Exogenous porcine somatotropin administered to late pregnant gilts alters liver and muscle functionalities in pig foetuses.

Neonatal maturity depends on the maternal capacity to provide nutrients for foetal growth. This study aimed to investigate the effects of systemic administration of recombinant porcine somatotropin (pST), one of the main regulators of growth and metabolism, to pregnant gilts during late gestation on circulating nutrients and expression levels of genes in liver and skeletal muscle of their 110-day-old foetuses. Gilts received either daily injections of sterile water (control [CTL] group, n = 15) or of 5 mg of pST (pST group, n = 17) from days 90 to 109 of gestation. At day 110 postconceptus, pairs of foetuses (one of small and one of average size within a litter) were selected. Circulating fructose concentrations were greater, but circulating concentrations of urea were lower in pST than in CTL foetuses. Expression levels of genes involved in carbohydrate and lipid metabolism were more affected by pST treatment in liver than in muscle. Hepatic molecular changes suggest an inhibition of energy-consuming processes (glycogen and lipid biosynthesis) and the activation of energy-producing pathway (mitochondrial oxidation) in pST compared to CTL foetuses. Expression levels of some genes involved in intracellular degradation of proteins were greater in the liver of pST foetuses, and combined with lower uremia, this suggests a higher utilisation of protein sources in pST foetuses than in CTL foetuses. In muscle, molecular changes were mainly observed in the IGF-insulin axis. Altogether, pST-treated gilts seem to have a greater ability to support foetal liver development by the reorientation of energy and protein metabolism.

Physiological traits of newborn piglets associated with colostrum intake, neonatal survival and preweaning growth.

Colostrum intake, which is critical for piglet survival after birth and growth up to weaning, greatly depends on piglet weight and vitality at birth. Our aim was to identify a set of biological variables explaining individual variations in colostrum intake, preweaning growth and risk of dying. Farrowing traits, morphological traits and colostrum intake were determined for 504 piglets born alive from 37 Landrace × Large White sows. A subset of 203 of these piglets was used to measure plasma neonatal concentrations of metabolites and hormones in blood collected from the umbilical cord at birth. From univariate analyses, we established that colostrum intake was positively associated with plasma neonatal concentrations of IGF-I, albumin, thyroid hormones (P < 0.001), and non-esterified fatty acids (P < 0.05), and was negatively associated with concentrations of lactate (P < 0.001). In a multivariable analysis, the variables explaining the variation in colostrum intake were piglet birth weight and rectal temperature 1 h after birth (positive effect, P < 0.001), time of birth after the onset of parturition, and fructose plasma concentrations at birth (negative effects, P < 0.001 and P < 0.05, respectively). Piglets that died within 3 days after birth had lower neonatal concentrations of albumin (P < 0.001), IGF-I and thyroxine (P < 0.01) than surviving piglets. Preweaning growth was positively associated with neonatal concentrations of IGF-I, thyroxine (P < 0.001), albumin and insulin (P < 0.05). Cortisol and glucose concentrations at birth were not related to colostrum intake, neonatal survival or preweaning growth. Multivariable analyses confirmed that colostrum intake was the predominant factor influencing piglet survival within 3 days after birth and preweaning growth. These results provide physiological indicators of piglet colostrum intake, besides birth weight. They also confirm the impact of time of birth during farrowing on colostrum intake and the crucial importance of physiological maturity at birth for postnatal adaptation.

A computed tomography scan application to evaluate adiposity in a minipig model of human obesity.

The aim of the present study was to describe and validate a computed tomography (CT) method to analyse adiposity distribution in Göttingen minipigs. Adiposity was evaluated in two groups of minipigs. In group 1 (n 8), measurements were performed before and after the induction of obesity. In group 2 (n 7), animals were fed rations designed to obtain heterogeneous adiposity before analyses. CT acquisitions were associated with anatomical, ultrasonography and body chemical measurements. Our CT method was based on acquisition of a single slice at a fixed anatomical landmark, calculation of individual X-ray density ranges for CT values and delineation of the three main adipose compartments (subcutaneous adipose tissue, SAT; retroperitoneal adipose tissue, RAT; and visceral adipose tissue, VAT). Our validation measures showed that the CT-scan method was accurate, sensitive and reliable. The CT data were found to be correlated with body weight, abdominal perimeter, ultrasonography, anatomical measurements and body chemical composition (from r 0.84 to 0.93, P < 0.001 for all), with a pitfall concerning the precise estimation of VAT. With increased body weight, the amount of adipose tissue increased and the relative proportion of SAT increased, whereas the relative proportion of RAT and VAT decreased (P < 0.001 for all). Adiposity measured by CT, and especially SAT, was found to be negatively correlated with insulin sensitivity (r 0.54, P < 0.05). In conclusion, a precise evaluation of the adipose compartments in minipigs was done by CT. Therefore, the use of Göttingen minipigs is relevant to further investigate the relationship between the different adipose tissues and obesity.

