I was reading a recent issue of Science News and was surprised to learn that we have taste receptors for bitterness in our lungs. Beyond that, it turns out that when these receptors are stimulated by bitter compounds that are inhaled, it has the effect of dilating the airways. In fact, inhaled quinine was found to be more effective than albuterol - the standard treatment.
This was puzzling since a bitter taste is generally an indication of something toxic, so one might expect the opposite response. However current speculation is that since many bacteria also produce bitter compounds, it would make sense that the smooth muscle around the airways would relax so as to permit cilia to better do their job of expelling mucous and any foreign substances - cilia also step up activity in response to bitter compounds.
