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Progesterone receptors in normal mammary glands of mice: characterization and relationship to development
Abstract:
Although progesterone receptors have been characterized in a number of target tissues for progesterone, including some mammary tumors, relatively little is known about these receptors in normal mammary tissues. In the present study using R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione), a synthetic progestin, we have identified and characterized the cytoplasmic progesterone receptors in normal mammary glands of mice. The receptor had a high binding affinity (Kd = 2.8 X 10(-9)M) for R5020 and was specific for progestins. The levels of receptor varied at different stages of mammary gland development; the levels were inversely proportional to the secretory activity of the gland. This negative corelation between receptors and secretion was further observed in studies in which lactational involution was induced experimentally. We propose that the functional significance of the modulation of progesterone receptors in normal mammary glands may be related to the known different effects of progesterone in this tissue.
Insights
Researchers identified and characterized cytoplasmic progesterone receptors in normal mouse mammary glands. Receptor levels were inversely related to secretory activity, suggesting a role in mammary gland function.
Area of Science:
- Endocrinology
- Molecular Biology
- Reproductive Biology
Background:
- Progesterone receptors are known in some target tissues and mammary tumors.
- Limited information exists on progesterone receptors in normal mammary tissues.
Purpose of the Study:
- To identify and characterize cytoplasmic progesterone receptors in normal mouse mammary glands.
- To investigate the relationship between progesterone receptor levels and mammary gland activity.
Main Methods:
- Utilized R5020, a synthetic progestin, for receptor identification and characterization.
- Assessed receptor binding affinity and specificity.
- Correlated receptor levels with different stages of mammary gland development and secretory activity.
Main Results:
- Identified and characterized cytoplasmic progesterone receptors in normal mouse mammary glands.
- The receptor exhibited high binding affinity (Kd = 2.8 X 10(-9)M) and specificity for progestins.
- Receptor levels were inversely proportional to mammary gland secretory activity.
- This inverse correlation was confirmed during experimentally induced lactational involution.
Conclusions:
- Progesterone receptor levels in normal mammary glands are modulated during development and lactation.
- The functional significance of progesterone receptor modulation may relate to progesterone's diverse effects on mammary tissue.
- Further research is needed to fully elucidate the role of progesterone receptors in normal mammary gland physiology.