Reproduction in Domestic Animals

328 CR Barb, GJ Hausman and CA LentsFig. 2. Schematic illustration of leptin coordination of energy homeostasisand neuroendocrine function: Leptin is secreted in response tochanges in energy balance. Leptin acts on the hypothalamus to controlfood intake, reproduction and, by suppressing expression of neuropeptideY (NPY) and agouti related peptide (AGRP) and upregulationof proopiomelanocortin (POMC), a-melanocyte stimulating hormone(a-MSH) and kisspeptin (KiSS)while peripheral administration of kisspeptin increasedserum concentrations of LH but not FSH or GH. Thesedata illustrate that kisspeptin can activate the brainpituitaryaxis and may be part of an importantmechanism regulating activation of the GnRH ⁄ LHrelease and initiating onset of puberty in swine. Moreoverit is tempting to speculate that the kisspeptinneuronal pathway may play a role in interfacingmetabolic status of the post-partum sow with theGnRH ⁄ gonadotropic axis and hence may affect thepost-weaning fertility of the sow.In conclusion evidence presented supports the conceptthat metabolic signals, which reflect changes in energybalance, affect both the hypothalamic GnRH ⁄ LH pulsegenerator and appetite. Changes in fat metabolism inresponse to changes in feed intake and energy balancealter adipocyte function and circulating concentrationsof IGF-I and leptin. A preponderance of evidence citedabove suggests that leptin may serve as the primarymetabolic signal interacting with neuropeptides such askisspeptin and NPY that link energy status with theneuroendocrine axis and subsequent reproduction(Fig. 2).ReferencesAherne FX, Kirkwood RN, 1985: Nutrition and sow prolificacy.J Reprod Fertil 33, 169–183.Ahima RS, Qi Y, Singhal NS, Jackson MB, Scherer PE, 2006:Brain adipocytokine action and metabolic regulation. Diabetes55, S145–S154.Almeida FR, Mao J, Novak S, Cosgrove JR, Foxcroft GR,2001: Effects of different patterns of feed restriction andinsulin treatment during the luteal phase on reproductive,metabolic, and endocrine parameters in cyclic gilts. J AnimSci 79, 200–212.Angell CA, Tubbs RC, Moore AB, Barb CR, Cox NM, 1996:Depressed luteinizing hormone response to estradiol in vivoand gonadotropin-releasing hormone in vitro in experimentallydiabetic swine. 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