NEW YORK (Reuters Health) - In a finding that may help explain why the artery disease atherosclerosis is more common among African Americans, US researchers have detected racial differences in blood vessel function.

Atherosclerosis, the build-up of fatty plaques in arteries that can lead to a heart attack or stroke, occurs more frequently in blacks than in whites, but the reasons for the higher prevalence are not fully understood. Some of the increased risk of artery disease seems to be related to higher rates of risk factors including diabetes, high blood pressure and tobacco use among African Americans.

But the new study's first author, Dr. Umberto Campia, of the National Heart, Lung and Blood Institute in Bethesda, Maryland, told Reuters Health that even after the higher rate of risk factors among African Americans is taken into account, blacks are still more likely than whites to develop atherosclerosis.

"There must be something that is not related to risk factors," Campia said in an interview.

In a previous study of tiny vessels called microvessels, Campia and colleagues detected abnormalities in vessel function in African Americans. But it was uncertain whether there were any racial differences in the function of larger vessels called "conduits" that serve as the body's pipelines for delivering blood. These conduit vessels are where atherosclerosis develops, Campia explained.

"We wanted to see if the abnormalities we found in the tiny vessels are also found in conduit vessels," he said.

To detect any racial differences in these larger vessels, the researchers, under senior author Dr. Julio A. Panza, compared 46 black adults and 46 white adults. All participants were healthy nonsmokers who did not have risk factors for atherosclerosis, such as high blood pressure, high cholesterol and diabetes.

The researchers performed two tests to see how well arteries in the arms worked. One test evaluated so-called flow-mediated dilation, which measures how well the endothelium, the lining of the blood vessel, acts to keep blood moving by widening the vessel. Another test measured how much arteries widened in response to nitroglycerin, a drug that promotes dilation of blood vessels.

In both tests, ultrasound scanning showed that arteries opened less in African Americans than in whites, the researchers report in the August 21st issue of the Journal of the American College of Cardiology. The difference remained even after the investigators took into account factors that could have affected vessel function, such as participants' artery width before the experiments and body mass index, or BMI, a measure of obesity that takes into account weight and height.

"We think that our findings explain, at least in part, why African Americans have a higher rate of atherosclerosis," Campia said.

Campia and his colleagues did not investigate the causes of the apparent differences, but he speculated that African Americans may have abnormalities in the way their arteries respond to a body chemical called nitric oxide, which promotes vessel widening.

SOURCE: Journal of the American College of Cardiology 2002;40.

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