Extraction of estrogens by human perfused uterus. Effects of membrane permeability and binding by serum proteins on differential influx into endometrium and myometrium.

The present study was undertaken to examine the extractions of estradiol, estrone, and estrone sulfate from the circulation of the human perfused uterus. The differential permeability of endometrial and myometrial vascular beds to estrogens was evaluated in uteri samples obtained during the proliferative and secretive phases of the menstrual cycle. The effects of binding by human serum proteins on estrogen influx into the endometrium and myometrium were also determined by the use of double-isotope, single-injection, timed tissue sampling techniques adapted to the extracorporeal perfusion of human uterus. Tritiated test estrogen was injected into the uterine artery as a mixture with 14C-butanol, a free diffusible reference substance. The influx of 14C-dextran (a membrane-impermeable compound) was used to test the aspecific influx from vasculature to extravascular space. Results show that in the human perfused uterus: (1) membrane permeability plays different roles in estrogen influxes between the endometrium and myometrium; (2) during the proliferative and secretive phase of the menstrual cycle the uterine microvessels are differently permeable to the free plus protein-bound estrogens; and (3) plasma proteins decrease the endometrial and myometrial uptakes of estrogens.