[Effects of intrauterine contraceptive devices (IUD) on rat ovarian steroidogenesis and conception control].

To elucidate the action mechanisms of the IUD, I examined the relationships between ovarian steroid levels and contraceptive mechanisms in IUD-inserted rats. Female Wistar rats, 59-61 days old, were used and a polyethylene tube was into the bilateral uterine horns. Half of animals were injected with 1 mg indomethacin at the 30th and 31st days after the operation. All animals were decapitated at 1 hr after the 2nd injection. The presence of the IUD significantly increased the uterine weights due to the hypertrophy of the uterine wall, and it significantly increased ovarian testosterone and tended to increase ovarian estradiol and the estradiol/progesterone ratio. However, administration of indomethacin did not reduce these increased levels back to the levels of sham-operated rats. These results indicate that the presence of the IUD increased ovarian testosterone and estradiol, disturbing the balance between estrogen and progestin, with estrogen becoming dominant. It seems that these changes bring about the delay of fertilized egg development and disrupts the development of proper conditions for implantation, so that implantation of the fertilized egg on the endometrium is inhibited. Furthermore, this study suggests that the changes of the ovarian steroid levels in IUD-inserted rats may involve the participation of unknown uterine factors but not prostaglandins.