Long-term estrogen replacement therapy after menopause may reduce heart attack risk not only by lowering blood-fat levels, but also by increasing blood flow to the heart and causing blood vessels to stay open wider and longer, according to a study led by Johns Hopkins researchers.
The results suggest that estrogen therapy triggers biochemical changes in cells lining the inside of coronary arteries that dilate and relax the vessels, so blood flow is augmented. Among the cellular changes are boosted production of nitric oxide and prostacyclin, chemicals that dilate the vessels; increased production of potassium, which alters electrical properties in heart muscle and promotes increased blood flow; and lowered production of calcium, which leads to vessels constricting. The findings are published in the March issue of American Heart Journal.
"One explanation for our results is that augmented coronary blood flow caused by estrogen may persist during long-term estrogen replacement therapy," says Roger S. Blumenthal, M.D., the study's lead author and an assistant professor of medicine at Hopkins. "Another explanation is that the coronary arteries may become tolerant to the dilating effect of long-term estrogen therapy."
Researchers gave single estrogen injections to 20 post-menopausal women -- half were on long-term estrogen therapy and half were not -- and monitored their blood pressure, heart rate and other blood flow measurements. The shots caused a 28.6 percent increase in coronary flow and 19.9 percent decrease in coronary resistance in the women not on estrogen therapy, but the improvements were temporary and only moderate compared to nitroglycerin, a chemical used to boost blood flow to the heart during angina.
Although the estrogen shots had no significant impact on the women already on estrogen therapy, results show these women had greater coronary flow and lower coronary resistance over the long term.
"Strong, healthy blood vessels play an important role in protecting the heart," says Blumenthal. "Chronically increased blood flow may favorably alter the dynamic balance between heart muscle supply and demand, while abnormal coronary constriction contributes to reduced blood flow in patients with exercise-induced angina, silent ischemia, unstable angina, heart attack and sudden death."
Long-term prospective studies are underway at Hopkins to determine the magnitude of estrogen's protective effect on the heart. Research suggests that long-term estrogen replacement may reduce heart disease, the nation's leading killer, by nearly 50 percent in older women.
The study, which was supported by Hopkins' Ciccarone Center for the Prevention of Heart Disease, included the University of Pittsburgh Medical Center.
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