Biology of leptin in the pig

The recently discovered protein, leptin, which is secreted by fat cells in response to changes in body weight or energy, has been implicated in regulation of feed intake, energy expenditure and the neuroendocrine axis in rodents and humans. Leptin was first identified as the gene product found deficient in the obese ob/ob mouse. Administration of leptin to ob/ob mice led to improved reproduction as well as reduced feed intake and weight loss. The porcine leptin receptor has been cloned and is a member of the class 1 cytokine family of receptors. Leptin has been implicated in the regulation of immune function and the anorexia associated with disease. The leptin receptor is localized in the brain and pituitary of the pig. The leptin response to acute inflammation is uncoupled from anorexia and is differentially regulated among swine genotypes. In vitro studies demonstrated that the leptin gene is expressed by porcine preadipocytes and leptin gene expression is highly dependent on dexamethasone induced preadipocyte differentiation. Hormonally driven preadipocyte recruitment and subsequent fat cell size may regulate leptin gene expression in the pig. Expression of CCAAT-enhancer binding protein (C/EBP) mediates insulin dependent preadipocyte leptin gene expression during lipid accretion. In contrast, insulin independent leptin gene expression may be maintained by C/EBP auto-activation and phosphorylation/dephosphorylation. Adipogenic hormones may increase adipose tissue leptin gene expression in the fetus indirectly by inducing preadipocyte recruitment and subsequent differentiation. Central administration of leptin to pigs suppressed feed intake and stimulated growth hormone (GH) secretion. Serum leptin concentrations increased with age and estradiol-induced leptin mRNA expression in fat was age and weight dependent in prepuberal gilts. This occurred at the time of expected puberty in intact contemporaries and was associated with greater LH secretion. Further work demonstrated that leptin acts directly on pituitary cells to enhance LH and GH secretion, and brain tissue to stimulate gonadotropin releasing hormone secretion. Thus, development of nutritional schemes and (or) gene therapy to manipulate leptin secretion will lead to practical methods of controlling appetite, growth and reproduction in farm animals, thereby increasing efficiency of lean meat production.     

Effect of a short duration feed withdrawal followed by full feeding on marbling fat in beef carcasses

The effect of feed withdrawal for 48 h, prior to initiation of the finishing (fattening) period (75 d) on carcass marbling fat was studied in 120 European × British cross-bred heifers with an average weight of 585 ± 39 kg. Heifers were randomized in a 2 × 2 factorial design experiment with two dietary management treatments, where half the heifers were provided the feed components of steam rolled barley and barley silage either free choice or as a total mixed ration (TMR) containing 87% steam rolled barley and 13% barley silage with ad libitum vitamins and minerals via salt blocks for all animals. Within each dietary management treatment, 30 heifers were denied feed (water was available) for 48 h prior to the two week adaptation to the high grain diet preceding the 75 d finishing period. At the end of the 48 h feed denial blood samples were collected from the jugular vein prior to feeding for determination of glucose and insulin concentrations, which indicated that 48 h feed withdrawal consistently decreased (P = 0.0001) plasma concentrations of both glucose and insulin but the ratios of the concentrations of glucose to insulin were not affected. At slaughter samples of subcutaneous fat from the brisket (BF) and skirt muscle (pars costalis diaphragmatis; PCD) were procured for determination of chemical fat content, fat dissected from the muscle and for enumeration of adipocytes, less than 35 μm in diameter and to determine the average cell size in the dissected fat and from the BF by flow-cytometry of adipocytes fixed in osmium tetroxide. The carcass characteristics were also obtained. Although no differences due feed withdrawal for 48 h were evident for carcass weight, percent lean (saleable) meat yield, rib eye area, average fat cover, fat content of PCD or BF, the US marbling score was increased (P = 0.048) and the amount of dissected fat from the muscle tended to be higher (P = 0.107), thus 81% of the carcasses graded “US Choice” or “Canada AAA,” or displayed at least a “small” amount of intramuscular fat as compared (P = 0.0807) to 68% of the heifers not denied feed. Based on more than three years of weekly prices of carcasses that graded “Canada AAA” and “Canada AA,” these experimental results suggested that the expected price of a finished heifer could increase by $4.61 Canadian if a 48 h feed withdrawal was imposed prior to initiation of the finishing phase. Although significant differences in adipocyte numbers due to a single time 48 h feed withdrawal prior to initiation of the finishing phase were not detected, the carcass quality factors were affected leading to an odds ratio of 1.84 times in favour of cattle carcasses to grade “Canada AAA” than if fed continuously.     

脂肪细胞定向和分化因子1(ADD1)基因的研究进展

脂肪细胞定向和分化因子1(ADD1)是重要的核转录因子。ADD1不但是脂肪分化过程中重要的转录因子,同时还可以调控与脂肪代谢相关酶基因的表达。在人类和老鼠的研究发现ADD1基因与肝脏、脾脏等非脂肪组织的脂肪沉积有明确的连锁关系。实验研究提示:ADD1基因可能是影响动物肉质性状和屠体性状的候选基因。     

Anti-diabetic effects of emodin involved in the activation of PPARγ on high-fat diet-fed and low dose of streptozotocin-induced diabetic mice

