Midpregnancy Elevation of Serum Androstenedione Levels in the C3H/HeN Mouse: Placental Origin*

The purpose of this study was to characterize the serum profile of androstenedione during pregnancy in the C3H/HeN mouse and to determine the site of its production. Serum androstenedione levels were characterized by a prominent midpregnancy elevation and were substantially higher than testosterone levels during pregnancy. The results of our studies support a placental site of production for androstenedione during midpregnancy: 1) uterine venous levels of androstenedione are higher than peripheral androstenedione levels at midpregnancy and during the second half of pregnancy, 2) developmental changes in the in vitro release of androstenedione by conceptuses coincide temporally with serum changes in androstenedione levels, 3) the day 10 placenta releases significantly more androstenedione in vitro than do other endocrine tissues from day 10 of pregnancy, and 4) serum androstenedione levels are maintained after bilateral ovariectomy on day 10 of pregnancy.