Inhibition of uterine contractility by progesterone and progesterone metabolites: mediation by progesterone and gamma amino butyric acidA receptor systems.

Progesterone and several progesterone metabolites are capable of inhibiting uterine contractility. Some progesterone metabolites have shown little or no affinity for the progesterone receptor but have been found to be potent modulators of theGABAA receptor system. This study examined whether the inhibition of uterine contraction by progesterone and its metabolites was progesterone receptor-mediated or gamma amino butyric acidA (GABA5) receptor-mediated. Uterine contractions were measured in annular rings of uterine tissue, 5 mm in length, from diestrous II rats, under a fixed tension of I gram. The steroids tested