Modulation of uterine GABAA receptors during gestation and by tetrahydroprogesterone.

Binding of a GABAA receptor agonist, [3H]muscimol, was studied in rat uterine membranes of non-pregnant rats and those at days 15 and 19 of pregnancy. Also, an interaction of the uterine GABAA receptors with tetrahydroprogesterone was examined. At day 15 of gestation [3H]muscimol binding was twice as high as in non-pregnant rats, but at day 19 it was reduced. These changes resulted from an increase of the receptor affinity and decrease of the receptor density, at days 15 and 19, respectively. Since tetrahydroprogesterone, in vitro, also increased [3H]muscimol binding, we propose that this steroid may participate in regulation of uterine function during pregnancy.