Perirenal Brown Adipose Tissue Research Articles

Global gene expression profiling of perirenal brown adipose tissue whitening in goat kids reveals novel genes linked to adipose remodeling

BackgroundBrown adipose tissue (BAT) is known to be capable of non-shivering thermogenesis under cold stimulation, which is related to the mortality of animals. In the previous study, we observed that goat BAT is mainly located around the kidney at birth, and changes to white adipose tissue (WAT) in the perirenal adipose tissue of goats within one month after birth. However, the regulatory factors underlying this change is remain unclear. In this study, we systematically studied the perirenal adipose tissue of goat kids in histological, cytological, and accompanying molecular level changes from 0 to 28 d after birth.ResultsOur study found a higher mortality rate in winter-born goat kids, with goat birthing data statistics. Then we used thermal imaging revealing high temperature in goat hips at postnatal 0 d and gradually decrease during 28 d. This is consistent with the region of perirenal BAT deposition and highlights its critical role in energy expenditure and body temperature regulation in goat kids. Additionally, we found a series of changes of BAT during the first 28 d after birth, such as whitening, larger lipid droplets, decreased mitochondrial numbers, and down-regulation of key thermogenesis-related genes (UCP1, DIO2, UCP2, CIDEA, PPARGC1a, C/EBPb, and C/EBPa). Then, we used RNA-seq found specific marker genes for goat adipose tissue and identified 12 new marker genes for BAT and 10 new marker genes for WAT of goats. Furthermore, 12 candidate genes were found to potentially regulate goat BAT thermogenesis. The mechanism of the change of this biological phenomenon does not involve a large-scale death of brown adipocytes and subsequent proliferation of white adipocytes. While apoptosis may play a limited role, it is largely not critical in this transition process.ConclusionsWe concluded that perirenal BAT plays a crucial role in thermoregulation in newborn goat kids, with notable species differences in the expression of adipose tissue marker genes, and we highlighted some potential marker genes for goat BAT and WAT. Additionally, the change from BAT to WAT does not involve a large-scale death of brown adipocytes and subsequent proliferation of white adipocytes.

PSUN84 Chronic Adrenergic Stimulation in Humans Increases Plasma Bile Acids and Expression of Bile Acid Synthesis Enzymes in White Adipose Tissue

Abstract Bile acids (BAs) are classically known as facilitators of fat digestion. Moreover, they are now known to be ligands for receptors involved in glucose and lipoprotein metabolism. BA synthesis was originally thought to be exclusive to hepatic tissue, but emerging evidence in rodents has demonstrated the expression of BA transporters and de novo synthetic enzymes in murine adipose tissue. We previously showed that chronic activation of brown adipose tissue (BAT) and white adipose tissue (WAT) in adult women via the β3-adrenergic receptor (ADRB3) agonist mirabegron increases total plasma BA levels. The largest increases were seen with primary unconjugated BAs. Overall, these data suggest that chronic adrenergic stimulation may increase the synthesis and activity of BA synthesis enzymes in human adipose tissue, which contributes to the increase in total plasma BAs. To confirm this hypothesis, we measured expression levels of BAT and BA synthesis enzymes in liver and adipose tissues collected from healthy patients and those with pheochromocytoma (pheo) who experienced chronic adrenergic activation. As expected, expression of thermogenic UCP1 and ADRB3 was higher in pheo peri-renal BAT than in liver tissue (76,000x, P<0.001; and 6,000x, P=0.02, respectively) or either healthy subcutaneous WAT or pheo subcutaneous WAT (≥1500x, P<0.001 for UCP1). Conversely, expression of the rate-determining enzyme in BA synthesis CYP7A1 was similar in liver and both WAT depots (P>0.05), and liver had slightly higher expression than BAT (3x, P=0.03). Otherwise, most of the principal BA synthesis genes’ expression levels demonstrated the following stepwise pattern: liver tissue > pheo WAT = subcutaneous WAT > BAT (CYP8B1, CYP27A1, AKR1D1, and BAAT). These results suggest that BA production in humans is not limited to the liver. Rather, human WAT in particular may contribute to the BA pool and could serve as a target for producing BA-mediated improvements in glucose and lipoprotein metabolism. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

Brown adipose tissue involution associated with progressive restriction in progenitor competence.

