Submitted to: Endocrine Update
Publication Type: Book / Chapter
Publication Acceptance Date: 12/9/2005
Publication Date: 6/17/2006
Citation: Barb, C.R., Hausman, G.J., Ramsay, T.G. 2006. Leptin in farm animals. In: Castracane, D.V., Henson, M.C., editors. Endocrine Update. New York, NY: Springer. p.263-308. Interpretive Summary: The 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, metabolism, immune function and the reproduction in farm animals. The leptin response to acute inflammation is uncoupled from appetite regulation and may serve as a marker for selecting genotypes that are more resistant to disease and stress. Metabolically, leptin regulates energy expenditure by inhibition lipid production. Specific hormones such as insulin and the adrenal hormone, cortisol, determine pre fat cell recruitment and subsequent fat cell size. These hormones play a role in regulating leptin gene expression in fat tissue. Across species leptin serves as a metabolic hormone which signals the nutritional state to the brain-pituitary axis thereby influencing secretion of pituitary hormones necessary reproduction and growth. 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.
Technical Abstract: The recently discovered protein, leptin, which is secreted by fat cells, has been implicated in regulation of feed intake or energy balance and the neuroendocrine axis in rodents, humans and large domestic animals. The leptin receptor which has been cloned and is a member of the class 1 cytokine family of receptors, is found in the brain and pituitary of all species studied to date. Neuropeptide Y has been proposed as the primary mediator of leptin action in the hypothalamus to regulate luteinizing hormone (LH) and growth hormone (GH) secretion. In vitro studies using both hypothalamic explants and pituitary cell culture provided evidence that supports a direct action of leptin at the level of brain and pituitary gland in the pig, but only the pituitary in cattle. Central administration of leptin increased LH secretion in the fasted cow and ewe, but not in control fed animals, indicating that metabolic state is an important factor in modulating the hypothalamic-pituitary response to leptin. Changing serum leptin concentrations and leptin mRNA expression were associated with onset of puberty in heifers and gilts. Thus, leptin appears to be an important link between metabolic status and the neuroendocrine axis.