Adipose tissue, longissimus muscle and anterior pituitary growth and function in clenbuterol-fed heifers

The present study was conducted to determine the effects of feeding clenbuterol on adipose tissue and longissimus muscle growth in heifers. For 50 d, 14 heifers were fed either a sucrose-based, clenbuterol supplement or a placebo in which the clenbuterol had been omitted. The heifers were slaughtered in two groups, based on initial weight. Adipose tissue from several anatomical sites and longissimus muscle (depending on slaughter group) were obtained fresh at slaughter. Changes in carcass characteristics elicited by clenbuterol were similar to those reported by others for steers and sheep. Subcutaneous (sc) and intramuscular (im), but not perirenal, adipocytes were smaller and there were more cells per g tissue in the adipose tissue depots of the clenbuterol-fed heifers. Clenbuterol decreased lipogenic enzyme activities, fatty acid-binding protein activity, basal lipolysis and acetate incorporation into glyceride-fatty acids (P less than .05) in sc adipose tissue, but had no effect (P greater than .05) on lipogenesis or lipolysis in im adipose tissue. Clenbuterol elicited a 20% increase in type II myofiber diameters (P less than .05) but had no effect on type I myofiber diameters. In vitro growth hormone release by perifused anterior pituitaries was not affected significantly by long-term in vivo exposure to clenbuterol. These data indicate that a depression in lipogenesis is the mechanism by which clenbuterol decreases subcutaneous fat accretion in cattle.     

Muscle metabolism and real-time ultrasound measurement of muscle and subcutaneous adipose tissue growth in lambs fed diets containing a beta-agonist

Rambouillet X Finn crossbred wether lambs were evaluated for differences in longissimus muscle cross-sectional area and overlaying subcutaneous adipose tissue thickness resulting from the use of the beta-agonist clenbuterol. Treatment groups received 0 and 2 ppm clenbuterol in the diet for approximately 40 d prior to slaughter. Longissimus muscle cross-sectional area and fat depth over the 12th-13th rib juncture were measured by real-time ultrasound before and during administration of the compound. At slaughter, muscle metabolism in vitro and carcass characteristics were measured. Based on comparisons with an initial-kill group of sheep, longissimus muscle cross-sectional area increased in control sheep by 12% (P greater than .05) over the 40-d experimental period, and increased in clenbuterol-fed sheep by 48% (P less than .05). Conversely, subcutaneous fat thickness increased significantly in the control sheep (88%) during this period, but was unchanged in the clenbuterol-fed animals. Warner-Bratzler shear force values of cooked longissimus samples from clenbuterol-fed sheep were significantly greater than shear force values in cooked samples from control lambs; this was not correlated with the extractable neutral lipid content of the muscle. Simple linear regression between ultrasound and carcass measurements of longissimus muscle cross-sectional area and subcutaneous fat thickness yielded correlation coefficients of .80 and .64, respectively. A significantly greater amount of net glycogen synthesis from [U-14C]glucose was observed in longissimus muscle strips from clenbuterol-fed animals than in muscle strips from control sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adipose tissue cellularity and muscle growth in young steers fed the beta-adrenergic agonist clenbuterol for 50 days and after 78 days of withdrawal

Angus steers (n = 40; approximate weight = 300 kg) were administered the beta-adrenergic agonist clenbuterol for 50 d (7 mg.hd-1.d-1), followed by a 78-d withdrawal period. Carcass fatness variables did not differ (P greater than .05) between treated and control animals either after 50 d or after 128 d. Weights of the 9-10-11th rib longissimus muscle were 25% larger, and longissimus cross-sectional areas were 28% greater, in clenbuterol-fed steers relative to controls from 0 to 50 d (P less than .05). After withdrawal these measurements increased no further in the treated steers. Marbling scores were decreased (P less than .05) in clenbuterol-fed steers after 50 d of treatment; this effect persisted after 128 d of withdrawal from treatment. Shear force values were increased 19% (P less than .05) by feeding clenbuterol for 50 d and remained greater (P less than .05) in treated animals after 128 d. Subcutaneous adipocytes in clenbuterol-fed steers were smaller (P less than .05) than those of controls after 50 d, and this effect was still apparent after the 78-d withdrawal period. Rates of lipogenesis did not differ (P less than .05) between treated and control animals at any time. Perirenal (p.r.) adipocytes were smaller (P less than .05) in treated animals after 50 d, but this effect disappeared by the end of the experiment. There was no indication of a bimodal distribution of smaller s.c. or p.r. adipocytes in either of the treatment groups. Apparent hyperplasia of s.c. adipocytes occurred in the area of the 9-10-11th rib in both treated (P less than .10) and control animals (P less than .05) from 0 to 50 d on trial. Within treated animals there was a significant increase (P less than .05) in total adipocytes in this depot during the withdrawal period. Although the effects of clenbuterol on muscle growth generally were reversed after 78 d, the effects of the beta-adrenergic agonist on adipose tissue development were more permanent.     

