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Title: LEPTIN: A METABOLIC SIGNAL AFFECTING CENTRAL REGULATION OF REPRODUCTION IN THE PIG.

Author
item Barb, Claude
item Hausman, Gary
item CZAJA, KRZYSZTOF - WARMIA AND MAZURY UNIV.

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2004
Publication Date: 7/20/2005
Citation: Barb, C.R., Hausman, G.J., Czaja, K. 2005. Leptin: a metabolic signal affecting central regulation of reproduction in the pig.. Domestic Animal Endocrinology. 29:186-192.

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 that a satiety signal. It severs as a metabolic signal exerting its effect by acting directly on the brain and pituitary gland to regulate luteinizing hormone (LH) secretion, necessary for stimulation of the reproductive system; feeding behavior and fat cell function via neural connection with fat depots. Thus, leptin appears to be an important link between nutrition 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), 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.