Substitution of starch for palm oil during gestation: impact on offspring survival and hepatic gene expression in the pig

Piglet neonatal mortality rates are high (~20%), so nutritional strategies to reduce this are highly desirable. Maternal fat substitution (FS) may promote the preweaning survival of piglets by improving their energy status. Therefore, the aim of the present study was to investigate the effects of FS throughout pregnancy on offspring viability, together with the gene expression of stress-related markers in the liver. Sixteen pregnant sows were randomly allocated to one of two isocaloric diets, control (C) or FS in the form of palm oil, fed from 0 to 110 days gestation. Glucose tolerance was examined on Day 108. Median and low birthweight offspring were allocated to tissue sampling at either 7 days or 6 months postnatal age. In response to a glucose tolerance test, FS sows exhibited a raised glucose area under the curve with no change in basal glucose. Average piglet mortality (up to Day 28) was increased fourfold in the FS group, with surviving median-sized piglets exhibiting significantly lower fatty acid binding protein 1 (FABP1) expression at 7 days. There were no effects on the abundance of any other stress- or metabolic-related genes examined. Thus, this study demonstrates that maternal FS throughout gestation causes maternal glucose intolerance that may be linked to the observed increase in piglet mortality. However, the surviving offspring do not exhibit any detectable differences in postnatal growth or hepatic gene profile in later life.

Gene expression of inflammatory markers in adipose tissue between obese women with polycystic ovary and normal obese women

OBJECTIVE

The pathogenesis of polycystic ovary syndrome (PCOS), a common endocrine disease and metabolic disturbance, is still unknown. The aim of the study was to investigate whether patients with PCOS display increased expression of inflammatory markers in adipose tissue.

PATIENTS AND METHODS

Two groups of women were investigated, those diagnosed with PCOS (n = 8) and age and BMI-matched normal women (n = 12). Their age was between 20-45 years and all subjects were apparently healthy and did not take any medications. Adipose tissue levels of mRNA of inflammatory markers were determined by use of real-time PCR.

RESULTS

There were no differences between obese patients and obese PCOS in levels of adipocytokines.

CONCLUSIONS

There were no effects of PCOS on the expression of any of the adipocytokines genes measured in subcutaneous adipose tissue.

Construction of a doxycycline inducible adipogenic lentiviral expression system

To provide a tool for research on regulating adipocyte differentiation, tetracycline inducible (Tet on) lentiviral expression vectors under the control of an adipose-specific promoter were constructed. The lowest basal expression in the absence of doxycycline and most efficient dose-dependent, doxycycline-induced transient overexpression was observed using vectors constructed with a combination of Tetracycline Responsive Element (TRE) and reverse tetracycline-controlled TransActivator advanced (rtTAadv), transfected in white (3T3-L1) and brown (HIB-1B) preadipocytes cell lines. The results demonstrate that doxycycline adipogenic inducible expression can be achieved using a pLenti TRE / rtTA adv under the control of the truncated aP2 promoter in HIB-1B preadipocytes.

Role of Ucp1 enhancer methylation and chromatin remodelling in the control of Ucp1 expression in murine adipose tissue

AIMS/HYPOTHESIS

Increasing the expression of the brown adipose tissue-specific gene uncoupling protein-1 (Ucp1) is a potential target for treating obesity. We investigated the role of DNA methylation and histone modification in Ucp1 expression in adipose cell lines and ex vivo murine adipose tissues.

METHODS

Methylation state of the Ucp1 enhancer was studied using bisulphite mapping in murine adipose cell lines, and tissue taken from cold-stressed mice, coupled with functional assays of the effects of methylation and demethylation of the Ucp1 promoter on gene expression and nuclear protein binding.

RESULTS

We show that demethylation of the Ucp1 promoter by 5-aza-deoxycytidine increases Ucp1 expression while methylation of Ucp1 promoter-reporter constructs decreases expression. Brown adipose tissue-specific Ucp1 expression is associated with decreased CpG dinucleotide methylation of the Ucp1 enhancer. The lowest CpG dinucleotide methylation state was found in two cyclic AMP response elements (CRE3, CRE2) in the Ucp1 promoter and methylation of the CpG in CRE2, but not CRE3 decreased nuclear protein binding. Chromatin immunoprecipitation assays revealed the presence of the silencing DiMethH3K9 modification on the Ucp1 enhancer in white adipose tissue and the appearance of the active TriMethH3K4 mark at the Ucp1 promoter in brown adipose tissue in response to a cold environment.

CONCLUSIONS/INTERPRETATION

The results demonstrate that CpG dinucleotide methylation of the Ucp1 enhancer exhibits tissue-specific patterns in murine tissue and cell lines and suggest that adipose tissue-specific Ucp1 expression involves demethylation of CpG dinucleotides found in regulatory CREs in the Ucp1 enhancer, as well as modification of histone tails.

Effect of plasma insulin and branched-chain amino acids on skeletal muscle protein synthesis in fasted lambs

The increase in fractional rate of protein synthesis (Ks) in the skeletal muscle of growing rats during the transition from fasted to fed state has been explained by the synergistic action of a rise in plasma insulin and branched-chain amino acids (BCAA). Since growing lambs also exhibit an increase inKswith level of feed intake, the objective of the present study was to determine if this synergistic relationship between insulin and BCAA also occurs in ruminant animals. Six 30 kg fasted (72 h) lambs (8 months of age) received each of four treatments, which were based on continuous infusion into the jugular vein for 6 h of: (1) saline (155 mmol NaCl/l); (2) a mixture of BCAA (0·778 μmol leucine, 0·640 μmol isoleucine and 0·693 μmol valine/min·kg); (3) 18·7 μmol glucose/min·kg (to induce endogenous insulin secretion); (4) co-infusion of BCAA and glucose. Within each period all animals received the same isotope of phenylalanine (Phe) as follows: (1) l-[1-13C]Phe; (2) l-phenyl-[ring2H5]-alanine; (3) l-[15N]Phe; (4) l-[ring 2,6-3H]Phe. Blood was sampled serially during infusions to measure plasma concentrations of insulin, glucose and amino acids, and plasma free Phe isotopic activity; biopsies were taken 6 h after the beginning of infusions to determineKsinm. longissimus dorsiandvastusmuscle. Compared with control (saline-infused) lambs,Kswas increased by an average of 40 % at the end of glucose infusion, but this effect was not statistically significant in either of the muscles sampled. BCAA infusion, alone or in combination with glucose, also had no significant effect onKscompared with control sheep.Kswas approximately 60 % greater forvastusmuscle than form. longissimus dorsi(P>0·01), regardless of treatment. It is concluded that there are signals other than insulin and BCAA that are responsible for the feed-induced increase inKsin muscle of growing ruminant animals.

The effect of dietary polyunsaturated fatty acids (PUFA) on infection with the nematodes Ostertagia ostertagi and Cooperia oncophora in calves

Diet-induced changes in the polyunsaturated fatty acid (PUFA) content of immune cells influences the immune phenotype that develops following infection. The aim of this study was to examine the effect of manipulating dietary PUFA supply on tissue fatty acids composition and immunity to a mixed infection with an abomasal and an intestinal nematode parasite in calves. Calves (n=24) were allocated into two treatment groups and fed 25 g/day of either fish oil (n-3 group) or a binary mixture of palm/rapeseed oil (normal group) as a supplement in milk replacer. Within each treatment group eight calves were infected with 2000 L3 Ostertagia ostertagi and Cooperia oncophora, three times per week for 8 weeks, the remaining calves were pair-fed uninfected controls. Faecal egg counts (FEC) were carried out twice weekly. At slaughter, the whole gut was removed intact for worm counts and tissue samples were taken for fatty acid analysis. Samples of abomasum, duodenum and mid-gut were also collected for immunohistological analysis. FEC were not significantly influenced by oil supplement but tended to remain higher in the palm/rapeseed oil-fed group (normal infected). The number of intestinal immature worms was significantly (p<0.05) higher in the n-3 group. Mucosal mast cell (MMC) and eosinophil numbers were significantly increased (p<0.05) by infection and were significantly lower (p<0.05) in the intestinal tissue of the fish oil supplemented and infected group (n-3 infected group). These results suggest that feeding an n-3 PUFA-rich supplement (fish oil) can influence cellular mediators of immunity to nematode infection. This is the first report of the establishment of patency and the subsequent development of immunity to a mixed infection with O. ostertagi and C. oncophora in calves undergoing early rumen development. The trend in the FEC, MMC and eosinophil numbers in the n-3 group suggests that decreasing the dietary n-6/n-3 PUFA ratio may be a worthwhile immunonutritional strategy for potentiating the immune response to nematode parasite infection in the calf.

