Kisspeptin, a Novel Hypothalamic Regulator of the Somatotropic and Gonadotropic Axes in Ruminants
Type of Degreedissertation
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Reproductive inefficiency in dairy cows is a worldwide problem. Factors that improve reproductive performance even slightly could have large impacts on the efficiency of food animal production. The neuropeptide kisspeptin is vital to the regulation of the hypothalamic-pituitary gonadal axis and required for normal reproduction. Evidence suggests that kisspeptin may be an integrator of metabolism and reproduction. Growth hormone is an important regulator of metabolism and it is necessary for optimal reproduction. Kisspeptin has been shown to stimulate growth hormone release both in vitro and in vivo. However, the mechanism(s) underlying kisspeptin-stimulated growth hormone release have not been elucidated in large domestic species, specifically ruminants. vi The effects of kisspeptin on luteinizing hormone release and growth hormone release in ruminants (cattle and sheep) during different physiologic conditions and following different routes are described here. A study also describes the effects of kisspeptin on ovulation in cattle. Peripheral administration of kisspeptin increases circulating luteinizing hormone in cattle and sheep. Kisspeptin stimulates circulating growth hormone concentrations in ovariectomized cows only after cows are pre-treated with exogenous gonadal steroids. The stage of lactation and possibly degree of negative energy balance enhances sensitivity of the gonadotropic axis but not the somatotropic axis to kisspeptin. Central but not peripheral treatment of ovariectomized sheep with kisspeptin increases growth hormone release suggesting a central effect. Lastly, data presented here support the notion that kisspeptin may be a useful ovulation-inducing agent in cattle. These results provide the first evidence that kisspeptin may be an integrator of the somatotropic and gonadotropic axes in ruminants. As a result, the potential to improve reproductive function in domestic species through manipulation of the somatotropic and gonadotropic axes may be realized.