Identification of gamma-aminobutyric acid and its binding sites in the rat ovary.

Gamma-aminobutyric acid (GABA), GABA synthesizing enzyme and GABA binding sites were measured in rat ovaries. The concentration of GABA in the ovary (0.56 microgram/mg protein) was less than that in the brain (1.2-3.4 microgram/mg protein), but was six-fold higher than any other non-neuronal tissue examined. Glutamate decarboxylase, the GABA synthesizing enzyme was also found in high concentrations in whole ovarian homogenate but not in enriched ovarian granulosa cells, testis, anterior pituitary or muscles. Furthermore, high affinity (Kd = 15-21 nM), specific GABA binding sites were identified in the ovaries by specific [3H]muscimol binding and the majority of GABA binding sites were associated with the granulosa cells. These data suggest a possible role of GABA in the regulation of ovarian functions.