Splanchnic metabolism of nitrogenous compounds and urinary nitrogen excretion in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera1,2,3

Effects of increased ammonia and/or arginine absorption across the portal-drained viscera (PDV) on net splanchnic (PDV and liver) metabolism of nitrogenous compounds and urinary N excretion were investigated in six catheterized Hereford x Angus steers (501 +/- 1 kg BW) fed a 75% alfalfa:25% (as-fed basis) corn-soybean meal diet (0.523 MJ of ME/[kg BW(0.75).d]) every 2 h without (27.0 g of N/kg of dietary DM) and with 20 g of urea/kg of dietary DM (35.7 g of N/kg of dietary DM) in a split-plot design. Net splanchnic flux measurements were obtained immediately before beginning and ending a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). For 3 d before and during arginine infusion, daily urine voided was measured and analyzed for N composition. Feeding urea increased PDV absorption (P < 0.01) and hepatic removal (P < 0.01) of ammonia N, accounting for 80% of increased hepatic urea N output (P < 0.01). Numerical increases in net hepatic removal of AA N could account for the remaining portion of increased hepatic urea N output. Arginine infusion increased hepatic arginine removal (P < 0.01) and hepatic urea N output (P < 0.03) and switched hepatic ornithine flux from net uptake to net output (P < 0.01), but numerical changes in net hepatic removal of ammonia and AA N could not account fully for the increase in hepatic urea N output. Increases in urine N excretion equaled quantities of N fed as urea or infused as arginine. Estimated salivary urea N excretion was not changed by either treatment. Urea cycle regulation occurs via a complex interaction of mechanisms and requires N sources other than ammonia, but the effect of increased ammonia absorption on hepatic catabolism of individual AA in the present study was not significant.

Splanchnic metabolism of nutrients and hormones in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera1,2,3

Effects of increased ammonia and/or arginine absorption on net splanchnic (portal-drained viscera [PDV] plus liver) metabolism of nonnitrogenous nutrients and hormones in cattle were examined. Six Hereford x Angus steers (501 +/- 1 kg BW) prepared with vascular catheters for measurements of net flux across the splanchnic bed were fed a 75% alfalfa:25% (as-fed basis) corn and soybean meal diet (0.523 MJ of ME/[kg BW(0.75).d]) every 2 h without (27.0 g of N/kg of DM) and with 20 g of urea/kg of DM (35.7 g of N/kg of DM) in a split-plot design. Net flux measurements were made immediately before and after a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). There were no treatment effects on PDV or hepatic O2 consumption. Dietary urea had no effect on splanchnic metabolism of glucose or L-lactate, but arginine infusion decreased net hepatic removal of L-lactate when urea was fed (P < 0.01). Net PDV appearance of n-butyrate was increased by arginine infusion (P < 0.07), and both dietary urea (P < 0.09) and arginine infusion (P < 0.05) increased net hepatic removal of n-butyrate. Dietary urea also increased total splanchnic acetate output (P < 0.06), tended to increase arterial glucagon concentration (P < 0.11), and decreased arterial ST concentration (P < 0.03). Arginine infusion increased arterial concentration (P < 0.07) and net PDV release (P < 0.10) and tended to increase hepatic removal (P < 0.11) of insulin, as well as arterial concentration (P < 0.01) and total splanchnic output (P < 0.01) of glucagon. Despite changes in splanchnic N metabolism, increased ammonia and arginine absorption had little measurable effect on splanchnic metabolism of glucose and other nonnitrogenous components of splanchnic energy metabolism.

An integrative model of amino acid metabolism in the liver of the lactating dairy cow

The objective of this work was to construct a dynamic model of hepatic amino acid metabolism in the lactating dairy cow that could be parameterized using net flow data from in vivo experiments. The model considers 22 amino acids, ammonia, urea, and 13 energetic metabolites, and was parameterized using a steady-state balance model and two in vivo, net flow experiments conducted with mid-lactation dairy cows. Extracellular flows were derived directly from the observed data. An optimization routine was used to derive nine intracellular flows. The resulting dynamic model was found to be stable across a range of inputs suggesting that it can be perturbed and applied to other physiological states. Although nitrogen was generally in balance, leucine was in slight deficit compared to predicted needs for export protein synthesis, suggesting that an alternative source of leucine (e.g. peptides) was utilized. Simulations of varying glucagon concentrations indicated that an additional 5 mol/d of glucose could be synthesized at the reference substrate concentrations and blood flows. The increased glucose production was supported by increased removal from blood of lactate, glutamate, aspartate, alanine, asparagine, and glutamine. As glucose output increased, ketone body and acetate release increased while CO(2) release declined. The pattern of amino acids appearing in hepatic vein blood was affected by changes in amino acid concentration in portal vein blood, portal blood flow rate and glucagon concentration, with methionine and phenylalanine being the most affected of essential amino acids. Experimental evidence is insufficient to determine whether essential amino acids are affected by varying gluconeogenic demands.

Consequences of exposure to serum, with or without vitamin E supplementation, in terms of the fatty acid content and viability of bovine blastocysts produced in vitro

To determine whether serum supplementation influenced fatty acid content of bovine blastocysts and whether vitamin E addition to culture medium containing serum could improve development in vitro, cleaved eggs were cultured in synthetic oviduct fluid supplemented with bovine serum albumin (BSA, 0.4% w/v, fraction V) (SVBSA), fetal calf serum (FCS, 10% v/v) (SFCS) or FCS (10% v/v) plus 100 μM vitamin E (SFCS + E). Blastocyst yields were recorded and fatty acid composition was determined by gas chromatography. Day 7 blastocysts were incubated with [2-14C] pyruvate for 3 h and then fixed for cell counts. Yields of good quality blastocysts were greatest from cleaved eggs cultured in serum-free conditions (P < 0.01). In the presence of serum, supplementation with vitamin E increased both total and good quality blastocyst yields (P < 0.01). Presence of serum increased fatty acid content (mean ± SEM) of blastocysts (SVBSA v. SFCS = 57 ± 2  v. 74 ± 2 ng embryo−1; P < 0.001). In contrast, pyruvate metabolism was greater in blastocysts produced without serum (27 ± 3 v. 21 ± 3 picomoles embryo−13 h−1; P < 0.01) but, on a per cell basis, no differences were detected. Addition of vitamin E to the serum-supplemented formulation did not alter either the fatty acid content (73 ± 2 ng embryo−1) or pyruvate metabolism index (19 ± 1 pmol embryo−13 h−1) of SFCS + E blastocysts. Thus, despite lipid accumulation, supplementary vitamin E improved blastocyst yields in embryos exposed to serum.

