肥胖基因及其产物的研究进展

Ob基因编码的Leptin具有降低脂肪,维持能量平衡,调节代谢、生殖、激素分泌,提高免疫机能等多方面的功能.本文在介绍Leptin、Leptin受体的基础上进一步对Leptin的生物学功能及其作用机制、Leptin的抗性做一简要论述,并提出了Leptin今后的研究方向及其在畜牧业上的应用前景.     

肥胖基因及其产物的研究进展

Ob基因编码的Leptin具有降低脂肪，维持能量平衡，调节代谢、生殖、激素分泌，提高免疫机能等多方面的功能。本文在介绍Leptin、Leptin受体的基础上进一步对Leptin的生物学功能及其作用机制、Leptin的抗性做一简要论述，并提出了Leptin今后的研究方向及其在畜牧业上的应用前景。     

动物肥胖基因（ob）的研究进展

肥胖基因（ob）调节动物生长和维持能量平衡的生物学功能都是通过其产物——瘦素蛋白（Leptin）来实现的.因此,控制Leptin在动物体内的表达水平可有效降低脂肪含量,提高瘦肉率,从而为畜牧产业带来可观的经济效益.就ob基因的研究进展进行了系统性的综述.     

能量影响初情期前母猪生殖机能的机理

日粮能量通过代谢激素:生长激素、胰岛素、瘦素(Leptin)、甲状腺素、IGF-Ⅰ以及葡萄糖等代谢信号为媒介,影响垂体促性腺激素分泌;此外,也可直接作用于卵巢,影响性腺激素分泌及卵巢发育。能量负平衡时,GH脉冲的频率和振幅提高,而血浆IGF-Ⅰ被抑制。Leptin浓度在短期限饲或禁饲时都低于正常组。胰岛素及Leptin在初情期前母猪生殖机能有重要作用,胰岛素是营养代谢与母猪生殖机能相互作用的一个媒介,IGF能够长期影响母猪生殖机能,甲状腺激素对初情期前母猪生殖机能有影响,因此能量通过代谢激素影响初情期前母猪生殖机能。     

Leptin的研究进展

Leptin是由脂肪细胞分泌的一种蛋白，自1994年被发现以来，对leptin的研究就成为最为的领域之一并取得了迅速进展，国外大量实验资料表明，leptin可以降低动物采量，维持动物能量平衡，调节动物 的繁殖机能，提高动物的免疫功能，本文就Leptin的研究进展和其应用前景作一综述。     

营养等不同因素对奶牛血浆Leptin的调节

1 前言 Leptin是肥胖基因(ob基因)分泌的一种蛋白质,具有广泛的生物学效应.它参与调节食欲、能量平衡、繁殖、造血功能和免疫功能等.Leptin主要在是脂肪组织和含有脂肪细胞的组织表达,它也在乳腺、子宫、肝脏、心包、胎盘和肾脏表达.     

Leptin的生物学效应及影响因素

Leptin,中文译名为瘦素、瘦蛋白、抗肥胖因子、苗条素,是脂肪细胞分泌的一种激素样蛋白质。现对瘦素及其在动物生产中的应用及影响其表达的因素进行了如下阐述。1 Leptin的生物学效应1.1对采食的影响血中Leptin浓度主要与脂肪组织的存储量有关,但并非简单的直线关系。动物处于饥饿状态时,其血中Leptin浓度存储量下降幅度大,在人工饲养时其水平的恢复要慢于体脂储存量的恢复。Leptin作为神经内分泌调节激素,能够提供调节信号,通过抑制食物摄取并提高代谢率来限制脂肪的储存,在能量平衡中起主要调节作用,尤其是在食物缺乏或饥饿状态下能有效…     

不同能量摄入水平对奶牛产乳性能及血液中Leptin和NPY浓度的影响研究

将30头围产期健康奶牛随机分为3组,每组均为10头,其中Ⅰ组为对照组,Ⅱ组和Ⅲ组为试验组;Ⅰ、Ⅱ、Ⅲ组分别于产前第28d开始饲喂标准日粮(能量摄入100%组)、标准日粮增加20%能量(能量摄入120%组)和标准日粮减少20%能量(能量摄入80%组),产后各组奶牛均饲喂标准泌乳日粮,至产后第56d结束,观察不同能量摄入水平对产后奶牛产乳性能及血液中瘦素(Leptin)和神经肽Y(NPY)浓度的影响。试验结果表明,产前饲喂低能日粮不仅提高了产后奶牛产乳性能,而且提高了产后奶牛血液中Leptin和NPY浓度。可见,奶牛不同能量摄入水平与产奶量及血液中Leptin和NPY浓度之间存在着密切的关系。     

