Evidence for the simultaneous uptake and release of certain estrogens by the splanchnic area in the dog

Splanchnic extractions of total radioactivity, unconjugated radioactive estrogens, radioactive estrone glucosiduronate, and radioactive estradiol-17beta glucosiduronate(s) were determined in dogs following the infusion of (3H)estrone glucosiduronate and of (3H)estrone. Splanchnic extractions of radioactive estradiol-17alpha-3-glucosiduronate were determined after (3H)estrone glucosiduronate infusion. The mean splanchnic extractions of total radioactivity after (3H)estrone glucosiduronate and (3H)estrone infusions were positive and similar (42.2 +/- 2.4% (SE) and 34.9 +/- 2.4% (SE), respectively). The mean splanchnic extraction of unconjugated radioactive estrogens after (3H)estrone glucosiduronate infusion (39.3 +/- 2.6%) was significantly less than that after (3H)estrone infusion (86.4 +/- 2.3%). The difference was best explained by different rates of formation of unconjugated from conjugated estrogens, suggesting, in turn, that simultaneous uptake and formation of unconjugated estrogens occur in the splanchnic area. The mean splanchnic extraction of extradiol-17alpha-3-glucosiduronate was 33 +/- 3.9%. The mean splanchnic extraction of radioactive estrone glucosiduronate after (3H)estrone glucosiduronate infusion was positive (54.7 +/- 2.3%) and after (3H)estrone infusion was negative (-50.8 +/-8.8%. The mean splanchnic extraction of estradiol-17beta glucosiduronate(s) was also positive (32 +/- 2.4%) after (3H)estrone glucosiduronate infusion and negative (-37.9 +/- 11.0%) after (3H)estrone infusion. These values are taken to indicate that simultaneous uptake and formation (from unconjugated estrogens) of both estrone glucosiduronate and estradiol-17beta glucosiduronate(s) occur in the splanchnic area, and that after (3H)estrone infusion, the rate of formation greatly exceeds t