Type A and coronary artery disease.

Type A and coronary artery disease 

Researchers may have added another piece to the puzzle concerning type A behavior's relationship with coronary artery disease.

Type A behavior is characterized by impatience and anger. During stressful situations, it increases blood pressure and heart rate and stimulates some chemical messengers in the nervous system. And it is thought these factors may lead to coronary artery disease. But scientists have not understood exactly how this happens.

The answer may be related to receptors on the outside of muscle cells lining coronary arteries, because they control arterial blood flow, according to Columbia University researchers in the Oct. 24 LANCET. Alpha receptors trigger the cells to constrict coronary arteries, and the beta receptors have an opposing effect. In severe type A individuals, chronic alpha-receptor stimulation is predominant, the researchers report. In the calmer, type B individuals, the proportions are reversed.

The recent finding, they suggest, may help scientists understand the mechanism of coronary artery disease. It also could change treatment programs, perhaps by incorporating the monitoring of a patient's ratio of alpha- to beta-receptor stimulation or by developing medications that act on receptor sites.

In the study, Jeffrey P. Kahn and his colleagues used 17 men ranging in age from 22 to 32. All had a family history of coronary artery disease. This was a criterion, Kahn says, because the volunteers would be at higher risk for the disease and also because of the closer correlation between type A behavior and blood-pressure rise as a response to stress among people with a family history.

The researchers assessed each volunteer's level of type A behavior with an extensive, structured interview. Each volunteer was ranked from 1 (severe type B behavior) to 5 (severe type A behavior).

The researchers then collected blood samples and determined the density of alpha receptors on platelets, which are essential for blood coagulation, and the density of beta receptors on lymphocytes, a type of white blood cell. Those receptors were chosen because scientists believe they correlate closely with receptor densities in coronary arteries, which were not accessible.

The findings indicate that as type A ranking increases, the ratio of of beta to alpha receptors increases, suggesting alpha receptors are preferentially stimulated in type A individuals, Kahn told SCIENCE NEWS. This occurs because as alpha receptors are stimulated, their number decreases; this phenomenon, Kahn says, is not fully understood.

Kahn says he is not sure whether type A behavior stimulates alpha receptors, whether alpha-receptor stimulation causes type A behavior, or whether something else causes both reactions. He also is not sure whether hostility, a key component of type A behavior, according to some researchers, is associated with chronic alpha-receptor stimulation.