Intestinal first-pass effects of estrone sulfate and estrone in the rat

Mixtures of (14C)-estrone and (3H)-estrone-sulfate (10 micrograms and 13 micrograms, respectively) were instilled into the lumina of intact jejunal loops of rats. Estrone was faster absorbed into portal blood than was estrone-sulfate (72% vs. 17% in 30 min). In portal blood the chemical forms derived from estrone were: unchanged estrone (72%), estrone-glucuronide (14%), estrone-sulfate (5%) and estradiol (9%); no estriol was formed. The chemical forms of estrone sulfate were: estrone-sulfate (86%), estrone (6%), estrone-glucuronide (2%), estradiol (2%) and estradiol-sulfate (4%). These metabolites were also found in the lumen. It is concluded that the intestinal first-pass effects do not significantly influence the hormonal activities of the two estrogens.