Human brown adipose tissue (BAT) undergoes progressive involution. This involution process is not recapitulated in rodents, and the underlying mechanisms are poorly understood. Here we show that the interscapular BAT (iBAT) of rabbits whitens rapidly during early adulthood. The transcriptomic remodeling and identity switch of mature adipocytes are accompanied by loss of brown adipogenic competence of progenitors. Single-cell RNA sequencing reveals that rabbit and human iBAT progenitors highly express the FSTL1 gene. When iBAT involutes in rabbits, adipocyte progenitors reduce FSTL1 expression and are refractory to brown adipogenic recruitment. Conversely, FSTL1 is constitutively expressed in mouse iBAT to sustain WNT signaling and prevent involution. Progenitor incompetence and iBAT paucity can be induced in mice by genetic deletion of the Fstl1 gene or ablation of Fstl1+ progenitors. Our results highlight the hierarchy and dynamics of the BAT progenitor compartment and implicate the functional incompetence of FSTL1-expressing progenitors in BAT involution.

Effects of maternal undernutrition during late pregnancy on the regulatory factors involved in growth and development in ovine fetal perirenal brown adipose tissue.

ObjectiveThe experiment was conducted to evaluate the effects of maternal undernutrition during late pregnancy on the expressions of genes involved in growth and development in ovine fetal perirenal brown adipose tissue (BAT).MethodsEighteen ewes with singleton fetuses were allocated to three groups at day 90 of pregnancy: restricted group 1 (RG1, 0.33 MJ metabolisable energy [ME]/kg body weight [BW]0.75/d, n = 6), restricted group 2 (RG2, 0.18 MJ ME/kg BW0.75/d, n = 6), and a control group (CG, ad libitum, 0.67 MJ ME/kg BW0.75/d, n = 6). The fetuses were removed at day 140 of pregnancy. All data were analyzed by using the analysis of variance procedure.ResultsThe perirenal fat weight (p = 0.0077) and perirenal fat growth rate (p = 0.0074) were reduced in RG2 compared to CG. In fetal perirenal BAT, the protein level of uncoupling protein 1 (UCP1) (p = 0.0001) was lower in RG1 and RG2 compared with CG and UCP1 mRNA expression (p = 0.0265) was decreased in RG2. The protein level of myogenic factor 5 (Myf5) was also decreased in RG2 (p = 0.0001). In addition, mRNA expressions of CyclinA (p = 0.0109), CyclinB (p = 0.0019), CyclinD (p = 0.0015), cyclin-dependent kinase 1 (CDK1) (p = 0.0001), E2F transcription factor 1 (E2F1) (p = 0.0323), E2F4 (p = 0.0101), and E2F5 (p = 0.0018) were lower in RG1 and RG2. There were decreased protein expression of peroxisome proliferator-activated receptor-γ (PPARγ) (p = 0.0043) and mRNA expression of CCAAT/enhancer-binding protein-α (C/EBPα) (p = 0.0307) in RG2 and decreased PPARγ mRNA expression (p = 0.0008) and C/EBPα protein expression (p = 0.0015) in both RG2 and RG1. Furthermore, mRNA expression of bone morphogenetic protein 4 (BMP4) (p = 0.0083) and BMP7 (p = 0.0330) decreased in RG2 and peroxisome proliferator-activated receptor co-activator-1α (PGC-1α) reduced in RG2 and RG1.ConclusionOur observations support that repression of regulatory factors promoting differentiation and development results in the inhibition of BAT maturation in fetal perirenal fat during late pregnancy with maternal undernutrition.

Melatonin Regulates Differentiation of Sheep Brown Adipocyte Precursor Cells Via AMP-Activated Protein Kinase.

