Sex steroid hormones do not enhance the direct stimulatory effect of kisspetin-10 on the secretion of growth hormone from bovine anterior pituitary cells

The aims of the present study were to clarify the effect of kisspeptin10 (Kp10) on the secretion of growth hormone (GH) from bovine anterior pituitary (AP) cells, and evaluate the ability of sex steroid hormones to enhance the sensitivity of somatotrophic cells to Kp10. AP cells prepared from 8-11-month-old castrated calves were incubated for 12 h with estradiol (E-2, 10-8 mol/L),progesterone (P-4, 10-8 mol/L), testosterone (T, 10-8 mol/L), or vehicle only (control), and then for 2 h with Kp10. The amount of GH released in the medium was measured by a time-resolved fluoroimmunoassay. Kp10 (10-6 or 10-5 mol/L) significantly stimulated the secretion of GH from the AP cells regardless of steroid treatments (P < 0.05), and E-2, P-4, and T had no effect on this response. The GH-releasing response to growth hormone-releasing hormone (GHRH, 10-8 mol/L) was significantly greater than that to Kp10 (P < 0.05). The present results suggest that Kp10 directly stimulates the release of GH from somatotrophic cells and sex steroid hormones do not enhance the sensitivity of these cells to Kp10. Furthermore, they suggest that the GH-releasing effect of Kp10 is less potent than that of GHRH.