Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/20/2010
Publication Date: 2/17/2010
Citation: Hausman, G.J., Barb, C.R. 2010. Adipose tissue and the reproductive axis: biological aspects. Book Chapter. 19:31-44. 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, although recent findings demonstrate other adipocyte protein products may play key roles in regulating the reproductive axis in the pig.
Technical Abstract: The discovery of leptin clearly demonstrated a relationship between body fat and the neuroendocrine axis since leptin influences appetite and the reproductive axis. Since adipose tissue is a primary source of leptin, adipose tissue is no longer considered as simply a depot to store fat. Recent findings demonstrate that numerous other genes i.e., neuropeptides, interleukins and other cytokines and biologically active substances such as leptin, insulin-like growth factor-I –II (IGF-I), IGF-II are also produced by adipose tissue, which could influence appetite and the reproductive axis. Targets of leptin in the hypothalamus include neuropeptide Y (NPY), proopiomelanocortin (POMC), and kisspeptin. Transsynaptic connection of hypothalamic neurons to porcine adipose tissue may result in a direct influence of the hypothalamus on adipose tissue function. Nutritional signals such as leptin are detected by the central nervous system and translated by the neuroendocrine system into signals which ultimately regulates luteinizing (LH) secretion. Furthermore, leptin directly affects gonadotropin releasing hormone (GnRH) release from the hypothalamus, LH from the pituitary gland and ovarian follicular steroidogenesis. Although, leptin is identified as a putative signal that links metabolic status and neuroendocrine control of reproduction, other adipocyte protein products may play key roles in regulating the reproductive axis in the pig.