In vitro studies with 16-C14-estrone: distribution between plasma and red blood cells of man.

Albrieux has reported that the blood cells of nonpregnant women contained at least twice as much estrogenic activity as the blood serum, while during pregnancy the estrogenic activity was equally distributed between cells and serum (1, 2); however, the specificity of the assay used in these studies is questionable. Bischoff, Katherman and Yee, using the uterine weight of immature rats as bioassay technique, investigated the in vitro distribution of estrogens in blood (3, 4); after an equilibrium period of 10 minutes at 37.5° C., it was found that the ratio of biological activity in red cells to that in serum of rabbit blood was from 0.39 to 0.11 for estrone. An increase in the total recovery of biologic activity could be produced by prolonging incubation, thus suggesting a partial transformation of estrone into a more biologically active steroid (4); the conditions of this activation were studied in detail (5) and Gray and Bischoff demonstrated quite conclusively that the increase in activity was due to the conversion of estrone to estradiol by human and rabbit red cells (6). Sandberg, Slaunwhite and Antoniades have observed that approximately 30 per cent of the 16-C14-estrone added to a sample of whole blood remained with the red cells, while in a reverse dialysis experiment 55 per cent of the radioestrone was associated with the red cells (7). The present work is an attempt to study further the in vitro distribution of 16-C14-estrone between plasma and red blood cells of man.