenal fat in fetal sheep. Pregnant ewes were fed either at or approximately 55% above maintenance energy requirements during late pregnancy and quantitative RT-PCR was used to measure peroxisome proliferator-activated receptor gamma, lipoprotein lipase, glycerol-3-phosphate dehydrogenase, adiponectin, and leptin mRNA expression. We report that exposure to metabolic and hormonal signals of increased nutrition before birth results in an increase in the expression of the adipogenic factor, peroxisome proliferator-activated receptor gamma, and in lipoprotein lipase, adiponectin, and leptin mRNA expression in fetal perirenal fat. We propose that an increase in maternal, and hence fetal, nutrition results in a precocial increase in adipogenic, lipogenic, and adipokine gene expression in adipose tissue and that these changes may be important in the development of obesity in later life.

Restriction of placental and fetal growth in sheep alters fetal blood pressure responses to angiotensin II and captopril

1. We have measured arterial blood pressure between 115 and 145 days gestation in normally grown fetal sheep (control group; n = 16) and in fetal sheep in which growth was restricted by experimental restriction of placental growth and development (PR group; n = 13). There was no significant difference in the mean gestational arterial blood pressure between the PR (42.7 +/- 2.6 mmHg) and control groups (37.7 +/- 2.3 mmHg). Mean arterial blood pressure and arterial PO2 were significantly correlated in control animals (r = 0.53, P < 0.05, n = 16), but not in the PR group. 2. There were no changes in mean arterial blood pressure in either the PR or control groups in response to captopril (7.5 microg captopril min-1; PR group n = 7, control group n = 6) between 115 and 125 days gestation. After 135 days gestation, there was a significant decrease (P < 0.05) in the fetal arterial blood pressure in the PR group but not in the control group during the captopril infusion (15 microg captopril min-1; PR group n = 7, control group n = 6). 3. There was a significant effect (F = 14.75; P < 0.001) of increasing doses of angiotensin II on fetal diastolic blood pressure in the PR and control groups. The effects of angiotensin II were different (F = 8.67; P < 0.05) in the PR and control groups at both gestational age ranges. 4. These data indicate that arterial blood pressure may be maintained by different mechanisms in growth restricted fetuses and normally grown counterparts and suggests a role for the fetal renin-angiotensin system in the maintenance of blood pressure in growth restricted fetuses.

Placental restriction alters the functional development of the pituitary-adrenal axis in the sheep fetus during late gestation

We have experimentally restricted placental growth in the sheep to investigate the impact of reduced substrate delivery on fetal pituitary proopiomelanocortin (POMC) mRNA levels and on circulating ACTH 1-39, immunoreactive ACTH, and cortisol concentrations during late gestation. Endometrial caruncles were removed in nine ewes before mating to reduce the number of placentomes formed [placental restriction group (PR)]. Fetal arterial PO2 and O2 saturation were reduced in the PR group (2.0 +/- 0.1 kPa and 42.8 +/- 1.1%, n = 9) when compared with control fetuses (3.1 +/- 0.1 kPa and 66.4 +/- 0.9%, n = 10). The ratio of anterior pituitary POMC mRNA:18 S ribosomal RNA was also lower (p < 0.05) in the PR group (0.49 +/- 0.05) when compared with the control group (0.80 +/- 0.12) after 140 d of gestation. In contrast, plasma concentrations of ACTH 1-39 and immunoreactive ACTH were similar in the PR and control groups throughout late gestation. Plasma ACTH 1-39 concentrations increased (p < 0.006) between 128 and 134 d of gestation, in both the PR (122-128 d: 2.70 +/- 0.34 pmol/L: 134-141 d; 7.07 +/- 1.57 pmol/L) and control (122-128 d; 3.36 +/- 0.56 pmol/L: 134-141 d; 10.78 +/- 2.88 pmol/L) groups. Combined adrenal weight was higher (p < 0.005) in the PR group (130 +/- 10 mg/kg) compared with controls (80 +/- 1 mg/kg) at 140 d of gestation, and plasma cortisol concentrations were also higher (p < 0.02) in PR than control fetuses between 127 and 141 d of gestation. These changes imply that the fetal hypothalamopituitary-adrenal axis is operating at a new central set point in the growth-restricted fetus.

