Gonadotropin-releasing hormone II and its receptor regulate motility, morphology, and kinematics of porcine spermatozoa in vitro

The second form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II) are abundantly produced within the porcine testis and immunolocalize within the seminiferous tubules, suggesting a role in spermatogenesis and/or sperm function. The objective of this study was to quantify GnRH-II and GnRHR-II abundance within boar reproductive tract tissues and examine their role in porcine sperm function. Immunoblotting revealed GnRHR-II abundance was 12-fold greater (P < 0.0001) within the testis compared with other reproductive organs. Within seminiferous tubules, GnRHR-II prominently immunolocalized to elongating spermatids. In ejaculated spermatozoa, GnRHR-II immunolocalized to the connecting piece. GnRH-II was also detected in seminal plasma, likely originating from the testis as GnRH-II concentrations were greatest in testicular homogenates (P < 0.0001) compared with other reproductive tissues. To assess the effects of GnRH-II/GnRHR-II on sperm function, extended semen samples were treated with GnRHR-II analogues and evaluated via computer-assisted sperm analysis (CASA). In Experiment 1, semen treatment with increasing concentrations of GnRHR-II agonist (D-ala⁶ GnRH-II) revealed that two concentrations (0.1 and 100 µM) tended to decrease the percentage of bent sperm tails versus vehicle-treated semen (P < 0.10). In Experiment 2, semen treatment with increasing concentrations of GnRHR antagonist (SB-75/Cetrorelix) indicated that only 10 µM SB-75 impaired CASA metrics compared with vehicle-treated samples (P < 0.05). In Experiment 3, semen treatment with both 100 µM D-ala⁶ GnRH-II and 10 µM SB-75 partially rescued sperm motility and morphology measures. These data suggest that GnRH-II and its receptor regulate porcine sperm function in an autocrine/paracrine manner.