In sheep industry, hypothermia caused by insufficient brown adipose tissue (BAT) deposits is one of the major causes of lamb deaths. Enhancing the formation and function of BAT in neonatal lamb increases thermogenesis and hence reduces economic losses. The aim of the present study was to explore the effect and mechanism of melatonin on sheep brown adipocyte formation and function. Sheep brown adipocyte precursor cells (SBACs) isolated from perirenal BAT were treated with melatonin (1 and 10 nM). The SBACs subjected to melatonin exhibited a decreased proliferation ability, accompanied by down-regulated proliferating cell nuclear antigen, cyclin D1, and CDK4 protein contents in a melatonin dose-dependent manner. Melatonin promoted brown adipocyte formation and induced the expression of brown adipogenic markers, including uncoupling protein 1 and PR domain-containing 16 during differentiation of SBAC. Moreover, the AMP-activated protein kinase α1 (AMPKα1) activity was positively correlated with brown adipocyte formation potential. Importantly, melatonin effectively activated AMPKα1. Furthermore, promotional effects of melatonin were abolished by AMPKα1 knockout, suggesting the involvement of AMPKα1 in this process. Collectively, these results suggested that melatonin enhanced brown adipocyte formation in SBACs in vitro through activation of AMPKα1.

Water-fat magnetic resonance imaging of adipose tissue compartments in the normal third trimester fetus.

Assessment of fetal adipose tissue gives information about the future metabolic health of an individual, with evidence that the development of this tissue has regional heterogeneity. To assess differences in the proton density fat fraction (PDFF) between fetal adipose tissue compartments in the third trimester using water-fat magnetic resonance imaging (MRI). Water-fat MRI was performed in a 1.5-T scanner. Fetal adipose tissue was segmented into cheeks, thorax, abdomen, upper arms, forearms, thighs and lower legs. PDFF and R2* values were measured in each compartment. Twenty-eight women with singleton pregnancies were imaged between 28 and 38weeks of gestation. At 30weeks' gestation (n=22), the PDFF was statistically different between the compartments (P<0.0001), with the highest PDFF in cheeks, followed by upper arms, thorax, thighs, forearms, lower legs and abdomen. There were no statistical differences in the rate of PDFF change with gestational age between the white adipose tissue compartments (P=0.97). Perirenal brown adipose tissue had a different PDFF and R2* compared to white adipose tissue, while the rate of R2* change did not significantly change with gestational age between white adipose tissue compartments (P=0.96). Fetal adipose tissue accumulates lipids at a similar rate in all white adipose tissue compartments. PDFF variances between the compartments suggest that accumulation begins at different gestational ages, starting with cheeks, followed by extremities, trunk and abdomen. Additionally, MRI was able to detect differences in the PDFF between fetal brown adipose tissue and white adipose tissue.

Relative expression and regulation by short-term fasting of lysophosphatidic acid receptors and autotaxin in white and brown adipose tissue depots.

Lysophosphatidic acid (lysoPtdOH) levels have previously been reported to decrease in rodents with short-term fasting. We investigated whether a 16 h fast would change expression of autotaxin, the predominant phospholipase D responsible for adipose-derived lysoPtdOH synthesis, or any of the lysophosphatidic acid receptors (1-6) in four white adipose tissue (WAT) depots and interscapular brown adipose tissue (BAT) in male C57Bl/6J mice fed ad libitum, or fasted for 16 h. Aside from small inductions of Lpar1 in epididymal WAT and Lpar2 in epididymal and inguinal WAT, no significant changes were observed in expression of the Lpar family members, or autotaxin in perirenal, retroperitoneal, epididymal, or inguinal WAT or BAT with fasting. Comparison of the relative expression of Lpar1-6 in various depots showed that Lpar6 was the predominant Lpar in both WAT and BAT, and suggests that further work on the adipose-specific role of Lpar6 is warranted.

Supplementary prenatal copper increases plasma triiodothyronine and brown adipose tissue uncoupling protein-1 gene expression but depresses thermogenesis in newborn lambs.