Comparison of plasma free-fatty-acid and blood-glycerol concentrations with measurement of lipolysis in porcine adipose tissue in vitro

Rates of adipose tissue lipid metabolism in vitro are often measured to evaluate the function in vivo of metabolic pathways and thus appraise the accretion or loss of depot fat. This study directly addressed the comparison of degradative metabolism in vitro and in vivo. The concentrations of plasma free-fatty-acids and blood-glycerol as putative representatives of lipolysis in vivo and the lipolytic rate in adipose tissue in vitro obtained at the time of blood sampling were both measured in the same pig. Concentrations of plasma free-fatty-acids and blood-glycerol were increased or decreased by infusion of the norepinephrine analog, isoproterenol or by infusion of the adrenergic antagonist, propranolol, respectively. Although lipolytic rates and sensitivity to isoproterenol in vitro changed during some acute hormonal manipulations of the pig, the modulation in vitro was usually small relative to the large changes observed in plasma free-fatty-acid and blood-glycerol concentrations. Some of the subtle changes in vitro may reflect biological responses to hormone infusion, e.g., desensitization of the response to adrenergic agonists, but the magnitude of rate changes in vitro negates prediction of the rates in vivo from rates in vitro. Extrapolation of lipolytic rates in vitro and several adipose tissue anabolic rates obtained from the literature indicate the improbability for prediction of rates and degree of fat accretion in pigs from metabolic rates in vitro.     

Effect of beta-adrenergic agonists on lipolysis and lipogenesis by porcine adipose tissue in vitro

The effects of the beta-adrenergic agonists isoproterenol, cimaterol, ractopamine and clenbuterol on lipolysis (release of glycerol and free fatty acids) and lipogenesis (incorporation of 14C into fatty acids from [14C]glucose) was examined in porcine adipose tissue explants in vitro. Lipolysis was stimulated by isoproterenol, cimaterol or ractopamine but not by clenbuterol. Insulin reduced the lipolytic effects of the beta-adrenergic agonists (isoproterenol, cimaterol and ractopamine). Lipogenesis was inhibited by all beta-adrenergic agonists tested (isoproterenol, cimaterol, ractopamine and clenbuterol). The antilipogenic effect of the beta-adrenergic agonists was reduced by the presence of insulin in the incubation. Although effects of the different beta-adrenergic agonists varied, all had some direct effects that could be expected to reduce adipose accretion. Effects of beta-adrenergic agonists in the pig are due in part to direct effects on adipose tissue.     

Acute changes in blood flow in pigs infused with beta-adrenergic agonists

Previous results indicate that clenbuterol decreases carcass adipose tissue accretion when administered to pigs but does not appear to stimulate the adipose tissue beta-adrenergic receptor. Clenbuterol increases plasma free fatty acid concentration when acutely infused in vivo, suggesting an indirect affect. One possible indirect effect is that clenbuterol could change blood flow to adipose tissue. Blood flow was measured with radiolabeled microspheres in tissues from pigs before and after infusion of a beta-adrenergic agonist for 30 min. High probability levels (up to P less than .2) were used to indicate trends due to extreme variability. Infusion of isoproterenol increased heart rate, plasma free fatty acid concentration and blood flow at many adipose tissue sites and at a few skeletal muscle sites. Infusion of isoproterenol decreased blood pressure. Infusion of clenbuterol increased heart rate and tended to increase blood flow to several skin and adipose tissue sites slightly. The results suggest that increased adipose tissue blood flow may contribute to the accelerated release of free fatty acids when clenbuterol is infused acutely in vivo.     

