Presence of gamma-aminobutyric acid and its specific receptor binding sites in the human term placenta.

The concentration of gamma-aminobutyric acid (GABA), the activity of glutamate decarboxylase (GAD), and the presence of specific GABA receptor binding sites have been examined in human term placentas. The estimated values of GABA concentration and GAD activity in the placenta were about 50 nmol/g tissue and 1.1 nmol/mg protein/h, respectively. A remarkable density of high-affinity and specific GABA binding sites has also been demonstrated in membranes of the human term placenta. These binding sites showed the properties of a GABAA receptor. The present findings suggest a possible role of GABA in the function of human placenta.