One primary research focus in GI disorders is how and why the system reacts to certain foods or other stimulants; specifically, researchers are investigating the primary factors responsible for regulating digestion.
Enterochromaffin (EC) cells, which are present throughout the digestive system, release serotonin (a chemical associated with the etiology of various diseases such as migraine, diarrhea, respiratory disturbances and hypertension) and are important in regulating gut motility.
Researchers from the Technical University of Munich and the Ludwig Maximillian University of Munich in Germany investigated whether EC cells in the intestine express nasal olfactory receptors (ORs, receptors used for smelling) to determine whether odorants present in spices, fragrances, cigarettes, detergents and cosmetics may cause serotonin release, thereby provoking a GI response.
To evaluate this connection, researchers studied human EC cells isolated from mucosal biopsies by laser microdissection and an EC derived cell line. The experiments revealed expression of several ORs in the isolated EC cells, as well as the cell line. Using digital fluorescence imaging, the team found that activation of the cells with odorants caused elevation of intracellular Ca2+, followed by serotonin release up to 10-fold that of the controls. Odorants like thymol (thyme), eugenol (cloves), bourgeonal (floral, lily-of-the-valley), helional (brown algae) and substances present in roses, bananas or raspberries, specifically, caused an elevation of Ca2+ levels.
The findings suggest that these types of odorants may cause a serotonin-related GI reaction. The effects could be inhibited by known OR antagonists, such as methyl isoeugenol (a competitive antagonist of eugenol) or by blocking Ca2+ influx (e.g., via Ca2+ channels with nifedipine, a drug used in the treatment of hypertension because it relaxes blood vessels).
“Our results show that odorants present in the gut may stimulate serotonin release via olfactory receptors expressed in human enterochromaffin cells in the gut mucosa,” said Petra Voland, Ph.D., of the Technical University of Munich, and one of the lead investigators of the study. “Serotonin controls peristalsis and is implicated in pathological conditions such as vomiting, diarrhea and irritable bowel syndrome. Thus, olfactory receptors are potential novel targets for the treatment of gastrointestinal diseases and motility disorders.”