Heifer estrous cycle stage impacts luteinizing and growth hormone response to kisspeptin

The reproductive neuropeptide, kisspeptin (KP), may have a role in regulation of growth hormone (GH) secretion. Expression of KP and its receptor (Kiss1r) are developmentally and hormonally regulated. This study was conducted to determine the effects of KP on plasma concentrations of luteinizing hormone (LH) and GH in pubertal heifers during different functional reproductive stages. Heifers received a single injection of KP (100 pmole / kg) or saline intravenously during proestrus, estrus, and diestrus, and serial blood samples were collected for 3 hours to determine the response of both LH and GH after treatment. Mean concentrations of LH were increased (P < 0.05) for animals receiving KP during proestrus and diestrus but not estrus. However, area under the LH curves following treatment with KP were increased (P < 0.05) during all reproductive stages tested. Mean concentrations of GH were unaffected by treatment. Administration of KP increased (P < 0.05) area under GH curves during proestrus and diestrus but not estrus. Thus, KP can stimulate increased circulating concentrations of LH and GH in pubertal heifers and functional reproductive stage affects the gonadotropic and somatotropic responses.