ObjectiveWe tested the hypothesis that increasing dietary copper (Cu) to gravid ewes would enhance brown adipose tissue (BAT) thermogenesis in their offspring.MethodsTwin-bearing ewes were assigned on d 70 of gestation to diets containing 3, 10, or 20 ppm dietary Cu (n = 8 per group). Twin lambs were assigned at birth to a cold (6°C) or warm (28°C) environmental chamber for 48 h. Blood was collected from ewes and from lambs and perirenal BAT was collected after 48 h in the environmental chambers.ResultsPrenatal Cu exposure increased ewe plasma triiodothyronine (T3) and thyroxine concentration (T4) (p<0.01) but prenatal Cu exposure had no effect on lamb plasma concentrations of T3, T4, glucose, or nonesterified fatty acid concentration (p≥0.08). The high level of prenatal Cu exposure depressed 48-h rectal temperature (p = 0.03). Cold exposure decreased BAT norepinephrine (NE) and increased BAT dopamine (p≤0.01), but prenatal Cu exposure had no effect on BAT cytochrome C oxidase activity or BAT NE or dopamine (p≥0.07). However, BAT of lambs from high-Cu ewes maintained higher uncoupling protein-1 (UCP1) gene expression than BAT of lambs from low- and medium-Cu ewes following warm or cold exposure in environmental chambers (p = 0.02). Cold exposure caused near depletion of BAT lipid by 48 h (p<0.001), increased BAT cytochrome c oxidase activity (p< 0.01), and depressed plasma fatty acid concentrations (p<0.001).ConclusionAlthough prenatal Cu exposure increased BAT UCP1 expression during warm and cold exposure, prenatal cold Cu exposure depressed 48-h rectal temperature. Cold exposure decreased BAT lipid content by over 80% and decreased lamb plasma fatty acid concentration by over 40%, indicating that fuel reserves for thermogenesis were nearly depleted by 48 h of cold exposure.

Activation of β3-adrenoceptors increases in vivo free fatty acid uptake and utilization in brown but not white fat depots in high-fat-fed rats.

Activation of brown adipose tissue (BAT) and browning of white adipose tissue (WAT) present potential new therapies for obesity and type 2 diabetes. Here, we examined the effects of β3-adrenergic stimulation on tissue-specific uptake and storage of free fatty acids (FFA) and its implications for whole body FFA metabolism in diet-induced obese rats using a multi-radiotracer technique. Male Wistar rats were high fat-fed for 12 wk and administered β3-agonist CL316,243 (CL, 1 mg·kg-1·day-1) or saline via osmotic minipumps during the last 3 wk. The rats were then fasted and acutely infused with a tracer mixture ([14C]palmitate and the partially metabolized R-[3H]bromopalmitate) under anesthesia. CL infusion decreased body weight gain and fasting plasma glucose levels. While core body temperature was unaffected, infrared thermography showed an increase in tail heat dissipation following CL infusion. Interestingly, CL markedly increased both FFA storage and utilization in interscapular and perirenal BAT, whereas the flux of FFA to skeletal muscle was decreased. In this rat model of obesity, only sporadic populations of beige adipocytes were detected in the epididymal WAT depot of CL-infused rats, and there was no change in FFA uptake or utilization in WAT following CL infusion. In summary, β3-agonism robustly increased FFA flux to BAT coupled with enhanced utilization. Increased BAT activation most likely drove the increased tail heat dissipation to maintain thermostasis. Our results emphasize the quantitative role of brown fat as the functional target of β3-agonism in obesity.

Characterization of brown adipose tissue by water-fat separated magnetic resonance imaging.

To evaluate the possibility of quantifying brown adipose tissue (BAT) volume and fat concentration with a high resolution, long echo time, dual-echo Dixon imaging protocol. A 0.42 mm isotropic resolution water-fat separated MRI protocol was implemented by using the second opposite-phase echo and third in-phase echo. Fat images were calibrated with regard to the intensity of nearby white adipose tissue (WAT) to form relative fat content (RFC) images. To evaluate the ability to measure BAT volume and RFC contrast dynamics, rats were divided into two groups that were kept at 4° or 22°C for 5 days. The rats were then scanned in a 70 cm bore 3.0 Tesla MRI scanner and a human dual energy CT. Interscapular, paraaortal, and perirenal BAT (i/pa/pr-BAT) depots as well as WAT and muscle were segmented in the MRI and CT images. Biopsies were collected from the identified BAT depots. The biopsies confirmed that the three depots identified with the RFC images consisted of BAT. There was a significant linear correlation (P < 0.001) between the measured RFC and the Hounsfield units from DECT. Significantly lower iBAT RFC (P = 0.0064) and significantly larger iBAT and prBAT volumes (P = 0.0017) were observed in the cold stimulated rats. The calibrated Dixon images with RFC scaling can depict BAT and be used to measure differences in volume, and fat concentration, induced by cold stimulation. The high correlation between RFC and HU suggests that the fat concentration is the main RFC image contrast mechanism.