Sow environment during gestation: part II. Influence on piglet physiology and tissue maturity at birth.

Sow environment during gestation can generate maternal stress which could alter foetal development. The effects of two group-housing systems for gestating sows on piglet morphological and physiological traits at birth were investigated. During gestation, sows were reared in a conventional system on a slatted floor (C, 18 sows), demonstrated as being stressful for sows or in an enriched system in larger pens and on deep straw bedding (E, 19 sows). On gestation day 105, sows were transferred into identical individual farrowing crates on a slatted floor. Farrowing was supervised to allow sampling from piglets at birth. In each litter, one male piglet of average birth weight was euthanized immediately after birth to study organ development and tissue traits. Blood samples were collected from 6 or 7 piglets per litter at birth and 2 piglets per litter at 4 days of lactation (DL4). At birth, mean piglet BW did not differ between groups (P > 0.10); however, the percentage of light ( 0.10) between C and E piglets, but the insulin to glucose ratio was greater (P = 0.02) in C than in E piglets. Compared with E piglets, C piglets had a lighter gut at birth (P = 0.01) and their glycogen content in longissimus muscle was lower (P < 0.01). In this muscle, messenger RNA levels of PAX7, a marker of satellite cells and of PPARGC1A, a transcriptional coactivator involved in mitochondriogenesis and mitochondrial energy metabolism, were greater (P < 0.05), whereas the expression level of PRDX6, a gene playing a role in antioxidant pathway, was lower (P = 0.03) in C than in E piglets. Other studied genes involved in myogenesis did not differ between C and E piglets. No system effect was observed on target genes in liver and subcutaneous adipose tissue. On DL4, C piglets exhibited a lower plasma antioxidant capacity than E piglets (P = 0.002). In conclusion, exposure of sows to a stressful environment during gestation had mild negative effects on the maturity of piglets at birth.

Sow environment during gestation: part I. Influence on maternal physiology and lacteal secretions in relation with neonatal survival.

In pig husbandry, pregnant females are often exposed to stressful conditions, and their outcomes on maternal and offspring health have not been well evaluated. The present study aimed at testing whether improving the welfare of gestating sows could be associated with a better maternal health during gestation, changes in the composition of lacteal secretions and improvement in piglet survival. Two contrasted group-housing systems for gestating sows were used, that is, a French conventional system on slatted floor (C, 49 sows) and an enriched system using larger pens on deep straw (E, 57 sows). On the 105th days of gestation (DG105), sows were transferred into identical farrowing crates on slatted floor. Saliva was collected from all sows on DG35, DG105 and DG107. Blood samples were collected on DG105 from all sows and on the 1st day of lactation (DL1) from a subset of them (C, n=18; E, n=19). Colostrum and milk samples were collected from this subset of sows at farrowing (DL0) and DL4. Saliva concentration of cortisol was greater in C than in E sows at DG35 and DG105, and dropped to concentrations comparable to E sows after transfer into farrowing crates (DG107). On DG105, plasma concentrations of haptoglobin, immunoglobulins G (IgG) and A (IgA), blood lymphocyte counts and plasma antioxidant potential did not differ between groups (P > 0.10), whereas blood granulocyte count, and plasma hydroperoxide concentration were lower in E than in C sows (P < 0.05). Concentrations of IgG and IgA in colostrum and milk did not differ between the two groups. The number of cells did not differ in colostrum but was greater in milk from E than C sows (P < 0.05). Pre-weaning mortality rates were lower in E than C piglets (16.7% v. 25.8%, P < 0.001), and especially between 12 and 72 h postpartum (P < 0.001). Plasma concentration of IgG was similar in E and C piglets on DL4. In conclusion, differences in salivary cortisol, blood granulocyte count and oxidative stress markers between groups suggested improved welfare and reduced immune solicitation during late gestation in sows of the E compared with the C system. However, the better survival observed for neonates in the E environment could not be explained by variations in colostrum composition.

