Peppermint Helps Relieve Irritable Bowel Syndrome

A new study describes how peppermint helps to relieve irritable bowel syndrome (IBS), which affects up to 20% of the population.

Researchers at the University of Adelaide (Australia) conducted a study to find out how peppermint (icilin) activates transient receptor potential ion channel melastatin subtype 8 (TRPM8) in colonic sensory pathways, since the underlying mechanisms of action are unclear. Laser capture microdissection, quantitative reverse transcription-polymerase chain reaction (RT-PCR), immunofluorescence, and retrograde tracing were used to localize TRPM8 to colonic primary afferent neurons. In vitro extracellular single-fiber afferent recordings were used to determine the effect of TRPM8 channel activation on the chemosensory and mechanosensory function of colonic high-threshold afferent fibers.

The researchers found that a subpopulation of splanchnic serosal and mesenteric afferents tested responded directly to icilin. Icilin also prevented mechanosensory desensitization and sensitization induced by capsaicin--the active component of chilli peppers--and the transient receptor potential (TRP)A1 agonist AITC, respectively. The researchers found that TRPM8 was localized to high-threshold visceral afferent neurons, and that it couples to TRPA1 to inhibit downstream chemosensory and mechanosensory actions. On visceral afferent peripheral endings, TRPM8 activation affected TRPV1 and TRPA1 downstream chemosensory and mechanosensory actions. The study was published ahead of print on April 11, 2011, in Pain.

"Our research shows that peppermint acts through a specific antipain channel called TRPM8 to reduce pain sensing fibers, particularly those activated by mustard and chilli. This is potentially the first step in determining a new type of mainstream clinical treatment for Irritable Bowel Syndrome (IBS),” said lead author Stuart Brierley, PhD, of the Nerve-Gut Research Laboratory. "Some people find their symptoms appear after consuming fatty and spicy foods, coffee and alcohol, but it is more complex than that. There appears to be a definite link between IBS and a former bout of gastroenteritis, which leaves nerve pain fibers in a heightened state, altering mechanisms in the gut wall and resulting in ongoing pain.”

IBS (spastic colon) is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements. Diarrhea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C or IBS-A, respectively). IBS may begin after an infection (postinfectious, IBS-PI), a stressful life event, or onset of maturity without any other medical indicators.

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