Low plasma levels of 2-hydrdxyestrone are consistent with its rapid metabolic clearance

Published plasma levels of the catechol estrogen 2-hydroxyestrone (2-OHE₁) are comparable to those of estrone and estradiol. In light of the very high (40,000 L/d) metabolic clearance rate of 2-OHEi, these concentrations imply unreasonable production rates. We therefore re-examined plasma 2-OHE₁ levels using a modified radiotnnmmoassay procedure. Plasma samples are extracted with ethyl acetate and passed over a short column of LH-20 Sephadex before equilibration with an antiserum directed against a 2-hydroxyestrone-17-(O-carboxymethyl)oxime-bovine serum albumin conjugate. Plasma 2-OHE₁ concentrations are indistinguishable from blank (< 15 pg/ml) in men and non-pregnant women, but rise to ~ 200 pg/ml during pregnancy. These values for 2-OHE₁ levels are consistent with the rapid metabolic clearance of this catechol estrogen.