Proteomic analysis of adipose tissue during the last weeks of gestation in pure and crossbred Large White or Meishan fetuses gestated by sows of either breed.

BACKGROUND: The degree of adipose tissue development at birth may influence neonatal survival and subsequent health outcomes. Despite their lower birth weights, piglets from Meishan sows (a fat breed with excellent maternal ability) have a higher survival rate than piglets from Large White sows (a lean breed). To identify the main pathways involved in subcutaneous adipose tissue maturation during the last month of gestation, we compared the proteome and the expression levels of some genes at d 90 and d 110 of gestation in purebred and crossbred Large White or Meishan fetuses gestated by sows of either breed. RESULTS: A total of 52 proteins in fetal subcutaneous adipose tissue were identified as differentially expressed over the course of gestation. Many proteins involved in energy metabolism were more abundant, whereas some proteins participating in cytoskeleton organization were reduced in abundance on d 110 compared with d 90. Irrespective of age, 24 proteins differed in abundance between fetal genotypes, and an interaction effect between fetal age and genotype was observed for 13 proteins. The abundance levels of proteins known to be responsive to nutrient levels such as aldolase and fatty acid binding proteins, as well as the expression levels of FASN, a key lipogenic enzyme, and MLXIPL, a pivotal transcriptional mediator of glucose-related stimulation of lipogenic genes, were elevated in the adipose tissue of pure and crossbred fetuses from Meishan sows. These data suggested that the adipose tissue of these fetuses had superior metabolic functionality, whatever their paternal genes. Conversely, proteins participating in redox homeostasis and apoptotic cell clearance had a lower abundance in Meishan than in Large White fetuses. Time-course differences in adipose tissue protein abundance were revealed between fetal genotypes for a few secreted proteins participating in responses to organic substances, such as alpha-2-HS-glycoprotein, transferrin and albumin. CONCLUSIONS: These results underline the importance of not only fetal age but also maternal intrauterine environment in the regulation of several proteins in subcutaneous adipose tissue. These proteins may be used to estimate the maturity grade of piglet neonates.

Review: divergent selection for residual feed intake in the growing pig.

This review summarizes the results from the INRA (Institut National de la Recherche Agronomique) divergent selection experiment on residual feed intake (RFI) in growing Large White pigs during nine generations of selection. It discusses the remaining challenges and perspectives for the improvement of feed efficiency in growing pigs. The impacts on growing pigs raised under standard conditions and in alternative situations such as heat stress, inflammatory challenges or lactation have been studied. After nine generations of selection, the divergent selection for RFI led to highly significant (P<0.001) line differences for RFI (-165 g/day in the low RFI (LRFI) line compared with high RFI line) and daily feed intake (-270 g/day). Low responses were observed on growth rate (-12.8 g/day, P<0.05) and body composition (+0.9 mm backfat thickness, P=0.57; -2.64% lean meat content, P<0.001) with a marked response on feed conversion ratio (-0.32 kg feed/kg gain, P<0.001). Reduced ultimate pH and increased lightness of the meat (P<0.001) were observed in LRFI pigs with minor impact on the sensory quality of the meat. These changes in meat quality were associated with changes of the muscular energy metabolism. Reduced maintenance energy requirements (-10% after five generations of selection) and activity (-21% of time standing after six generations of selection) of LRFI pigs greatly contributed to the gain in energy efficiency. However, the impact of selection for RFI on the protein metabolism of the pig remains unclear. Digestibility of energy and nutrients was not affected by selection, neither for pigs fed conventional diets nor for pigs fed high-fibre diets. A significant improvement of digestive efficiency could likely be achieved by selecting pigs on fibre diets. No convincing genetic or blood biomarker has been identified for explaining the differences in RFI, suggesting that pigs have various ways to achieve an efficient use of feed. No deleterious impact of the selection on the sow reproduction performance was observed. The resource allocation theory states that low RFI may reduce the ability to cope with stressors, via the reduction of a buffer compartment dedicated to responses to stress. None of the experiments focussed on the response of pigs to stress or challenges could confirm this theory. Understanding the relationships between RFI and responses to stress and energy demanding processes, as such immunity and lactation, remains a major challenge for a better understanding of the underlying biological mechanisms of the trait and to reconcile the experimental results with the resource allocation theory.

