Administration of minute quantities of 17β-estradiol on the nasal area terminates early pregnancy in inseminated female mice

It is well established that chemical emissions of novel males disrupt intrauterine implantation of fertilized ova in inseminated female mice, but the specific nature of these chemicals is not known. Given that novel males excrete androgens and estrogens in their urine and feces, the current experiments were designed to determine whether nasal application of these steroids could disrupt pregnancy. Nasal application of testosterone propionate to females during early pregnancy had no impact on gestation. However, nasal application of 17beta-estradiol terminated all pregnancies in females at all doses greater than or equal to approximately 1 microg/day. Nasal application of 17beta-estradiol benzoate similarly terminated all pregnancies in females at very low doses. In subcutaneous administration, 17beta-estradiol is also the most potent steroid in disrupting pregnancy compared to other estrogens and androgens. These data suggest the possibility that males' emission of estrogens is among factors mediating the Bruce effect.