Table 3

Rate of metabolic conversion of [3H]E1 to major estrogen metabolites by male and female liver microsomes

E1 Metabolites FormedAverage Rate ± S.D. (Range) of E1 Metabolite Formation
Male Subjects (n = 21)Female Subjects (n = 12)Total (n = 33)
pmol/mg of protein/min
y-OH-E2 1.6 ± 1.6 (0.3–7.1)2.0 ± 1.8 (0.4–5.5)1.7 ± 1.7 (0.3–7.1)
y-OH-E1 9.5 ± 8.2 (1.6–36.0)13.5 ± 9.9 (3.4–35.3)11.0 ± 9.0 (1.6–36.0)
 6β-OH-E1 4.5 ± 2.5 (2.0–12.9)5.8 ± 2.9 (2.3–12.6)5.0 ± 2.7 (2.0–12.9)
 16α-OH-E1 +16β-OH-E1 7.1 ± 5.6 (1.6–24.0)9.8 ± 7.3 (3.1–24.6)8.1 ± 6.3 (1.6–24.6)
 6-keto-E1 +M25.6 ± 1.6 (3.3–9.0)5.3 ± 2.8 (2.8–12.0)5.5 ± 2.1 (2.8–12.0)
 4-OH-E2 3.6 ± 2.3 (1.1–9.8)3.5 ± 2.4 (1.1–8.4)3.6 ± 2.3 (1.1–9.8)
 2-OH-E2 11.1 ± 6.0 (4.2–27.2)9.5 ± 5.6 (3.3–21.8)10.5 ± 5.8 (3.3–27.2)
 2-OH-E1 70.4 ± 38.9 (22.1–166.8)67.9 ± 48.1 (28.8–188.3)69.5 ± 41.7 (22.1–188.3)
 4-OH-E1 14.6 ± 9.1 (4.7–41.7)17.2 ± 11.2 (5.7–41.4)15.6 ± 9.8 (4.7–41.7)
 E2 52.0 ± 12.6 (32.7–74.0)43.5 ± 14.7 (21.2–69.4)48.9 ± 13.8 (21.2–74.0)
 X76.3 ± 42.9 (31.1–206.3)98.9 ± 45.2 (41.3–186.8)84.5 ± 44.4 (31.1–206.3)

Note: The incubation mixtures consisted of human liver microsomes (1 mg/ml of microsomal protein), 20 μM E1 (containing 2 μCi [3H]E1), 2 mM NADPH, and 5 mM ascorbic acid in a final volume of 0.5 ml 0.1 M Tris-HCl/0.05 M HEPES buffer, pH 7.4. Incubations were carried out for 20 min at 37°C, and the formation of estrogen metabolites was determined by HPLC analysis as described under Materials and Methods. As indicated, each value is the mean ± S.D. from 21 male subjects or 12 female subjects or all 33 subjects combined, and the values in parentheses indicate the range from the lowest to the highest rate. The final rate of formation for 2, 4, or 6-hydoxy/keto E1 metabolites was corrected by taking into account the loss of radioactivity during the NADPH-dependent microsomal metabolism of [2,4,6,7-3H]E1.