Stress puts squeeze on clogged vessels.

Mental stress may deliver a double whammy to people suffering from coronary artery disease, suggests a team of cardiologists. Their research indicates stress causes vessels already choked with atherosclerotic plaque to narrow even more, thereby increasing a person's chance of suffering dangerous ischemia--bouts of reduced blood flow to the heart that can lead to a heart attack.

When faced with a stressful situation, the adrenal gland pumps out epinephrine, a hormone that boosts heart rate and constricts blood vessels. A new study presented this week at the American Heart Association's 64th scientific sessions in Anaheim, Calif., hints that people with coronary artery disease suffer not just from plaque-clogged vessels, but also from an impaired vascular ability to handle stress.

Cardiologist Alan C. Yeung of the Harvard Medical School in Boston and his colleagues studied 26 men and women who had symptoms of coronary artery disease, such as chest pain. The team looked at each recruit's coronary arteries, the main blood vessels supplying the heart. Using an X-ray method called angiography, Yeung's group obtained a baseline picture of the arteries, classifying them as relatively smooth, irregular (with a modest amount of plaque) or stenosed (clogged with plaque).

The researchers then told the recruits to count backward by sevens from a random three-digit number -- a laboratory challenge often used to provoke stress.

When the researchers compared the baseline angiograms with those taken during the counting test, they discovered that, on average, stenosed arteries constricted 24 percent more during the test, while irregular vessels constricted 9 percent more. The average dilation of the smooth arteries remained unchanged, although most of the smooth vessels did dilate to some extent, Yeung says.

An analysis of blood flow confirmed those results: The team found that flow increased an average of 10 percent in the smooth vessels, but declined by 27 percent in the irregular and stenosed vessels.

The researchers speculate that people with healthy blood vessels react to epinephrine's vessel-constricting message by stepping up production of a natural, nitroglycerine-like substance called endothelium-derived relaxing factor (EDRF). This theory suggests that endothelial cells, which line the vessel interior, actually secrete EDRF to relax the blood vessel. Previous research by the same team (SN: 11/25/89, P.349) indicated that people with very early atherosclerosis may lose their ability to fine-tune vessel diameter, perhaps because of a problem with EDRF.

"Healthy vessels secrete EDRF to balance the constricting effect of [epinephrine]," Yeung says. "But if you have unhealthy vessels, that balancing act is gone."

If further studies can prove EDRF's constriction-preventing prowess, researchers may one day devise therapies aimed specifically at improving the coronary arteries' ability to respond to stress, Yeung speculates. That advance might help prevent ischemic attacks, helping to lessen the risk of heart attack, he adds.