Garlic (Allium sativum L.) belongs to a large genus of plants (over 500 species) that includes onions, leeks, chives, and shallots. The sulfur-based compounds produced by these plants make them pungent. In many cultures around the world, garlic has a long history of use in folk medicine as a stimulant and diuretic; it has also been used to treat high cholesterol and high blood pressure. Garlic supplements have become widely popular in the United States, with sales of more than $100 million annually. A UK firm recently launched a new product – from V-Net Beverage, a U.S. functional drinks company – containing garlic extract. Although several health benefits have been attributed to garlic extracts, including hypotensive and vasorelaxant activities, questions remain about the mechanisms underlying these effects.
Researchers at the University of California, San Francisco recently discovered that the active ingredients in garlic work in a way that is similar to the chemicals in chili peppers. During research on the mechanisms of pain sensation, Prof. David Julius and his colleagues tested how the cells of rats react to garlic and allicin, an organic compound present in garlic. They found that garlic extracts and purified allicin excite sensory pain neurons in rats by binding to protein receptors on the surface of nerve endings in parts of the mouth. A cell membrane channel, called TRPA1, reacts by opening and allowing ions to enter into the nerve cells. This produces a release of neurotransmitters, which cause blood vessel dilation, inflammation, and a sensation of discomfort.
The researchers also found that the potent compounds found in chili peppers can cause similar reactions. Learning more about how nerves respond to these substances can aid researchers in understanding and treating arthritis, muscular problems, and other chronic health conditions.