Immunochemical detection of nitric oxide synthase in human tissue

To date three distinct isoforms of nitric oxide synthase (NOS) have been identified. Two isoforms are considered to be expressed constitutively-neu-ronal NOS (nNOS; type I NOS) and endothelial NOS (eNOS; type III NOS). The third isoform is not generally present in normal cells and tissues but is induced in response to infection, inflammation or trauma-inducible NOS (iNOS; type II NOS). In 1990 Bredt and Synder (1) succeeded in developing antibodies to rat brain NOS (nNOS) and used immuncytochemistry subsequently to furnish one of the first anatomical descriptions of the distribution and localization of nNOS. Today numerous antibodies to all three NOS isoforms isolated from various tissues and different animal species are available and the application of immunocytochemistry is commonplace in the investigation of NOS in healthy and diseased tissues including human (2-6) (Fig. 1 Fig. 2 Fig. 3).