ANATOMIC DISTRIBUTION OF NITRIC-OXIDE SYNTHASE IN THE HEART

Nitric oxide synthase is a useful maker for nitric oxide's scope. Loca lized by either NADPH-diaphorase histochemistry or immunohistochemical methods, most nitric oxide synthase activity in the normal heart is p resent in endothelium along the extensive network of arteries, veins a nd capillaries within myocardium. This endothelial isoform of nitric o xide synthase also exists in the endocardium lining the cavities. Neur onal nitric oxide synthase appears much less prominent, although the e xact amount of this isoform in the heart is uncertain. Scattered nerve s and ganglion cells are localized by the histochemical methods. While there is no inducible nitric oxide synthase in the normal heart, macr ophages associated with repair following various forms of cardiac dama ge contain this isoform. For all nitric oxide synthases, however, spec ies variation and variability among models underscore the importance o f correlative studies of structure and function.