Effects of increase of brain GABA levels on the hypothalamic-pituitary-luteinizing hormone axis in rats

The effects of increasing brain GABA levels by administration of aminooxyacetic acid (AOAA), a GABA-transaminase inhibitor, on tonic and induced LH release were evaluated in ovariectomized rats. Pulsatile LH release was clearly inhibited by AOAA. Mean plasma LH levels fell, the frequently of pulses decreased, and the intervals between pulses increased. An absence of LH pulses was seen in some animals. Administration of the GABA antagonist, bicuculline, prevented these modifications. In addition, it enhanced mean plasma LH levels. AOAA blunted the rise of plasma LH levels produced by either oestradiol or progesterone in oestradiol-primed ovariectomized rats. In contrast, the AOAA treatment apparently facilitated the inhibitory feedback of oestradiol on LH release. The acute release of LH produced by LRH injection was not altered by AOAA. The results support the view that brain GABA exerts an inhibitory action on LH release in the rat.