Localization and changes in NADPH-diaphorase reactivity and nitric oxide synthase immunoreactivity in rat pulp following tooth preparation

Inflammatory changes in the dental pulp are accompanied by release of a wid e variety of chemical mediators. Nitric oxide, an oxidative free radical pr oduced by the enzyme nitric oxide synthase (NOS), has been implicated in mu ltiple inflammatory processes, which makes it a suitable marker for changes which likely occur following tooth pulp insult. Since limited information on nitric oxide in the pulp is available, it is necessary first to examine relative distributions of NOS in uninflamed and inflamed rat pulp. We accom plished this by characterizing regions of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity and the distribution of both macro phage NOS (macNOS) and neuronal NOS (nNOS) immunoreactivity in normal and i nflamed rat molar pulp at multiple time points. The results showed that: (1 ) deep cavity preparation on the mesial surface of the molar produced a tim e-dependent inflammation, with acute inflammation early progressing to chro nic, granulomatous inflammation with necrosis later that spread preferentia lly down the mesial root; (2) control (non-prepared) teeth showed a relativ ely faint and homogeneous distribution of NADPH-d and macNOS reactivity but no discernible nNOS reactivity; (3) inflamed teeth displayed localized inc reased intensity of NADPH-d and macNOS reactivity surrounding the inflamed area of pulp, but no increased nNOS activity; (4) pulp vessels supplying th e inflamed area showed increased NADPH-d reactivity, but no increased macNO S or nNOS reactivity; and (5) neither NADPH-d, macNOS, nor nNOS reactivity was observed in pulpal nerves. Therefore, nitric oxide may mediate the pulp al inflammatory response through its effects on the paralesional pulp tissu e and surrounding endothelial/vascular structures.