Invited review: Pre- and postnatal adipose tissue development in farm animals: from stem cells to adipocyte physiology.

Both white and brown adipose tissues are recognized to be differently involved in energy metabolism and are also able to secrete a variety of factors called adipokines that are involved in a wide range of physiological and metabolic functions. Brown adipose tissue is predominant around birth, except in pigs. Irrespective of species, white adipose tissue has a large capacity to expand postnatally and is able to adapt to a variety of factors. The aim of this review is to update the cellular and molecular mechanisms associated with pre- and postnatal adipose tissue development with a special focus on pigs and ruminants. In contrast to other tissues, the embryonic origin of adipose cells remains the subject of debate. Adipose cells arise from the recruitment of specific multipotent stem cells/progenitors named adipose tissue-derived stromal cells. Recent studies have highlighted the existence of a variety of those cells being able to differentiate into white, brown or brown-like/beige adipocytes. After commitment to the adipocyte lineage, progenitors undergo large changes in the expression of many genes involved in cell cycle arrest, lipid accumulation and secretory functions. Early nutrition can affect these processes during fetal and perinatal periods and can also influence or pre-determinate later growth of adipose tissue. How these changes may be related to adipose tissue functional maturity around birth and can influence newborn survival is discussed. Altogether, a better knowledge of fetal and postnatal adipose tissue development is important for various aspects of animal production, including neonatal survival, postnatal growth efficiency and health.

Increased expressions of genes and proteins involved in mitochondrial oxidation and antioxidant pathway in adipose tissue of pigs selected for a low residual feed intake.

Adipose tissue is a primary sensor for nutrient availability and regulates many functions including feed intake and energy homeostasis. This study was undertaken to determine the molecular responses of adipose tissue to differences in feed intake and feed efficiency. Subcutaneous adipose tissue was collected from two lines of pigs divergently selected for residual feed intake (RFI), a measure of feed efficiency defined as the difference between actual and expected feed intake, and from a subset of high-RFI pigs that were feed-restricted at the level of the voluntary feed intake of low-RFI pigs during the growing-finishing period. Transcriptomics analyses indicated that the number of genes that were differentially expressed ( < 0.01) between low- and high-RFI pigs ( = 8 per group at each stage) in adipose tissue was much lower when pigs were considered at 19 kg (postweaning) than at 115 kg BW (market weight). Extended investigations were performed at 115 kg BW to compare low-RFI ( = 8), high-RFI ( = 8), and feed-restricted high-RFI ( = 8) pigs. They included in silico pathway analyses of the differentially expressed (DE) genes ( < 0.01) and a complementary proteomic investigation to list adipose proteins with a differential abundance ( < 0.10). Only 23% of the DE genes were affected by both RFI and feed restriction. This indicates that the responses of adipose tissue to RFI difference shared only some common mechanisms with feed intake modulation, notably the regulation of cell cycle (including ) and transferase activity pathway. Two carboxylesterase genes (, ) involved in lipolysis, were among the most overexpressed genes in the low-RFI pigs; they were also affected by feed restriction within the high-RFI line. About 60% of the molecular changes between low- and high-RFI pigs were specific to genetic divergence in feed efficiency, independently of feed intake. Different genes and proteins known to be associated with mitochondrial oxidative metabolism were overexpressed in adipose tissue of low-RFI pigs compared with high-RFI pigs; other proteins participating in the generation of energy were also affected by feed restriction within the high-RFI line. Finally, mitochondrial antioxidant genes were upregulated in low-RFI pigs vs. high-RFI pigs. Altogether, increased oxidative and antioxidant processes in adipose tissue might be associated with improved feed efficiency.

The cortisol response to ACTH in pigs, heritability and influence of corticosteroid-binding globulin.