不同能量摄入水平对围产期奶牛脂肪组织Leptin mRNA和HSL mRNA表达的影响

选用围产期健康奶牛30头随机均分为3组,其中组为对照组,组和组为试验组。Ⅰ、Ⅱ、Ⅲ组于产前28d开始分别饲喂中国奶牛饲养标准(2000)标准日粮(能量摄入100%组)、标准日粮增加20%日粮(能量摄入120%组)和标准日粮减少20%日粮(能量摄入80%组),产后各组奶牛均饲喂同一标准日粮至56 d。试验各组奶牛分别于产前28、14 d、产后1、14、28、56 d尾根部手术采取脂肪样品,采用荧光RT-PCR法对脂肪组织Leptin mRNA及HSL mRNA表达水平进行定量分析。结果表明,不同能量摄入水平显著影响脂肪组织Leptin mRNA和HSL mR-NA表达。低能饲喂明显提高了脂肪组织中Leptin mRNA表达,降低了HSL mRNA表达;高能饲喂明显降低了脂肪组织中Leptin mRNA表达,提高了HSL mRNA表达。     

瘦蛋白及其在动物繁殖中的研究进展

瘦蛋白(Leptin)是肥胖基因(ob基因)表达的蛋白质产物,主要产生于脂肪组织,向大脑反馈能量储存的信息并激活下丘脑中枢,调节进食和能量的消耗.此外,Leptin还可以通过直接或间接地影响下丘脑--垂体--性腺轴来调控动物的繁殖性能.笔者从Leptin的生物学基础、作用机理及繁殖调控等方面予以综述,并指出了其在家畜繁殖上的应用前景.     

动物乳汁中瘦素的研究进展

为了更好的理解乳汁中瘦素的来源和功能，作者综述了在人等哺乳类动物的妊娠、泌乳阶段乳腺中leptin及其受体的基因表达，血液和乳中的瘦素含量。乳腺的多种组织能够表达leptin，其作为一种分泌因子,影响乳腺上皮细胞的生长分化；上皮细胞能够将leptin从血液中转运出来，这是leptin在乳中存在的主要原因。乳中的leptin蛋白可能对新生儿有生理作用。     

Leptin as an indicator for carcass composition in farm animals

The function of leptin in livestock species has been intensively studied during recent years. Due to the associations between plasma leptin concentrations and body fat, leptin could be used as an indicator for the in vivo evaluation of carcass composition in breeding programs. This review specifically discusses leptin mRNA expression in several fat tissues, the relationship between plasma leptin and body fat and the influence of fasting on this association. It also refers to the limitations of the use of plasma leptin concentrations as a predictor for selection purposes in breeding animals. Furthermore, single nucleotide polymorphisms in the leptin gene have some effects on carcass traits and the leptin gene is considered to be a candidate gene for a marker‐assisted selection. However, these results are very inconsistent across various populations and need to be confirmed in future studies before leptin can be used efficiently in breeding programs and management.     

Leptin in ruminants. Gene expression in adipose tissue and mammary gland, and regulation of plasma concentration

This paper reviews data on leptin gene expression in adipose tissue (AT) and mammary gland of adult ruminants, as well as on plasma leptin variations, according to genetic, physiological, nutritional and environmental factors. AT leptin mRNA level was higher in sheep and goat subcutaneous than visceral tissues, and the opposite was observed in cattle; it was higher in fat than in lean selection line in sheep; it was decreased by undernutrition and increased by refeeding in cattle and sheep, and not changed by adding soybeans to the diet of lactating goats; it was increased by injection of NPY to sheep, and by GH treatment of growing sheep and cattle. Insulin and glucocorticoids in vitro increased AT leptin mRNA in cattle, and leptin production in sheep. Long daylength increased AT lipogenic activities and leptin mRNA, as well as plasma leptin in sheep. Mammary tissue leptin mRNA level was high during early pregnancy and was lower but still expressed during late pregnancy and lactation in sheep. Leptin was present in sheep mammary adipocytes, epithelial and myoepithelial cells during early pregnancy, late pregnancy and lactation, respectively. Plasma leptin in cattle and sheep was first studied thanks to a commercial “multi-species” kit. It was positively related to body fatness and energy balance or feeding level, and decreased by β-agonist injection. The recent development of specific RIA for ruminant leptin enabled more quantitative study of changes in plasma leptin concentration, which were explained for 35–50% by body fatness and for 15–20% by feeding level. The response of plasma leptin to meal intake was related positively to glycemia, and negatively to plasma 3-hydroxybutyrate. The putative physiological roles of changes in leptin gene expression are discussed in relation with published data on leptin receptors in several body tissues, and on in vivo or in vitro effects of leptin treatment.     

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.     

Chicken leptin: properties and actions

Chicken leptin cDNA shows a high homology to mammalian homologous, with an expression localized in the liver and adipose tissue. It is noteworthy, that the hepatic expression is most likely associated with the primary role that this organ plays in lipogenic activity in avian species. As in mammals, chicken leptin expression is regulated by hormonal and nutritional status. This regulation is tissue-specific and with a high sensitivity in the liver compared to adipose tissue. The blood leptin levels are regulated by the nutritional state with high levels in the fed state compared to the fasted state. The recombinant chicken leptin markedly inhibits food intake as reported in mammals, suggesting the presence of an hypothalamic leptin receptor. The chicken leptin receptor has been identified and all functional motifs are highly conserved compared to mammalian homologous. Chicken leptin receptor is expressed in the hypothalamus but also in other tissues such as pancreas, where leptin inhibits insulin secretion and thus may have a key role in regulating nutrient utilization in this species.     

