Neuronal and endothelial nitric oxide synthase immunoreactivity and NADPH-diaphorase staining in rat and human pancreas: influence of fixation.

In this study, we wished to clarify the distribution and co-localization of nitric oxide synthase and NA-DPH-diaphorase (NADPH-d) in nerve cells, nerve fibres and parenchymal cells in exocrine and endocrine pancreas, and to assess the influence of fixation on the staining pattern obtained. For this purpose, we applied nitric oxide synthase immunocytochemistry and NADPH-d histochemistry to rat and human pancreas under different fixation conditions. Antibodies to neuronal and endothelial nitric oxide synthase were similarly applied. We found complete co-localization of neuronal nitric oxide synthase and NADPH-d in ganglion cells, and in nerve fibres around acini, excretory ducts, blood vessels and in islets of Langerhans of rat and human pancreas. Immunoreactivity for endothelial nitric oxide synthase was co-localized with NADPH-d in endothelial cells. However, in NADPH-d reactive islet and ductal epithelial cells we could detect neither brain nor endothelial nitric oxide synthase immunoreactivity with any fixation protocol applied. There were marked differences in NADPH-d staining of both neurons and parenchymal cells under different fixation conditions. These results indicate the existence of different types of NADPH-d, which are associated or not associated with nitric oxide synthase(s), and which are differently influenced by various fixation procedures in rat and human pancreas.