Blockade of the LH surge and ovulation by GABA-T inhibitory drugs that increase brain GABA levels in rats

Abstract

The present experiments were designed to evaluate the effects of GABA increase in the brain on the LH surge and ovulation in female rats. GABA-transaminase (GABA-T) inhibitory drugs were administered intraperitoneally in the early afternoon hours on the day before the expected ovulation. Gamma-acetylenic GABA (GAG) prevented the proestrus LH surge and ovulation in freely moving adult female rats. In a similar manner, GAG blunted the enhanced LH release found at 1800 h on the preovulatory day and the subsequent ovulation in PMSG-treated 32-day-old rats. LH secretion and ovulation in these animals was restored by administration of the selective GABA antagonist, bicuculline. The other GABA-T inhibitors, amino-oxyacetic acid and γ-vinyl GABA, produced similar effects to GAG in the PMSG-treated rats. These results indicate that the increase of brain GABA levels during the preovulatory day alters LH release and prevents ovulation in rats.