Prevalence and pattern of brown adipose tissue distribution of 18F-FDG in patients undergoing PET-CT in a subtropical climatic zone

The uptake of F-FDG in brown adipose tissue (BAT) may have important implications in understanding the pathophysiology of BAT and obesity. Because of the thermal implications of BAT uptake of F-FDG, this study aimed to contribute to existing knowledge by assessing patients scanned in a subtropical environment with particular reference to ethnicity. A retrospective study was carried out to determine the prevalence and pattern of BAT uptake in patients undergoing F-FDG PET-CT imaging in a PET facility located in a subtropical climatic zone. Standardized uptake values were obtained for regions of BAT uptake of F-FDG, and the distribution pattern was assessed according to anatomical region, sex, age, BMI and ethnicity. Following a reveiw of a total of 386 scans, 38 patients showed BAT uptake of F-FDG (9.85%), with the mass and activity of BAT being greater in women than in men (11.95 and 6.88%, respectively). BAT uptake of F-FDG in the neck/supraclavicular, axillary and mediastinal regions was greater in adults whose BMI was less than 18 kg/m. However, perirenal BAT activity was shown to be greater in obese individuals. The frequency of BAT uptake of F-FDG was 55% in winter as against 45% during summer (P<0.012). There was no statistical difference in BAT uptake between black and white patients. This study shows the pattern and prevalence of BAT in patients in a subtropical environment. Although the average seasonal temperatures are higher in a subtropical climate, a seasonal variation in BAT expression was observed, although there were no differences with respect to patient ethnicity.

Arginine nutrition and fetal brown adipose tissue development in nutrient-restricted sheep

Intrauterine growth restriction is a significant problem worldwide, resulting in increased rates of neonatal morbidity and mortality, as well as increased risks for metabolic and cardiovascular disease. The present study investigated the role of maternal undernutrition and L-arginine administration on fetal growth and development. Embryo transfer was utilized to generate genetically similar singleton pregnancies. On Day 35 of gestation, ewes were assigned to receive either 50 or 100% of their nutritional requirements. Ewes received i.v. injections of either saline or L-arginine three times daily from Day 100 to Day 125. Fetal growth was assessed at necropsy on Day 125. Maternal dietary manipulation altered circulating concentrations of leptin, progesterone, and amino acids in maternal plasma. Fetal weight was reduced in nutrient-restricted ewes on Day 125 compared with 100% fed ewes. Compared with saline-treated underfed ewes, maternal L-arginine administration did not affect fetal weight but increased weight of the fetal pancreas by 32% and fetal peri-renal brown adipose tissue mass by 48%. These results indicate that L-arginine administration enhanced fetal pancreatic and brown adipose tissue development. The postnatal effects of increased pancreatic and brown adipose tissue growth warrant further study.

Dietary supplementation of high levels of saturated and monounsaturated fatty acids to ewes during late gestation reduces thermogenesis in newborn lambs by depressing fatty acid oxidation in perirenal brown adipose tissue.