In the search for biological basis of robustness, this study aimed (i) at the determination of the heritability of the cortisol response to ACTH in juvenile pigs, using restricted maximum likelihood methodology applied to a multiple trait animal model, and (ii) at the study of the relationships between basal and stimulated cortisol levels with corticosteroid-binding globulin (CBG), IGF-I and haptoglobin, all important players in glucose metabolism and production traits. At 6 weeks of age, 298 intact male and female piglets from 30 litters (30 dams and 30 boars) were injected with 250 µg ACTH(1-24) (Synacthen). Blood was taken before ACTH injection to measure basal levels of cortisol, glucose, CBG, IGF-I and haptoglobin, and 60 min later to measure stimulated cortisol levels and glucose. Cortisol increased 2.8-fold after ACTH injection, with a high correlation between basal and stimulated levels (phenotypic correlation, r p=0.539; genetic correlation, r g=0.938). Post-ACTH cortisol levels were highly heritable (h 2=0.684) and could therefore be used for genetic selection of animals with a more reactive hypothalamic-pituitary-adrenocortical axis. CBG binding capacity correlated with cortisol levels measured in basal conditions in males only. No correlation was found between CBG binding capacity and post-ACTH cortisol levels. Basal IGF-I concentration was positively correlated with BW at birth and weaning, and showed a high correlation with CBG binding capacity with a strong sexual dimorphism, the correlation being much higher in males than in females. Basal haptoglobin concentrations were negatively correlated with CBG binding capacity and IGF-I concentrations. Complex relationships were also found between circulating glucose levels and these different variables that have been shown to be related to glucose resistance in humans. These data are therefore valuable for the genetic selection of animals to explore the consequences on production and robustness traits, but also point at pigs as a relevant model to explore the underlying mechanisms of the metabolic syndrome including the contribution of genetic factors.

Divergent selection for residual feed intake affects the transcriptomic and proteomic profiles of pig skeletal muscle.

Improving feed efficiency is a relevant strategy to reduce feed cost and environmental waste in livestock production. Selection experiments on residual feed intake (RFI), a measure of feed efficiency, previously indicated that low RFI was associated with lower feed intake, similar growth rate, and greater lean meat content compared with high RFI. To gain insights into the molecular mechanisms underlying these differences, 24 Large White females from 2 lines divergently selected for RFI were examined. Pigs from a low-RFI ("efficient") and high-RFI ("inefficient") line were individually fed ad libitum from 67 d of age (27 kg BW) to slaughter at 115 kg BW (n = 8 per group). Additional pigs of the high-RFI line were feed restricted to the daily feed intake of the ad libitum low-RFI pigs (n = 8) to investigate the impact of selection independently of feed intake. Global gene and protein expression profiles were assessed in the LM collected at slaughter. The analyses involved a porcine commercial microarray and 2-dimensional gel electrophoresis. About 1,000 probes were differentially expressed (P < 0.01) between RFI lines. Only 10% of those probes were also affected by feed restriction. Gene functional classification indicated a greater expression of genes involved in protein synthesis and a lower expression of genes associated with mitochondrial energy metabolism in the low-RFI pigs compared with the high-RFI pigs. At the protein level, 11 unique identified proteins exhibited a differential abundance (P < 0.05) between RFI lines. Differentially expressed proteins were generally not significantly affected by feed restriction. Mitochondrial oxidative proteins such as aconitase hydratase, ATP synthase subunit α, and creatine kinase S-type had a lower abundance in the low-RFI pigs, whereas fructose-biphosphate aldolase A and glyceraldehyde-3-phosphate dehydrogenase, 2 proteins involved in glycolysis, had a greater abundance in those pigs compared with high-RFI pigs. Antioxidant proteins such as superoxide dismutase and glutathione peroxidase 3 at the mRNA level and peroxiredoxin-6 at the protein level were also less expressed in LM of the most efficient pigs, likely related to lower oxidative molecule production. Collectively, both the transcriptomic and proteomic approaches revealed a lower oxidative metabolism in muscle of the low-RFI pigs and all these modifications were largely independent of differences in feed intake.

Delayed muscle development in small pig fetuses around birth cannot be rectified by maternal early feed restriction and subsequent overfeeding during gestation.

