γ-Aminobutyric acid suppresses enhancement of hamster sperm hyperactivation by 5-hydroxytryptamine

Sperm hyperactivation is regulated by hormones present in the oviduct. In hamsters, 5-hydroxytryptamine (5HT) enhances hyperactivation associated with the 5HT₂ receptor and 5HT₄ receptor, while 17β-estradiol (E₂) and γ-aminobutyric acid (GABA) suppress the association of the estrogen receptor and GABA_A receptor, respectively. In the present study, we examined the regulatory interactions among 5HT, GABA, and E₂ in the regulation of hamster sperm hyperactivation. When sperm were exposed to E₂ prior to 5HT exposure, E₂ did not affect 5HT-enhanced hyperactivation. In contrast, GABA partially suppressed 5HT-enhanced hyperactivation when sperm were exposed to GABA prior to 5HT. GABA suppressed 5HT-enhanced hyperactivation associated with the 5HT₂ receptor although it did not suppress 5HT-enhanced hyperactivation associated with the 5HT₄ receptor. These results demonstrate that hamster sperm hyperactivation is regulated by an interaction between the 5HT₂ receptor-mediated action of 5HT and GABA.