Glucagon increases energy expenditure independently of brown adipose tissue activation in humans.

AIMS: To investigate, for a given energy expenditure (EE) rise, the differential effects of glucagon infusion and cold exposure on brown adipose tissue (BAT) activation in humans. METHODS: Indirect calorimetry and supraclavicular thermography was performed in 11 healthy male volunteers before and after: cold exposure; glucagon infusion (at 23 °C); and vehicle infusion (at 23 °C). All volunteers underwent (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET)/CT scanning with cold exposure. Subjects with cold-induced BAT activation on (18)F-FDG PET/CT (n = 8) underwent a randomly allocated second (18)F-FDG PET/CT scan (at 23 °C), either with glucagon infusion (n = 4) or vehicle infusion (n = 4). RESULTS: We observed that EE increased by 14% after cold exposure and by 15% after glucagon infusion (50 ng/kg/min; p < 0.05 vs control for both). Cold exposure produced an increase in neck temperature (+0.44 °C; p < 0.001 vs control), but glucagon infusion did not alter neck temperature. In subjects with a cold-induced increase in the metabolic activity of supraclavicular BAT on (18)F-FDG PET/CT, a significant rise in the metabolic activity of BAT after glucagon infusion was not detected. Cold exposure increased sympathetic activation, as measured by circulating norepinephrine levels, but glucagon infusion did not. CONCLUSIONS: Glucagon increases EE by a similar magnitude compared with cold activation, but independently of BAT thermogenesis. This finding is of importance for the development of safe treatments for obesity through upregulation of EE.

Suboptimal maternal nutrition during early fetal kidney development specifically promotes renal lipid accumulation following juvenile obesity in the offspring.

Reduced maternal food intake between early-to-mid gestation results in tissue-specific adaptations in the offspring following juvenile-onset obesity that are indicative of insulin resistance. The aim of the present study was to establish the extent to which renal ectopic lipid accumulation, as opposed to other markers of renal stress, such as iron deposition and apoptosis, is enhanced in obese offspring born to mothers nutrient restricted (NR) throughout early fetal kidney development. Pregnant sheep were fed either 100% (control) or NR (i.e. fed 50% of their total metabolisable energy requirement from 30-80 days gestation and 100% at all other times). At weaning, offspring were made obese and, at approximately 1 year, kidneys were sampled. Triglyceride content, HIF-1α gene expression and the protein abundance of the outer-membrane transporter voltage-dependent anion-selective channel protein (VDAC)-I on the kidney cortex were increased in obese offspring born to NR mothers compared with those born to controls, which exhibited increased iron accumulation within the tubular epithelial cells and increased gene expression of the death receptor Fas. In conclusion, suboptimal maternal nutrition coincident with early fetal kidney development results in enhanced renal lipid deposition following juvenile obesity and could accelerate the onset of the adverse metabolic, rather than cardiovascular, symptoms accompanying the metabolic syndrome.

Adipose tissue and fetal programming.

Adipose tissue function changes with development. In the newborn, brown adipose tissue (BAT) is essential for ensuring effective adaptation to the extrauterine environment, and its growth during gestation is largely dependent on glucose supply from the mother to the fetus. The amount, location and type of adipose tissue deposited can also determine fetal glucose homeostasis. Adipose tissue first appears at around mid-gestation. Total adipose mass then increases through late gestation, when it comprises a mixture of white and brown adipocytes. BAT possesses a unique uncoupling protein, UCP1, which is responsible for the rapid generation of large amounts of heat at birth. Then, during postnatal life some, but not all, depots are replaced by white fat. This process can be utilised to investigate the physiological conversion of brown to white fat, and how it is re-programmed by nutritional changes in pre- and postnatal environments. A reduction in early BAT deposition may perpetuate through the life cycle, thereby suppressing energy expenditure and ultimately promoting obesity. Normal fat development profiles in the offspring are modified by changes in maternal diet at defined stages of pregnancy, ultimately leading to adverse long-term outcomes. For example, excess macrophage accumulation and the onset of insulin resistance occur in an adipose tissue depot-specific manner in offspring born to mothers fed a suboptimal diet from early to mid-gestation. In conclusion, the growth of the different fetal adipose tissue depots varies according to maternal diet and, if challenged in later life, this can contribute to insulin resistance and impaired glucose homeostasis.

