Fig. 3.

Quantification of 2- and 4-hydroxylation of E₂ in rat breasts. The 2- and 4-hydroxylase activity assay was used in order to examine estrogen metabolism in the breast tissue of rats from the cholesterol, cholesterol + vitamin C, cholesterol + ANF, E₂, vitamin C + E₂ and ANF + E₂ groups. Radioactive ³H-E₂ was used to trace the formation of catechol estrogens by rat breast microsomes. The 2- and 4-OHE₂ generated during the reaction were separated from one another by using a thin layer chromatography method, and the amounts of each radioactive catechol estrogen were quantified by using a scintillation counter and corrected for the amount of microsomal protein added to the reactions. Data are expressed as picomoles catechol estrogen formed/minute/μg protein ± standard error. The symbol ‘*’ indicates a P value <0.05 compared with control values. The absolute values are listed above each bar. No differences in 2-hydroxyestradiol (2-OHE₂) formation were detected between any of the treatment groups. 4-OHE₂ generation was significantly higher than control levels in the E₂ and vitamin C + E₂ groups. The presence of ANF inhibits E₂-induced increases in 4-hydroxylation in rat breast.