In normal premenopausal women, the amount of 27HC generated from cholesterol is relatively low compared to the level of estrogen circulating in the blood, leading to enhanced cardiovascular protection. In contrast, when the level of 27HC is higher relative to estrogen, such as during the postmenopausal period or as a consequence of high cholesterol, the researchers speculate that 27HC out-competes estrogen to bind with estrogen receptors, blocking the function of the receptors and resulting in a loss of protection.
This model may help explain why women are better protected than men from cardiovascular disease until they reach menopause, said Dr. Mangelsdorf.
The findings also may help explain why a large clinical trial that evaluated certain hormone replacement therapies (HRT) in postmenopausal women a component of the 15-year Womens Health Initiative had to be halted in 2002 when the hormones appeared to increase a womans risk of heart disease.
In the Womens Health Initiative research program, the women who began taking HRT were an average of 13 years postmenopause, Dr. Manglesdorf said. By the time they started taking this estrogen again, the damage caused by 27HC binding to the estrogen receptors in the cardiovascular system may already have occurred. Once you lose estrogens protection for such an extended period of time, you cant get it back.
The researchers also found that 27HC works predominantly on estrogen receptors in the cardiovascular system. When it binds to estrogen receptors in other tissues, such as reproductive tissues, it has no effect on their reproduction-related functions. This prope
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| Contact: Amanda Siegfried amanda.siegfried@utsouthwestern.edu 214-648-3404 UT Southwestern Medical Center Source:Eurekalert |