Suboptimal maternal nutrition, during early fetal liver development, promotes lipid accumulation in the liver of obese offspring.

Maternal nutrition during the period of early organ development can modulate the offspring's ability to metabolise excess fat as young adults when exposed to an obesogenic environment. This study examined the hypothesis that exposing offspring to nutrient restriction coincident with early hepatogenesis would result in endocrine and metabolic adaptations that subsequently lead to increased ectopic lipid accumulation within the liver. Pregnant sheep were fed either 50 or 100% of total metabolisable energy requirements from 30 to 80 days gestation and 100% thereafter. At weaning, offspring were made obese, and at ~1 year of age livers were sampled. Lipid infiltration and molecular indices of gluconeogenesis, lipid metabolism and mitochondrial function were measured. Although hepatic triglyceride accumulation was not affected by obesity per se, it was nearly doubled in obese offspring born to nutrient-restricted mothers. This adaptation was accompanied by elevated gene expression for peroxisome proliferator-activated receptor γ (PPARG) and its co-activator PGC1α, which may be indicative of changes in the rate of hepatic fatty acid oxidation. In contrast, maternal diet had no influence on the stimulatory effect of obesity on gene expression for a range of proteins involved in glucose metabolism and energy balance including glucokinase, glucocorticoid receptors and uncoupling protein 2. Similarly, although gene expressions for the insulin and IGF1 receptors were suppressed by obesity they were not influenced by the prenatal nutritional environment. In conclusion, excess hepatic lipid accumulation with juvenile obesity is promoted by suboptimal nutrition coincident with early development of the fetal liver.

Influence of prenatal nutrition and obesity on tissue specific fat mass and obesity-associated (FTO) gene expression.

The recent discovery of an association between body composition, energy intake and the fat mass and obesity-associated (FTO) gene represents a promising new therapeutic target in obesity prevention. In a well, pre-established large animal model, we investigated the regulation of FTO gene expression under conditions either leading to obesity or increased risk of obesity related disorders: i) a sedentary 'Western' lifestyle and ii) prenatal exposure to nutrient restriction. Pregnant sheep were either fed to fully meet their nutritional requirements throughout gestation or 50% of this amount from early-to-mid gestation. Following weaning, offspring were either made obese through exposure to a sedentary obesogenic environment or remained lean. A significant positive relationship between placental FTO gene expression and fetal weight was found at 110 days gestation. In both the newborn and adult offspring, the hypothalamus was the major site of FTO gene expression. Hypothalamic FTO gene expression was upregulated by obesity and was further increased by prenatal nutrient restriction. Importantly, we found a strong negative relationship between the hypothalamic FTO gene expression and food intake in lean animals only that may imply FTO as a novel controller of energy intake. In contrast, FTO gene expression in the heart was downregulated in obese offspring born to nutrient restricted mothers. In addition, FTO gene expression was unaffected by obesity or prenatal diet in insulin-dependent tissues, where it changed with age possibly reflecting adaptations in cellular energetic activity. These findings extend information gained from human epidemiology and provide new insights into the regulation of in vivo energy metabolism to prevent obesity.

The differential effects of the timing of maternal nutrient restriction in the ovine placenta on glucocorticoid sensitivity, uncoupling protein 2, peroxisome proliferator-activated receptor-gamma and cell proliferation.

