Postmenopausal Estrogen Types
The correct answer is A: estrone and estradiol are the primary estrogens present in postmenopausal women's bodies.
Predominant Estrogen Forms After Menopause
Estrone (E1) is the most abundant circulating estrogen in postmenopausal women, serving as the principal estrogen after ovarian function ceases 1, 2, 3. After menopause, most endogenous estrogen is produced by conversion of androstenedione (secreted by the adrenal cortex) to estrone by peripheral tissues 1.
Key Physiologic Changes
- Estrone and its sulfate conjugate (estrone sulfate) are the most abundant circulating estrogens in postmenopausal women 1
- Estrone sulfate serves as a circulating reservoir for the formation of more active estrogens 1
- In postmenopausal women, a significant proportion of circulating estrogens exist as sulfate conjugates 1
Estradiol's Role Postmenopause
Estradiol (E2) remains present but at much lower concentrations than in premenopausal years 4. Estradiol is converted reversibly to estrone, and both can be converted to estriol 1.
- In one study of women over age 70, estradiol was below the limit of detection in 66.1% of women, while estrone was below detection in only 0.9% 4
- Estrone is a strong predictor of circulating estradiol levels, with a robust association between E1 and E2 concentrations 4
- Estradiol functions primarily as a paracrine or intracrine factor in postmenopausal women rather than as a circulating endocrine hormone 3
Why Not Estriol?
Estriol is the major urinary metabolite of estrogen but is not a primary circulating estrogen in postmenopausal women 1, 2. Both estradiol and estrone can be converted to estriol, which is then excreted 1.
Clinical Significance
- Peripheral tissue conversion is the primary source of postmenopausal estrogen, occurring in adipose tissue, liver, skeletal muscle, kidney, brain, and hair follicles 2, 3
- Local tissue production can result in estrogen concentrations at specific sites (such as breast tissue) that are one order of magnitude greater than circulating levels 3
- The aromatase enzyme in peripheral tissues converts androgens to estrogens, which is why aromatase inhibitors are used in postmenopausal breast cancer treatment 5