Anordiol is more potent than anordrin for terminating pregnancy when administered with RU 486

Anordiol produces pregnancy loss in the rat--via the embryo or via the uterus?

Anordiol, the dihydroxylated metabolite of anordrin, is an antiestrogen with estrogenic activity that is known to inhibit fertility. The following study was conducted to determine the mechanism of this antifertility effect. Anordiol was administered orally to rats, prior to implantation, on Day 2 of pregnancy. Control animals were treated with the vehicle only. The effectiveness of the agent in terminating pregnancy was determined on Day 14 of pregnancy. Anordiol was 100% effective in abolishing pregnancy at a dose of 0.6 mg/Kg. Administration of smaller doses resulted in a decreased number of implanting embryos, in a dose-dependent manner. An additional dose of anordiol on Day 3 of pregnancy yielded similar results. To determine whether pregnancy impairment by anordiol is exerted via the embryo or via the uterus, reciprocal embryo transfers were performed. Day 5 blastocysts were transferred into the uteri of pseudopregnant rats. In one set of experiments, the donor rats were treated with anordiol, and in the second set the recipient rats were treated. The results indicate that the effects of anordiol administration are exerted via the embryo as well as the uterus.

Effect of mifepristone and antiestrogens on uterine PGF2 alpha and PGE2 concentrations in ovariectomized and pregnant rats

Four antiestrogens (anordiol, tamoxifen, RU 39411, ICI 182780) and the antiprogestin, mifepristone (RU 486), were administered to the following three animal models: (1) ovariectomized rats, (2) mated rats treated post-coitally; and (3) pregnant rats treated post-implantation. The antiestrogens were administered alone or in combination with mifepristone at doses effective in preventing and/or terminating pregnancy in rats. The objective of the study was to determine whether these drugs influenced uterine concentrations of prostaglandins (PGF2 alpha and PGE2). Antiestrogens administered alone to ovariectomized rats did not effect uterine PGE2 or PGF2 alpha concentrations; whereas the combination of anordiol/mifepristone increased uterine PGF2 alpha concentration, resulting in an increase in the PGF2 alpha/PGE2 ratio. Mated rats were treated post-coitally for three consecutive days with anordiol, tamoxifen, estradiol and mifepristone alone and with the combination of anordiol/mifepristone and tamoxifen/mifepristone. An increase in uterine PGF2 alpha concentrations and in the PGF2 alpha/PGF2 ratio occurred only in anordiol/mifepristone treated group. A decrease in uterine PGE2 concentrations occurred in animals treated with anordiol, tamoxifen and estradiol, resulting in an increase in the PGF2 alpha/PGE2 ratio. Anordiol (5.0 mg/kg/day) and mifepristone (4.0 mg/kg/day) alone and the combination of anordiol/mifepristone (2.5/1.0 mg/kg/day) administered to pregnant rats on day 7, 8 and 9 of pregnancy induced an increase in PGF2 alpha levels without affecting uterine PGE2 concentration. The changes in PGF2 alpha concentrations induced by anordiol and the combination of anordiol/mifepristone resulted in an increase in the PGF2 alpha/PGE2 ratio. The antiestrogens tested except for ICI 182780 possessed agonist activity when assayed by measuring their capacity to increase the uterine weights in ovariectomized rats. Also, ICI 182789 was the only antiestrogen that did not influence uterine PG concentrations. It can be concluded that ICI 182780 is the only "pure" antiestrogen among those tested. The present results show that antiestrogens and the combination of mifepristone plus anordiol at doses preventing implantation and terminating pregnancy increase uterine PGF2 alpha and/or decrease PGE2 concentrations, resulting in an alteration of PGF2 alpha/PGE2 ratio. These findings suggest that there exists a critical balance of PGF2 alpha to PGE2 concentrations in the uterus required for the normal passage of fertilized ova through the oviduct, initiating implantation of the blastocysts, development of embryos, and maintenance of pregnancy.