Carcass composition and adipose tissue metabolism in growing sheep

Experiments were conducted to investigate biological variables that influence fat accretion in growing ram lambs. Carcass composition and adipose tissue development were measured in Columbia-sired ram lambs from 32.0 to 73.9 kg body weight. Five or six ram lambs were slaughtered every 2 mo, from 4 to 10 mo of age. The percentage of carcass fat-free dry matter decreased with age from 30.9 to 27.5% (P less than .05), while the percentage of carcass fat increased from 17.7 to 33.4%. Similarly, offal fat-free dry matter decreased with age (from 24.5 to 21.5), and there was nearly a threefold increase in the percentage of offal fat (P less than .05 for both measures). Subcutaneous adipocyte diameter and lipogenesis in vitro increased from 4 to 6 mo of age, and did not increase further with age. A bimodal distribution of adipocytes was apparent in the 4-mo-old lambs, but was not observed in any other age group. The presence of glucose in incubation media stimulated acetate incorporation into fatty acids in vitro in adipose tissue from 8- and 10-mo-old lambs. However, glucose did not affect the rate of lipogenesis from lactate. The data indicate early, rapid increases in carcass fat accretion, which corresponded to similar increases in lipogenesis and lipogenic enzyme activities.     

Effect of cimaterol on sheep adipose tissue lipid metabolism

Effects of dietary cimaterol (5 mg/kg) on adipose tissue metabolism of wether lambs were studied. Lipogenesis, lipolysis, fatty acid composition and adipocyte size and number were measured. Cimaterol feeding increased lipogenesis; however, this effect was not statistically significant. Insulin (1,000 microU/ml) stimulated lipogenesis of adipose tissue from control sheep. However, this elevated rate was abolished by in vitro cimaterol. Insulin had no stimulatory effect on lipogenesis in cimaterol-fed sheep. Lipolysis was depressed by cimaterol feeding. However, 10(-4) M cimaterol stimulated lipolysis in the adipose tissue from both control and cimaterol-fed sheep. Insulin inhibited stimulated lipolysis in adipose tissue from control sheep but had no effect on the stimulated lipolysis in cimaterol-fed sheep. Mean adipocyte diameter was smaller (from 74 to 70 microns) and adipocyte size distribution also was changed in the cimaterol-fed sheep. Adipocyte number per gram of tissue was not affected by cimaterol. There was a significant increase in percentage of unsaturated fatty acids in adipose tissue from cimaterol-fed sheep. These results indicate that lipogenic and lipolytic responses to insulin and cimaterol in sheep adipose tissue were altered by cimaterol feeding. The carcass fat content decrease in cimaterol-fed sheep may be attributed to the reduction in adipocyte size.     

Effect of clenbuterol on growth,nitrogen and energy balances and endocrine status in food-restricted sheep

The aim of this study was to examine the effect of the beta2-adrenoceptor clenbuterol on food-restricted sheep. Clenbuterol was administered as a dietary admixture (4 mg/ kg diet) to a group of male Serra da Estrela sheep (n = 6). The animals were housed individually in metabolic cages and fed for 45 days at 65% of estimated requirement for energy maintenance. An untreated group with the same energy intake level was included as a control. Changes in body mass, nitrogen and energy balances and insulin, insulin-like growth factor (IGF-1), and triiodothyronine (T3 ) levels in the experimental animals were monitored. During the 4th week of the trial, clenbuterol-treated sheep showed increased mass gains, greater energy retention and serum IGF-1 levels and decreased T3 serum concentrations. This study showed that clenbuterol may induce a protective effect in sheep subjected to periods of food deprivation, based on the body mass and digestible energy effects manifested by treated animals.     

