Localization and Changes in NADPH-Diaphorase Reactivity and Nitric Oxide Synthase Immunoreactivity in Rat Pulp Following Tooth Preparation

Abstract

Inflammatory changes in the dental pulp are accompanied by release of a wide variety of chemical mediators. Nitric oxide, an oxidative free radical produced by the enzyme nitric oxide synthase (NOS), has been implicated in multiple 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 accomplished this by characterizing regions of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity and the distribution of both macrophage NOS (macNOS) and neuronal NOS (nNOS) immunoreactivity in normal and inflamed rat molar pulp at multiple time points. The results showed that: (1) deep cavity preparation on the mesial surface of the molar produced a time-dependent inflammation, with acute inflammation early progressing to chronic, granulomatous inflammation with necrosis later that spread preferentially down the mesial root; (2) control (non-prepared) teeth showed a relatively faint and homogeneous distribution of NADPH-d and macNOS reactivity but no discernible nNOS reactivity; (3) inflamed teeth displayed localized increased intensity of NADPH-d and macNOS reactivity surrounding the inflamed area of pulp, but no increased nNOS activity; (4) pulp vessels supplying the inflamed area showed increased NADPH-d reactivity, but no increased macNOS or nNOS reactivity; and (5) neither NADPH-d, macNOS, nor nNOS reactivity was observed in pulpal nerves. Therefore, nitric oxide may mediate the pulpal inflammatory response through its effects on the paralesional pulp tissue and surrounding endothelial/vascular structures.

Sequential expression of endothelial nitric oxide synthase, inducible nitric oxide synthase, and nitrotyrosine in odontoblasts and pulp cells during dentin repair after tooth preparation in rat molars

“…In osteoblast-like cells, iNOS is activated by pro-inflammatory cytokines (Hukkanen et al 1995). After rat tooth preparation, iNOS is observed in the cells surrounding the necrotic tissue (Law et al 1999). Similarly, Di Nardo Di Fig.…”

“…eNOS has also been demonstrated in the odontoblasts of normal dental pulp (Felaco et al 2000). Moreover, NADPH-diaphorase and iNOS are expressed in pulp cells after rat tooth preparation and in human inflamed pulp, respectively (Law et al 1999;Di Nardo Di Maio et al 2004). However, to the best of our knowledge, no study has reported that odontoblasts express iNOS, eNOS, or NO-reactive products during dentin repair.…”

An overview of the dental pulp: its functions and responses to injury

“…The enzyme NADPH-diaphorase involved in the production of nitric oxide, a potent vasodilator, is present in the odontoblasts. 26,27 Their capacity to synthesize the inflammatory mediator PGI 2 has been demonstrated and this may excite nerves in the vicinity resulting in a brief hyperalgesia. 28 Although there is abundant information on the structural aspects of odontoblasts, very little is known about the dynamic aspect of these cells, especially in the mature pulp.…”

The effect of local nitric oxide synthase inhibition on the diameter of pulpal arteriole in dental bond material-induced vasodilation in rat

“…Having tried to minimize the pulp irritation (e.g. thermal, bacterial), we assume the iNOS-derived NO may only have a minor role, if any, in this study (Kerezoudis et al, 1993b;Law et al, 1999;Felaco et al, 2000;Jukic et al, 2002;Di Nardo Di Maio et al, 2004).…”