Radioimmunoassay and Metabolism of the Catechol Estrogen 2-Hydroxyestradiol

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Abstract
Plasma levels of 2-hydroxyestradiol (2-OHE2)were measured using a new RIA procedure. Values were below the detection limit of the assay (2 elevated its plasma concentration to 155 pg/ml, consistent with a plasma MCR (MCRp) of approximately 20,000 liters/day. The infusion of [3H] 2-OHE2 to equilibrium and chromatographic separation of the extracted plasma metabolites yielded an MCRp of about 13,000 liters/day; the major plasma metabolite comigrated with 2-methoxyestradiol, and [3H]/-methoxyestrone was also formed. The MCRp of 2-OHE2 is approximately half that of 2-hydroxyestrone (2-0HE/), but much higher than those of other steroids. As is true for 2-OHE1, the clearance of 2-OHE2 must occur primarily in the blood compartment. Together, the measured MCRP values and estrogen receptor affinities of 2-OHE2 and 2-OHE 1 predict a relative potency for effects upon gonadotropin secretion which i close to that observed in vivo.

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