Renal clearances of estriol conjugates in normal human pregnancy at term

In late human pregnancy more than 90 per cent of the total estriol (E3) in body fluids consists of four conjugates, estriol-3-sulfate (E3-3S), estriol-16-glucosiduronate (E3-16G), estriol-3-glucuronide (E3-3G), and estriol-3-sulfate-16-glucosiduronate (E3-3S-16G). Since the relative amounts of E3 in blood and urine would be determined by the kidney, the renal clearance of each conjugate was determined and compared with inulin and p-aminohippuric acid (PAH) clearance, as measures of glomerular filtration rate (GFR) and the effective renal plasma flow. Five women were studied in the lateral decubitus position with inulin and PAH infusion. Samples of blood and urine were collected at 40 minute intervals and analyzed. The method for E3 conjugates involved separation of the four conjugates on Sephadex LH-20, enzyme hydrolysis, and radioimmunoassay. Renal clearances for E3-3S and E3-3S-16G were below inulin. E3-3G approximated inulin; E3-16G exceeded inulin and approached PAH. In plasma E3-3S-16G represented 48.4 +/- 7.2 per cent; in urine E3-16G represented 69.5 +/- 7.3 per cent of total E3. Thus, different conjugates predominate in blood and urine.