Intrauterine variations in nutrient allowance can alter body composition and tissue features of the porcine offspring around birth. This study aimed to determine the effects of fetal weight variations between littermates and of maternal dietary regimen during gestation on fetal muscle traits just before birth. Fourteen pregnant gilts were reared under a conventional (control, CTL; n=7) or an experimental (treatment, TRT; n=7) dietary regimen during gestation. The dietary treatment provided 70% of the protein and digestible energy contents of the CTL diet during the first 70 days of gestation and then, 115% of the protein and digestible energy contents up to farrowing. At 110 days of gestation, sows were sacrificed and one fetus having a low (824±140 g) and one having a normal (1218±192 g) BW per litter were sampled. Irrespective of maternal dietary regimen, the longissimus muscle of the small fetuses exhibited higher expression levels of DLK1/Pref1 and NCAM1/CD56, two genes known to be downregulated during normal skeletal muscle development. Expression levels of the embryonic isoform of the myosin heavy chain (MyHC), both at the mRNA and at the protein levels, were also higher in small fetuses. In addition, the ratios of perinatal to embryonic and of adult fast to developmental MyHC isoforms were generally lower in light fetuses compared with their medium-weight littermates. These modifications suggest a delayed myofiber development in spontaneous growth-retarded fetuses. Finally, GLUT1 was expressed to a lesser extent in the muscle of small v. normal fetuses, suggesting decreased ability for glucose uptake in muscle. Initial feed restriction and subsequent overfeeding of sows during gestation led to a lower expression of the myogenic factor MYOD1, a prerequisite for myogenic initiation in skeletal muscle. This maternal strategy was also associated with a lower expression level of insulin-like growth factor 1 receptor (IGFR) but an upregulation of IGF2. This suggests an altered susceptibility of muscle cells to IGFs' signal in fetuses from treated sows. Altogether, intrauterine growth restriction impaired fetal muscle development, and restricted feeding followed by overfeeding of gestating sows did not allow small fetuses to recover normal contractile and metabolic characteristics.

Pertinent plasma indicators of the ability of chickens to synthesize and store lipids.

Excessive deposition of body fat is detrimental to production efficiency. The aim of this study was to provide plasma indicators of chickens' ability to store fat. From 3 to 9 wk of age, chickens from 2 experimental lines exhibiting a 2.5-fold difference in abdominal fat content and fed experimental diets with contrasted feed energy sources were compared. The diets contained 80 vs. 20 g of lipids and 379 vs. 514 g of starch per kg of feed, respectively, but had the same ME and total protein contents. Cellulose was used to dilute energy in the high-fat diet. At 9 wk of age, the body composition was analyzed and blood samples were collected. A metabolome-wide approach based on proton nuclear magnetic resonance spectroscopy was associated with conventional measurements of plasma parameters. A metabolomics approach showed that betaine, glutamine, and histidine were the most discriminating metabolites between groups. Betaine, uric acid, triglycerides, and phospholipids were positively correlated (r > 0.3; P < 0.05) and glutamine, histidine, triiodothyronine, homocysteine, and ß-hydroxybutyrate were negatively correlated (r < -0.3; P < 0.05) with relative weight of abdominal fat and/or fat situated at the top of external face of the thigh. The combination of plasma free fatty acids, total cholesterol, phospholipid, ß-hydroxybutyrate, glutamine, and methionine levels accounted for 74% of the variability of the relative weight of abdominal fat. On the other hand, the combination of plasma triglyceride and homocysteine levels accounted for 37% of the variability of fat situated at the top of external face of the thigh. The variations in plasma levels of betaine, homocysteine, uric acid, glutamine, and histidine suggest the implication of methyl donors in the control of hepatic lipid synthesis and illustrate the interplay between AA, glucose, and lipid metabolisms in growing chickens.

Mechanisms by which somatotropin decreases adipose tissue growth.

When growing pigs are treated daily with recombinantly derived porcine somatotropin (pST) for 30-60 d there is a dose-dependent decrease in lipid accretion. Maximal doses of pST can reduce lipid accretion by as much as 70%. The reduction in lipid accretion occurs because of a marked decrease in glucose transport and lipogenesis that is the result of a pST-dependent decrease in the ability of insulin to stimulate these processes in the adipocyte; lipolysis is not affected. The decrease in insulin sensitivity is not due to a decrease in insulin binding or insulin receptor kinase activity. Little is understood about the somatotropin (ST) intracellular signal pathway(s) that mediate the biological effects of ST. These effects are chronic rather than acute as was previously believed. This pattern likely reflects that ST decreases transcription of important insulin-responsive genes such as the muscle-adipose tissue transporter gene (GLUT4) and key lipogenic enzymes.

Influence of ovariectomy on metabolic and endocrine parameters during sexual development in the female pig.

