Differential activity of nitric oxide synthase in human nasal mucosa and polyps

Nitric oxide (NO) plays an important regulatory role in airway function and seems to be implicated in the pathophysiology of several airway diseases. To better understand the involvement of NO in the upper airways, we examined the presence of nitric oxide synthase (NOS) activity in human nasal mucosa and nasal polyp tissues. Nasal mucosa was obtained from seven patients undergoing septoplasty, and nasal polyps came from nine patients following polypectomy. NOS activity was quantified in tissue homogenates using the citrulline release assay and localized in tissue sections using reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. The results showed that nasal polyps (n = 9) contained higher levels of total NOS activity (mean +/- SD 5.94 +/- 5.71, range 1.29-18.0 pmol.min-1.mg protein) than nasal mucosa tissues (n = 7) (0.28 +/- 0.22, range 0.01-0.57 pmol.min-1.mg protein). In addition, nasal polyps mainly contained inducible NOS activity (4.67 +/- 4.57, range 1.23-15.5 pmol.min-1.mg protein) whereas in nasal mucosa all NOS activity detected was in constitutive form. In both cases, NOS activity was localized in the epithelial cells. Since NO synthase is induced in inflamed upper airways, we conclude that NO may be an important inflammatory mediator in the respiratory system and that the epithelium may be a source of NO production in the human upper airways.