Kisspeptin/GnRH1 system in Leydig cells of horse (Equus caballus): Presence and function

The objectives of this study were to evaluate in horse testes the expression of kisspeptin (KiSS) and GnRH1 neuropeptides and their cognate receptors, KiSS1R and GnRH1R, as well as their action on testosterone, GnRH1, prostaglandin F2α (PGF2α), and PGE2 synthesis and cyclooxygenase 1 (COX1) and COX2 activity by Leydig cells in vitro. Testes were obtained from 9 sexually mature horses by surgical castration. Immunohistochemistry, evidenced the presence of KiSS, KiSS1R, GnRH, and GnRH1R in Leydig cells, whereas germinal and Sertoli cells were positive only for GnRH1. Transcripts for both neuropeptides and their cognate receptors were revealed in isolated Leydig cells by RT-PCR. Isolated and purified Leydig cells were in vitro cultured with agonists and antagonists of KiSS (KiSS-10 and KiSS-234, respectively) and GnRH1 (buserelin and antide, respectively). KiSS-10 and buserelin increased (P < 0.01) COX1 activity and testosterone and PGF2α basal secretion, while decreased (P < 0.01) that of PGE2. KiSS-10 and buserelin did not affect COX2 activity. GnRH1 basal production was increased (P < 0.01) by KiSS-10, but not by buserelin. Antide counteracted the KiSS and GnRH1 effects, whereas KiSS-234 influence only those of KiSS. Summarizing, the KiSS/GnRH1 system is present in horse Leydig cells and modulates their endocrine activity. In particular, the endocrine effects of KiSS are mediated by GnRH1, so suggesting that hypothalamic-like interaction between KiSS and GnRH1 occurs also in Leydig cells.