Nutrient-hormone interaction in the ovine liver: methionine supply selectively modulates growth hormone-induced IGF-I gene expression

This study tested the hypothesis that specific amino acids are responsible for modulating the insulin-like growth factor-I (IGF-I) response to growth hormone (GH) in ovine hepatocytes. Cells were grown in media of defined amino acid composition, based on physiological concentrations (P.C.) of amino acids in sheep plasma. Relative to culture in 5 x P.C., amino acid limitation to 0.2 x P.C. had inhibitory effects on IGF-I RNA expression, peptide release and p70 S6 kinase phosphorylation (P<0.01 in each case). Limitation of methionine levels to 0.2 x P.C. against a background of 5 x P.C. for the other amino acids blocked GH-stimulated IGF-I peptide release and RNA expression, although basal expression was unaffected. In contrast, limitation of the other amino acids present in the culture medium had no effect on basal or GH-stimulated IGF-I expression. Selective methionine limitation to 0.2xP.C. levels had no effect on cellular or secretory protein synthesis rates relative to cells grown in complete 5 x P.C. medium but did cause a partial reduction in p70 S6 kinase phosphorylation, which was also observed when medium was selectively limited for other essential amino acids. The addition of rapamycin (5 ng/ml) to cells grown in 5xP.C. media completely abolished p70 S6 kinase phosphorylation (P<0.001), implicating mTOR in the response of S6 kinase phosphorylation to changing amino acid supply. By contrast, inclusion of rapamycin (100 ng/ml) had no effect on levels of IGF-I gene expression. These results indicate that methionine is the key limiting amino acid involved in the modulation of IGF-I expression in the ovine liver. This nutrient-hormone interaction is a highly selective phenomenon, occurring against a background of modest effects on general protein synthetic control. The partial inhibitory effects of methionine on mTOR activity are not sufficient to account for this selectivity of action.

Chronic cold exposure has no effect on brown adipose tissue in newborn lambs born to well-fed ewes

It has been previously shown in twin-bearing ewes fed only 60% of their metabolizable energy requirements for late pregnancy that chronic cold exposure induced by winter shearing of the ewes results in larger lambs with more brown adipose tissue. This effect appears to be primarily due to prevention of a decline in fetal body and tissue weights between 145 days' gestation and 2 h after birth (i.e. 147 days' gestation) in lambs born to underfed shorn ewes. The present study therefore examined the impact, in ewes that were well fed (i.e. received 100% of their metabolizable energy requirements) during the final month of gestation, of chronic cold exposure induced by winter shearing on lamb birthweight and perirenal adipose tissue composition as measured 2 h after birth. Perirenal adipose tissue was analysed for its thermogenic activity (i.e. GDP binding to mitochondria) and catecholamine content. These observations were combined with similar measurements made in near-term (i.e. 145 days' gestation) fetuses sampled from well-fed unshorn ewes. There was no difference between lambs born to shorn or unshorn ewes with respect to birthweight or perirenal adipose tissue weight and composition. Perirenal adipose tissue weight was higher in lambs born to unshorn ewes than in fetuses. The thermogenic activity of adipose tissue was 2-fold higher in lambs born to unshorn ewes compared with 145-day-old fetuses. Epinephrine was detectable only at very low levels in fetal perirenal adipose tissue, increasing 10-fold after birth, with no difference between lambs born to shorn or unshorn ewes. In newborn lambs, plasma growth hormone concentration was lower and insulin concentration higher in shorn compared with unshorn groups. In conclusion, chronic cold exposure induced by winter shearing had no effect on brown adipose tissue development in lambs born to well-fed ewes.

Effect of feeding level and thyroxine on adipose tissue development and growth in postnatal lambs

We investigated the influence of exogenous thyroxine (T4) administration in conjunction with level of feeding on adipose tissue and liver growth in postnatal lambs. Pairs of lambs were fed either 100 g (i.e. low fed) or 200 g (i.e. high fed) of milk powder per litre of reconstituted milk replacer over the first month of life. Half of the pairs of lambs were fed a bolus dose of T4 (15 mg (kg body weight)-1) daily until 8 days of age. Perirenal adipose tissue and hepatic tissue were sampled at either 8 or 35 days of age. High fed lambs grew faster, possessed more adipose tissue and had larger livers than low fed lambs at 8 and 35 days of age. T4 administration resulted in a lower thermogenic activity (i.e. GDP binding) in adipose tissue at 8 days of age in low, but not high fed lambs. There was no difference between groups in colonic temperature or oxygen consumption. Between 17 and 35 days of age high fed lambs previously treated with T4 had lower daily milk consumption than untreated siblings, but still attained the same growth rate. Plasma insulin-like growth factor-I concentrations were greater in high than low fed lambs, a relationship that was not influenced by T4 treatment. In adipose tissue, iodothyronine 5' deiodinase activity was not influenced by T4 administration and was greater in high than low fed lambs. Hepatic iodothyronine 5' deiodinase activity was not influenced by T4 administration in low fed lambs, but was reduced by T4 in high fed lambs. In conclusion, T4 administration over the first 8 days of life can accelerate the rate of decline in thermogenic activity of uncoupling protein-1. This effect is not observed when the level of feeding is increased. Following withdrawal of T4 treatment, high fed T4-treated lambs were able to maintain the same growth rate as untreated lambs despite having a lower food intake.

Insulin stimulates phenylalanine uptake across the hind limb in fed lambs

Five lambs ( approximately 6 mo of age and 30 kg), with an external iliac artery and vein catheterized and fed to maintain body weight, were used to examine effects of close arterial infusion of insulin and branched-chain amino acids (BCAA) on net phenylalanine (Phe) uptake across the hind limb. Treatments, administered randomly on five consecutive days to each lamb, were 400 min infusions of: i) saline (control); ii) insulin to double iliac artery concentration (low insulin); iii) as ii but to quadruple insulin concentration (high insulin); iv) 30 micromol/min leucine and 22.5 micromol/min each isoleucine and valine (BCAA) and v) co-infusion of ii and iv. Blood was sampled over the last 200 min from the iliac vein and right ventricle of the heart. High insulin caused a slight decrease (-13%, P < 0.05) in systemic glucose concentration, but did not alter systemic insulin concentration. Insulin, at both doses and in combination with BCAA, resulted in 9-fold greater net Phe uptake (P < 0.05) than the control, as did BCAA alone. Because BCAA alone increased net Phe uptake, these may have stimulatory effects directly or may enhance endogenous insulin. Maximum stimulation was achieved with low insulin because there was no increase in net Phe uptake with high insulin or from co-infusion with BCAA. Insulin, at low concentrations, may be important to growth in animals with marginal nutrition.

Growth hormone and amino acid supply interact synergistically to control insulin-like growth factor-I production and gene expression in cultured ovine hepatocytes

Many of the anabolic effects of growth hormone (GH) are indirect, occurring through GH-stimulated production of insulin-like growth factor-I (IGF-I) by the liver. As well as being regulated by GH, plasma IGF-I concentrations have been demonstrated to depend upon the level of dietary protein intake, with low protein diets being associated with reduced circulatory IGF-I levels. This inhibitory effect cannot be reversed by GH injection, suggesting that liver sensitivity to GH becomes impaired.To investigate the mechanisms through which protein supply affects GH sensitivity, primary cultures of ovine hepatocytes were grown in defined media, containing various proportions (0.2, 1.0 and 5.0) of jugular amino acid concentrations in fed sheep. Production of IGF-I by these cells was measured after 24 and 48 h in culture by radioimmunoassay. In the first 24-h period basal IGF-I production was the same in all defined media, and GH caused an approximately 2-fold increase in IGF-I release in cells grown in 1.0xor 5.0xamino acid media (P<0.01). Although GH appeared to increase IGF-I release in this period for cells grown in 0.2xamino acid media, this effect was not statistically significant. In the period from 24-48 h in defined media, both basal and GH-stimulated IGF-I production was dependent on amino acid availability (P<0.05 and P<0.001 respectively). Factorial analysis of variance demonstrated a strong positive interaction (P<0.001) between the effects of amino acid availability and GH, such that GH increased IGF-I production by more than 2-fold in cells grown in 5.0xamino acid media (P<0.01) but had no effect on production by cells grown in 1.0xor 0.2xamino acid media. Measurement of steady state concentrations of exon 1-derived IGF-I mRNAs using an RNase protection assay demonstrated that the observed effects on IGF-I peptide secretion were strongly associated with parallel effects at the RNA level. Incorporation of (35)S-methionine into cellular proteins over a 4-h period starting 20 h after transfer to defined culture media was not significantly reduced in 1.0xcompared with 5.0x amino acid media, although rates under both of these conditions were significantly higher than those seen in 0.2xamino acid media (P<0.01). The lack of correspondence between the dose-dependent effects of amino acid supply on cellular protein synthesis and those on basal and GH-stimulated IGF-I production, suggests that amino acid supply modulates IGF-I production through selective mechanisms. Steady state levels of the CCAAT/enhancer-binding protein beta (C/EBPbeta) isoforms, liver-enriched activating protein (LAP) and liver-enriched inhibitory protein (LIP) were determined by Western blotting. When levels of LAP were expressed relative to LIP levels in the same extracts, a significant decrease in the LAP:LIP ratio was observed in response to amino acid limitation (P<0.05). These data strengthen earlier arguments that synergistic interaction between the effects of amino acids and GH on hepatic IGF-I gene expression underlie nutrition-dependent changes in circulating IGF-I titres. The association between these effects and altered levels of C/EBPbeta isoforms suggests that CCAAT/enhancer mediated control of IGF-I gene expression may be involved in this phenomenon.