饲养方式对滩羊羔羊肌肉及脂肪组织中脂肪酸组成的影响

为探究饲养方式对滩羊羔羊肌肉和脂肪组织中脂肪酸组成的影响,试验选择24只健康且体重相近（14.16 kg±0.58 kg）的2月龄滩羊羔羊随机分成舍饲组和放牧组,每组12只,于4月龄屠宰取其背最长肌、股二头肌、膈肌、皮下脂肪、肾周脂肪、尾部脂肪,用气相色谱仪测定脂肪酸含量。结果表明：①在肌肉组织饱和脂肪酸中,与放牧组相比,舍饲组滩羊羔羊股二头肌丁酸、棕榈酸含量显著提高（P<0.05）,膈肌辛酸、月桂酸、肉豆蔻酸含量显著降低（P<0.05）。在肌肉组织不饱和脂肪酸中,与放牧组比较,舍饲组滩羊羔羊背最长肌棕榈油酸、花生四烯酸含量显著降低（P<0.05）,γ-亚麻酸、α-亚麻酸含量显著提高（P<0.05）,二十碳五烯酸（EPA）、n-3多不饱和脂肪酸（n-3 PUFA）极显著提高（P<0.01）;股二头肌花生四烯酸含量显著降低（P<0.05）,十七碳一烯酸、α-亚麻酸、EPA、n-3 PUFA含量极显著提高（P<0.01）;膈肌棕榈油酸含量显著降低（P<0.05）。②在脂肪组织饱和脂肪酸中,与放牧组比较,舍饲滩羊羔羊皮下脂肪十一碳酸、十五碳酸含量显著降低（P<0.05）,十三碳酸含量极显著降低（P<0.01）;肾周脂肪葵酸、肉豆蔻酸含量显著降低（P<0.05）,丁酸、硬脂酸含量极显著提高（P<0.01）;尾脂十一碳酸含量显著降低（P<0.05）。在脂肪组织不饱和脂肪酸中,与放牧组比较,舍饲滩羊羔羊皮下脂肪十八碳二烯酸含量极显著提高（P<0.01）,肉豆蔻油酸、棕榈油酸、γ-亚麻酸含量极显著降低（P<0.01）;肾周脂肪十八碳一烯酸、α-亚麻酸、n-3PUFA含量显著提高（P<0.05）,肉豆蔻油酸含量显著降低（P<0.05）,十七碳一烯酸、二十碳二烯酸、十八碳二烯酸含量极显著提高（P<0.01）;尾脂肉豆蔻油酸、棕榈油酸含量显著降低（P<0.05）,十八碳二烯酸含量极显著提高（P<0.01）。综上,不同饲养方式对滩羊羔羊肌肉和脂肪组织脂肪酸含量存在一定影响,舍饲滩羊羔羊股二头肌中饱和脂肪酸含量及肾周脂肪中不饱和脂肪酸含量显著高于放牧滩羊羔羊。     

Clenbuterol-induced desensitization in murine adipocytes: relationship to in vivo effectiveness

In vitro lipolytic response of isolated murine fat cells to epinephrine (EPI) or clenbuterol (CB) was used to evaluate the potential for the beta 2-adrenergic agonist, CB, to induce cellular resistance to further beta-adrenergic stimulation. Feeding CB (20 mg/kg diet) to mice for 1, 3 or 6 wk decreased adipocyte sensitivity to EPI or CB by 35-45%, with no differences in magnitude of this desensitization across time. Basal and maximal rates of lipolysis were similar for control- and clenbuterol-fed mice. In agreement with the feeding studies, a 2 hr preincubation of control-fat tissue with either 10 microM EPI or 100 microM CB, followed by adipocyte isolation and restimulation with EPI, reduced adipocyte sensitivity by 50%. In addition, maximal rates of lipolysis were decreased 24% and 34% for EPI and CB treated tissue, respectively. The similar adaptive responses of the adipocytes to CB exposure in vivo or in vitro suggest that CB interacts directly with fat cells in vivo and can induce tolerance. Mice fed CB for 12 wk had 33% smaller epididymal fat pads compared to controls, but pad weight differences were only 10% if feeding of CB was discontinued 1 wk before the 12 wk analysis. The reversal in fat pad gain with a 1 wk removal of CB from the diet indicates at least partial effectiveness of CB through 12 wk. The modest beta-adrenergic desensitization established by wk 1 was similar on wk 6 suggesting that CB-induced adipocyte resistance is of little consequence to the fat-reducing properties of CB administration.     

