It turns out that receptors for bitter tastes are also found in the smooth muscles of the lungs and airways. These muscles relax when they're exposed to bitter tastes, according to a report Sunday from researchers from the University of Maryland College of Medicine in Baltimore in the online edition of the journal Nature Medicine.
That surprised Dr. Stephen B. Liggett, a lung expert who noted that bitter tastes often are associated with poisonous plants, causing people to avoid them.
Liggett said he expected the bitter-taste receptors in the lungs to produce a "fight or flight" reaction, causing chest tightness and coughing so people would leave the toxic environment.
"But that's not what we found," Liggett said.
Instead, when scientists tested some nontoxic bitter compounds on mice and on human airways in the laboratory, the airways relaxed and opened more widely.
The compounds "all opened the airway more profoundly than any known drug that we have for treatment of asthma or chronic obstructive pulmonary disease," Liggett said.
"That's the fun of science, when you find something you didn't expect," he said in a telephone interview.
Liggett, who hopes to begin tests in humans within a year, said that eating bitter tasting foods or compounds would not help in the treatment of asthma. Instead, he said, to get a sufficient dose people will need to use aerosolized compounds, which can be inhaled.
Fortunately there are thousands of compounds known to have a bitter taste, such as quinine and many drugs, he said. Researchers can begin testing them to determine which have the best results, with few or no side effects.
The presence of bitter taste receptors on the hair-like cilia in the airways was reported last year by Michael J. Welsh of the University of Iowa. It was suggested that the cilia might react by moving to push a noxious aerosol out of the airways, and Liggett said that may be the case.
But the new research by Deepak A. Deshpande and Liggett centers on receptors in the smooth muscles, rather than the cilia. The lung receptors were limited to bitter tastes, Liggett said, and did not include the ability to sense salty, sour, sweet and savory tastes, which the tongue can detect.
Unlike the taste receptors in the tongue, the ones in the airways react to the taste but do not send signals to the brain.
The research was supported by the U.S. National Heart, Lung and Blood Institute.
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Online:
Nature Medicine: http://nature.com/naturemedicine
National Heart, Lung and Blood Institute:
http://www.nhlbi.nih.gov/
