NON-PROTEIN-BOUND OESTROGENS IN PLASMA AND URINARY EXCRETION OF UNCONJUGATED OESTROGENS IN NON-PREGNANT WOMEN

Abstract

The concentrations of oestrone and oestradiol-17β in peripheral plasma and the urinary excretion of unconjugated oestrone and unconjugated oestradiol-17β were measured by radioimmunoassay in 31 matched samples from seven young women. The concentrations of oestrone and oestradiol-17β not bound to protein in the plasma samples were measured following equilibrium dialysis. The urinary excretion of unconjugated oestrone (0·70 ± 0·34 nmol/24 h, mean ±s.d., n = 28) was found to be significantly, but poorly, correlated with the concentration of non-protein-bound oestrone in plasma (10·2 ± 3·8 pmol/l) (r = 0·44, P < 0·05). Similarly, the urinary excretion of unconjugated oestradiol-17β (0·29 ± 0·16 nmol/24 h, n = 30) was found to be significantly, but still rather poorly correlated with the concentration of non-protein-bound oestradiol-17β in plasma (7·4 ± 5·3 pmol/l) (r = 0·58, P< 0·001). Since the calculated proportions of oestrone and oestradiol-17β in plasma not bound to protein (3·4 ± 0·3% and 1·7 ± 0·2% respectively) remained fairly constant (coefficient of variation 9 and 10% respectively), measurement of oestrone or oestradiol-17β in plasma provided a better guide to the biologically available (non-protein-bound) hormone than did measurement of urinary unconjugated oestrogen. The mean renal clearance of both non-protein-bound oestrone and non-protein-bound oestradiol-17β (50 ± 21 and 36 ± 23 ml/min) was less than that of creatinine (114 ± 31 ml/min) indicating absorption and/or metabolism of each hormone by the kidney tubule.