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To evaluate the effect of ammonium persulphate (AP) inhalation on NANC inhibitory (i-NANC) neurotransmitters of guinea pig airways, we exposed eight guinea pigs to AP (1 mg/m3), by aerosol inhalation for 30 minutes daily for three weeks. Control animals inhaled saline aerosol. After the last exposure, the isolated trachea was mounted in an organ bath and electrically stimulated in the presence of hyoscine, piperoxane and propranolol. The i-NANC responses were evaluated as decreases in intraluminal pressure and expressed as area under the curve (AUC, Pa x seconds). The isolated tracheae were treated with a-chymotrypsin, L-NAME, zinc protoporphyrin IX and ODQ, that inhibit the production or action of the single neurotransmitters, like peptides, NO and CO. In the exposed individuals, the NANC relaxations were below 50%, as compared to controls (P < 0.01). NO and CO were the neurotransmitters responsible for all the i-NANC responses, in similar proportions either in exposed individuals or in controls. In conclusion, ammonium persulphate exposure impairs the i-NANC control of airway tone without specifically affecting any neurotransmitter.

In the gut, 5-HT acts as a paracrine signalling molecule released by enterochromaffin cells and as a transmitter released by some descending serotonergic interneurons. It has a prominent role in the regulation of motility, vascular tone, secretion and perception both in normal and under certain pathophysiological conditions, such as the carcinoid syndrome and the irritable bowel syndrome (IBS). Serotonin is known to markedly influence bowel function by activating at least five receptor types (5-HT(1,2,3,4,7)). Among all 5-HT receptors, those belonging to the 5-HT3 (a ionotropic receptor) and 5-HT4 (a metabotropic receptor) type are the most extensively studied in gastroenterology, resulting in commercially available (although not worldwide) serotonergic agents for the treatment of IBS and functional dyspepsia. Recently, 5-HT7 receptors have been found to participate in the accommodation process of the circular muscle during the preparatory phase of ileal peristalsis. Since an exaggerated accommodation of the gut wall may contribute to abdominal distension and bloating, 5-HT7 receptor ligands may offer innovative opportunities for the pharmacological treatment of functional bowel disorders.