Metabolic Clearance Rates of Catechol Estrogens in Rats

MCRs of the catechol estrogens 4-hydroxyestra-diol (4-OHE2) and 2-hydroxyestradiol (2-OHE2) and of the parent estrogen 17β-estradiol (E2) were determined in rats. Long term ovariectomized Wistar rats were infused with the steroids at a constant rate for 3 days via a catheter placed in the abdominal aorta.Blood samples were drawn discontinually by retroorbital puncture, and the serum concentrations of E2, 4-OHE2, and 2-OHE2 were measured by RIA. Steady state was reached within 24 h of infusion. Mean serum MCRs were calculated to be 740 ± 117 ml/h for E2, 2700 ± 1000 ml/h for 4-OHE2) and 8300 ± 1700 ml/h for 2-OHE2. Thus, the MCRs of the catechol estrogens were definitely higher than the MCR of E2, resulting in an apparent ratio of 1:4:11 (E2:4-OHE2:2-0HE2). (Endocrinology 113: 1781,1983)