Rheum palmatum Linn has been widely applied in the clinical treatment of diabetes mellitus. It has been found that emodin as the major bioactive component of R. palmatum L exhibits the competency to activate peroxisomal proliferator-activated receptor-γ (PPARγ) in vitro. So the aim of this study was to evaluate the anti-diabetic effects of emodin through the activation of PPARγ on high-fat diet-fed and low dose of streptozotocin (STZ)-induced diabetic mice. The diabetic mice were intraperitoneally injected with emodin for three weeks. No changes of food consumption and the body weight in emodin-treated mice were monitored daily during the entire experiment. At the end of experiment, the levels of blood glucose, triglyceride and total cholesterol in serum were significantly decreased after emodin treatment. However, serum high-density lipoprotein cholesterol (HDLc) concentration was significantly elevated. The glucose tolerance and insulin sensitivity in emodin-treated group were significantly improved. Furthermore, the results of quantitative RT-PCR analysis showed that emodin significantly elevated the mRNA expression level of PPARγ and regulated the mRNA expressions of LPL, FAT/CD36, resistin and FABPs (ap2) in liver and adipocyte tissues. No effects on the mRNA expressions of PPARα and PPARα-target genes were observed. Taken together, the results suggested that the activation of PPARγ and the modulation of metabolism-related genes were likely involved in the anti-diabetic effects of emodin.     

CEBPA基因的生物学效应及其在畜禽生产中的研究进展

增强子结合蛋白α(CEBPA)是CCAAT/增强子结合蛋白家族中的一员,CEBPA基因对脂肪细胞分化、发育和脂肪沉积有重要作用。在人类中,CEBPA基因异常表达可能导致肥胖、糖尿病以及白血病等疾病;在畜牧生产上,CEBPA基因的表达对牛、羊、猪和禽类的生长与脂肪沉积有重要影响。本文对CEBPA基因的分布、结构和功能进行总结,并对近几年CEBPA基因在疾病和畜禽生产方面的研究进展进行综述。     

用脂肪细胞膜免疫技术提高猪胴体品质

为了在满足动物营养需要和有效控制疫病的基础上进一步提高动物生产体系的经济效益，满足市场不断变化的需求，一直在探索和发展新的促进动物生长和提高胴体品质的技术手段。在认识到激素类制剂的残留和危害后，一种更新的非激素途径——脂肪细胞膜免疫技术日益受到关注。它高效、安全和作用持久的特点成为具有广泛研究和应用前景的新技术。     

不同经济类型猪种脂肪细胞的发育及其脂肪合成能力的比较研究

通过脂肪组织固定技术，将脂肪组织分离为体积不同的脂肪细胞，发现不同经济类型的猪种在不同年龄阶段其脂肪细胞的生长发育过程存在明显差异。肥胖型香猪的脂肪沉积在５￣８月期间是由脂肪细胞的肥大作用引起的；瘦肉型长白猪的脂肪细胞明显小于香猪，单位组织重的脂肪细胞数极显著地高于香猪。同时研究表明，体积不同的脂肪细胞合成脂肪的能力差异极显著，表现为细胞体积越大其合成脂肪的能力越强，不受品种和年龄的影响。     

不同剂量脂肪膜抗体对大鼠脂肪沉积的影响及其机制

过多的脂肪沉积影响肉的品质。(110±10)g雌性(♀)SD大鼠(Rattus norvegicus)150只,随机分成5组,分别在基础日粮中添加0、75、500、1000和6000mg/kg含脂肪细胞膜卵黄抗体的阳性卵黄粉。75d屠宰,采集血样、肠系膜脂、子宫周脂、肾脂肪囊和下丘脑。放射免疫法测定血清Insulin和Leptin浓度。用RT-PCR方法,以18S rRNA作内标分析不同部位脂肪组织中Leptin、Bcl-2和Bax mRNA和下丘脑Ob基因b型受体(Ob-Rb)mRNA表达,并测定各部位脂肪组织DNA和RNA含量。结果显示,卵黄抗体处理可降低大鼠腹腔内总脂重和腹腔内总脂指数,其中75和6000mg/kg阳性卵黄粉组效果明显,但对体重、摄食量和腓肠肌重无显著影响。6000mg/kg阳性卵黄粉组可降低血清甘油三酯,升高血清游离脂肪酸;降低子宫周脂和肾脂肪囊DNA含量和总量。75mg/kg阳性卵黄粉组可降低子宫周脂和肾脂肪囊DNA总量;两剂量组均可降低血清胰岛素、子宫周脂和肾脂肪囊Leptin mRNA表达,上调下丘脑Ob-Rb mRNA表达;降低子宫周脂Bcl-2mRNA和Bax mRNA表达,...     

猪脂肪组织表达序列标签(ESTs)的研究

 对猪脂肪组织cDNA文库的2104个克隆进行EST研究,其中563个ESTs在猪种中已有匹配序列,682个在人类及其它物种中可以找到同源序列,376个ESTs为未知新基因,有298个因序列质量差无法做分析,185个在EST库中有同源序列。所分析的376个新ESTs中,其中有159个具有ORF结构,43个具有Poly(A)和CpG特征,这些结果初步显示了猪脂肪组织的功能基因表达特点。     

脂肪细胞膜免疫研究进展

脂肪细胞膜免疫技术作为一种高效、安全、作用持久的方法,用于降低肉品脂肪含量,并已在大鼠、绵羊和猪的体脂调控方面取得了显著成效。对脂肪细胞膜免疫方法、作用机理以及脂肪细胞膜免疫中存在的问题进行了综述,并展望了脂肪细胞膜免疫技术的发展方向和应用前景。