Studies on the Transport of Estrogens by the Rat Small Intestine in Vivo

Abstract

Summary

Rats intraduodenally administered 17β-estradiol-6,7 -³H (E), ethynylestradiol-6, 7 -³H (EE) or ethynylestradiol-6, 7 -³H-3-cyclopentyl-1-¹⁴C ether (EECPE) were killed at 7.5-, 30- or 120-min intervals. Intestinal lumen contents, intestinal wall homogenates and portal plasma were analyzed for free and conjugated steroids. After 7.5 min, more than 80% of the administered dose of E or EE had been absorbed. Characterization of the steroids present in the various ether extractable fractions (free steroid) indicated that, unlike EE, E had undergone rapid metabolic transformation with estrone accounting for 70% of the total radioactivity in the intestinal wall and portal blood. This transformation to the less potent estrone could be responsible for the reduced biological activity of orally administered E.