Nutrient restriction (NR) during critical windows of pregnancy has differential effects on placento-fetal growth and development. Our study, therefore, investigated developmental and metabolic adaptations within the ovine placenta following NR at different critical windows during the first 110 days of gestation (term=147 days). Thus, the effects of NR on cell proliferation, glucocorticoid sensitivity, IGF1 and 2 receptor, peroxisome proliferator-activated receptor gamma (PPARG), and uncoupling protein (UCP)2 gene expression in the placenta were examined. Singleton bearing sheep (n=4-8 per group) were fed either 100% of their total metabolizable energy requirements throughout the study or 50% of this amount between 0-30, 31-65, 66-110, and 0-110 days gestation. A significant reduction in cell proliferation and increased gene expression for the glucocorticoid and IGF2 receptors, PPARG, and UCP2 were detected in placentae sampled from mothers who were nutrient restricted between days 66 and 110 of gestation, only, relative to controls. This window of gestation coincides with the maximum placental growth and the start of exponential growth of the fetus when there are substantially increased metabolic demands on the placenta compared with earlier in gestation. Consequently, increased glucocorticoid sensitivity and suppressed IGF2 action could contribute to a switch in the placenta from proliferation to differentiation, thereby improving its nutrient transfer capacity. Upregulation of PPARG and UCP2 would promote placental fatty acid metabolism thereby limiting glucose utilization. These compensatory placental responses may serve to maintain fetal growth but could result in adverse adaptations such as the early onset of the metabolic syndrome in later life.

Effects of maternal cold exposure and nutrient restriction on the ghrelin receptor, the GH-IGF axis, and metabolic regulation in the postnatal ovine liver.

Maternal cold exposure of pregnant sheep promotes fetal growth, whereas nutrient restriction (NR) can reverse this effect. The present study was designed to establish whether cold exposure induced by winter shearing of the mother at 70 days gestation (term=147 days), with or without NR (induced by a 50% reduction in maternal food intake from 110 days gestation), has specific effects on mRNA abundance of hepatic genes related to growth and liver energy metabolism that could regulate postnatal body and liver growth. Measurements of hepatic gene expression for the GH secretagog receptor-1a (GHSR-1A), peroxisome proliferator-activated receptor (PPAR)alpha, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase activity together with glycogen content were made in the livers of offspring at 1 and 30 days of age. Maternal NR reduced liver mass at day 1, whereas offspring of cold-exposed mothers had larger livers at day 30 irrespective of maternal diet. Cold exposure resulted in the up-regulation of GHSR-1A mRNA abundance and reduced glucose-6-phosphatase activity at 1, but not 30 days of age, whereas IGF-II mRNA was decreased at 1 and 30 days. PPARalpha mRNA abundance was enhanced, while PEPCK was reduced in 30-day old offspring of cold-exposed mothers. NR caused reductions in IGF-I mRNA and, at 1-day postnatal age, down-regulated GHR, while, at 30 days, reduced GHSR-1A gene expression and hepatic glycogen content. In conclusion, we have shown that maternal cold exposure and NR have different effects on the hepatic GH-IGF and metabolic axis that may contribute to changes in liver growth over the first month of life.

Maternal nutrient restriction in early pregnancy programs hepatic mRNA expression of growth-related genes and liver size in adult male sheep.

The liver is a major metabolic and endocrine organ of critical importance in the regulation of growth and metabolism. Its function is determined by a complex interaction of nutritionally regulated counter-regulatory hormones. The extent to which hepatic endocrine sensitivity can be programed in utero and whether the resultant adaptations persist into adulthood is unknown and was therefore the subject of this study. Young adult male sheep born to mothers that were fed either a control diet (i.e.100% of total live weight-maintenance requirements) throughout gestation or 50% of that intake (i.e. nutrient restricted (NR)) from 0 to 95 days gestation and thereafter 100% of requirements (taking into account increasing fetal mass) were entered into the study. All mothers gave birth normally at term, the singleton offspring were weaned at 16 weeks, and then reared at pasture until 3 years of age when their livers were sampled. NR offspring were of similar birth and body weights at 3 years of age when they had disproportionately smaller livers than controls. The abundance of mRNA for GH, prolactin, and IGF-II receptors, plus hepatocyte growth factor and suppressor of cytokine signaling-3 were all lower in livers of NR offspring. In contrast, the abundance of the mitochondrial protein voltage-dependent anion channel and the pro-apoptotic factor Bax were up regulated relative to controls. In conclusion, maternal nutrient restriction in early gestation results in adult offspring with smaller livers. This may be mediated by alterations in both hepatic mitogenic and apoptotic factors.

The future of neonatal therapeutic trials.

