Johns Hopkins scientists have shown that natural levels of estrogen offer females three times more protection against brain damage from strokes than their estrogen-lacking male counterparts.
The study in rats, funded by the National Institutes of Health, concludes that the amount of brain that is "spared" once nourishing blood flow falls is related, in part, to circulating estrogen level.
"From our data, it seems likely that residual blood flow to the brain during stroke is conserved when estrogen is present in adequate amounts," says Patricia Hurn, Ph.D., an assistant professor of research anesthesiology and critical care medicine. "We are now in the process of determining how much estrogen is required for neuroprotection and the biological and cellular mechanisms involved."
Hurn and her team created strokes in anesthetized male and female rats by blocking blood flow for two hours through the middle cerebral artery, a brain blood vessel commonly linked to cerebrovascular disease and stroke in humans.
"When we measured blood flow levels, we found female rats were somehow able to get more blood around the blockage of the artery," she says. She will present her results November 21 at the annual meeting of the Society for Neuroscience in Washington, D.C.
When they created strokes in female rats whose ovaries had been surgically removed, cutting estrogen levels by almost half, stroke damage was essentially the same as in the males.
She and her colleagues are now treating both male and female animals with varying amounts of estrogen and creating strokes to determine the links between estrogen dose and brain protection.
"This will be an important step toward determining whether we can use estrogen as a brain-protective therapy," says Hurn. They also will look at the role of nitric oxide and enzymes that help dilate blood vessels.
Women are generally at lower risk than men for cardiovascular disease, including "brain attack" or stroke.
"Many studies in humans and animals showed that estrogen is protective in heart disease, but our understanding of estrogen's effects in the brain as a neuroprotective agent is very limited," says Hurn. "Hormone replacement therapies are commonly prescribed for women who are undergoing natural or surgical menopause, and this could pose a potential risk or benefit for a woman when a stroke occurs.
"We need more information both for these women and for those with cerebrovascular disease who might benefit from hormone therapies," she concludes.
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