An immunohistochemical and in situ hybridisation study of the postnatal development of uncoupling protein-1 and uncoupling protein-1 mRNA in lamb perirenal adipose tissue

In the lamb, the uncoupling protein-1 (UCP1) content of perirenal adipose tissue at birth is an important factor in heat production by non-shivering thermogenesis and the prevention of hypothermia. This study examines UCP1 gene expression and protein content in perirenal adipose tissue over the first 15 days of life by in situ hybridisation and immunohistochemistry. UCP1 mRNA was detected at birth in 30% of adipocytes, and in approximately 24% of fat cells at 2 days of life. However, by 5 days of age and thereafter UCP1 mRNA was undetectable. Immunoreactive UCP1 was present in all adipocytes at birth and at 2 days of age, and remained detectable in a decreasing proportion of cells until day 10 of life. By 15 days of age no immunoreactive UCP1 was detected and the perirenal adipose tissue had the appearance of white fat. It is concluded that UCP1 gene expression is suppressed in most adipocytes in perirenal adipose tissue of newborn lambs, and gene expression rapidly falls in the remaining adipocytes over the first 5 days of postnatal life. In contrast, immunoreactive UCP1, a characteristic of brown adipose tissue, was present in many adipocytes for up to 10 days of age, suggesting that UCP1 has a long half-life in lambs. All adipocytes in perirenal adipose tissue of newborn lambs appear to be functionally brown, but over the first 2 weeks of postnatal life there is a complete transformation to white adipocytes.

Adipose tissue development during early postnatal life in ewe-reared lambs

This study examines the precise time course that brown adipose tissue (BAT) takes to adopt the characteristics of white adipose tissue in postnatal lambs. Perirenal adipose tissue was sampled from ewe-reared lambs within 1 h of birth and at 1, 2, 4, 7, 14, 21 and 30 days of age and analysed for the amount of mRNA for uncoupling protein (UCP), the amount and activity of UCP, and protein, mitochondrial protein and lipid content. This was combined with measurements of colonic temperature and jugular venous plasma concentrations of thyroid hormones and insulin-like growth factor-1 (IGF-1). Over the first 4-7 days of age, large quantities of UCP mRNA were associated with a peak in plasma triiodothyronine concentration at 2 days of age followed by a maximal amount and activity of UCP at 4 days and a basal colonic temperature of 39.3 degrees C. Between 7 and 30 days there was a large increase in lipid deposition as the amount and activity of UCP and the amount of UCP mRNA declined to basal values and colonic temperature was maintained at 40 degrees C. A significant positive relationship between perirenal adipose tissue lipid content and plasma IGF-1 concentration was observed throughout the study period. It is concluded that ovine adipose tissue maturation occurs in two distinct phases over the first month of life. The precise time scale of this process could be regulated in part by the lamb's body temperature which determines whether adipose tissue is required for heat production (i.e. BAT) or as an endogenous energy source (i.e. white adipose tissue).

Maternal manipulation of brown adipose tissue and liver development in the ovine fetus during late gestation

We examined the effect of maternal chronic cold exposure, induced by winter-shearing ewes 4 weeks before their predicted lambing date, on brown adipose tissue (BAT) and liver development in lambs. Fetuses were sampled from under-fed (60% of energy requirements for maintenance and pregnancy of an unshorn ewe) shorn or unshorn ewes at 126, 140 and 145 d of gestation. Lambs were sampled from ewes within 2 h of birth. Throughout gestation fetal body, BAT and liver weights were similar in shorn and unshorn groups. The level of GDP binding to mitochondrial uncoupling protein remained low throughout gestation, but increased dramatically after birth. Lambs born to shorn ewes possessed more mitochondrial protein and exhibited a significantly higher total thermogenic activity in BAT. Type I iodothyronine 5' deiodinase (EC 3.8.1.4) activity in BAT peaked at birth, as did hepatic iodothyronine 5' deiodinase activity and was significantly greater in lambs born to under-fed shorn ewes, which exhibited a higher plasma triiodothyronine concentration. Chronic maternal adaptations to prolonged cold exposure appear to enable pregnant ewes to compensate for the negative effects of under-feeding on fetal growth and development.

Substrate specificity of the mammary tissue anionic amino acid carrier operating in the cotransport and exchange modes

The substrate specificity of the rat mammary tissue high affinity, Na+-dependent anionic amino acid transport system has been investigated using explants and the perfused mammary gland. D-Aspartate appears to be transported via the high affinity, Na+-dependent L-glutamate carrier. Thus, D-aspartate transport by rat mammary tissue was Na+-dependent and saturable with respect to extracellular D-aspartate with a Km and Vmax of 32.4 microM and 49.0 nmol/2 min per g of cells respectively. The uptake of D-aspartate by mammary explants was cis-inhibited by L-glutamate and L-aspartate, but not by D-glutamate. L-glutamate uptake by mammary tissue explants was cis-inhibited by beta-glutamate, L-cysteate, L-cysteine sulfinate and dihydrokainate but not by DL-alpha-aminoadipate. In addition, dihydrokainate, but not DL-alpha-aminoadipate inhibited D-aspartate and L-glutamate uptake by the perfused gland. D-Aspartate efflux from mammary tissue explants was trans-accelerated by external L-glutamate in a dose-dependent fashion (50-500 microM). The effect of L-glutamate on D-aspartate efflux was dependent on the presence of extracellular Na+. D-Aspartate, L-aspartate and L-cysteine sulfinate (at 500 microM) also markedly trans-stimulated D-aspartate efflux from mammary tissue explants. In contrast, L-cysteine. D-glutamate, L-leucine, dihydrokainate and DL-alpha-aminoadipate were either weak stimulators of D-aspartate efflux or were without effect. D-Aspartate efflux from the perfused mammary gland was trans-stimulated by L-glutamate but not by D-glutamate and only weakly by L-cysteine (all at 500 microM). It appears that the mammary tissue high affinity anionic amino acid carrier can operate in the exchange mode with a similar substrate specificity to that of the co-transport mode.

Mammary protein synthesis is acutely regulated by the cellular hydration state

The effect of cell-volume pertubations on mammary tissue protein synthesis has been examined. Cell-swelling, induced by a hyposmotic shock, increased the rate of incorporation of radiolabelled leucine and methionine into trichloroacetic acid precipitable material. The incorporation of radiolabel under both isosmotic and hyposmotic conditions was inhibited by cycloheximide. The increases in mammary protein synthesis as a result of cell-swelling may be attributable to an increase in casein synthesis. Conversely, cell-shrinking, as a consequence of a hyperosmotic challenge, almost abolished mammary protein (casein) synthesis. The finding that cell-volume pertubations had no significant effect on steady-state casein mRNA levels suggests that the regulation, within the time course of the experiments, is at the level of translation. The results strongly suggest that mammary cell volume may be an important cellular signal in the control of mammary protein synthesis in general and casein synthesis in particular.

