Genetic variation in plasma androgens and ovarian aromatase activity during mouse pregnancy.

Genetic variation in fetal survival, maternal plasma androgen levels, and ovarian aromatase activity was examined mid (Day 9) and late gestation (Day 16) in strains of mice that differ in reproductive performance (A/J, C57BL/6J, C8/JIs, C17/JIs, and S15/JIs). At both gestational stages, females selected for large litter size (S15/JIs) carried more fetuses than any of the other strains examined. Particularly at midpregnancy, S15/JIs females also maintained higher plasma levels of androstenedione and testosterone relative to both control strains, C8/JIs and C17/JIs. Consistent with previously reported changes in peripheral estrogen levels during mouse pregnancy, aromatase activity was higher on Day 16 than on Day 9. This study demonstrates genetic variation in fetal survival that is correlated with increased maternal androgen levels. A stage-specific gestational increase in aromatase activity occurs in several strains of mice and is associated with elevated plasma estrogen during the second half of pregnancy.