How peppermint helps to relieve irritable bowel syndrome
"Transient receptor potential (TRP) channels as drug targets for diseases of the digestive system" in Pharmacology and Therapeutics (2011)
"Approximately 20 of the 30 mammalian transient receptor potential (TRP) channel subunits are expressed by specific neurons and cells within the alimentary canal. They subserve important roles in taste, chemesthesis, mechanosensation, pain and hyperalgesia and contribute to the regulation of gastrointestinal motility, absorptive and secretory processes, blood flow, and mucosal homeostasis. In a cellular perspective, TRP channels operate either as primary detectors of chemical and physical stimuli, as secondary transducers of ionotropic or metabotropic receptors, or as ion transport channels. The polymodal sensory function of TRPA1, TRPM5, TRPM8, TRPP2, TRPV1, TRPV3 and TRPV4 enables the digestive system to survey its physical and chemical environment, which is relevant to all processes of digestion. ...
Functional implications of TRPM8 in the digestive system. TRPM8 is activated by temperatures in the cool to cold range and makes an important contribution to cold-induced pain ([Bautista et al., 2007], [Colburn et al., 2007], [Dhaka et al., 2007] and [Knowlton et al., 2010]). Apart from low temperatures, TRPM8 is stimulated by various chemical entities including menthol, icilin, geraniol, L-carvone, isopulegol and linalool (Table 1). These sensory modalities of TRPM8 are likely to explain the refreshing taste of menthol. Also keeping with this property is the finding that intragastric administration of the TRPM8 agonist menthol induces thermogenesis in mice (Masamoto et al., 2009).
Expressed by extrinsic primary afferent neurons and intrinsic systems within the GI tract, TRPM8 may play a chemosensory role in the alimentary canal. This contention is supported by the observation that the mixed TRPA1/TRPM8 agonist icilin is able to stimulate murine nodose ganglion neurons in culture (Zhang et al., 2004). However, systematic studies of the chemosensory role of TRPM8-bearing primary afferent neurons in the gut have not yet been reported, and the precise functional implications of TRPM8 in the digestive system await to be explored. In the murine colon, menthol induces a long lasting relaxation of smooth muscle, which remains unaffected by tetrodotoxin (Penuelas et al., 2007). It is questionable if this motor effect of menthol is due to activation of TRPM8 because the presence of TRPM8 in the murine gut has not unequivocally been established ([Zhang et al., 2004] and [Penuelas et al., 2007]). Whether the cooling-induced contraction of the rat gastric fundus (Mustafa & Oriowo, 2005) and guinea-pig ileum (Holzer & Lembeck, 1979) involves TRPM8 has not conclusively been investigated." [Emphases mine.]
"TRP channels in neurogastroenterology: opportunities for therapeutic intervention" in British Journal of Pharmacology (2011)
"It is clear that several different TRP [transient receptor potential] channels play important roles in the cellular apparatus that controls gastrointestinal function. They are involved in the regulation of gastrointestinal motility and absorption, visceral sensation and visceral hypersensitivity. TRP channels can be considered as interesting targets to tackle digestive diseases, motility disorders and visceral pain."
"The Cold and Menthol Receptor TRPM8 Is Expressed in Epithelial Cells of the Human and Murine Gastric Antrum" in AGA Abstracts (2009)
"Menthol, a secondary alcohol produced by the peppermint herb, Mentha piperita, is widely used in food industry as a cooling and soothing tastant or odorant. Menthol is also present in herbal drugs designed to treat abdominal discomfort and pain (eg. Iberogast®). Peppermint oil, with menthol as major constituent, reduces gastric spasms during upper endoscopy and slows small intestinal transit. By activation of the transient receptor potential melastatin 8 channel (TRPM8), a Ca2+-permeable, cold-activated member of the TRP superfamily of cation channels, menthol induces Ca2+ influx in a subset of sensory neurons from dorsal root and trigeminal ganglia. Knowledge about the presence of TRPM8 and its possible function in the gastrointestinal tract is however rare."
"A novel role for TRPM8 in visceral afferent function" in Pain (2011)
"Transient receptor potential ion channel melastatin subtype 8 (TRPM8) is activated by cold temperatures and cooling agents, such as menthol and icilin. Compounds containing peppermint are reported to reduce symptoms of bowel hypersensitivity; however, the underlying mechanisms of action are unclear. Here we determined the role of TRPM8 in colonic sensory pathways."
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