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.     

Effects of a high-protein, low-energy diet in finishing lambs: 2. Weight change, organ mass, body composition, carcass traits, fatty acid composition of lean and adipose tissue, and taste panel evaluation

An experiment was conducted to evaluate the effects of a high protein – low energy diet on body composition of feedlot lambs The objective was to assess the capability of such a diet to reduce body fat while preserving lean body mass. Three dietary regimens were compared: a typical feedlot diet (CON), barley straw at libitum (STR), and barley straw supplemented with fish meal (SFM). The latter two diets caused an energy deficit in the experimental animals. Significant treatment effects on mass of metabolic organs, body composition, and carcass data were observed. Conventional analysis of sensory data and fatty acid profiles of adipose and muscle tissue identified few significant dietary effects, yet discriminant analysis clearly separated all treatment groups. It was concluded that protein supplementation of ruminants in the catabolic state does not conserve protein mass. Given the high cost of protein supplementation, the post hoc modification of body composition of feedlot lambs is not a viable option. It is suggested that the production of feedlot lambs with a desirable degree of fatness should employ a feeding strategy dynamically adapted to the changes in protein – energy balance required by the growing ruminant.     

Localization of leptin and leptin receptor in the bovine adenohypophysis

The present study was carried out to detail the cellular localization of leptin (Lep) and the leptin receptor (LepR) in the bovine adenohypophysis. Lep immunoreactivity (Lep-ir) was found in about 30% of adenohypophysial cells in the gland. Immunochemistry of Lep and specific hormones using serial sections revealed that Lep-ir was present in 60.4% of somatotrophs, 15.9% of gonadotrophs, 6.5% of mammotrophs, 6.5% of thyrotrophs and 2.4% of corticotrophs. Both the common short isoform (OBRa) and the long isoform (OBRb) of LepR mRNA were expressed in the bovine adenohypophysis. LepR immunoreactivity (LepR-ir) was found in only 2.8% of the adenohypophysial cells and over 50% of LepR-ir cells were gonadotrophs, in which most of the cells were distributed in the zona tuberalis. The findings on Lep and LepR in the adenohypophysial cells indicate that Lep may regulate gonadotroph function through autocrine/paracrine pathway in the bovine adenohypophysis.     

Early pregnancy alters the metabolic responses to restricted nutrition in sheep

This study investigated whether a 27-day period of nutrition at half-maintenance during early pregnancy (up to Day 14) could alter maternal endocrine responses. Forty-six ewes were fed all or half of their maintenance requirements and slaughtered on Day 14 of the oestrous cycle or pregnancy. We used real time RT-PCR to study gene expression of growth hormone receptor (GHR) and leptin in adipose tissue and GHR, GHR1A and of the insulin-like growth factor I (IGF-I) in the liver. Blood profiles of metabolites and metabolic hormones were also determined. Throughout the experiment, underfed animals presented lower body weight and body condition, greater plasma concentrations of non-esterified fatty acids (NEFA), and lower plasma concentrations of leptin, compared to adequately fed animals. Undernutrition affected the patterns of gene expression in adipose and hepatic tissues, and the responses differed between pregnant and non-pregnant ewes. In adequately fed ewes, pregnancy up-regulated leptin mRNA expression in adipose tissue, a response that was impaired in underfed ewes. The hepatic expression of IGF-I mRNA was increased by pregnancy in underfed animals while no effect was observed in adequately fed ewes. It remains to be determined whether the changes in the endocrine milieu are paralleled by modifications in uterine gene expression that could alter the environment of the embryo during early pregnancy.     

ob基因及其表达产物的生物学效应

ob基因自从被克隆后,围绕其表达产物的作用机理和生物学效应进行了大量的研究,最近研究证明Leptin对小鼠大脑发育有重要功能,标志着Leptin的研究进入了一个新的阶段,今后将从单一的营养调控研究转向兼顾神经生物学的研究,更深入研究Leptin作用机理。同时国内外学者从分子领域探究ob基因在畜禽育种上的作用,做了很多的工作,也取得了重要的成果。本文总结了ob基因的重要生物学效应,为理解ob基因的作用机制和进一步研究人类肥胖治疗和提高动物生长繁殖性状水平提供必要的支持。     

重组瘦蛋白对猪生长性能的影响

通过腹腔注射重组瘦蛋白研究其对猪生长性能的影响。结果显示,腹腔注射不同剂量的重组瘦蛋白,在注射后的1-2周内使猪采食量减少5%-7%(p<0.05),2周后采食量逐渐恢复正常;使猪的日增重和料重比有所降低,但差异不显著(p>0.05)。表明重组瘦蛋白对猪的生长性能无明显影响。     

鱼类ob基因研究进展

ob基因是近年发现的新基因,因它表达的蛋白质与动物的摄食、能量调控、繁殖、免疫、肥胖等方面紧密相关,是近年研究的热点。     

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。     

The Effect of Different Physical Exercise on Plasma Leptin,Cortisol, and Some Energetic Parameters Concentrations in Purebred Arabian Horses

Leptin is a hormone that coordinates food intake, energy expenditure, and metabolic rate; it is, however, unknown how exercise influences plasma leptin concentration in horses. The aim of the study was to evaluate the exercise-induced changes in plasma leptin concentration in purebred Arabian horses competing in races and endurance rides. A total number of 26 horses (12 purebred Arabian racehorses aged 3–5 years and 14 endurance horses aged 7–14 years) were studied during performing routine physical exercise. From each horse, blood samples were collected at rest and immediately after the exercise session. Concentrations of plasma leptin, cortisol, lactic acid, uric acid, triacylglycerols, glycerol and free fatty acids were determined. Exercise-induced increase in cortisol and free fatty acid values were higher in endurance horses than in racehorses. Neither endurance nor race exercises influenced the plasma leptin concentration. Further research is needed to elucidate the effects of different types of exercise on leptin synthesis and secretion in horses.     

口服鲨烯对大鼠Leptin、体脂沉积和繁殖的影响

将22日龄Wistar雄鼠32只,分对照组(饲料中不含鲨烯)和试验组(每千克饲料中含鲨烯1 000mg),宰杀后测定血Leptin、血糖、胆固醇、甘油三酯和睾酮水平及体重脂肪指数和体重睾丸指数,同时,各组留6只与雌鼠交配,待观察产仔数.结果显示,对照组和试验组饲料消耗没有差异,但试验组大鼠体重、体重脂肪指数、血Leptin、血糖、胆固醇和甘油三酯水平显著比对照组低,而试验组大鼠的体重睾丸指数、血睾酮水平和产仔数显著比对照组高.提示口服鲨烯可防止正常鼠体重和体脂肪增加并可降低肥胖鼠体重脂肪指数及降低血Leptin、血糖、胆固醇和甘油三酯的水平;同时,鲨烯可促进睾丸生长发育和睾酮分泌,增加产仔数.