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November 17, 2008
Vessel rhythms may tell heart attack peak times

By Quinn Eastman

It’s not just the stress of going to work. Daily rhythms in the activity of cells that line blood vessels may help explain why heart attacks and strokes occur most often in early morning hours, researchers from Emory School of Medicine have found.

Endothelial progenitor cells are essentially stem cells that come from the bone marrow and multiply into endothelial cells, which maintain blood vessels and prevent clots that lead to strokes and heart attacks.

“The aim of our research was to look at the circadian pattern of both endothelial function — the ability of blood vessels to relax — and the abundance of the progenitor cells,” says Ibhar Al Mheid, a postdoctoral cardiology researcher.

He presented his results Nov. 10 at the American Heart Association Scientific Sessions in New Orleans.

Working with cardiologist Arshed Quyyumi, Al Mheid examined a dozen healthy middle-aged subjects every four hours for 24 hours. Both the ability of blood vessels to relax and endothelial progenitor cells’ ability to grow peaked at midnight, while cell numbers peaked at 8 p.m.

“Endothelial function is particularly depressed in the early morning hours,” Al Mheid says.

He hypothesizes that an innate circadian timer in the brain, which other scientists have shown to be influenced by light and dark and daily activities, drives the cyclical variations in cell activity and endothelial function.