Regulation and Role of Leptin: Pigs

Authors: Barb, Claude; Hausman, Gary

Submitted to: Encyclopedia of Animal Science
Publication Type: Book / Chapter
Publication Acceptance Date: 4/13/2007
Publication Date: 1/15/2008
Citation: Barb, C.R., Hausman, G.J. 2008. Regulation and Role of Leptin: Pigs. Encyclopedia of Animal Science. www.informaworld.com/10.1081/E-EAS-120043425.

Interpretive Summary: The recently discovered protein, leptin, secreted by fat cells in response to changes in body weight and energy, regulates appetite and metabolism. Evidence supports the idea that leptin is more than a satiety signal but acts as an integrated response of all the peripheral tissues with its primary regulation of the overall metabolic status of the animal. This metabolic status is impacted by age, diet, body composition and energy balance, reproductive status, genetics, disease and infection which in tern can affect leptin expression and secretion. In addition, leptin serves as a metabolic signal interacting with neuropeptides that link energy status with the neuroendocrine axis and can directly modulate ovarian activity. Thus, leptin appears to be an important link between nutrition, peripheral metabolism and reproduction in the pig.

Technical Abstract: 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), and Agouti protein are produced by porcine adipose tissue, which could have a profound effect on appetite, immune function 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. Thus, leptin appears to be an important link between nutrition, peripheral metabolism and reproduction in the pig.