The effect of copper in vivo on specific progesterone binding by human endometrial cytosol

Copper has been shown to interfere with specific progesterone binding by human endometrial and myometrial cytosol in vitro. These results suggested that one possible mode of action of the copper-bearing intrauterine devices (IUDs) is through interference with the action of progesterone at its target sites. A prospective study was carried out to determine whether the proposed mode of action of copper-bearing IUDs could be demonstrated in vivo. The results of this study revealed a significant difference in specific progesterone-binding capacity between proliferative and secretory endometria (P less than 0.001). However, when secretory endometria of the controlled subjects were compared with those of the copper-bearing IUD wearers, no significant difference was observed in the specific progesterone-binding capacity (P greater than 0.2). These data suggested that copper released from copper-bearing IUDs in vivo may not interfere with the binding of progesterone to its receptors in vitro. It is doubtful that the contraceptive effectiveness of copper-bearing IUDs could be due to the ability of copper to prevent progesterone from exerting its full effects on the endometrium.