Effect of rearing temperature on perirenal adipose tissue development and thermoregulation following methimazole treatment of postnatal lambs

This study examined the effect of ambient temperature on perirenal adipose tissue development and thermoregulation over the first month of postnatal life in lambs treated with a drug that reduces thyroid hormone synthesis (methimazole; at a dose of 50 mg day-1 (kg body weight)-1). Twin lambs were hand-reared at a fixed level of nutrition in either a warm (WR; 25 degrees C) or cool (CR; 10-15 degrees C) ambient temperature. Oxygen consumption, heart rate and colonic temperature were measured during non-rapid eye movement sleep in different ambient temperatures (6, 15, 25 and 34-36 degrees C) at 7, 14 and 28 days of age. Plasma thyroid hormone concentrations decreased with postnatal age and were higher in CR than in WR lambs. All lambs increased plasma thyroid hormone concentrations and O2 consumption during cold exposure but this was associated with a mean increase in colonic temperature in WR lambs at 7 or 28 days. Colonic temperature increased with the onset of panting at all ages when lambs were exposed to 34-36 degrees C, a response that was greatest at 28 days in CR lambs. An increase in colonic temperature with age was observed in CR but not WR lambs. Heart rate declined with age only in the WR group. At 8 and 29 days there were no significant differences between WR and CR groups in the occurrence of shivering or in the thermogenic activity (i.e. GDP binding to mitochondria) of perirenal adipose tissue. At 29 days WR lambs possessed more adipose tissue with a higher lipid and DNA content. It is concluded that modest changes in rearing temperature can have a large influence on the control of body temperature and thyroid hormone response to methimazole treatment. CR lambs are able to maintain higher plasma thyroid hormone concentrations and exhibit improved thermoregulation compared with WR lambs without any detectable differences in brown adipose tissue function.

Responses in milk constituents to intravascular administration of two mixtures of amino acids to dairy cows

Four Holstein-Friesian cows were used to investigate the effects of intravascular infusions of AA mixtures on milk constituents. Cows were in wk 11 to 28 of lactation and were fed a basal concentrate (142 g of CP/kg of DM) and grass silage (149 g of CP/kg of DM) in a 60:40 ratio (percentage of DM). Cows were fed hourly, and feed intake was fixed at 95% of ad libitum intake for each experimental period. Each cow received a 4-d jugular saline infusion, followed by a 5-d jugular infusion of a mixture of AA. Two mixtures of AA were used in a crossover design. The first mixture contained both the essential AA and non-essential AA found in milk protein (total AA); this mixture was infused at 400 g of AA/d. The other mixture represented the essential AA fraction only and was infused at 208 g/d. Infusion of total AA increased milk protein concentration from 32.4 to 35.0 g/kg, and essential AA increased milk protein concentration from 32.5 to 36.9 g/kg; milk protein yield increased by 87 g/d (total AA) and 143 g/d (essential AA). Intravascular administration of AA specifically stimulated milk protein concentration, and the efficiency with which the AA were used was higher than had been previously reported when AA supply was increased either by dietary supplementation or by abomasal infusion.

Effect of beta 3-adrenergic agonist (Zeneca D7114) on thermoregulation in near-term lambs delivered by cesarean section

We investigated the effect of a beta 3-adrenergic agonist, Zeneca D7114, on thermoregulation in near-term lambs delivered by cesarean section. Lambs were delivered into a cool ambient temperature of 15 degrees C, and between 60 and 80 min of life were given an oral dose of Zeneca D7114 (10 mg.kg body weight-1) dissolved in 20 mL of milk, or milk alone. During the first 0.5 h of life colonic temperature decreased in all lambs, and then increased to plateau levels (39.6-40.4 degrees C) after 120-150 min of life, in 19 out of 23 lambs studied. In the remaining lambs, colonic temperature failed to return to normothermic values, plateauing at 34.3 degrees C. All control lambs were observed to shiver throughout the study, but after Zeneca D7114 treatment 7 out of 10 normothermic lambs stopped shivering, and plateau colonic temperature was 0.8 degree C higher. Hypothermic beta 3-agonist-treated lambs had significantly lower rates of heat production, breathing frequency, and plasma triiodothyronine and cortisol concentrations than normothermic lambs. the level of GDP binding and norepinephrine content of brown adipose tissue (BAT) sampled from hypothermic beta 3-agonist-treated lambs was significantly lower than in normothermic lambs. There was no difference in GDP binding in BAT between control and Zeneca D7114-treated groups, but the Hb content was higher in the latter group. It is concluded that administration of Zeneca D7114 to euthyroid lambs enhances their ability to thermoregulate and restore colonic temperature without altering the thermogenic activity of BAT. This response may be mediated by increasing blood flow to BAT and/or an improvement in the animal's thermal efficiency (i.e. decreased heat loss) due to a reduced reliance on shivering thermogenesis.

The mechanism of L-glutamate transport by lactating rat mammary tissue

The transport of L-glutamate by lactating rat mammary gland has been examined using both tissue explants and a perfused mammary preparation. L-Glutamate uptake by mammary tissue explants was predominantly via a Na(+)-dependent pathway: Li+, choline+ and NMDG+ could not substitute for Na+. L-Glutamate efflux from preloaded explants was also influenced by the transmembrane Na(+)-gradient. These results are consistent with (Na(+)-glutamate) cotransport. The Na(+)-dependent system for L-glutamate transport in tissue explants was saturable (Km = 112.5 +/- 19.7 microM; Vmax = 71.3 +/- 10.4 nmol/min per g cells) and selective for anionic amino acids. Thus, D- and L-aspartate were high affinity inhibitors of L-glutamate uptake whereas neutral amino acids were relatively ineffective. D-Aspartate inhibited L-glutamate uptake in a competitive fashion. L-Glutamate uptake by the perfused mammary gland was (a) Na(+)-dependent (b) saturable (Km = 18.1 +/- 4.9 microM; Vmax = 40.3 +/- 3.7 nmol/min per g tissue) and (c) selective for anionic amino acids. The results suggest that the (Na(+)-glutamate) cotransporter is situated in the blood-facing aspect of the mammary epithelium.

Influence of rearing temperature on lung development following methimazole treatment of postnatal lambs

This study examines the effect of ambient temperature on lung development over the first month of postnatal life in lambs treated with a drug which inhibits thyroid hormone synthesis (methimazole, 50 mg day-1 (kg body wt-1)). Twin lambs were hand-reared at a fixed level of nutrition in either a warm (WR, 25 degrees C) or cool (CR, 10-15 degrees C) ambient temperature. Plasma thyroid hormone concentrations were significantly (P < 0.05) lower in WR lambs, but there were no differences between WR and CR groups in thyroid gland weight or hepatic iodothyronine 5'-deiodinase activity at 8 or 29 days of age. Lung weights and the ratio of lung weight to O2 consumption were similar in WR and CR groups at 8 days but both were significantly lower (P < 0.01) in CR lambs at 29 days. Lung weight at 29 days was significantly (P = 0.002) correlated with plasma triiodothyronine concentration in CR but not WR lambs, and laryngeal braking of expiratory airflow was observed in three of seven CR lambs but not in WR lambs. Four WR, but no CR, lambs exhibited a rapid deterioration in health or died unexpectedly between 14 and 21 days of age. These WR lambs were characterized by having small lungs and slower growth rates. It is concluded that in WR lambs chronically treated with methimazole, both lung development and the ability of an individual to adapt effectively to methimazole treatment are compromised. In CR lambs, although lung growth may be reduced this does not appear to compromise O2 consumption or health.