We hypothesized that dietary supplementation of (n-6) plus (n-3) PUFA during late gestation would increase uncoupling protein-1 (UCP1) gene expression and thereby increase thermogenic capacity of newborn lambs. Thirty twin-bearing ewes were fed rumen-protected fat (2, 4, or 8%) high in saturated and monounsaturated fatty acids (SMFA) or high in (n-6) and (n-3) PUFA. Lambs (n = 7-10 per ewe treatment group) were placed in a cold chamber at 0 degrees C for 2 h. Rectal temperature was higher at birth and increased more with cold exposure in lambs from ewes fed 2 or 4% supplemental fat than in lambs from ewes fed 8% SMFA (fat type x fat level interaction, P = 0.001). Cytochrome c oxidase activity was greatest in brown adipose tissue (BAT) lambs from ewes fed 2% SMFA or 4% PUFA (fat type x fat level interaction, P = 0.01). BAT of lambs from ewes fed 2 or 4% PUFA had nearly 7-fold more (P = 0.05) UCP1 mRNA than BAT of lambs from ewes fed 8% PUFA. UCP1 expression decreased by over 80% by 24 h of age. Supplementation of 8% fat tended to depress palmitate esterification into lipids (P = 0.07) and decreased palmitate oxidation (P = 0.003) in lamb BAT in vitro, especially in those lambs from ewes fed 8% SMFA. Thus, supplementing the diets of ewes with 8% SMFA depressed cold tolerance in newborn lambs, which was reflected in their decreased ability to oxidize fatty acids in vitro.

High linoleic acid safflower seed supplementation for gestating ewes: Effects on ewe performance, lamb survival, and brown fat stores1

Objectives of this study were to determine whether feeding high-linoleic safflower seed to gestating ewes increases cold tolerance and survival in lambs, and whether brown adipose tissue (BAT) stores in lambs are affected by prepartum safflower seed supplementation. In Trial 1, 234 gestating ewes (122 in yr 1 and 112 in yr 2; 75.5 and 81.2 +/- 0.6 kg initial BW for yr 1 and 2, respectively) were allotted randomly to one of two dietary treatments (four pens*treatment(-1)*yr(-1)). Ewes were fed alfalfa-based diets containing (DM basis) either 2.8 (LF) or 5.7% (HF) dietary fat beginning 55 (yr 1) and 42 (yr 2) +/- 1 d prepartum. In Trial 2, 40 Rambouillet cross ewes gestating twins (82.9 +/- 1.7 kg BW) were used in 2 yr (20/yr) and were fed diets containing (DM basis) either 1.9 (LF) or 4.9% (HF) dietary fat beginning 53.4 +/- 1.4 d prepartum. The basal diet was 37.5% each of grass and alfalfa hays and 25% corn silage (DM basis). Cracked safflower seeds (18% CP, 32% fat, 25.6% linoleic acid; DM basis) were used as the supplement in HF, whereas safflower meal and corn were used as the supplement in LF for both trials. At parturition, one lamb from each ewe was selected randomly for slaughter. Perirenal (PR) and pericardial (PC) BAT was excised and weighed, and the carcass was frozen for compositional analysis. In Trial 1, more lambs from HF 0.03; 15.4 vs. 5.8 +/- 2.8%), and dams survived (P = 0.03; 88.4 vs. 78.3 +/- 2.9%), fewer died due to starvation (P = there was a tendency for fewer to die due to pneumonia (P = 0.07; 0.0 vs. 1.7 +/- 0.6%). Ewes fed HF tended to wean more lambs per ewe (P = 0.09; 1.4 vs. 1.2 +/- 0.06) but had similar lamb weight weaned per ewe (P = 0.51; 23.1 +/- 1.22 kg). In Trial 2, prepartum ewe plasma NEFA and glucose concentrations increased with advancing gestation (P < 0.001). Lamb rectal temperature tended (P = 0.08) to be higher in LF lambs and tended (P = 0.06) to increase following parturition. Perirenal BAT weight did not differ among treatments (33.01 +/- 1.66 g; P = 0.28; 0.62 +/- 0.30% BW; P = 0.60). Lambs from LF dams tended (P = 0.08) to have greater PC BAT weight; however, the effect was not significant when expressed as a percentage of BW (0.13 +/- 0.007; P = 0.98). High-linoleic safflower seeds fed during the last 45 d of gestation may be beneficial in improving lamb survivability. Our data do not indicate this response was a result of increased BAT stores. More research is necessary to determine mechanisms that enhance lamb survival when high-linoleic saf-flower seed is fed during gestation.

Effect of postnatal age and a beta(3)-adrenergic agonist (Zeneca D7114) administration on uncoupling protein-1 abundance in the lamb.