Leptin: a metabolic signal affecting central regulation of reproduction in the pig

The discovery of the obesity gene and its product, leptin, it is now possible to examine the relationship between body fat and the neuroendocrine axis. A minimum percentage of body fat may be linked to onset of puberty and weaning-to-estrus interval in the pig. Adipose tissue is no longer considered as only a depot to store excess energy in the form of fat. Recent findings demonstrate that numerous genes, i.e., relaxin, interleukins and other cytokines and biologically active substances such as leptin, insulin-like growth factor-I (IGF-I), IGF-II and Agouti protein are produced by porcine adipose tissue, which could have a profound effect on appetite and the reproductive axis. Hypothalamic neurons are transsynaptically connected to porcine adipose tissue and may regulate adipose tissue function. In the pig nutritional signals such as leptin are detected by the central nervous system (CNS) and translated by the neuroendocrine system into signals, which regulate appetite, hypothalamic gonadotropin-releasing hormone (GnRH) release and subsequent luteinizing hormone (LH) secretion. Furthermore, leptin directly affects LH secretion from the pituitary gland independent of CNS input. Changes in body weight or nutritional status are characterized by altered adipocyte function a reduction in adipose tissue leptin expression, serum leptin concentrations and a concurrent decrease in LH secretion. During pubertal development serum leptin levels, hypothalamic leptin receptor mRNA and estrogen-induced leptin gene expression in fat increased with age and adiposity in the pig and this occurred at the time of expected puberty. In the lactating sow serum and milk leptin concentrations were positively correlated with backfat thickness and level of dietary energy fed during gestation as well as feed consumption. Although, these results identify leptin as a putative signal that links metabolic status and neuroendocrine control of reproduction, other adipocyte protein products may play an important role in regulating the reproductive axis in the pig.     

Serum leptin and its adipose gene expression during pubertal development,the estrous cycle,and different seasons in cattle

Circulating concentrations of leptin and IGF-I, leptin gene expression, and serum binding of [126I]ovine leptin in cattle during pubertal development, as well as leptin gene expression and circulating concentrations of leptin during the estrous cycle and different calendar seasons, were investigated. Multivariate regression analysis was utilized to evaluate temporal changes in BW, leptin mRNA, and serum concentrations of IGF-I and leptin normalized to the week of puberty (Exp. 1). Body weight accounted for most of the variation associated with the onset of puberty in the full regression model (R2 = 0.99; P < 0.01). However, serum leptin was closely related to changes in BW (r = 0.85; P < 0.02) and in the absence of BW was most predictive of pubertal onset (r2 = 0.73; P < 0.01). Mean concentrations of leptin increased (P < 0.0001) linearly from 16 wk before until the wk of pubertal ovulation in yearling heifers reaching sexual maturation from early spring to midsummer. Leptin mRNA transformed to a percent of the value at puberty increased (P < 0.02) as puberty approached, but serum leptin and leptin mRNA values were not well correlated. We found no evidence of leptin-binding proteins in serum of developing heifers. Combined mean serum concentrations of IGF-I (ng/mL) during periods III and IV (-9 wk to wk of puberty; 216.6 +/- 9) were 21% higher (P < 0.0001) than combined mean concentrations of IGF-I during periods I and II (-19 to wk of puberty; 193 +/- 10). In mature heifers and cows (Exp. 2), serum leptin tended to decrease (P = 0.10) during the late luteal/early follicular phase of the estrous cycle, which corresponded to a reduction (P < 0.03) in adipocyte leptin gene expression. In mature ovariectomized cows, serum concentrations of leptin increased (P < 0.001) by 34% from early winter to the summer solstice and remained unchanged throughout the remainder of the year (Exp. 3). Results from these studies indicate that marked increases in both circulating leptin and leptin gene expression occur in developing heifers during pubertal development and are associated with increases in serum IGF-I and BW. Seasonal effects on circulating leptin observed in mature cows from winter to summer could also plausibly account for a portion of the prepubertal rise in serum leptin observed in heifers.     

Effects of low-dose leptin and gender on the physiology of the mouse (Mus musculus)

Exogenous leptin was given intraperitoneally to five male and five female mice at 0.2-0.3 mg/kg/day for 3 days. The plasma glucose and thyroxine concentrations as well as the hepatic and kidney enzyme activities were determined. The hepatic glycogen phosphorylase activity was suppressed by leptin treatment in the male mice. The other parameters were not significantly influenced by exogenous leptin, but there was a trend towards increased gluconeogenesis and glycogen storage due to leptin treatment. Enzyme activities of glucose and fat metabolism as well as the responses to leptin administration were sexually dimorphic. Discriminant analysis separated the control and the leptin-injected males and females to four distinct groups. Leptin seems to have minor but widespread effects on the energy metabolism of a nonmutant rodent. In nature, one function of leptin could be carbohydrate preservation.