The Renal Clearance of Endogenous Estrogens in Late Pregnancy*

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Abstract
The urine: plasma concentration ratios (U/P) and renal clearance values for estrone and estradiol-17[beta] differed markedly from those for estriol. The mean U/P ratios for estriol and estradiol were 2.08 and 1.47, respectively, while the mean U/P ratio for estriol was 37.4. The mean renal clearances for estrone and estradiol-17[beta] were 11.95 and 8.80 ml/min, while the mean renal clearance of estriol was 205.5 ml/min, a value significantly higher than the simultaneously-determined mean endogenous creatinine clearance of 131.3 ml/min. This indicates that estriol is secreted in part at least by the renal tubule, probably as a glucosiduronate. Probenecid administration reduced the urinary excretion rate and renal clearance of all three estrogens, at the same time raising the plasma estrogen concentration.