Interactions among progesterone, estradiol, and γ-aminobutyric acid in rat spermatozoal hyperactivation

Our previous study in hamsters indicated that progesterone (P) induces enhancement of spermatozoal hyperactivation, while 17β-estradiol (Eβ) and γ-aminobutyric acid (GABA) suppress this enhancement. Since P has also been shown to enhance hyperactivation of rat spermatozoa in another study conducted by our team, we examined the effects of Eβ and GABA on the P-enhanced hyperactivation of rat spermatozoa in the present study. Our results showed that Eβ suppressed P-enhanced hyperactivation in a dose-dependent manner through an estrogen receptor. In contrast, GABA did not affect P-enhanced hyperactivation. Instead, 5–500 fM GABA significantly enhanced spermatozoal hyperactivation, and this GABA-induced enhancement of hyperactivation was associated with a GABAA receptor. In conclusion, P-enhanced hyperactivation of rat spermatozoa was suppressed by Eβ although it was not suppressed by GABA. Moreover, low concentrations of GABA enhanced rat spermatozoal hyperactivation.