Effect of clomiphene on rat zygotes

Preovulatory administration of clomiphene citrate to mice causes fetal growth retardation and neural tube defects (exencephaly) by an indirect maternal effect

Clomiphene citrate was administered to female mice at different doses and different times prior to ovulation, in the preimplantation period after ovulation, and after implantation. Pregnancy outcome was determined on day 15 of gestation, when the number of implantations and resorptions were calculated relative to the number of ovulations, and fetuses were assessed for size and stage of development and morphological abnormalities. Preovulatory administration of clomiphene citrate caused decreased implantation rates and growth retardation of surviving fetuses, the degree of the effect being dependent on the dose and the time of drug injection relative to ovulation. The implantation rate was lowest, and the degree of fetal growth retardation highest, when clomiphene citrate was administered immediately before ovulation. An increased incidence of exencephaly was found in the fetuses of females injected with clomiphene citrate prior to ovulation. Transfer of blastocysts from treated mice to untreated fosters showed the effect of clomiphene citrate on implantation and fetal growth to be predominantly mediated through the female reproductive tract, rather than a direct effect on the embryo itself. Administration of clomiphene citrate in the preimplantational period resulted in complete inhibition of implantation, while the only effect when administration was after implantation was a slight reduction in fetal weight. These results indicate that preovulatory clomiphene citrate impairs uterine function, which has an indirect effect on the growth and development of the postimplantation embryo.

Effect of clomiphene on nuclear estrogen receptor of the fallopian tube during ovum transport in rabbits

The effect of clomiphene on nuclear estrogen receptors of the Fallopian tube during ovum transport in the rabbit has been studied. Nuclear binding capacity was observed in ampulla (A), ampullary-isthmic junction (AIJ), isthmus (I), uterine-isthmic junction (UIJ) and uterus (U). Receptor concentration decreased in all segments of the tube after administration of clomiphene in mated animals. The bindings are of high affinity and low capacity. Important alterations were observed during transport when compared to that of 14, 24, 34, 48, 72, 144 and 168 hr post-coitum (p.c). At 24 hr p.c binding increased only in I and decreased in A and AIJ. Retention of eggs at I at 24 hr p.c showed as increase in binding at I. Egg transport was accelerated and eggs reached prematurely in the uterus due to the influence of clomiphene. Binding in I remained constant from 48 hr p.c to 144 hr p.c but concurrently the binding level increased in U from 34 hr p.c. The elevation of nuclear estrogen receptor level was maximum at 24 hr p.c which coincided with increased plasma estrogen level. The result of such study showed that clomiphene depleted nuclear estrogen receptor complex in the fallopian tube before transfer to the uterus. Further, observation indicated that clomiphene acted directly on the rate of egg transport because of the variations in estrogen receptors during different time periods. Thus, clomiphene reduced the quantity of estrogen receptor i.e., insensitiveness to estrogen. The variations in estrogen binding to its receptor and plasma level at different post-coital periods are modulated by clomiphene resulting in the acceleration of egg transport and prevention of pregnancy.

The effects of enclomiphene and zuclomiphene citrates on mouse embryos fertilized in vitro and in vivo

The ovulatory agent clomiphene citrate, a racemic mixture of the estrogenic zuclomiphene and antiestrogenic enclomiphene isomers, has been associated with gamete/embryo toxicity in various animal models. To assess the potential effects of these isomers on fertilization and early embryogenesis, 3200 embryos were obtained from mouse oocytes fertilized in vivo and in vitro and exposed to increasing concentrations of zuclomiphene, enclomiphene, and clomiphene citrate in culture. Fertilization rates (p less than 0.01), blastocyst formation rates (p less than 0.02), and degeneration rates (p less than 0.005) were all adversely affected in a dose-dependent fashion. There were no statistically significant differences between the two isomers. Preincubation with 17 beta-estradiol did decrease the degenerative changes induced by clomiphene citrate but did not improve the decreased rate of blastocyst formation. These findings suggest adverse effects of a high concentration of clomiphene citrate and its isomers on fertilization and early mouse embryo growth that may have implications in the clinical use of this drug.

Embryo toxicity of clomiphene citrate on mouse embryos fertilized in vitro and in vivo

The effect of the ovulatory agent clomiphene citrate on fertilization and early embryogenesis was investigated with the use of in vitro fertilized mouse oocytes. Alterations in early embryogenesis with clomiphene citrate exposure were further studied with the use of embryos obtained from mouse oocytes fertilized in vivo. In the nontreated group, the fertilization rate was 81%, and 61% of the oocytes reached the blastocyst stage by 96 hours. Both fertilization and blastocyst formation declined in a dose-dependent fashion when clomiphene citrate was added to the culture media in concentrations greater than or equal to 10 micrograms/ml (p less than 0.001). The rate of progressive embryo cleavage was also slower at 48 and 72 hours after drug exposure. Mouse embryos fertilized in vivo demonstrated similar findings, with decreased blastocyst formation and increased degeneration rates, again at clomiphene citrate concentrations greater than or equal to 10 micrograms/ml (p less than 0.01). Exposure to the drug beyond 24 hours had no additional effect. It appears that clomiphene citrate-exposed embryos may undergo subtle changes that later manifest themselves in the form of decreased embryo growth rates and increased embryo degeneration rates.

Direct ovarian effect of clomiphene citrate in the rabbit

The effects of clomiphene citrate (CC) on ovulation and ovum maturation were studied using the isolated perfused rabbit ovary. CC (10(-5) M) added to the perfusate with human chorionic gonadotropin (50 IU) did not affect ovulatory efficiency, ovulation time, oocyte maturation, or degeneration of ovulated ova and follicular oocytes. During perfusion without human chorionic gonadotropin, the percentage of follicular oocytes with germinal vesicle breakdown was significantly increased in response to CC (10(-5) M or 10(-7) M); a greater percentage of follicular oocytes was degenerated. Estradiol (100 ng/ml) added to the perfusate reversed the effect of CC on degeneration of follicular oocytes. Of follicular oocytes from ovaries perfused with CC, 79.3% were degenerated; in contrast, 25% were degenerated in ovaries treated with CC plus estradiol. These data suggest that CC has a direct ovarian effect and that ovum degeneration associated with CC may be related to an antiestrogenic action.

The in vivo and in vitro effects of clomiphene citrate on ovulation, fertilization, and development of cultured mouse oocytes

Clinical data indicate a high rate of discrepancy between ovulation and pregnancy rates and a high abortion rate in anovulatory women treated with clomiphene citrate. An animal model was used to examine the in vivo and in vitro effects of the drug on fertilization and preimplantation development. This work indicates that mice treated with clomiphene in the early follicular phase of pregnant mare's serum-induced cycles show a dose-dependent decrease in ovulated oocytes. No effect was seen on the further development of these ova. When the drug was administered in the late follicular phase, a dose-dependent decrease was seen in the rate of successful copulation, ovulation, and embryo development. Concomitant 17 beta-estradiol treatment reversed the copulatory, ovulatory, and developmental effects of clomiphene. A short in vitro treatment of oocytes with clomiphene prior to in vitro fertilization resulted in an increased proportion of degenerated and unfertilized ova. Moreover, this treatment caused a dose-dependent decrease in blastocyst formation.

Clomid administration to pregnant rats causes abnormalities of the reproductive tract in offspring and mothers

In rats, a single injection of clomiphene citrate (Clomid) during pregnancy causes multiple abnormalities of the reproductive tract in the offspring and mothers. These abnormalities probably result from the ability of Clomid to cause long-term estrogenic stimulation.