RESUMO
Two isoforms of the gonadotropin-releasing hormone (GnRH), GnRH-I and GnRH-II, are expressed in mammals, and the presence of one or more GnRH-like peptides has been demonstrated in the male reproductive tract. GnRH and its receptors (GnRHR) are present in human and non-human primate testis, prostate, epididymis, seminal vesicle, spermatozoa and seminal human plasma. GnRH-II is site-specific and acts directly in an inhibitory or stimulatory fashion. Previous studies speculated that GnRH-II could disrupt specific sperm processes, such as sperm motility or capacitation and could be utilized as an effective contraceptive agent. Our study aimed to investigate the in-vitro effects of GnRH-I and GnRH-II on Vervet monkey sperm function. Electro-ejaculated semen samples from 10 Vervet monkeys (Chlorocebus aethiops) were used to select motile sperm populations. Sperm aliquots were incubated with GnRH-I and GnRH-II at different concentrations for 1 h, where after sperm motility and kinematic parameters were assessed using the automated Sperm Class Analyser. Additional sperm aliquots were incubated with two 10-amino acid control peptides, a non-related peptide and an inactive peptide to exclude the possible influence on sperm motility from other peptides with a structure similar to GnRH. Additionally, a GnRHR-I antagonist (GnRHR-A), Cetrorelix, was tested to establish its antagonistic capability on GnRH. The effect of selected concentrations of GnRH-I and GnRH-II on sperm vitality and acrosome intactness was also evaluated after 10- and 60 min exposure. Analysis of the percentage total sperm motility revealed that different concentrations for GnRH-I and GnRH-II inhibited sperm motility significantly. While sperm progressiveness was also notably affected and a trend of decreased sperm kinematics were evident, no effect was found on sperm vitality or acrosome intactness. The non-related and inactive peptides had no impact on sperm motility. The GnRHR-A demonstrated no effect on sperm motility and effectively blocked the inhibitory outcome on the motility of both GnRH isoforms. While GnRH-I or GnRH-II at low-dose concentrations resulted in in-vitro inhibition of sperm motility, it appears to have no adverse effects on other sperm functional parameters evaluated. These collective observations possibly indicate an essential role for GnRH in the in-vivo process of sperm selection in the female reproductive tract.