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Updated: Aug 19, 2026
Mammary Epithelial Transplant Procedure
Published on: June 11, 2010
Distribution of antiestrogen-specific binding sites in normal and neoplastic mammary gland
Abstract:
Recently, several investigators have demonstrated the presence of triphenylethylene antiestrogen binding sites in the cytoplasm of many tissues, which specifically bind to radioactive tamoxifen with high affinity. Although mammary gland is one of the principal target organs for antiestrogen action, the characterization of antiestrogen binding in mammary tissues has not been reported. We have studied the antiestrogen binding properties of [3H]tamoxifen in the mammary glands of virgin, pregnant and lactating rats as well as in the N-methyl-N-nitrosourea-induced mammary tumors. Tritium labeled tamoxifen bound specifically and with high affinity (Kd = 10(-9) M) to components present in 25,000 g supernatant. Unlabeled estradiol or DES did not compete for these sites, whereas unlabeled tamoxifen showed competitive inhibition. The mammary glands contained threefold higher levels of cytoplasmic binding sites as compared to the mammary tumors. Mammary glands from the pregnant rats bound tamoxifen to a greater extent than that of either virgin or lactating rats. The functional relevance of these binding sites is still unknown.
Insights
Researchers identified specific antiestrogen binding sites in rat mammary glands that bind tamoxifen. These sites were more abundant in mammary glands than tumors and higher during pregnancy.
Area of Science:
- Endocrinology
- Molecular Pharmacology
- Cancer Research
Background:
- Triphenylethylene antiestrogen binding sites are known in various tissues.
- These sites bind radioactive tamoxifen with high affinity.
- Antiestrogen binding characterization in mammary tissues was previously unreported.
Purpose of the Study:
- To characterize antiestrogen binding properties of [3H]tamoxifen in rat mammary glands.
- To compare binding in virgin, pregnant, and lactating rats.
- To investigate binding in N-methyl-N-nitrosourea-induced mammary tumors.
Main Methods:
- Studied [3H]tamoxifen binding in rat mammary gland and tumor cytosols.
- Assessed binding affinity (Kd) and specificity using unlabeled competitors.
- Compared binding levels across different physiological states and tumor presence.
Main Results:
- Specific, high-affinity binding of [3H]tamoxifen (Kd = 10(-9) M) was observed.
- Binding sites were competitively inhibited by unlabeled tamoxifen but not estradiol or DES.
- Mammary glands showed threefold higher binding than mammary tumors.
- Pregnant rat mammary glands exhibited greater tamoxifen binding than virgin or lactating rats.
Conclusions:
- Rat mammary glands possess specific cytoplasmic binding sites for tamoxifen.
- Binding site levels vary with physiological state (pregnancy) and tumor presence.
- The functional significance of these mammary antiestrogen binding sites requires further investigation.