Neonatology has undoubtedly benefited from clinical trials. Nevertheless, more treatments based on inadequate experimental evidence are given than those that are supported by a validated evidence base. Clinicians seeking the basis for their current and future clinical practice are faced with challenges in the shadow of recent UK legislation and government recommendations. All patients must be protected from inappropriate research, but the benefits of regulations must be appropriately balanced with those of properly conducted clinical trials. It is ethically difficult both to persist with treatments of unproven benefit and unknown harm and to deny infants potentially valuable therapies. It is important that trials are conducted within the new legislative framework, but their future may rest with innovative solutions and the determination of all involved in the process.

Developmental programming, adiposity, and reproduction in ruminants.

Although sheep have been widely adopted as an animal model for examining the timing of nutritional interventions through pregnancy on the short- and long-term outcomes, only modest programming effects have been seen. This is due in part to the mismatch in numbers of twins and singletons between study groups as well as unequal numbers of males and females. Placental growth differs between singleton and twin pregnancies which can result in different body composition in the offspring. One tissue that is especially affected is adipose tissue which in the sheep fetus is primarily located around the kidneys and heart plus the sternal/neck region. Its main role is the rapid generation of heat due to activation of the brown adipose tissue-specific uncoupling protein 1 at birth. The fetal adipose tissue response to suboptimal maternal food intake at defined stages of development differs between the perirenal abdominal and pericardial depots, with the latter being more sensitive. Fetal adipose tissue growth may be mediated in part by changes in leptin status of the mother which are paralleled in the fetus. Then, over the first month of life plasma leptin is higher in females than males despite similar adiposity, when fat is the fastest growing tissue with the sternal/neck depot retaining uncoupling protein 1, whereas other depots do not. Future studies should take into account the respective effects of fetal number and sex to provide more detailed insights into the mechanisms by which adipose and related tissues can be programmed in utero.

Maternal Body Weight and Gestational Diabetes Differentially Influence Placental and Pregnancy Outcomes.

CONTEXT: Maternal obesity and gestational diabetes mellitus (GDM) can both contribute to adverse neonatal outcomes. The extent to which this may be mediated by differences in placental metabolism and nutrient transport remains to be determined. OBJECTIVE: Our objective was to examine whether raised maternal body mass index (BMI) and/or GDM contributed to a resetting of the expression of genes within the placenta that are involved in energy sensing, oxidative stress, inflammation, and metabolic pathways. METHODS: Pregnant women from Spain were recruited as part of the "Study of Maternal Nutrition and Genetics on the Foetal Adiposity Programming" survey at the first antenatal visit (12-20 weeks of gestation) and stratified according to prepregnancy BMI and the incidence of GDM. At delivery, placenta and cord blood were sampled and newborn anthropometry measured. RESULTS: Obese women with GDM had higher estimated fetal weight at 34 gestational weeks and a greater risk of preterm deliveries and cesarean section. Birth weight was unaffected by BMI or GDM; however, women who were obese with normal glucose tolerance had increased placental weight and higher plasma glucose and leptin at term. Gene expression for markers of placental energy sensing and oxidative stress, were primarily affected by maternal obesity as mTOR was reduced, whereas SIRT-1 and UCP2 were both upregulated. In placenta from obese women with GDM, gene expression for AMPK was also reduced, whereas the downstream regulator of mTOR, p70S6KB1 was raised. CONCLUSIONS: Placental gene expression is sensitive to both maternal obesity and GDM which both impact on energy sensing and could modulate the effect of either raised maternal BMI or GDM on birth weight.

Maternal nutritional programming of fetal adipose tissue development: differential effects on messenger ribonucleic acid abundance for uncoupling proteins and peroxisome proliferator-activated and prolactin receptors.

