research from Pennsylvania suggests that smoking heavily for many years may activate a receptor in smokers' lungs that makes them more susceptible to cancer. And once activated, the receptor stays switched on, even after decades without a puff. Jill Siegfried and her team at the University of Pittsburg and their colleagues at Louisiana State University Medical Center studied cultures of epithelial cells taken from the lungs of 35 people. Twenty-eight were current or past smokers and seven had never smoked.
When these receptors are present in mature lungs, the hormones which bind to them are thought to stimulate unnecessary cell growth, possibly leading to cancer. One of the receptors binds to a hormone called gastrin-releasing peptide ( grp ), which is known to be active during foetal lung development. The grp receptor was active in 10 out of 13 cell cultures from the long-term heavy smokers. None of the lighter smokers and only one of the four nonsmokers had activated grp receptors. Three people in the long-term heavy smokers group had quit smoking more than 20 years ago, but their grp receptors were still on.
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