Estrogen sulfotransferase and 17 beta-hydroxysteroid dehydrogenase activities in guinea-pig chorion through gestation

Estrogen sulfotransferase (EST) activity measured under optimal in vitro conditions in the 105,000 g cytosols (HSS) of homogenized intrauterine tissues (amnion, chorion, endometrium, decidua basalis and placenta) from guinea-pigs at the 50th day of gestation indicated that the highest specific activity occurred in the chorion. EST activity in the chorion increased from day 34 (early gestation) to peak around day 45 (mid-gestation), before significantly decreasing around day 50 and further declining to barely detectable levels beyond day 60 (late gestation, the onset of parturition). 17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) activity in the chorion was almost completely membrane associated. The specific activity of the 17 beta-HSD reduction reaction in the 105,000 g pellet was 2.5-fold higher at mid-gestation than at late gestation, while the specific activity of the 17 beta-HSD oxidation reaction was 1.7-fold higher at mid-gestation as compared with late gestation. When intact pieces of chorion tissue from mid- and late gestation were incubated with 5 nM [3H]estradiol (E2), approx. 80% of the recovered free estrogen was E1 (estrone). Only chorion from animals at the onset of parturition were able to produce detectable amounts of E2 from 5 nM [3H]E1. Under the same experimental conditions the ratio of estradiol sulfate (E2S) to estrone sulfate (E1S) isolated from the media and methanol washes of late gestation chorion tissue was 3-4 times greater than for the day 45 tissue.