Accumulation of steroids in rabbit preimplantation blastocysts

Abstract

The concentrations of progesterone, androstenedione, testosterone, estrone and estradiol were measured by radioimmunoassay in blastocysts and uterine fluid flushings collected from rabbits 110-159 h post coitum (p.c.). None of the blastocysts or uterine flushings contained detectable levels of androstenedione, testosterone or estrone. All uterine flushings contained large amounts of progesterone, and some of the flushings also contained estradiol. A small amount of progesterone (.apprx. 7.5 pg/blastocyst) was 1st detectable in some blastocysts at 135 h p.c.; progesterone levels/blastocyst then increased progressively, reaching levels of about 122-158 pg/blastocyst at 159 h p.c. Micropuncture of blastocysts at 159 h p.c. indicated that .gtoreq. 90% of the progesterone in the embryo was in the blastocoelic fluid. Blastocysts from rabbit uterine horns containing estradiol also contained estradiol, but those in which estradiol was detected were never observed in uteri lacking the hormone. Rabbit blastocysts probably accumulate both progesterone and estradiol from uterine fluid.