beta-Adrenergic receptor agonists increase apoptosis of adipose tissue in mice

beta-Adrenergic receptor (beta-AR) agonists increase muscle mass and decrease body fat in rodents and livestock. With oral administration, however, the effects of beta1-AR and beta2-AR can be different, depending on the species tested. We tested the effects of clenbuterol, a beta2-AR agonist, and ractopamine, a beta1/beta2-AR agonist, on growth, adiposity and adipose tissue apoptosis in male and female mice by feeding diets containing control, 200 ppm clenbuterol, or 200 or 800 ppm ractopamine. Food intake (FI) was measured daily; body weight (BW) and temperatures (BT) were measured on days 0, 3, 7, 10, 14, 17, and 20. On day 21 mice were sacrificed, body composition was determined using PIXImus densitometry, and muscle and adipose tissues were collected. There were no treatment effects on BT, FI, BW, feed efficiency or body composition. Retroperitoneal (Rp) and epididymal/parametrial (Epi/Par) fat pad masses were reduced in both 800 ppm ractopamine (40+/-3mg and 207+/-20mg, respectively) and clenbuterol (35+/-7 mg and 211+/-22 mg) treated mice compared to control (66+/-8 mg and 319+/-30 mg, P<0.05). Brown adipose tissue (BAT) mass was greater (P<0.05) in clenbuterol treated mice compared to other treatments. Adipose tissue apoptosis (% DNA fragmentation) was increased in Epi/Par fat pads in clenbuterol (5.2+/-1.1%) and 800 ppm ractopamine (4.1+/-0.8%) treated mice compared to control (1.7+/-0.4%, P<0.05). These findings show that WAT apoptosis can be induced by activation of beta-AR in mice, although the mechanism is unknown.     

玉米RNA对小鼠脂肪沉积的影响

本试验旨在探讨玉米RNA对小鼠脂肪沉积的影响。将20只28日龄C57BL/6J小鼠随机分为2组,每组10个重复,每个重复1只小鼠。对照组灌服生理盐水,试验组灌服玉米RNA(100μg/d),试验期4周。试验结束时检测小鼠的生长性能、血清生化指标、体组成、体成像、器官指数及脂肪相关基因的表达。结果显示:试验组小鼠体重和附睾脂肪组织指数显著低于对照组(P<0.05),且整体脂肪含量明显减少,表明小鼠脂肪沉积减少。血脂检测结果显示,与对照组相比,试验组血清球蛋白(GLB)含量显著增加(P<0.05),高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)和总胆固醇(TC)含量极显著增加(P<0.01);脂肪相关基因检测结果显示,与对照组相比,试验组脂肪合成相关基因脂肪酸合成酶(FAS)和CCAAT增强子结合蛋白α(C/EBP-α)mRNA相对表达量极显著上调(P<0.01),过氧化物酶体增殖剂激活受体-γ(PPAR-γ)及脂肪分解基因脂肪甘油三酯脂肪酶(ATGL)和激素敏感脂酶(HSL)mRNA相对表达量显著上调(P<0.05),表明小鼠脂肪合成和脂肪分解增加。综上所述,玉米RNA能同时促进小鼠脂肪合成代谢和脂肪分解代谢,最终抑制脂肪沉积,为植物源核酸调控动物脂肪沉积影响因素的探索提供新证据。     

Effect of dietary clenbuterol and cimaterol on muscle composition, beta-adrenergic and androgen receptor concentrations in broiler chickens

Illegal dietary supplementation with beta(2)-agonists has been shown to increase protein deposition and decrease fat accretion in domestic animals. In poultry the metabolic and endocrine responses to beta(2)-agonists are not fully elucidated. In this trial the effects of dietary clenbuterol (1 p.p.m.) and cimaterol (1 p.p.m.) on muscle composition and endocrine response of male broiler chickens were studied. Dietary clenbuterol induced a slight, but in general not significant, improvement of zootechnical performances and carcass yields. Chemical composition of muscle was not influenced by dietary treatments, even if a slight improvement of protein content was observed in treated groups. No effects on fatty acid composition of meat were detected. Both clenbuterol and cimaterol treatments caused a downregulation in testicular androgen receptors and in pulmonary, cardiac and central nervous system beta-adrenergic receptors.     