During pubertal maturation, the increase in blood concentrations of sexual steroids is associated with a spurt in plasma IGF-I in primates, rats and cattle. However, data on the influence of sex steroids on plasma IGF-I during this physiological period are contradictory. Therefore, the present experiment was undertaken to understand better the relationships between pubertal development, energy metabolic regulation and the IGF-I/IGFBP system in crossbred gilts (Large White x Landrace). Circulating concentrations of hormones and metabolites were examined in ovariectomized (n = 6) and sham-operated females (n = 9) during sexual development. Surgery and first blood samplings were performed at 70 days of age. Growth curves were similar in ovariectomized and entire females. First oestrus and ovulation occurred between 178 and 209 days in entire gilts. From 84 days of age, plasma FSH concentration was lower in sham-operated than in ovariectomized gilts (P < 0.01) showing the negative feedback exerted by ovarian secretions on the gonadotrophin axis in entire gilts. Preprandial concentration of plasma glucose was not influenced by age whereas plasma free fatty acids decreased with age (P < 0.01). Concentrations of both metabolites were similar in ovariectomized and entire gilts. Plasma IGF-I and 43-39 kDa IGFBP levels increased whereas plasma 34 kDa IGFBP decreased with age (P < 0.01) and none of the levels differed between ovariectomized and entire gilts (P > 0.1). This experiment shows that gonadal steroids are not involved or play only a minor role in the control of IGF-I and IGFBP plasma levels during pubertal development in the female pig.

GH and insulin affect fatty acid synthase activity in isolated porcine adipocytes in culture without any modifications of sterol regulatory element binding protein-1 expression.

The ability of GH to decrease fatness and insulin-regulated events such as lipogenic enzyme activities is well known in pigs. Nevertheless, the precise mechanism underlying these actions has not been elucidated yet. Expression of the transcription factor sterol regulatory element binding protein (SREBP)-1 has been reported as a key mediator of insulin action in rat hepatocytes and adipose cell lines. The present study aimed to determine whether the regulation of lipogenesis by GH and/or insulin in porcine adipocytes also involved SREBP-1. Isolated adipocytes, obtained from perirenal or s.c. adipose tissue samples of female pigs (51+/-0.4 kg; n=17), were cultured in serum-free medium in the absence or presence of these hormones for up to 4 days. Glucose incorporation and fatty acid synthase activity were increased by insulin in a dose-dependent manner in adipocytes of both sites. The increase was maximal at 1.7 and 17 nM in s.c. and perirenal adipocytes respectively, suggesting inter-depot differences in the regulation of lipogenesis by insulin. These insulin-stimulated events were decreased by GH (1 nM). No change in SREBP-1 mRNA levels was observed in response to GH and/or insulin. Taken together, these data indicate that the regulation of lipogenesis by insulin and GH appears to not involve changes in SREBP-1 mRNA levels in porcine adipocytes.

Effect of GH administration on GH and IGF-I receptors in porcine skeletal muscle and liver in relation to plasma GH-binding protein.

The present study was undertaken to determine the effect of GH administration on GH and IGF-I receptors in skeletal muscle compared with liver in growing pigs. Plasma IGF-I and GH-binding protein (GHBP) levels were also determined. Twelve Large White pigs (castrated males) were treated daily with 100 micrograms pituitary porcine GH (pGH) per kg body weight or vehicle for 41 days intramuscularly. Relative to controls, pGH administration increased plasma IGF-I concentrations by 3.3-fold. Administration of pGH had no effect on plasma GHBP levels. In liver, 125I-labelled bovine GH (bGH)-specific binding (P < 0.05) and GH receptor (GHR) mRNA levels (P < 0.05) were higher in pGH-treated than in control pigs. In longissimus dorsi (LD), 125I-labelled bGH specific binding did not differ significantly between the two groups while GHR mRNA levels (P < 0.05) were lower in pGH-treated than in control pigs. Administration of pGH had no effect on 125I-labelled bGH-specific binding and GHR mRNA levels in trapezius (TR). 125I-Labelled IGF-I-specific binding in liver was unaffected by pGH administration. Similarly, in liver, LD and TR, IGF-I receptor mRNA levels were not different between pGH-treated and control animals. It can be concluded that (1) GH binding and IGF-I receptor mRNA are not affected by GH in skeletal muscle, (2) GH influences GHR in a tissue-specific manner and (3) hepatic GHR and GHBP levels are not co-regulated.

