The role of sexual steroid hormones in the direct stimulation by Kisspeptin-10 of the secretion of luteinizing hormone, follicle-stimulating hormone and prolactin from bovine anterior pituitary cells

The aims of the present study were to clarify the effect of Kisspeptin-10 (Kp10) on the secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL) from bovine anterior pituitary (AP) cells and evaluate the ability of sex steroids to enhance the sensitivity of gonadotropic and lactotropic cells to Kp10. AP cells prepared from 7-week-old male calves were incubated for 12 h with estradiol (E 2; 10 −8 M), progesterone (P 4; 10 −8 M), testosterone (T; 10 −8 M), or vehicle only (control), and then for 2 h with Kp10 (10 −6 M). The amounts of LH, FSH and PRL released into the culture medium after the 2-h incubation period were examined. Kp10 significantly stimulated the secretion of LH from the AP cells treated with E 2 and T ( P < 0.05), but not from the P 4-treated cells. In contrast, Kp10 had no effect on the secretion of FSH regardless of the steroid treatment. Kp10 significantly stimulated the secretion of PRL ( P < 0.05), the sexual steroid hormones having no effect. The LH- or FSH-releasing response to gonadotropin-releasing hormone (GnRH; 10 −8 M) and PRL-releasing response to thyrotropin-releasing hormone (TRH; 10 −8 M) were significantly greater than those to Kp10 ( P < 0.05). The present results suggest that E 2 and T, but not P 4, enhance the sensitivity of gonadotropic cells to the secretion of LH in response to Kp10. However, Kp10 had no stimulatory effect on the secretion of FSH regardless of the effect of sex steroids. Kp10 directly stimulates the secretion of PRL from the pituitary cells, and sex steroids do not enhance the sensitivity of lactotropic cells to Kp10. Furthermore, the LH- and FSH-releasing effect and the PRL-releasing effect of Kp10 are less potent than that of GnRH and TRH, respectively.