不同日龄阿勒泰大尾羊脂肪组织形态学及血脂指标的比较

为了研究阿勒泰大尾羊不同部位脂肪组织沉积的变化规律,本试验选取90和270日龄健康、雄性阿勒泰大尾羊各6只,分别采集了90和270日龄时肾周脂、尾脂、腹部皮下脂肪组织样和血清,采用冰冻脂肪组织切片油红O滴染技术和Motic显微数字图像处理系统,测定脂肪细胞面积,并采用放射性免疫技术和酶联免疫法测定了血脂指标.结果显示,90日龄时,阿勒泰大尾羊尾脂脂肪细胞面积极显著高于肾周脂脂肪细胞面积(P<0.01),270日龄时,尾脂和腹部皮下脂肪脂肪细胞面积均极显著高于肾周脂脂肪细胞面积(P<0.01),但脂肪细胞的面积在尾脂和皮下脂肪之间无显著差异(P>0.05);与90日龄相比,270日龄阿勒泰大尾羊肾周脂脂肪细胞面积显著增高(P<0.05),而尾脂脂肪细胞面积极显著降低(P<0.01);90日龄阿勒泰大尾羊血清中leptin和HSL含量极显著高于270日龄(P<0.01),而血清中AST和ALT含量极显著低于270日龄(P<0.01).结果表明,阿勒泰大尾羊从90日龄生长至270日龄时,肾周脂脂肪细胞面积呈增加的趋势,而尾脂脂肪细胞的面积呈减少的趋势,这种变化可能与血清瘦素、激素敏感脂肪酶、天门冬氨酸氨基转氨酶和丙氨酸氨基转移酶含量有关.     

Adipose tissue angiogenesis

A review of adipose tissue angiogenesis includes the morphological and cytochemical development of adipose tissue vasculature and the concept of primitive fat organs. Spatial and temporal relationships between fetal vascular and fat cell development are discussed, including depot- and genetic-dependent arteriolar differentiation. The relationship between connective tissue deposition and elaboration of adipose tissue vasculature is discussed with respect to regulating adipocyte development in a depot-dependent manner. In vitro studies indicated that depot-dependent vascular traits may be attributable to intrinsic growth characteristics of adipose tissue endothelial cells. These studies indicate that adipogenesis may be regulated by factors that drive angiogenesis. Fundamental aspects of angiogenesis, including basement membrane breakdown, vasculogenesis, angiogenic remodeling, vessel stabilization, and vascular permeability were reviewed. Critical angiogenic factors include vascular endothelial growth factor (VEGF), VEGF receptors, angiopoietins (Ang), ephrins, matrix metalloproteinases, and the plasminogen enzymatic system. Vascular endothelial growth factor is the most critical factor because it initiates the formation of immature vessels and disruption of a single VEGF allele leads to embryonic lethality in mice. Expression of VEGF is influenced by hypoxia, insulin, growth factors, and several cytokines. Angiogenic factors secreted and/or produced by adipocytes or preadipocytes are discussed. Vascular endothelial growth factor expression and secretion by adipocytes is regulated by insulin and hypoxia, and is associated with adipose tissue accretion. Vascular endothelial growth factor accounts for most of the angiogenic activity of adipose tissue. The proposed role of leptin as an adipogenic factor is reviewed with respect to efficacy on various aspects of angiogenesis relative to other angiogenic factors. The VEGF and leptin genes are both hypoxia inducible, but potential links between VEGF and leptin gene expression have not been examined. Finally, several studies including a study of mice treated with antiangiogenic factors indicate that adipose tissue accretion can be controlled through the vasculature per se.     

