Effect of Clomiphene on Blastocyst Nidation in the Rat

Abstract

Blastocysts from albino female rats that received a single, subcutaneous, nidation-inhibiting injection of clomiphene on day 1 of gestation were transferred on day 5 to the uteri of untreated, pseudopregnant hooded female rats or to the sterile uterine horns of unilaterally pregnant, untreated hooded female rats. The recovery of live albino fetuses from hooded recipients indicated that the contraceptive effect of clomiphene was not due to direct cytotoxic action on the developing zygote but to alteration of the maternal organism. This finding was further substantiated by (a) the failure of females injected with clomiphene to maintain the viability of blastocysts transferred to them from untreated females and by (b) the inhibition of decidual formation in pseudopregnant females after injection of a nidation-inhibiting level of clomiphene. The amount of clomiphene necessary to prevent nidation by a single subcutaneous injection on day 1 of gestation was 0.5 mg/kg body weight for Sprague-Dawley albino females and 1.0 mg/kg body weight for Long-Evans hooded females. No gross malformations or skeletal changes were noted among the live fetuses obtained from the untreated, vehicle-injected, or clomiphene-injected females used in this study.