Leucine and protein metabolism in the lactating dairy cow mammary gland: responses to supplemental dietary crude protein intake

Mammary gland protein metabolism, determined by an arteriovenous difference technique, was monitored in four Holstein-Friesian dairy cows in response to supplemental dietary protein (provided as rumen-protected soyabean meal) during late lactation (weeks 24-30). Each cow was offered two isoenergetic diets composed of grass silage (170 g crude protein/kg dry matter) plus either a low (108 g/kg) or medium (151 g/kg) crude protein concentrate in a single crossover design involving two 21 d periods. On day 21, arteriovenous measurements across the mammary gland were made during a 13 h continuous i.v. infusion of [1-(13)C]leucine and with frequent (2 hourly) milk sampling during the final 6 h. Although total milk yield was slightly increased (+1 kg/d) by protein supplementation, milk protein yield was not significantly affected. Whole body protein flux (protein synthesis plus oxidation) was not significantly affected by supplementation. Total mammary gland protein synthesis (milk plus non-milk protein) was also not affected by supplementation but on both diets gland synthesis was always greater (by 20-59 percent) than milk protein output. The fractional oxidation rate of leucine by the mammary gland was significantly increased by protein supplementation (0-047 v. 0-136). Although the enrichment of leucine in secreted milk protein continued to increase, the final value (at 13 h) was 0-94 of the arterial plasma free leucine plateau value (not significantly different), suggesting almost exclusive use of plasma free leucine for milk protein synthesis. Based on current feeding schemes for dairy cattle, a fixed proportion (0-65 0-75) of the additional protein intake (+490 g/d) should have been partitioned into milk protein. Instead, leucine oxidation by the mammary gland was increased. Whether oxidation of other amino acids was also enhanced is unknown but if amino acid oxidation and the 'additional' non-milk protein synthesis occurring in the gland are not crucial to milk synthesis, then by reducing such activities improvements in the efficiency of converting absorbed amino acid into milk protein can be achieved.

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.

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.

Brown adipose tissue and liver development during early postnatal life in hand-reared and ewe-reared lambs

This study examined the effects of modest changes in ambient temperature in hand-reared lambs (experiment one) and in ewe-reared lambs (experiment two). Lambs were killed at either 8 or 31 days of age and perirenal adipose tissue was identified as being brown adipose tissue (BAT) from measurements of thermogenic activity (i.e. GDP binding to uncoupling protein in isolated mitochondria) or thermogenic capacity (i.e. detection of uncoupling protein by immunoblotting). In addition, type I and II iodothyronine 5' monodeiodonase (5'MDI) activities were assayed in perirenal adipose tissue, plus type I 5'MDI activity in liver. Plasma samples were also taken for measurements of glucose, lactate, insulin, triiodothyronine (T3) and thyroxine (T4) concentrations. In experiment one, lambs were hand-reared at either warm (WR; 25 degrees C) or cool (CR; 10-15 degrees C) ambient temperatures. Mean growth rate over the first 8 days of life in CR lambs was 88 g/day and increased to 128 g/day over the first month of life. Growth rate in WR lambs was constant at 141 g/day. Thermogenic activity of BAT was significantly higher in CR than WR lambs, but total weight and tissue lipid content of perirenal adipose tissue were significantly lower in the CR group. In both WR and CR lambs, the thermogenic activity of BAT fell by an average of 71% between 8 and 31 days. At 31 days of age, uncoupling protein in mitochondria could be detected only by immunoblotting in adipose tissue sampled from CR lambs. There was no effect of ambient temperature on type I or type II 5'MDI activity in BAT or liver; it decreased in adipose but not liver tissue between 8 and 31 days of age. The plasma concentrations of glucose, insulin and T3 tended to decline with age in CR but not in WR lambs. In ewe-reared lambs perirenal adipose tissue weight and tissue lipid content more than doubled between 8 and 31 days of age, but the level of GDP binding decreased from 85 to 5 pmol/mg mitochondrial protein over this period. Liver weight increased by 55% between 8 and 31 days of age, but hepatic 5'MDI activity remained unchanged. The plasma concentrations of T3, T4 and lactate, but not glucose or insulin, increased between 8 and 31 days of age. It is concluded that hand-rearing lambs at a cool ambient temperature significantly delays postnatal development, to the extent that BAT characteristics are retained. Ewe-rearing lambs enhances the rate at which BAT adopts the characteristics of white adipose tissue, and it prevents the postnatal decline in plasma concentrations of thyroid hormones.

Environmental effects on thermoregulation and breathing patterns during early postnatal development in hand-reared lambs

This study examines the effect of hand-rearing developing lambs in a warm (WR; 25 degrees C) or cool (CR; 10-15 degrees C) ambient temperature on the control of thermoregulation and breathing patterns, when maintained at a fixed level of nutrition over the first month of postnatal life. Measurements were made during non-rapid eye movement sleep whilst lambs were maintained for at least 1 h at warm (28-19 degrees C) and cold (14-5 degrees C) ambient temperatures at 1, 7, 14 and 30 days of age. All lambs were able to maintain normal body temperature, but oxygen consumption was higher in CR lambs at 14 and 30 days of age. At 1 day of age shivering was rarely observed in any lambs, but at 7 and 14 days of age more WR than CR lambs responded to cold exposure via shivering. Plasma concentrations of triiodothyronine were higher at 7 and 14 days of age in CR lambs. Breathing frequencies were similar in WR and CR lambs, and from 7 days of age the incidence of expiratory laryngeal braking was higher in warm compared with cold study temperatures. By 30 days of age the recruitment of this mechanism was greater in CR lambs. Mean growth rate was slower over the first week of postnatal life in CR compared with WR lambs. This difference decreased over the first month of life, as growth rate increased from 83 to 130 g day-1 in the CR group but remained constant at approximately 150 g day-1 in the WR lambs. Total weight of the lungs and heart, but not the liver, were lower at 1 month but not at 1 week of postnatal life in CR lambs. It is concluded that a modest decrease in the ambient temperature in which postnatal lambs are reared, when on a fixed feed intake, alters lung size, the recruitment of laryngeal braking and the control of body temperature.

Hepatic detoxification of ammonia in the ovine liver: possible consequences for amino acid catabolism

The effects of either low (25 mumol/min) or high (235 mumol/min) infusion of NH4Cl into the mesenteric vein for 5 d were determined on O2 consumption plus urea and amino acid transfers across the portal-drained viscera (PDV) and liver of young sheep. Kinetic transfers were followed by use of 15NH4Cl for 10 h on the fifth day with simultaneous infusion of [1-13C]leucine to monitor amino acid oxidation. Neither PDV nor liver blood flow were affected by the additional NH3 loading, although at the higher rate there was a trend for increased liver O2 consumption. NH3-N extraction by the liver accounted for 64-70% of urea-N synthesis and at the lower infusion rate the additional N required could be more than accounted for by hepatic removal of free amino acids. At the higher rate of NH3 administration additional sources of N were apparently required to account fully for urea synthesis. Protein synthesis rates in the PDV and liver were unaffected by NH3 infusion but both whole-body (P < 0.05) and splanchnic tissue leucine oxidation were elevated at the higher rate of administration. Substantial synthesis of [15N]glutamine occurred across the liver, particularly with the greater NH3 supply, and enrichments exceeded considerably those of glutamate. The [15N]urea synthesized was predominantly as the single labelled, i.e. [14N15N], species. These various kinetic data are compatible with the action of ovine hepatic glutamate dehydrogenase (EC 1.4.1.2) in periportal hepatocytes in the direction favouring glutamate deamination. Glutamate synthesis and uptake is probably confined to the perivenous cells which do not synthesize urea.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of amino acids on the metabolic fate of 15NH4Cl in isolated sheep hepatocytes