The early origins of obesity and insulin resistance: timing, programming and mechanisms

Maternal obesity is associated with an increased risk of developing gestational diabetes mellitus and it also results in an increased risk of giving birth to a large baby with increased fat mass. Furthermore, it is also contributes to an increased risk of obesity and insulin resistance in the offspring in childhood, adolescence and adult life. It has been proposed that exposure to maternal obesity may therefore result in an 'intergenerational cycle' of obesity and insulin resistance. There is significant interest in whether exposure to maternal obesity around the time of conception alone contributes directly to poor metabolic outcomes in the offspring and whether dieting in the obese mother before pregnancy or around the time of conception has metabolic benefits for the offspring. This review focusses on experimental and clinical studies that have investigated the specific impact of exposure to maternal obesity during the periconceptional period alone or extending beyond conception on adipogenesis, lipogenesis and on insulin signalling pathways in the fat, liver and muscle of the offspring. Findings from these studies highlight the need for a better evidence base for the development of dietary interventions in obese women before pregnancy and around the time of conception to maximize the metabolic benefits and minimize the metabolic costs for the next generation.

Epigenetics of programmed obesity: alteration in IUGR rat hepatic IGF1 mRNA expression and histone structure in rapid vs. delayed postnatal catch-up growth

Maternal food restriction (FR) during pregnancy results in intrauterine growth-restricted (IUGR) offspring that show rapid catch-up growth and develop metabolic syndrome and adult obesity. However, continued nutrient restriction during nursing delays catch-up growth and prevents development of obesity. Epigenetic regulation of IGF1, which modulates growth and is synthesized and secreted by the liver, may play a role in the development of these morbidities. Control (AdLib) pregnant rats received ad libitum food through gestation and lactation, and FR dams were exposed to 50% food restriction from days 10 to 21. FR pups were nursed by either ad libitum-fed control dams (FR/AdLib) or FR dams (FR/FR). All pups were weaned to ad libitum feed. Maternal FR resulted in IUGR newborns with significantly lower liver weight and, with the use of chromatin immunoprecipitation, decreased dimethylation at H3K4 in the IGF1 region was observed. Obese adult FR/AdLib males had decreased dimethylation and increased trimethylation of H3K4 in the IGF1 region. This corresponded to an increase in mRNA expression of IGF1-A (134 ± 5%), IGF1-B (165 ± 6%), IGF1 exon 1 (149 ± 6%), and IGF1 exon 2 (146 ± 7%) in the FR/AdLib compared with the AdLib/AdLib control group. In contrast, nonobese FR/FR had significantly higher IGF1-B mRNA levels (147 ± 19%) than controls with no difference in IGF1-A, exon 1 or exon 2. Modulation of the rate of IUGR newborn catch-up growth may thus protect against IGF1 epigenetic modifications and, consequently, obesity and associated metabolic abnormalities.

Periconceptional nutrition programs development of the cardiovascular system in the fetal sheep

It has been proposed that fetal adaptations to intrauterine nutrient deprivation permanently reprogram the cardiovascular system. We investigated the impact of restricted periconceptional nutrition and/or restricted gestational nutrition on fetal arterial blood pressure (BP), heart rate, rate pressure product, and the fetal BP responses to ANG II and the angiotensin-converting enzyme inhibitor captopril during late gestation. Restricted periconceptional nutrition resulted in an increase in fetal mean arterial BP between 115 and 125 days gestation (restricted 41.5 +/- 2.8 mmHg, n = 12; control 38.5 +/- 1.5 mmHg, n = 13) and between 135 and 147 days gestation (restricted 50.5 +/- 2.2 mmHg, n = 8; control 42.5 +/- 1.9 mmHg, n = 10) as well as an increase in the rate pressure product in twin, but not singleton, fetuses between 115 and 147 days gestation. Mean BP and fetal plasma ACTH were also positively correlated in twin, but not singleton, fetuses. This is the first demonstration that maternal undernutrition during the periconceptional period results in an increase in fetal arterial BP. This increase occurs concomitantly with an increase in fetal ACTH but is not dependent on activation of the fetal renin-angiotensin system.

