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Abstract
The distribution of the enzyme nicotinamide adenine dinucleotide phosphate (NADPH)
diaphorase was examined histochemically in the retina, iris, ciliary processes, cornea
and conjunctiva of the rabbit eye. The epithelial cells of the ciliary process, iris,
conjunctiva and, to a lesser extent, the cornea all showed intense staining. In the
retina, staining for NADPH diaphorase was intense in the inner segments of the photoreceptors
and a sparsely distributed population of amacrine cells. In addition, another population
of amacrine cells, some presumed ganglion cells as well as a number of horizontal
cells, stained less intensely for the enzyme. The retina, ciliary processes and, as
a comparison, the cerebellum of the rabbit all contain nitric oxide synthetase (NOS)
activity, as each tissue can metabolize citrulline from arginine. This process is
Ca2+ dependent and is reduced by the NOS inhibitor, NG-monomethyl-L-arginine. The
presence of NOS activity in the ciliary processes and the localization of NADPH diaphorase
in the ciliary epithelial cells are of significance as they suggest that the ciliary
epithelial cells may contain NOS which would imply a role for nitric oxide in aqueous
humour production.