Nitric oxide (NO) is present in air derived from the nasal airways. However, the precise origin and physiological role of airway-derived NO are unknown. We report that NO in humans is produced by epithelial cells in the paranasal sinuses and is present in sinus air in very high concentrations, close to the highest permissible atmospheric pollution levels. In immunohistochemical and mRNA in situ hybridization studies we show that an NO synthase most closely resembling the inducible isoform is constitutively expressed apically in sinus epithelium. In contrast, only weak NO synthase activity was found in the epithelium of the nasal cavity. Our findings, together with the well-known bacteriostatic effects of NO, suggest a role for NO in the maintenance of sterility in the human paranasal sinuses.

High values (800-6000 parts per billion) of nitric oxide (NO) in expelled air from the stomach were shown in humans by chemiluminescence technique. These NO values were more than 100 times higher than those found in orally exhaled air. Intragastric NO production is probably non-enzymatic, requiring an acidic environment, as NO in expelled air was reduced by 95% after pretreatment with the proton pump inhibitor omeprazole. Furthermore, large amounts of NO were formed in vitro from lettuce and saliva when placed in hydrogen chloride (pH <2). In conclusion, large amounts of NO are formed intragastrically in humans and this source of NO may be of importance for the integrity of the gastric mucosa in health and disease. Measurements of NO in expelled air might be of value as a non-invasive, method for estimation of gastric acidity. (Gut 1994; 35: (budesonide) regularly and the other three inhaled a P2 agonist or sodium cromoglycate when necessary. All subjects were tested when they were subjectively free from respiratory tract infections and none reported any symptoms of dyspepsia. The procedures used in this study have been reviewed and approved by the local ethical committee. NITRIC OXIDE VALUES IN EXPELLED AIR FROM THE STOMACHVoluntary regurgitation of air was performed three to five minutes after intake of 30 cl of carbonated water with a pH of 5-5 (Ramlosa; Pripps AB, Sweden). Expelled air was led into a Teflon tubing system from which air was continuously sampled (0-8 1/min) into an NO chemiluminescence analyser (CLD 700; Eco Physics, Durnten, Switzerland), and peak concentrations of NO were registered on a chart recorder. The detection limit for NO was 1 part per billion (ppb) and calibrations at known concentrations of NO in N2, using an electromagnetic flow controller (Environics Inc, Middletown CT, US) were performed. The chemiluminescence assay is highly specific for NO and does not interfere with other nitrogen oxides.2 Measurements of NO in expelled air from the stomach were made after 10 hours of fasting in combination with one of the following pretreatment procedures: (1) no pretreatment (control); (2) intake of 50 g of iceberg lettuce (nitrate load). The mean nitrate content in ordinary iceberg lettuce is 1-3 g/kg5;

P Pr ri im ma ar ri il ly y n na as sa al l o or ri ig gi in n o of f e ex xh ha al le ed d n ni it tr ri ic c o ox xi id de e a an nd d a ab bs se en nc ce e i in n K Ka ar rt ta ag ge en ne er r' 's s s sy yn nd dr ro om me e NO was almost absent (98% reduced) in air sampled directly from the nose in four children with Kartagener's syndrome (4±1 parts per billion (ppb)), compared to age-matched controls (221+14 (ppb)). Tracheostomized adult subjects had considerably higher NO values in nasally (22±3 ppb) and orally (14±2 ppb) exhaled air, compared to levels in air exhaled through the tracheostomy (2±0 ppb). Treatment with intranasal corticosteroids for 14 days, or with antibiotics for 1 week, did not affect exhaled NO.These results clearly show that, basically, all NO in exhaled air of healthy subjects originates from the upper respiratory tract, with only a minor contribution from the lower airways. Furthermore, the absence of nasal NO in children with Kartagener's syndrome could be of use as a simple noninvasive diagnostic test. Eur Respir J., 1994,

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