ABSTRACT
BACKGROUND AND OBJECTIVES: Nitric oxide (NO) production in the respiratory epithelium and the demonstration of inducible nitric oxide synthase in ciliated epithelium of the upper airway have recently been reported. The aim of this study was to investigate the expression of inducible nitric oxide synthase in the nasal epithelium after capsaicin treatment, which stimulates the substance P innervation. MATERIALS AND METHODS: In vivo treatment -Capsaicin (112 nM) was applied to the nasal cavities of the rat and guinea pig, and 30 nl of normal saline was applied for the control groups. After 2 hours, animals were sacrificed with cardiac perfusion of 4% paraformaldehyde and septal mucosa were removed. The 8 nm serial frozen tissue sections were made, and the expression of inducible nitric oxide synthase was determined using nicotinamide adenine diphosphate-diaphorase histochemistry. In vitro treatment- The nasal septum of the rats and the trachea of the guinea pigs were incubated in DMEM culture media with or without 112 nM capsaicin for experimental or control groups. After 0, 30 or 120 minutes of incubation, the tissues were fixed and processed for nicotinamide adenine diphosphate-diaphorase histochemistry. RESULTS: Both in vivo and in vitro studies demonstrated that the strong positive histochemical reactivity were observed in the respiratory epithelium of the rats and guinea pigs after capsaicin treatment compared to control groups. CONCLUSION: These data imply that capsaicin induces the expression of inducible nitric oxide synthase and that the substance P innervation of the nasal mucosa may have a protective role in the airway defense mechanism through nitric oxide production.