A little bit of stress can sometimes be good for us. It activates hormones that help us breathe more easily, for example. But for asthmatics, stress only makes things worse. Now, a group of researchers believe they have found a molecular mechanism that could help explain why.
Stress works its effects partially through the hormones adrenaline and cortisol. Usually, adrenaline opens up airways by docking with the beta2-adrenergic receptors (beta2-AR) on cells. Cortisol helps mute allergic responses by connecting to the glucocorticoid receptors (GR).
To understand why asthmatics get worse with stress, psychologists Greg Miller and Edith Chen from the University of British Columbia in Vancouver, Canada, graded the everyday stress levels of 38 healthy and 39 asthmatic children. They then looked at the levels of beta2-AR and GR gene expression in each child’s white blood cells. Healthy children who were stressed had higher levels of beta2-AR expression than did those who were chilled out. This would explain why adrenaline could ease the breathing of the stressed kids: There are more cell receptors to pick up the signal. The pattern was reversed in the asthmatic children; those with chronic stress had lower beta2-AR expression levels than those who were typically relaxed. While there wasn't a clear relationship between stress and GR expression levels, the researchers did discover that profound stress had an impact. If an already stressed child experienced a very stressful event, such as the death of a relative, gene expression of both receptors dropped.
As for why asthmatic children respond differently to stress, Miller says the jury's still out. In the meantime, the results could help explain why asthma medication is less effective under stress, says Miller. A lower expression of receptors means fewer targets on the cell surface for the medicines, he says. The team reports its findings online today in Proceedings of the National Academy of Sciences.
Epidemiologist Rosalind Wright of the Harvard School of Public Health agrees that this study could have implications for asthma management. Stress reduction may soon be used in conjunction with standard medical treatments for asthma, she says.
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