We examined the effect of time after birth and beta(3)-adrenergic agonist (Zeneca D7114) administration on uncoupling protein-1 (UCP1) abundance and thermoregulation in the lamb. Forty twin lambs, all born normally at term, were maintained at a cold ambient temperature of between 3 and 8 degrees C. At 0.5, 1.75, 5.25, 11.25 and 23.25 h after birth eight sets of twins were fed 20 ml of formula milk +/- 10 mg kg(-1) of beta(3)-adrenergic agonist, and 45 min after feeding brown adipose tissue (BAT) was sampled. Colonic temperature was measured and BAT analysed for UCP1 abundance, GDP-binding to mitochondrial protein (i.e. thermogenic activity) and catecholamine content. Colonic temperature declined between 1.25 and 6 h from 40.2 degrees C to 39.2 degrees C and then increased to 39.8 degrees C at 12 h, but increased after feeding at all ages. UCP1 abundance increased from 1.25 h after birth, to peak at 2 h after birth in controls, compared with 6 h after birth in beta(3)-adrenergic agonist-treated lambs. The level of GDP-binding to mitochondrial protein did not change significantly with age but was increased by beta(3)-adrenergic agonist treatment. The noradrenaline (norepinephrine) content of BAT increased between 1.25 and 12 h after birth, irrespective of beta(3)-adrenergic agonist administration. The total weight of perirenal BAT plus its lipid, protein and mitochondrial protein content declined over the first 6 h of life. UCP1 development continues over the first 24 h of neonatal life, and can be manipulated by beta(3)-adrenergic agonist administration. This may represent one method of improving thermoregulation in newborn lambs. Experimental Physiology (2001) 86.1, 65-70.

Effect of maternal nutrient restriction in early to mid gestation and thyrotrophin-releasing hormone on lamb survival following Caesarean section delivery near to term.

We investigated the influence of restricted maternal nutrition between 28 and 77 days gestation on survival and thermoregulatory adaptation following Caesarean section delivery near to term. This study was designed to examine the hypothesis that adaptation after birth would be compromised in those lambs born to nutrient restricted ewes. We further hypothesised that this would be due in part to inadequate hypothalamic-pituitary-thyroidal function. Lambs born to nutrient restricted ewes were untreated (RU) or treated with thyrotrophin-releasing hormone (TRH; RT) immediately prior to umbilical cord clamping. Single bearing ewes consumed either 6.60 MJ x day(-1) (controls, n = 4) or 3.00 MJ x day(-1) (nutrient restricted, n = 15) from 28-77 days gestation, after which all ewes consumed 7.20 MJ x day(-1). All lambs born to control ewes commenced continuous breathing and began to shiver following Caesarean section delivery and survived to 6 h after birth. Only 4 out of 9 RU lambs established continuous breathing and survived to 6 h after birth compared with all RT lambs. Six hours after birth, RT lambs possessed perirenal brown adipose tissue with a higher thermogenic activity than 6 h old RU or control lambs. Lamb birth weight was similar in all groups. In conclusion, near-term lambs born to ewes nutrient restricted in early to mid gestation are at increased risk of death following Caesarean section delivery. Survival after birth can be significantly enhanced if TRH is administered to the lambs immediately before delivery.

Beta2-agonist ritodrine, unlike natural catecholamines, activates thermogenesis prematurely in fetal sheep.

Prolonged administration of the beta2-adrenergic agonist ritodrine to fetal sheep increases nonesterified fatty acid mobilization. To investigate whether changes in fetal growth or functional development of brown adipose tissue (BAT) also occur, ritodrine was infused at 5 microg/min iv into eight fetal sheep (6 twins and 2 singletons at 125-128 days of gestation) for 5 days and then at twice this rate for a further 7-11 days. Fetal growth was reduced significantly (P < 0.02) during ritodrine infusion relative to controls (5.8 +/- 17.5 vs. 79.7 +/- 10.3 g/day), with growth of skeletal muscles ceasing. Ritodrine reduced perirenal BAT weight by 50% from 18.6 +/- 1.89 to 9.3 +/- 0.60 g (P < 0.01) and its lipid content by >70% from 6.5 +/- 0.96 to 1.9 +/- 0.45 g (P < 0.01). Mitochondrial protein in BAT was also less (P < 0.002), but GDP binding to uncoupling protein increased (P < 0.05). In similar experiments, epinephrine and norepinephrine increased plasma nonesterified fatty acid initially, but neither altered perirenal BAT composition. The beta2-adrenergic agonist ritodrine appears able to promote lipid mobilization and thermogenesis in utero.

