Ultrastructural localization of NADPH-diaphorase activity in the endothelial cells of human nasal respiratory mucosa

The cavernous sinuses are the most peculiar feature of the nasal angioarchi tecture, due to their ability to retain a large quantity of blood in reply to a variety of topical and systemic stimuli. Recently, nitric oxide (NO) h as seemed to be crucially involved in the nasal vascular regulation. The di stribution of NO-synthase (NOS), the enzyme that catalyzes the formation of NO, tvas studied in the endothelium of nasal blood vessels by the ultracyt ochemical detection of reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) enzymic activity. The endothelium of the cavernous sin uses appeared strongly, positive, whereas the endothelium of arterioles was occasionally labeled. The endothelial cells of capillaries and venules wer e found to be NADPH-d negative. The strong enzymic activity observed in the cavernous sinuses suggests a major role of NO in the capacitance vessels c ompared to the resistance vessels. The hypothesis of a reciprocal inhibitio n between the NOS enzymic pathways present in the respiratory epithelium an d in the endothelium of cavernous sinuses is put forward. The nasal disorde rs characterized by anomalous vasomotility and vascular permeability could be caused in part by the irregular control of these complex interactions.