Comparison of the adverse effects of adrenal and ovarian steroids on early pregnancy in mice

In one experiment, female C57- and HS-stain mice were inseminated according to standard procedures and randomly assigned to conditions involving administration of various adrenal and ovarian steroids in the first trimester of pregnancy. The pattern of effects was similar in the two strains, although generally C57 females produced fewer and smaller litters than did HS females. Oestradiol benzoate injections completely blocked pregnancy at doses far less than those effective for other steroids. Corticosterone injections did not produce any significant pregnancy block. Androstenedione injections produced a pregnancy block at 500 micrograms per day. Dehydroepiandrosterone produced a mild pregnancy block at both 500 micrograms and 100 micrograms per day. In a second experiment, the dose-response curve for oestradiol was examined. Daily doses of 0.333 microgram and greater completely blocked pregnancy, a dose of 0.111 microgram did so in the majority of females, and smaller doses had little effect. These results, taken together with other data, suggest that oestrogenic action may mediate the stress-induced block of pregnancy.