Ruminants characteristically absorb a large proportion of dietary nitrogen across the portal-drained viscera as ammonia nitrogen which is detoxified by conversion to urea in the liver. In theory, ammonia can supply both nitrogen atoms of the urea molecule via mitochondrial (carbamoyl phosphate) and cytoplasmic (aspartate) precursor pathways of the ornithine cycle but the effect of amino acids on the flux of nitrogen from ammonia to each of the two urea nitrogen atoms has not been determined. We report a study designed to determine the distribution of [15N] ammonia between [15N1]urea and [15N2]urea in sheep hepatocytes in response to ammonia concentrations (0.33, 0.67 and 1.00 mM) in the presence or absence of amino acids. In the absence of amino acids, the enrichment of [15N2]urea rose more rapidly during incubations than [15N1]urea and attained enrichments of 66-88% within 5 min of incubation. At the end of 2.5 h of incubation, [15N2]urea represented 60% and 90% of the total urea molecules at low and high ammonia concentrations, respectively. The enrichments of glutamate and aspartate were similar to [15N1]urea in the cells at the end of the incubations, even in the presence of unlabelled amino acids, supporting the concept of mitochondrial ammonia being in equilibrium with cytosolic aspartate formation. In the presence of amino acids basal urea synthesis increased but ammonia uptake and 15NH4Cl conversion to urea was less than in the absence of amino acids. The rate of formation of [15N1]urea was greater in incubations containing amino acids but when ammonia concentration in the media was raised only [15N2]urea flux increased with no change in either [15N1]urea or the unlabelled species. Measurement of media amino acid concentrations after 2.5 h of incubation in the presence of amino acids revealed that arginine, glutamine, glycine and alanine were removed while there was net formation of aspartate, threonine, serine, glutamate, and the branched chain amino acids. However, less than 12% of the 15N transfer appeared in free amino acids. The increases in basal and unlabelled urea synthesis in the presence of amino acids could be numerically accounted as the sum of arginine and glutamine removal from incubations. It is concluded that in sheep hepatocytes 15NH4Cl removal leads to quantitative formation of [15N2]urea, even in the presence of a physiological mixture of amino acids. The increase in the formation of the [15N1]urea in the presence of amino acids can be explained by the preferential utilisation of the amide nitrogen of glutamine for urea synthesis.

Effect of ambient temperature during 1st day of life on thermoregulation in lambs delivered by cesarean section

We examined the effect of delivering near-term twin lambs by cesarean section into a warm (30 degrees C) or cool (15 degrees C) ambient temperature on the control of thermoregulation. Heat production was measured 20-30 h after birth during non-rapid-eye-movement sleep at 29 and 14 degrees C. At 29 degrees C there was no difference in heat production between groups, but at 14 degrees C cool-delivered (CD) lambs exhibited a 62% greater metabolic response. Irrespective of delivery temperature, 15 of the 18 lambs used shivering thermogenesis during cold exposure, indicating a reduction in the ability to use nonshivering thermogenesis in brown adipose tissue (BAT). Mean plasma concentrations of thyroxine and triiodothyronine were 35 and 45% greater, respectively, in CD lambs than in warm-delivered lambs. The level of guanosine 5'-diphosphate binding in BAT was lower than in normally delivered lambs and was not different between CD and warm-delivered lambs. Cesarean section delivery prevents the rise in BAT thermogenic activity, which results in an increased reliance on shivering thermogenesis to maintain colonic temperature. Under these conditions, delivery into a cool environment increases the plasma concentration of thyroid hormones, which benefits the neonate by enabling a greater thermogenic response via shivering.

Hindlimb protein turnover and muscle protein synthesis in lambs: a comparison of techniques

A combination of arterio-venous difference, kinetic isotope transfer and blood flow rate techniques were used to measure tyrosine metabolism across hindlimb tissues of nine growing lambs (average live weight 36.5 kg) fed on a range of dry matter intakes. Muscle protein synthesis was measured using a continuous infusion technique and compared with simultaneous estimates of hindlimb protein turnover calculated from the values for tyrosine metabolism. When the specific radioactivity (SRA) of tyrosine in the arterial plasma free pool was assumed to be the same as the SRA of tyrosine in the direct precursor pool of protein synthesis, hindlimb protein synthesis (ksav; 3.66 (SEM 0.50) %/d) was significantly (P < 0.001) higher (68%) than muscle protein synthesis (ksp; 2.18 (SEM 0.31) %/d) but was similar to the value for muscle protein synthesis calculated using the homogenate free tyrosine SRA (ksh; 3.35 (SEM 0.42) %/d). Hindlimb and muscle protein synthesis (y) were both significantly related to dry matter intake (chi) (ksav, r2 0.667, P = 0.007; ksh, r2 0.968, P < 0.001) and there was no significant difference between the slopes (P = 0.532) and intercepts (P = 0.945) of the two regression lines. The results demonstrate that hindlimb protein turnover cannot be quantitatively compared with muscle protein synthesis, probably due to high protein metabolic activity in non-muscular tissues within the hindlimb, although similar responses in protein synthetic rate to the level of feed intake were observed between hindlimb and muscle tissues.

Effect of the prenatal maternal environment on the control of breathing during non-rapid-eye-movement sleep in the developing lamb

This study examines the effects of altering the prenatal maternal metabolic and hormonal environment via chronic cold exposure of under-fed ewes on developmental changes in breathing control of developing lambs. Breathing frequency and timing were measured during non rapid-eye-movement (non-REM) sleep in lambs born from either shorn or unshorn ewes after being maintained for at least one hour at warm (28-19 degrees C) and cool (14-5 degrees C) ambient temperatures at 1, 4, 14 and 30 days of age. Breathing frequency and oxygen consumption were significantly higher in 1 day old lambs born from shorn ewes compared with those lambs born from unshorn ewes, at both warm and cool ambient temperatures. In the shorn group breathing frequency decreased between 1 and 4 days of age and continued decreasing upto 30 days of age, during which period inspiratory and to a greater extent expiratory time, lengthened. Laryngeal "braking" of expiratory airflow was observed in more than 50% of lambs born from shorn ewes during non-REM sleep in the warm at 4, 14 and 30 days of age, and in the cold at 14 and 30 days of age. In contrast, lambs born from unshorn ewes showed no change in breathing frequency between 1 and 4 days of age, but a decrease was observed between 4 and 14 days of age, whilst laryngeal "braking" of expiratory airflow was rarely observed at any age.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of maternal cold exposure on brown adipose tissue and thermogenesis in the neonatal lamb

1. This study examines the effect of chronic cold exposure during pregnancy, induced by winter shearing twin-bearing ewes 4 weeks before predicted lambing date, on O2 consumption and CO2 production during non-rapid-eye-movement (REM) sleep in lambs maintained for at least 1 h at warm (28-18 degrees C) and cold (14-5 degrees C) ambient temperatures at 1, 4, 14 and 30 days of age. This was combined with measurement of the thermogenic activity (GDP binding to uncoupling protein in mitochondrial preparations) of perirenal adipose tissue from lambs immediately after birth and at 33 days of age. 2. Lambs born from shorn (cold-exposed) ewes were 15% heavier (P < 0.01) and possessed 21% (P < 0.01) more perirenal adipose tissue that contained 40% more protein and mitochondrial protein than unshorn (P < 0.05) controls. Total GDP binding in perirenal adipose tissue was 40% greater (P < 0.05) in lambs born from shorn ewes but there was no difference in lipid content of this tissue between the two groups. 3. At 1 day of age, lambs born from shorn ewes exhibited a 16% higher (P < 0.05) rate of O2 consumption (per kilogram bodyweight) at the warm temperature and a 40% greater metabolic response to the cold ambient temperature. All lambs born from shorn ewes responded to cold exposure without shivering (i.e. via non-shivering thermogenesis) whilst shivering was measured in four out of seven lambs in the unshorn group. These differences had disappeared by 4 days of age as a result of a 25% increased (P < 0.01) rate of O2 consumption in the warm in lambs born from unshorn ewes and a 20% decrease (P < 0.05) in the response to the cold in lambs from shorn ewes. Shivering during cold exposure was measured in six out of nine lambs born from shorn ewes indicating a rapid alteration in thermoregulatory responses to cold during the first few days of life. 4. The levels of GDP binding and mitochondrial protein in perirenal adipose tissue fell by one-third in both groups of lambs during the first 33 days of life whereas lipid content either increased or was unchanged. This indicated that brown adipose tissue (BAT) was developing the characteristics of white adipose tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of a β2-adrenergic agonist, cimaterol and corticosterone on growth and carcass composition of male rats

1. Growth rate and carcass composition were measured in rats treated with cimaterol or vehicle only for 21 days, with corticosterone administered during the last 7 days of cimaterol or vehicle only treatment. 2. Cimaterol significantly stimulated the amount of protein in the carcass as well as gastrocnemius and plantaris muscles by 9-15%, and decreased carcass fat by 24%. 3. Corticosterone treatment significantly decreased protein in the carcass and soleus, plantaris and gastrocnemius muscles by 13-33%. 4. The catabolic effects of corticosterone on carcass and muscle protein were reduced by pretreatment with cimaterol, suggesting that beta-adrenergic agonists may have some potential use in preventing muscle wasting during stressed states.