Maternal nutrient restriction at specific stages of gestation has differential effects on fetal development such that the offspring are programmed to be at increased risk of a range of adult diseases, including obesity. We investigated the effect of maternal nutritional manipulation through gestation on fetal adipose tissue deposition in conjunction with mRNA abundance for uncoupling protein (UCP)1 and 2, peroxisome proliferator-activated receptors (PPAR)alpha and gamma, together with long and short forms of the prolactin receptor (PRLR). Singleton-bearing ewes were either nutrient restricted (3.2-3.8 MJ day(-1) metabolizable energy) or fed to appetite (8.7-9.9 MJ day(-1)) over the period of maximal placental growth, i.e. between 28 and 80 d gestation. After 80 d gestation, ewes were either fed to calculated requirements, (6.7-7.5 MJ day(-1)), or to appetite (8.0-10.9 MJ day(-1)). At term, offspring of nutrient-restricted ewes possessed more adipose tissue, an adaptation that was greatest in those born to mothers that fed to requirements in late gestation. This was accompanied by an increased mRNA abundance for UCP2 and PPARalpha, an adaptation not seen in mothers re-fed to appetite. Maternal nutrition had no effect on mRNA abundance for UCP1, PPARgamma, or PRLR. Irrespective of maternal nutrition, mRNA abundance for UCP1 was positively correlated with PPARgamma and the long and short forms of PRLR, indicating that these factors may act together to ensure that UCP1 abundance is maximized in the newborn. In conclusion, we have shown, for the first time, differential effects of maternal nutrition on key regulatory components of fetal fat metabolism.

Prolactin, the prolactin receptor and uncoupling protein abundance and function in adipose tissue during development in young sheep.

A primary role of the prolactin receptor (PRLR) during fetal and postnatal development has been suggested to be the regulation of uncoupling protein (UCP) expression. We, therefore, determined whether: (1) the rate of loss of UCP1 from brown adipose tissue after birth was paralleled by the disappearance of PRLR; and (2) administration of either pituitary extract prolactin (PRL) containing a mixture of posttranslationally modified forms or its pseudophosphorylated form (S179D PRL) improved thermoregulation and UCP1 function over the first week of neonatal life. PRLR abundance was greatest in adipose tissue 6 h after birth before declining up to 30 days of age, a trend mirrored by first a gain and then a loss of UCP1. In contrast, in the liver--which does not possess UCPs--a postnatal decline in PRLR was not observed. Administration of PRL resulted in an acute increase in colonic temperature in conjunction with increased plasma concentrations of non-esterified fatty acids and, as a result, the normal postnatal decline in body temperature was delayed. S179D PRL at lower concentrations resulted in a transient rise in colonic temperature at both 2 and 6 days of age. In conclusion, we have demonstrated a close relationship between the ontogeny of UCP1 and the PRLR. Exogenous PRL administration elicits a thermogenic effect suggesting an important role for the PRLR in regulating UCP1 function.

Experimental evidence for long-term programming effects of early diet.

Nutritional manipulation targeted at specific periods of embryo or placental development can result in substantial changes in fetal organ development despite no effects on fetal weight. In particular, kidney and fat mass are greater in nutrient restricted offspring in conjunction with higher mRNA abundance for leptin, insulin-like growth factors I/II and glucocorticoid receptors. As young adults, nutrient restricted offspring exhibit a blunting of the cardiovascular baroreflex. They also demonstrate increased plasma leptin following sympathetic stimulation, not observed in controls, indicating resetting of adipocyte sensitivity to stress. In conclusion, global nutrient restriction confined to periods of early development programmes adult physiology in a manner that may predispose to later disease given the appropriate environmental stimuli.

Maternal undernutrition during early to midgestation programs tissue-specific alterations in the expression of the glucocorticoid receptor, 11beta-hydroxysteroid dehydrogenase isoforms, and type 1 angiotensin ii receptor in neonatal sheep.