Effect of fetal thyroidectomy on brown adipose tissue and thermoregulation in newborn lambs.

The effect of fetal thyroidectomy on thermoregulation in newborn lambs was investigated. Seven of 14 lambs born normally at term were thyroidectomized at Day 127 of gestation. Colonic temperature and oxygen consumption were measured during non-rapid eye movement sleep 6-45 h after birth. All lambs were then killed and perirenal brown adipose tissue was sampled for measurement of thermogenic activity (guanosine diphosphate binding), uncoupling protein and lipid contents. Thyroidectomized lambs tended to have a mean colonic temperature 2.35 degrees C lower (P = 0.067) than controls and two became hypothermic (i.e. colonic temperature < 35 degrees C). Thyroidectomized lambs exhibited lower rates of oxygen consumption (P = 0.05) and an increased incidence of shivering thermogenesis. The perirenal adipose tissue of these lambs had a lower thermogenic activity (P < 0.01), less uncoupling protein (P < 0.01) and higher lipid content (P = 0.072) compared with intact controls. It is concluded that fetal thyroidectomy results in a decreased ability of newborn lambs to utilize nonshivering thermogenesis in brown adipose tissue as well as increasing the incidence of hypothermia. These changes are associated with decreased synthesis of uncoupling protein and functional development of brown adipose tissue in the late gestation fetus.

Effect of maternal glucose infusion on brown adipose tissue and liver development in the neonatal lamb.

The effect of maternal glucose infusion over the final 5-7 days of gestation in under-fed ewes on perirenal brown adipose tissue (BAT) and liver development in lambs over the first month of neonatal life was examined. During glucose infusion, higher maternal plasma concentrations of glucose and thyroid hormones, and lower plasma concentrations of non-esterified fatty acids and 3-hydroxybutyrate were observed, compared with saline-infused controls. These differences were not observed 1-1.5 h before parturition when plasma concentrations of glucose, lactate, cortisol and thyroid hormones all increased in control ewes. Lamb birthweight and liver and BAT weights were similar between groups, but lambs born to glucose-infused ewes had a higher hepatic glycogen content and greater iodothyronine 5'deiodinase activities in liver and BAT. The norepinephrine, epinephrine and dopamine contents were also greater in BAT sampled from lambs born to glucose infused ewes. Three lambs born to glucose-infused ewes failed to survive beyond the second week of life and exhibited abnormally low plasma triiodothyronine concentrations. It is concluded that maternal glucose infusion stimulates development of the fetal sympathetic nervous system during late gestation but this adaptation does not appear to improve postnatal survival.

N-Methyladrenaline: age-dependent urinary excretion, perinatal organ content and relation with ‘classical’ catecholamines

Using high performance liquid chromatography with electrochemical detection we determined free dopamine, noradrenaline, adrenaline and N-methyladrenaline in: (1) urines from newborns ( n = 32), children ( n = 45) and adults ( n = 19) and (2) adrenals, organ of Zuckerkandl, dorsal roots and perirenal brown adipose tissue from deceased fetuses ( n = 2), very premature ( n = 6) and term ( n = 2) newborns and infants ( n = 2). Data from children and adults showed that contributions of adrenaline and N-methyladrenaline to the sum of urinary free catecholamines increase with age. Relative amounts of adrenaline and N-methyladrenaline increased in both adrenal and extra adrenal chromaffin tissues from late gestation up to several months of postnatal life. Increase of adrenal N-methyladrenaline content follows endocrine maturation of the medulla, phenylethanolamine- N-methyltransferase induction and subsequent adrenaline synthesis. Relative amounts of N-methyladrenaline in extra adrenal chromaffin tissue increase in a period that is associated with its regression. Further investigations are necessary to elucidate the function and possible clinical chemical usefulness of N-methyladrenaline.