Effect of dietary protein intake and intravenous glucose infusion on plasma concentrations of insulin-like growth factor-I in lambs

Two separate experiments were carried out to examine the effect of dietary protein intake on basal and GH-stimulated plasma insulin-like growth factor-I (IGF-I) concentrations during either saline or glucose infusion into the jugular vein. In experiment 1, six castrated male lambs (27.1 +/- 1.2 kg live weight (LW)) were fed a diet restricted in both metabolizable energy (ME; 0.18 MJ/kg LW per day) and nitrogen (2.0 g/kg LW per day) intakes, while in experiment 2 a further six lambs were fed a similar restricted ME intake but an increased nitrogen intake (3.0 g/kg LW per day). In both experiments glucose (experiment 1, 0.009 mmol/kg LW per min; experiment 2, 0.015 mmol/kg LW per min) or saline (0.25 ml/min) was infused for 6 days and plasma samples were obtained from the jugular vein at hourly intervals on day 4 (basal) or on days 5 and 6 after an i.v. GH challenge. In experiment 1 there was no increase in plasma IGF-I concentrations in response to the GH challenge during saline infusion, but during glucose infusion the plasma concentration of IGF-I increased to a peak after 24 h and declined over the next 20 h. Basal concentrations of IGF-I, insulin and glucose were significantly higher during glucose infusion. In experiment 2 the area under the IGF-I peak in response to the GH challenge was the same for the infusions of saline and glucose but the peak value for IGF-I was significantly higher during glucose infusion due to higher concentrations in the basal period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of isoproterenol infusion on the hindlimb metabolism of growing wether lambs

The effect of a mixed beta 1/beta 2-adrenergic agonist, isoproterenol, on hindlimb metabolism was studied in growing wether lambs using arteriovenous difference and blood flow rate techniques. Isoproterenol (48 micrograms kg-1 d-1), or saline, was infused into a jugular vein of five wether lambs (30 to 35 kg) for five days and samples taken on the fifth day of treatment. Infusion of isoproterenol significantly increased blood flow, oxygen uptake and tyrosine uptake across the hindlimb. Hindlimb non-esterified fatty acid uptake was increased but not significantly (P = 0.11) and arterial growth hormone concentration was not altered by isoproterenol infusion. Results suggest that beta-adrenergic agonists promote lean tissue deposition by increased muscle blood flow rate and amino acid uptake.

Lipid metabolism in shorn and unshorn pregnant sheep

The aim of the present study was to determine how the long-term metabolic adaptations to winter shearing of the pregnant ewe result in significant changes in the rates of lipid mobilization and utilization of non-esterified fatty acids (NEFA) in comparison with unshorn controls. Continuous infusions of [1-14C]palmitic acid, [2-3H]glycerol and NaH14CO3 were used to measure whole-body lipid metabolism in fed (estimated metabolizable energy (ME) intake 9.54 MJ/d) and under-fed (estimated ME intake of 3 MJ/d), shorn and unshorn sheep over the final 4 weeks of pregnancy. Whole-body carbon dioxide, estimated heat production, total NEFA entry and oxidation rates were all significantly higher in fed shorn ewes compared with unshorn controls, even though there was no difference in the arterial plasma NEFA concentration. These differences may be mediated via an increase in the plasma concentrations of thyroid hormones in shorn animals. As a result of under-feeding any significant differences in lipid metabolism between shorn and unshorn groups were removed. In all sheep the mean total NEFA entry rate as measured using [1-14C]palmitic acid was 3.4 times the value obtained using [2-3H]glycerol. It is concluded that when sheep are fed on a diet from which no more than half the required ME for late pregnancy is obtained, then lipolysis of body fat depots occurs via the incomplete breakdown of adipose tissue triglycerides. This effect is significantly greater in the fed shorn pregnant ewe which exhibits higher entry and oxidation rates of NEFA.

Effect of short term intravenous infusion of noradrenaline on energy metabolism in shorn and unshorn pregnant sheep

The effect of a three hour intravenous noradrenaline (NA) infusion, at a dose of 0.8 micrograms min-1 kg-1 bodyweight, on energy metabolism was studied in five pairs of shorn and unshorn pregnant ewes. The concentration of oxygen and carbon dioxide in blood was significantly higher in shorn animals during saline infusion, but this difference between shorn and unshorn groups was removed by NA infusion. Significant increases in the plasma concentrations of glucose, lactate, non-esterified fatty acids (NEFA), 3-hydroxybutyrate and glycerol occurred in both shorn and unshorn animals during NA infusion. There was a 48 per cent larger rise in the plasma NEFA concentration during NA infusion in the unshorn group, suggesting that the lipolytic effect of exogenous NA is greater in these animals. NA infusion had no effect on the plasma concentration of thyroid hormones in both groups of ewes, while growth hormone levels fell and cortisol increased in all animals. The plasma insulin concentration was significantly reduced during NA treatment in the unshorn group, but was unchanged in shorn animals. These results may be a consequence of sympathetic activity already being elevated in shorn ewes due to chronic exposure to an environmental temperature below the thermoneutral zone.

Glucose metabolism in shorn and unshorn pregnant sheep

1. Whole-body, hind-limb and uterine tissue metabolism of glucose was studied using a combination of isotopic and arterio-venous difference techniques in shorn and unshorn pregnant sheep over the final 4 weeks of pregnancy. This was combined with the measurement of the concentrations of oxygen and carbon dioxide in arterial blood and plasma concentrations of lactate, acetate, non-esterified fatty acids, 3-hydroxybutyrate, glycerol, growth hormone (GH), insulin, glucagon, cortisol, thyroxine and 3,5,3'-triiodothyronine (T3). 2. Glucose entry rate was 28% higher in shorn ewes compared with unshorn controls, even though there was no difference in the arterial plasma concentration of glucose. This effect may have been caused by a decrease in the molar rate, insulin: glucagon (I:G), which was 40% lower in shorn ewes as a result of a significant decrease in the plasma concentration of insulin. There was no difference in the plasma concentration of cortisol or GH. 3. Blood flow across the hind-limb or uterine tissues was not significantly different between shorn and unshorn groups, neither were the net glucose uptake, glucose oxidation rate or contribution of glucose to O2 consumption across these tissues. 4. Insulin-tolerance tests performed on a separate group of shorn and unshorn ewes showed an increased sensitivity to the hypoglycaemic effects of insulin in the shorn group. 5. There was no significant difference between shorn and unshorn animals in the contribution of glucose to CO2 output or in the proportion of glucose entry rate oxidized. CO2 entry rate was 18% higher in shorn ewes compared with unshorn controls which resulted in a 26% higher estimated value for heat production. There was a 47% increase in glucose oxidation rate in shorn ewes but there was no significant difference in the proportion of total heat production which was derived from glucose. The arterial concentrations of O2 and CO2 were significantly higher in shorn ewes, which may be an indication of the higher metabolic rate in these animals. This effect may be mediated via a significant rise in plasma T3 concentration in the shorn group. 6. It is concluded that as a result of long-term cold exposure there is a significant increase in whole-body glucose entry and oxidation rates in the shorn pregnant ewe. The increase in insulin sensitivity at the same time as a decrease in plasma insulin concentration may represent a mechanism to ensure continued glucose supply to insulin-sensitive tissues while the concomitant decrease in plasma I:G stimulates hepatic gluconeogenesis.