We have investigated the effects of maternal nutrient restriction in the sheep during the period of rapid placental growth (i.e. 28-77 days gestation; term = 147 days) on feto-placental growth and expression of the glucocorticoid receptor (GR), types 1 and 2 11beta-hydroxysteroid dehydrogenase (11betaHSD1, 11betaHSD2), and types 1 and 2 angiotensin II receptor (AT1, AT2) in fetal and neonatal offspring. Ewes (n = 63) of similar age, body weight, and body composition were randomly allocated to a nutrient-restricted (NR) group in which they consumed 3.2 MJ/day metabolizable energy (ME; equivalent to 50% of predicted requirements) or to a control group in which they consumed 6.7 MJ/day ME (equivalent to 110% of predicted requirements). After 77 days gestation, ewes from both dietary groups consumed close to 100% of ME requirements up to term. Newborn offspring of NR ewes were of similar body weight, but had increased crown-rump length, greater placental weight, and increased placental/body weight ratio (P < 0.01) compared with controls. Their kidneys were heavier (P < 0.05), but shorter in length, with increased ratios of transverse width to length (P < 0.001). GR messenger RNA (mRNA) expression in neonatal offspring from NR ewes was increased in adrenal, kidney, liver, lung, and perirenal adipose tissue (P < 0.01). Conversely, 11betaHSD1 mRNA expression was unaffected, except in perirenal adipose tissue, where it was higher in lambs born to NR ewes (P < 0.01). 11betaHSD2 mRNA expression was decreased in adrenals and kidney (P < 0.001). Maternal NR also resulted in significantly increased AT1 expression in those tissues in which expression of GR was increased and/or 11betaHSD2 was decreased, i.e. adrenals, kidney, liver, and lung. AT2 expression was unaffected by maternal NR. Although 11betaHSD2 mRNA was undetectable in term placenta, it was abundant in midgestation placenta and was lower after maternal NR (P < 0.001). There was close agreement between levels of 11betaHSD enzyme (i.e. 11beta-dehydrogenase and 11-oxoreductase) activities and abundance of 11betaHSD1 mRNA and 11betaHSD2 mRNA expression. The persistence of tissue-specific increases in the expression of GR, 11betaHSD1 and AT1 and decreases in the expression of 11betaHSD2 in adrenals and kidney in newborn offspring in response to a defined period of maternal nutrient restriction during early to midgestation suggests that gene expression has been programmed by nutrient availability to the fetus before birth. These data suggest key potential mechanisms by which maternal nutrition prenatally programs physiological pathways, such as the renin-angiotensin system, in the offspring that may lead to raised blood pressure and other cardiovascular disease risk factors in later life.

Maternal endocrine adaptation throughout pregnancy to nutritional manipulation: consequences for maternal plasma leptin and cortisol and the programming of fetal adipose tissue development.

Maternal nutrient restriction at specific stages of gestation has differential effects on fetal development such that the offspring are programmed to be at increased risk of adult disease. We investigated the effect of gestational age and maternal nutrition on the maternal plasma concentration of leptin and cortisol together with effects on fetal adipose tissue deposition plus leptin, IGF-I, IGF-II ligand, and receptor mRNA abundance near to term. Singleton bearing ewes were either nutrient restricted (NR; consuming 3.2-3.8 MJ/d of metabolizable energy) or fed to appetite (consuming 8.7-9.9 MJ/d) over the period of maximal placental growth, i.e. between 28 and 80 d gestation. After 80 d gestation, ewes were either fed to calculated requirements, consuming 6.7-7.5 MJ/d, or were fed to appetite and consumed 8.0-10.9 MJ/d. Pregnancy resulted in a rise in plasma leptin concentration by 28 d gestation, which continued up to 80 d gestation when fed to appetite but not with nutrient restriction. Plasma cortisol was also lower in NR ewes up to 80 d gestation, a difference no longer apparent when food intake was increased. At term, irrespective of maternal nutrition in late gestation, fetuses sampled from ewes NR in early gestation possessed more adipose tissue, whereas when ewes were fed to appetite throughout gestation, fetal adipose tissue deposition and leptin mRNA abundance were both reduced. These changes may result in the offspring of NR mothers being at increased risk of obesity in later life.

Determinants of fetal leptin synthesis, fat mass, and circulating leptin concentrations in well-nourished ewes in late pregnancy.

