The aims of the present study were to clarify the effect of Kisspeptin-10 (Kp10: a shorter variant of kisspeptin retaining full biological activity) on the secretion of growth hormone (GH) from cultured bovine anterior pituitary (AP) cells, and evaluate the role of sexual steroids and Kp10 on the secretion of GH in vitro. The AP cells which were prepared from 8 to 11-month-old castrated calves were incubated for 12 h with estradiol (10nM), or progesterone (10nM), or testosterone (10nM), or vehicle only (control), and followed by a 2-h incubation period with Kp10. The amounts of GH released in media after a 2-h incubation period were measured by a time-resolved fluoroimmunoassay. Kp10 (1µM, 10µM) significantly stimulated the secretion of GH from the AP cells regardless of steroids treatments (P<0.05), and estradiol, progesterone, and testosterone showed no effect on enhancement of GH secretion in response to Kp10. The GH-releasing response to growth hormone- releasing hormone (GHRH, 10nM) was significantly greater than that of Kp10 (P<0.05). The present results suggest that Kp10 directly stimulates the release of GH from somatotrophic cells, and sexual steroids don't enhance the sensitivity of somatotrophic cells to Kp10. Furthermore, they suggest that the GH-releasing effect of the Kp10 is less potent than that of GHRH.