Ontogeny of GH receptor and GH-binding protein in the pig.

The present study was undertaken to examine the developmental pattern of GH receptor (GHR) and GHR gene expression in skeletal muscle (longissimus dorsi and trapezius (TR)) and liver from the last third of gestation until 1 year of age in male Large White (LW) and Meishan (MS) pigs. Plasma GH-binding protein (GHBP) levels were also measured. 125I-Labelled bovine GH (bGH) specific binding (not determined in foetal TR) and GHR mRNA were detected in skeletal muscle from 75 days of gestation until the adult stage with no clear age-related changes. By contrast, 125I-labelled bGH specific binding and GHR mRNA were undetectable or barely detectable in foetal liver. After birth, 125I-labelled bGH specific binding (P < 0.001) and GHR mRNA in liver increased with age. The level of bGH binding to liver membranes was higher in MS than in LW pigs at 1, 45, 80 and 120 days of age and did not differ between breeds at the other ages. Specific binding of 125I-labelled human GH (hGH) to plasma GHBP was easily detected as early as 75 days of gestation and increased with age (P < 0.001). The level of hGH binding to plasma GHBP was higher in MS than in LW pigs at 1, 80 and 120 days of age. It can be concluded that (1) the developmental expression of the GHR is tissue-specific, (2) the presence of GHBP in foetuses despite the absence of GHR in liver suggests that other tissues such as skeletal muscle could contribute to the generation of GHBP and (3) the presence of GHR in skeletal muscle as early as 75 days of gestation suggests that GH may play a role in foetal muscle growth.

Pharmacodynamic evaluation of a PEGylated analogue of human growth hormone releasing factor in rats and pigs.

The aim of this study was to assess the in vivo efficacy of monoPEGylated GRF(1-29)NH(2) having one PEG(5000) chains attached to either lysine 12 or 21 as compared to the GRF(1-29)NH(2) in rats and pigs. This analogue termed GRF-1PEG(5000) was tested after a single intravenous administration in rats and after a single intravenous or subcutaneous injection in pigs. After 1 h administration, GH concentrations returned to values close to controls in the group of rats injected with GRF(1-29)NH(2). In animals injected with the same dose of GRF-1PEG(5000), the AUC values corresponding to the whole period 0.5-48 h and particularly to the 0.5-8 h period were higher than in the placebo or in the GRF(1-29)NH(2) groups. Interestingly, two additional peaks were observed at about 6 and 8 h following administration. An increase in the response of the endogenous GH peaks was also observed in pigs administered GRF-1PEG(5000) by intravenous route. When GRF-1PEG(5000) was administered subcutaneously to pigs, a significant increase, as compared to placebo and GRF(1-29)NH(2,) in both GH and IGF-I levels was observed. This new analogue might find therapeutic application in paediatric growth hormone deficiency or in aging.

Regulation of development and metabolism of adipose tissue by growth hormone and the insulin-like growth factor system.

White adipose tissue plays a key role in the regulation of the energy balance of vertebrates. This tissue is also now recognized to secrete a variety of factors such as leptin, which is thought to be involved in the modulation of adipose mass. Unlike other tissues, adipose tissue mass has considerable capacity to expand. The review deals primarily on the regulation of development and metabolism of adipose tissue by growth hormone (GH) and the insulin-like growth factor (IGF) system, with a special focus on the pig. The anti-insulin effects of GH are well-documented in pigs as in other species. In vitro exposure of adipose precursor cells to GH leads to a decrease in differentiation of those cells in pigs, in contrast to data obtained in murine cell lines. In vivo treatment and prolonged in vitro incubation of adipose tissue or isolated adipocytes with GH result in a decrease in glucose transport and lipogenesis, especially at the level of the fatty acid synthase gene, resulting in a reduction of the lipid content and adipose tissue mass. The mechanism by which GH antagonizes insulin stimulation of lipogenesis is still unresolved, as it is not mediated by protein kinase A, protein kinase C and Janus kinase-2 at the signaling level, or upstream stimulatory factor 1 or sterol regulatory element binding protein-1 at the transcriptional level. GH is apparently the main regulator of IGF-I mRNA expression in adipose tissue, however, the effects of IGF-I on this tissue are rather unclear.