We have investigated the factors regulating leptin synthesis, fat deposition, and circulating leptin concentrations in fetuses of well nourished ewes in late pregnancy. Vascular catheters were surgically inserted in 17 pregnant ewes and their fetuses at 103-120 d gestation (term = 147 +/- 3 d). Ewes were fed a diet providing either 100% (control; n = 9) or approximately 155% (well fed; n = 8) of the maintenance energy requirements and fetal perirenal and interscapular fat depots were collected at 139-141 d gestation. There was a significant relationship between the relative mass of fetal unilocular fat and fetal glucose (relative mass of unilocular fat, 1.14; fetal glucose, +0.16; r = 0.50; P < 0.04; n = 17), but not insulin, concentrations in the control and well-fed groups. In contrast to the controls, there was a positive relationship between the relative abundance of leptin mRNA and fetal insulin, but not glucose, concentrations in fetal perirenal adipose tissue in the well-fed group. A moderate increase in maternal nutrition also resulted in a strong reciprocal relationship between uncoupling protein 1 and leptin expression in fetal perirenal adipose tissue in late gestation (well-fed group: uncoupling protein 1 mRNA:18S rRNA, -0.51; leptin mRNA:beta-actin mRNA, +1.53; r = 0.80; P < 0.02; n = 8). These studies provide evidence that fetal glucose and insulin differentially regulate fetal fat deposition and leptin mRNA expression within the fetal perirenal fat depot in the well nourished animal during late gestation.

Endocrine and nutritional regulation of fetal adipose tissue development.

In the fetus, adipose tIssue comprises both brown and white adipocytes for which brown fat is characterised as possessing the unique uncoupling protein (UCP)1. The dual characteristics of fetal fat reflect its critical role at birth in providing lipid that is mobilised rapidly following activation of UCP1 upon cold exposure to the extra-uterine environment. A key stage in the maturation of fetal fat is the gradual rise in the abundance of UCP1. For species with a mature hypothalamic-pituitary axis at birth there is a gradual increase in the amount and activity of UCP1 during late gestation, in conjunction with an increase in the plasma concentrations of catecholamines, thyroid hormones, cortisol, leptin and prolactin. These may act individually, or in combination, to promote UCP1 expression and, following the post-partum surge in each hormone, UCP1 abundance attains maximal amounts. Adipose tIssue grows in the fetus at a much lower rate than in the postnatal period. However, its growth is under marked nutritional constraints and, in contrast to many other fetal organs that are unaffected by nutritional manipulation, fat mass can be significantly altered by changes in maternal and, therefore, fetal nutrition. Fat deposition in the fetus is enhanced during late gestation following a previous period of nutrient restriction up to mid gestation. This is accompanied by increased mRNA abundance for the receptors of IGF-I and IGF-II. In contrast, increasing maternal nutrition in late gestation results in less adipose tIssue deposition but enhanced UCP1 abundance. The pronounced nutritional sensitivity of fetal adipose tIssue to both increased and decreased maternal nutrition may explain why the consequences of an adverse nutritional environment persist into later life.

The effect of maternal prolactin infusion during pregnancy on fetal adipose tissue development.

The present study determines whether maternal administration of prolactin (PRL) to dams promotes the abundance of the brown adipose tissue-specific uncoupling protein-1 (UCP1) in fetal and neonatal rat pups. Recombinant PRL (24 micro g/kg per day), or an equivalent volume of saline, were infused into dams (n=19 per group) throughout pregnancy from 12 h after mating. Interscapular brown adipose tissue was sampled either from fetuses at 19.5 days of gestation (term=21.5 days) or from neonatal rat pups at approximately 18 h after birth. The abundance of UCP1 was determined by immunoblotting on adipose tissue samples from individual pups and pooled from groups of pups. This analysis was complemented by immunocytochemistry on representative adipose tissue samples. Maternal PRL infusion resulted in a greater abundance of UCP1 in fetal rats at 19.5 days of gestation (control: 97.2+/-8.4% reference; PRL: 525.6+/-74.4% reference; P<0.001) and in neonates 18 h after birth. In contrast, the abundance of the outer mitochondrial membrane protein voltage-dependent anion channel was unaffected by PRL. Neonatal adipose tissue sampled from pups born to PRL-infused dams possessed fewer lipid droplets, but more UCP1, as determined by immunocytochemistry. Fetal, but not maternal, plasma leptin concentrations were also increased by maternal PRL administration. In conclusion, as rats are altricial, and the potential thermogenic activity of brown adipose tissue develops over the first few days of postnatal life, these changes prior to, and at the time of, birth implicate PRL in fetal and neonatal adipose tissue maturation.