Origins of fetal growth restriction

Regulation of growth of the fetus and its placenta begins before pregnancy. Early in pregnancy the mother sets the rate of growth of the fetus on a trajectory, which may be modified by events later in pregnancy. Low maternal weight for height, history of previous small babies, maternal undernutrition, pregnancy disorders, e.g. pre-eclampsia, are associated with low birthweight. Maternal smoking is a major factor in developed countries; infections and undernutrition in developing countries.Recently, there has been emphasis on adverse long-term outcomes including ischaemic heart disease, hypertension and diabetes associated with poor fetal growth. Experimental studies in animals show that some of these outcomes can readily be induced by restriction of fetal growth. Progress in determining successful treatments to improve the growth of the fetus has lagged behind these epidemiological and experimental findings. However, nutrient supplements improve growth in undernourished women and smoking cessation also improves fetal size and outcome.

Maternal undernutrition increases arterial blood pressure in the sheep fetus during late gestation

1. We have investigated the effect of a 50 % reduction in maternal nutrient intake during the last 30 days of pregnancy on arterial blood pressure and on arterial blood pressure responses to angiotensin II (AII) and the angiotensin converting enzyme (ACE) inhibitor captopril in the sheep fetus at 115-125 and at 135-145 days gestation (term = 147 +/- 3 days gestation). 2. Fetal plasma glucose concentrations were lower in the undernourished (UN) group compared to the control animals. There was no difference, however, in fetal plasma cortisol or adrenocorticotrophic hormone (ACTH) concentrations between the UN and control groups between 115 and 145 days gestation. 3. During the first 10 days of undernutrition, maternal plasma concentrations of cortisol were increased in the UN group compared to controls. At 115-125 days gestation, fetal arterial blood pressure was also higher in the UN group compared with controls and there was an inverse relationship (r = -0.62, P < 0.05) between mean arterial pressure and the fetal plasma concentrations of ACTH in the UN group. Fetal blood pressure responses to increasing doses of angiotensin II were also higher (P < 0.05) in UN compared to control animals at 115-125 days gestation. 4. Between 135 and 145 days gestation, fetal arterial blood pressure was increased in UN fetal sheep and mean arterial blood pressure was correlated with fetal plasma concentrations of cortisol. 5. Increased arterial blood pressure and responsiveness to AII measured in the fetuses of nutrient-restricted ewes may be related in part to fetal exposure to the actions of cortisol derived from transplacental transfer during the first 10 days after the start of the restricted feeding regime.

The transition from fetal growth restriction to accelerated postnatal growth: a potential role for insulin signalling in skeletal muscle

A world-wide series of epidemiological and experimental studies have demonstrated that there is an association between being small at birth, accelerated growth in early postnatal life and the emergence of insulin resistance in adult life. The aim of this study was to investigate why accelerated growth occurs in postnatal life after in utero growth restriction. Samples of quadriceps muscle were collected at approximately 140 days gestation (term approximately 150 days gestation) from normally grown fetal lambs (Control, n = 7) and from growth restricted fetal lambs (placentally restricted: PR, n = 8) and from Control (n = 14) and PR (n = 9) lambs at 21 days after birth. The abundance of the insulin and IGF1 receptor protein was higher in the quadriceps muscle of the PR fetus, but there was a lower abundance of the insulin signalling molecule PKC, and GLUT4 protein in the PR group. At 21 days of postnatal age, insulin receptor abundance remained higher in the muscle of the PR lamb, and there was also an up-regulation of the insulin signalling molecules, PI3Kinase p85, Akt1 and Akt2 and of the GLUT4 protein in the PR group. Fetal growth restriction therefore results in an increased abundance of the insulin receptor in skeletal muscle, which persists after birth when it is associated with an upregulation of insulin signalling molecules and the glucose transporter, GLUT4. These data provide evidence that the origins of the accelerated growth experienced by the small baby after birth lie in the adaptive response of the growth restricted fetus to its low placental substrate supply.