Effects of anordiol, an antiestrogen, on the reproductive organs of the male rat

Anordiol, an antiestrogen, was administered at doses of 2.5 and 10 mg/kg day-1 for 30 and 60 days to adult male rats. A significant decrease in serum LH, FSH, and testosterone levels occurred in the treated animals as compared to controls. Serum testosterone and LH levels decreased to about 15-35% of control value on day 15 of treatment and reached undetected levels thereafter. Serum FSH level also decreased to about 25-50% of control value by day 15 of treatment and remained at this level. Significant decrease in the weights of the tests and accessory reproductive organs occurred following anordiol treatment, while the body weights remained at pretreatment level. Histological examination of the tests revealed significant decrease in the diameter of the seminiferous tubules and in the number of germ cell elements. Spermatogenesis was arrested at the secondary spermatocyte stage. Leydig cells appeared atrophic and contained pyknotic nuclei. The epididymis, prostate, and seminal vesicle showed degenerative changes. The secretory activity of the glandular epithelium of the prostate gland appeared to be markedly reduced. In conclusion, anordiol acts by blocking gonadotropin production and/or release by the pituitary; thereby testosterone production by Leydig cells is not stimulated, causing spermatogenesis arrest.

Comparative effectiveness of three antiprogestins alone and in combination with anordiol in terminating pregnancy in the rat

The effectiveness of mifepristone, onapristone, and ORG 31806 alone or in combination with anordiol to terminate pregnancy in the rat was evaluated. ORG 31806 at a dose of 2 mg/kg/day, mifepristone at 4 mg/kg/day, and onapristone at 8 mg/kg/day, terminated pregnancy in all treated animals. Anordiol, an antiestrogen, at a dose of 5 mg/kg/day, terminated pregnancy in all treated animals. Anordiol acted synergistically with all three antiprogestins terminating pregnancy in the rat. The antiprogestins at doses that were either partially effective or non-effective became 100% effective when administered with a non-effective dose of anordiol. Thus, combination of ORG 31806 (1 mg/kg/day) plus anordiol (0.31 mg/kg/ day), mifepristone (1 mg/kg/day) plus anordiol (0.62 mg/ kg/day), and onapristone (2 mg/kg/day) plus anordiol (2.5 mg/kg/day) terminated pregnancy in all treated animals. These combinations of the antiprogestins and anordiol decreased significantly the serum progesterone levels but not serum 17 beta-estradiol levels. The present results indicate that the most potent combination was ORG 31806 plus anordiol.

Anordiol and RU486 synergize to produce preimplantation pregnancy loss by increasing embryo transport (rat)

RU486, an antiprogestational agent, and anordiol (dihydroxylated metabolite of anordrin) which has an estrogenic and antiestrogenic activity, are known to inhibit fertility. These agents were administered orally, alone or together, to rats prior to implantation, on Day 2 of pregnancy. Control animals were fed with the vehicle only. The effectiveness of the agents in terminating pregnancy in female rats was determined on Day 14 of pregnancy. Anordiol presented a dose-dependent effect on abolishing pregnancy, being 100% effective at 2.5 mg/Kg and non-effective at 0.6 mg/Kg. RU486 did not prevent pregnancy even at a dose of 4 mg/Kg. Doses of RU486 and anordiol that were ineffective when administered alone, prevented pregnancy in 70% of the rats when these agents were given together. To determine the mechanism by which these drugs prevent pregnancy, oviducts and uteri of rats were examined for presence of embryos on Day 3 of pregnancy. Only 29% of embryos were recovered from the oviducts of rats treated with 2.5 mg/Kg anordiol (compared to 89% in control group) plus an additional 9% from the uteri. In combination, anordiol and RU486 had a synergistic effect on embryo transport in the rats' reproductive tract, without any apparent accumulation in the uterus. These results led us to conclude that the pregnancy preventing action of anordiol plus RU486 is mostly due to accelerated transport of the embryos in the reproductive tract prior to implantation.

Potentiating effect of epostane on pregnancy terminating activity of RU 486 in the rat

The effectiveness of a combination of RU 486, an antiprogestin, and epostane, a 3 beta-hydroxysteroid dehydrogenase inhibitor, for termination of pregnancy in female rats was determined. Epostane administered at doses ranging from 8 to 48 mg/Kg/day on days 7, 8, and 9 of pregnancy did not influence the progress of the pregnancy. RU 486 in doses of 1, 2, and 4 mg/Kg/day terminated pregnancy in 0, 40, and 100% of rats, respectively. The combination of epostane (48 mg/Kg/day) plus RU 486 (1 and 2 mg/Kg/day) terminated pregnancy with complete resorption of fetuses in all treated animals. Unexpectedly, the drug combination that terminated pregnancy used a dose of epostane that was not highly effective in lowering serum progesterone levels when epostane was administered alone. Thus, in the rat, the synergistic action of epostane plus RU 486 may not be dependent upon reduced progesterone secretion plus receptor blockage as anticipated. The present results suggest that the combination of epostane plus RU 486 is effective for pregnancy termination.