Radioimmunoassay for 4-Hydroxyestrone 4-Methyl Ether in Human Urine

Summary

4-Hydroxyestrone 4-methyl ether (4-OHE₁ 4-Me) was converted to its 17-(O-carboxymethyl)oxime and then coupled to bovine serum albumin. The injection of this steroid-protein conjugate into rabbits induced the formation of antibodies with high specificity and affinity for 4-OHE₁ 4-Me. With this antiserum a radioimmunoassay was developed which allowed the measurement of 4-OHE₁ 4-Me with a lower limit of detection of 6 pg/tube. Using a simple and practicable method for the hydrolysis and purification of urine, the excretion rates of 4-OHE₁ 4-Me were reliably measured in healthy human subjects: male children 0.1 μg/24 h, female children 0.2 μg/24 h, men (20-45 years) 0.7 μg/24 h, men (> 50 years) 0.5 μg/24 h, women, follic. 0.5 μg/24 h, periov. 0.6 μg/24 h, luteal 0.6 μg/24 h, women pregn., first trim. 2.3 μg/24 h, sec. trim. 2.9 μg/24 h, third trim. 5 μg/24 h, women postmenop. 0.5 μg/24 h. These urinary excretion rates of 4-OHE₁ 4-Me are significantly lower than those of 4-hydroxyestrone. Comparing the ratios 4-OHE₁ 4-Me/4-hydroxyestrone with those of 2-hydroxyestrone 2-methyl ether/2-hydroxyestrone, it becomes obvious that endogenous 4-hydroxyestrogens are methylated in vivo to a much lesser extent than the isomeric 2-hydroxyestrogens, a finding which could partly explain why 4-hydroxyestrogens have higher biologic potencies than their 2-hydroxylated isomers.

Key-Words:

Catecholestrogens - 4-Hydroxyestrogens - 4-Hydroxyestrone 4-Methyl Ether - Radioimmunoassay - Metabolism