Prenatal programming of postnatal obesity: fetal nutrition and the regulation of leptin synthesis and secretion before birth

Exposure to either an increased or decreased level of intrauterine nutrition can result in an increase in adiposity and in circulating leptin concentrations in later life. In animals such as the sheep and pig in which fat is deposited before birth, leptin is synthesised in fetal adipose tissue and is present in the fetal circulation throughout late gestation. In the sheep a moderate increase or decrease in the level of maternal nutrition does not alter fetal plasma leptin concentrations, but there is evidence that chronic fetal hyperglycaemia and hyperinsulinaemia increase fetal fat mass and leptin synthesis within fetal fat depots. Importantly, there is a positive relationship between the relative mass of the 'unilocular' component of fetal perirenal and interscapular adipose tissue and circulating fetal leptin concentrations in the sheep. Thus, as in the neonate and adult, circulating leptin concentrations may be a signal of fat mass in fetal life. There is also evidence that leptin can act to regulate the lipid storage, leptin synthetic capacity and potential thermogenic functions of fat before birth. Thus, leptin may act as a signal of energy supply and have a 'lipostatic' role before birth. Future studies are clearly required to determine whether the intrauterine and early postnatal nutrient environment programme the endocrine feedback loop between adipose tissue and the central and peripheral neuroendocrine systems that regulate energy balance, resulting in an enhanced risk of obesity in adult life.

Differential effects of maternal obesity and weight loss in the periconceptional period on the epigenetic regulation of hepatic insulin-signaling pathways in the offspring

Our aim was to determine the effect of exposure to maternal obesity or to maternal weight loss around conception on the programming of hepatic insulin signaling in the offspring. We used an embryo transfer model in sheep to investigate the effects of exposure to either maternal obesity or to weight loss in normal and obese mothers preceding and for 1 wk after conception on the expression of hepatic insulin-signaling and gluconeogenic factors and key miRNAs involved in insulin signaling in the offspring. We found that exposure to maternal obesity resulted in increased hepatic miR-29b (P<0.05), miR-103 (P<0.01), and miR-107 (P<0.05) expression, a decrease in IR (P<0.05), phopsho-Akt (P<0.01), and phospho-FoxO1 (P<0.01) abundance, and a paradoxical decrease in 11βHSD1 (P<0.05), PEPCK-C (P<0.01), and PEPCK-M (P<0.05) expression in lambs. These changes were ablated by a period of moderate dietary restriction imposed during the periconceptional period. Maternal dietary restriction alone also resulted in decreased abundance of a separate subset of hepatic insulin-signaling molecules, namely, IRS1 (P<0.05), PDK1 (P<0.01), phospho-PDK1 (P<0.05), and aPKCζ (P<0.05) and in decreased PEPCK-C (P<0.01) and G6Pase (P<0.01) expression in the lamb. Our findings highlight the sensitivity of the epigenome to maternal nutrition around conception and the need for dietary interventions that maximize metabolic benefits and minimize metabolic costs for the next generation.

Regulation of leptin synthesis and secretion before birth: implications for the early programming of adult obesity

A series of epidemiological, clinical and experimental studies have shown that there are associations between the fetal and neonatal nutritional environment and the amount and distribution of adipose tissue in adult life. This review considers the evidence for these relationships and discusses the potential impact of the prenatal nutritional experience on the development of the endocrine and neuroendocrine systems that regulate energy balance, with a particular emphasis on the role of the adipocyte-derived hormone, leptin. In the rodent, leptin derived from the mother may exert an important influence on the development of the appetite regulatory neural network and on the subsequent regulation of leptin synthesis and the risk for obesity in the offspring. In species such as the human and sheep, there is also recent evidence that the synthesis and secretion of adipocyte-derived hormones, such as leptin, are regulated in fetal life. Furthermore, the hypothalamic neuropeptides that regulate energy intake and expenditure in adult life are also present within the fetal brain and may be regulated by the prevailing level of maternal and hence fetal nutrient and hormonal signals, including leptin. This work is important in determining those initiating mechanisms within the 'fat-brain' axis in early life that precede the development of adult obesity.

Early origins of heart disease: low birth weight and determinants of cardiomyocyte endowment

1. World-wide epidemiological and experimental animal studies demonstrate that adversity in fetal life, resulting in intrauterine growth restriction, programmes the offspring for a greater susceptibility to ischaemic heart disease and heart failure in adult life. 2. After cardiogenesis, cardiomyocyte endowment is determined by a range of hormones and signalling pathways that regulate cardiomyocyte proliferation, apoptosis and the timing of multinucleation/terminal differentiation. 3. The small fetus may have reduced cardiomyocyte endowment owing to the impact of a suboptimal intrauterine environment on the signalling pathways that regulate cardiomyocyte proliferation, apoptosis and the timing of terminal differentiation.