多浪羊与小尾寒羊皮下脂肪组织转录组分析

旨在探索多浪羊（D组）与小尾寒羊（X组）皮下脂肪组织中的特异性表达基因,并研究其潜在的作用,为理解绵羊脂肪组织发育规律以及对脂代谢相关疾病的预防和治疗研究提供依据。本研究选取脂肪沉积能力存在差异、健康无病、体况良好、种内个体体重相近（约50 kg）的雌性成年多浪羊和小尾寒羊为试验材料,分为D组（试验组）和X组（对照组）,每组3个重复,采集位于背最长肌的皮下脂肪组织,应用RNA-Seq技术和生物信息学方法进行转录组测序并对结果进行分析。以|Fold change|≥2,P adjust≤0.05为标准筛选差异表达基因,通过对差异表达基因进行GO功能注释和KEGG通路富集分析,得到与脂肪沉积和脂代谢有关的差异基因。为了验证测序数据的可靠性,本研究随机选取了6个差异表达基因进行qRT-PCR验证。结果显示,在6个样本中共检测到38 672个已知的mRNAs,新的mRNAs为1 606个,在两组中共有839个差异表达基因,其中有320个差异基因在多浪羊组中上调表达,有519个差异基因在多浪羊组中下调表达。通过GO功能注释分析发现,差异表达基因主要参与脂质分解代谢过程、脂质生物合成过程、脂质分解代谢负调控过程、MAPK级联反应调控、对甘油三酯的反应等生物学过程。KEGG通路富集结果显示,差异表达基因显著富集到了PI3K-Akt、MAPK、胰岛素以及PPAR等信号通路中。qRT-PCR结果与测序结果一致,表明测序结果可靠。通过对多浪羊和小尾寒羊皮下脂肪组织进行转录组测序以及生物信息学分析,筛选到与脂肪沉积和脂代谢相关的差异表达基因,这些基因主要参与脂质生物合成、脂质代谢等过程,其中COL1A1、AKT2、SCD、LPL、PCK1与PPP2R5A可能在多浪羊与小尾寒羊的皮下脂肪组织的沉积与代谢中发挥重要作用。     

Acute and long-term lipogenic response to insulin and clenbuterol in bovine intramuscular and subcutaneous adipose tissues

The present study was conducted to determine whether insulin and clenbuterol affected either short-term (2-h) incubations or long-term (48-h) tissue cultures of i.m. and s.c. adipose tissue explants. Samples were taken from control steers and steers fed 7 mg.head-1.d-1 clenbuterol for 50 d, after which time the drug was withdrawn from the diet for 90 d prior to slaughter. Neither short-term incubations nor long-term explant cultures contained bovine serum albumin (BSA). Insulin (6.67 x 10(-9) M) had no effect (P greater than .05) on lipogenesis in s.c. and i.m. adipose tissue in 2-h tissue incubations of fresh adipose tissue. There was a substantial decrease in activity during the culture period, which was ameliorated somewhat in s.c. adipose tissue by the presence of insulin in the culture media. Clenbuterol exposure for 48 h in vitro decreased the production of lipids from acetate in both adipose tissue depots but had no effect in short-term adipose tissue incubations. Results from the present study confirm that omitting BSA from incubation media does not enhance the responsiveness of bovine s.c. adipose tissue or the less mature i.m. adipose tissue to insulin. Insulin may maintain greater cell viability in 48-h explant cultures.     

Adipose tissue lipolytic rate in genetically obese and lean swine

In vitro lipolytic rate was determined in adipose tissue from genetically obese and lean pigs. There were about 20 pigs/genetic strain at 25 and 80 kg and 10 pigs/strain at 50 kg body weight. When expressed on a cellular basis, the in vitro adipose tissue basal (no exogenous hormone) lipolytic rate was similar in obese and lean pigs at 25 and 50 kg body weight. At 80 kg body weight the basal rate was greater in obese than in lean pigs. The in vitro adipose tissue epinephrine-stimulated lipolytic rate expressed on a cell basis was greater at 25 kg, was similar at 50 kg body weight and tended (P less than or equal to .1) to be greater at 80 kg in obese compared with lean pigs. The in vitro sensitivity of lipolysis to epinephrine was slightly greater in lean compared with obese pigs. The data obtained in vitro indicate that obese pigs do not have low adipose tissue lipolytic rates compared with lean pigs. Consequently, adipose tissue lipolysis does not appear to be a major metabolic factor leading to the excessive fat accretion in these obese pigs.     

Side effects of clenbuterol as a repartitioning agent

Clenbuterol, a synthetic beta-adrenergic agonist drug, can be used to increase the ratio of protein to fat in the carcase of meat animals. During the first one to three days of its administration to sheep or calves clenbuterol increased their heart rate, and in sheep it decreased blood pressure. Continued administration had no further effect on heart rate or blood pressure but in sheep dose levels above 1.5 mg/day depressed appetite for up to five days; at all dose levels clenbuterol brought about a long term increase in metabolic rate.