Nitric oxide synthase distribution in the rat intestine: a histochemical analysis

Nitric oxide is an inhibitory transmitter of nonadrenergic, noncholinergic neurons and is purported to be an endothelium-derived relaxant-type factor in the mammalian gut. This study aimed to provide a complete report on the distribution of NO synthase in the rat small and large intestine.

NO synthase was visualized histochemically through this enzyme's reduced nicotinamide adenine dinucleotide phosphate diaphorase activity and the distribution of staining within the gut wall.

The presence of NO synthase activity in myenteric neurons and their efferents to the circular muscle was confirmed. The largest proportion of stained cells per ganglion was found in the ileum, and the smallest proportion was in the colon. Stained neural elements were also found within the submucosa throughout the intestine. Stained cells within the myenteric and submucous nerve plexi displayed both type I and type II morphologies, with the latter being more numerous. In addition to neural staining, submucosal arterioles showed a regular pattern of small patches of staining unrelated to any perivascular innervation.

These findings indicate an extensive neural and vascular localization of NO generation potential throughout the wall of the rat intestine, thus providing a structural basis for the functional diversity of NO.