Impact of placental restriction on the development of the sympathoadrenal system

We have investigated the impact of chronic restriction of placental function on circulating catecholamine concentrations and responses to the indirectly acting, sympathomimetic amine, tyramine, in the fetal sheep in late gestation. In 10 ewes, endometrial caruncles or placental placentation sites were removed before conception (placental restriction (PR) group). Fetal sheep in the PR group were hypoxemic throughout late gestation and growth-restricted (3.02 +/- 0.35 kg) when compared with control fetal sheep (4.30 +/- 0.29 kg; n = 8) at 140 d of gestation. Fetal plasma concentrations of noradrenaline and adrenaline were higher (p < 0.05) in the PR (7.06 +/- 3.17 pmol/mL and 2.89 +/- 2.01 pmol/mL, respectively) than in the control group (3.55 +/- 0.54 pmol/mL and 1.30 +/- 0.48 pmol/mL, respectively) throughout late gestation. Plasma noradrenaline, but not adrenaline concentrations, increased significantly between 110 and 140 d of gestation in both the PR and control group, and there was a significant inverse relationship between plasma noradrenaline and arterial PO2 in the PR and control groups (plasma noradrenaline = 12.34 - 0.40 PO2). In the PR group, plasma noradrenaline increased (p < 0.05) after tyramine infusion from 4.51 +/- 1.28 pmol/mL to a peak of 19.40 +/- 3.56 pmol/mL. In the control group, noradrenaline increased from 2.08 +/- 0.30 pmol/mL to a peak of 12.23 +/- 1.67 pmol/mL after tyramine infusion. There was no difference, however, in the maximal proportional changes in plasma noradrenaline concentrations in the PR (319 +/- 55%) and control (449 +/- 100%) groups after tyramine. We conclude that the most likely source of the increased plasma catecholamines in the PR group is enhanced catecholamine synthesis and secretion from developing sympathetic neurons.

Development of circadian sleep-wake rhythms in preterm and full-term infants

We have compared the roles of neurologic maturity and environmental time cues in the development of the entrained circadian sleep-wake rhythm in the preterm and term human infant. The preterm infants (n = 19) spent some time after birth in a hospital nursery with no environmental time cues, whereas the term infants (n = 22) were exposed from birth to a cyclical light and dark environment with one major caregiver. The circadian sleep-wake rhythm in the preterm infants entrained after a similar time of exposure to an environment with daily time cues but at an earlier postconceptional age when compared with the term group. We conclude, therefore, that it is the length of exposure to environmental time cues, rather than neurologic maturity, that determines the entrainment of the circadian rhythm of sleep and wakefulness in the human infant.

Leptin alters the structural and functional characteristics of adipose tissue before birth

This study aimed to determine for the first time whether leptin can act to alter the structural and functional characteristics of adipose tissue before birth. Leptin (0.48 mg/kg/day) or saline was infused intravenously into fetal sheep for 4 days from either 136 or 137 days of gestation (term=147+/-3 days). Circulating leptin concentrations were increased approximately four- to fivefold by leptin infusion. Leptin infusion resulted in a significant increase in the proportion of smaller lipid locules present within fetal perirenal adipose tissue (PAT), and this was associated with a significant increase in the proportion of multilocular tissue and a significant decrease in the proportion and relative mass of unilocular tissue in fetal PAT. The relative abundance of leptin mRNA in fetal PAT was significantly lower in the leptin-infused group, and there was a positive correlation between the relative abundance of leptin mRNA and the proportion of unilocular adipose tissue in fetal PAT. The amount of uncoupling protein 1 tended to be higher (P=0.06) in leptin-infused compared with saline-infused fetuses. This is the first demonstration that leptin can act to regulate the lipid storage characteristics, leptin synthetic capacity, and potential thermogenic functions of fat before birth.

