Uterine estrogen sulfatase activity at the time of blastocyst implantation in the rat.

The conversion of estrone sulfate (E1S) to estrone (E1) was measured during the in vitro incubation of the labeled sulfoconjugate with implantation sites (IS) and nonimplanted regions (NIS) of uterine horns from 6-day pregnant rats. Extensive metabolism of E1S occurred in both tissues, being noticeably less (29.31%) in IS than in NIS. Estrogen sulfatase activity present in the uterus of ovariectomized virgin rats was found to be higher than in both uterine regions of the pregnant rats. We suggest that E1S present in uterine fluids may be accessible to be metabolized into unconjugated estrogens by both intrauterine tissues of 6-day pregnant rats. This metabolism could be locally modulated in IS through the participation of the estrogen sulfatase, the activity of which is in turn controlled by the presence of free estrogens, possibly synthesized and/or secreted by the embryo, which has been shown to inhibit the sulfohydrolase activity.