Prenatal undernutrition, glucocorticoids and the programming of adult hypertension

1. A range of epidemiological studies has shown that poor intra-uterine growth is associated with an increased prevalence of cardiovascular disease, non-insulin-dependent diabetes mellitus and the Metabolic syndrome in adult life. 2. Because these associations are independent of adult lifestyle or current size, it has been postulated that a reduced intra- uterine nutrient supply perturbs fetal growth and, concomitantly, alters or programmes the structure and function of developing systems. 3. A reduced fetal nutrient supply may be a consequence of poor placental function or inadequate maternal nutrient intake. 4. It has been proposed that one outcome of either a suboptimal placental or maternal nutrient supply is exposure of the fetus to excess glucocorticoids, which act to restrict fetal growth and to programme permanent changes in the cardiovascular, endocrine and metabolic systems. 5. While a range of studies in the rat has investigated the impact of maternal undernutrition on arterial blood pressure in the offspring, there have been relatively few studies in species, such as the sheep, in which the responses of the cardiovascular and neuroendocrine systems to intra-uterine undernutrition can be measured before birth. 6. The present review summarizes recent evidence that poor placental function or inadequate maternal nutrition each results in an increased exposure of fetal sheep tissues to glucocorticoids and, in specific, changes in the regulation of fetal arterial blood pressure. 7. These studies are important in determining how the timing, type and duration of fetal nutrient restriction are each important in determining the nature of the fetal neuroendocrine and cardiovascular adaptive responses and their pathophysiological sequelae in later life.

Impact of maternal periconceptional overnutrition on fat mass and expression of adipogenic and lipogenic genes in visceral and subcutaneous fat depots in the postnatal lamb

Women entering pregnancy with a high body weight and fat mass have babies who are at increased risk of becoming overweight or obese in later life. We investigated whether maternal overnutrition in the periconceptional period results in an increased fat mass and expression of adipogenic and lipogenic genes in offspring and whether dietary restriction can reverse these changes. Nonpregnant donor ewes (n = 23) were assigned to one of four groups: control-control fed at 100% maintenance energy requirements (MER) for at least 5 months, control-restricted fed 100% MER for 4 months and 70% MER for 1 month, high-high (HH) fed ad libitum (170-190% MER) for 5 months, or high-restricted (HR) fed ad libitum for 4 months and 70% MER for 1 month. Single embryos were transferred to nonobese recipient ewes, and lamb fat depots were weighed at 4 months. Peroxisome proliferator-activated receptor-γ, glyceraldehyde-3-phosphate dehydrogenase, lipoprotein lipase, leptin, and adiponectin mRNA expression was measured in the lamb fat depots. Total fat mass was higher in female lambs in the HH but not HR group than controls. There was a relationship between donor ewe weight and total fat mass and G3PDH mRNA expression in perirenal fat in female lambs. There was no effect of periconceptional nutritional treatment on peroxisome proliferator-activated receptor-γ, glyceraldehyde-3-phosphate dehydrogenase, lipoprotein lipase, leptin, and adiponectin mRNA expression in any fat depot. Thus, exposure to maternal overnutrition in the periconceptional period alone results in an increased body fat mass in the offspring and that a short period of dietary restriction can reverse this effect.

Sex-specific effects of placental restriction on components of the metabolic syndrome in young adult sheep

Prenatal and early postnatal life experiences, reflected by size at birth and postnatal catch-up growth, contribute to the risk of developing the metabolic syndrome in adulthood, but their relative importance is unclear. Therefore, we determined the effects of restricted placental and fetal growth on components of the metabolic syndrome in young adult sheep and the relationships of the latter to size at birth and early postnatal growth. Fasting plasma metabolites, glucose tolerance (by intravenous glucose tolerance test, IVGTT), insulin secretion and sensitivity, and resting blood pressure were measured in 22 control and 20 placentally restricted (PR) 1-yr-old sheep. In male sheep, PR increased the initial rise in glucose during an IVGTT and reduced diastolic blood pressure, and small size at birth independently predicted reduced adult size, glucose tolerance, and fasting plasma insulin and insulin disposition of glucose metabolism but increased insulin disposition of circulating FFAs. Also in males, high fractional growth rates in early postnatal life independently predicted impaired early glucose clearance during an IVGTT. In female animals, PR increased insulin sensitivity of glucose metabolism and reduced fasting plasma FFAs, and thinness at birth predicted increased adult size, fasting blood glucose, and pulse pressure. In conclusion, PR and small size at birth are associated with more components of the metabolic syndrome in adult male than in adult female sheep, with few independent effects of early postnatal growth. These sex differences in the onset and extent of adverse metabolic consequences after prenatal restraint in the sheep are consistent with observations in humans.