EVANS BLUE EXTRAVASATION IN RAT DENTAL-PULP AND ORAL-TISSUES INDUCED BY ELECTRICAL-STIMULATION OF THE INFERIOR ALVEOLAR NERVE

Whether increased extravasation of plasma protein may occur in the rat incisor pulp as a result of antidromic stimulation of afferent nerves was investigated, and this preinflammatory reaction compared with that in adjacent soft tissues. In anaesthetized rats, the inferior alveolar nerve was exposed and stimulated electrically (10-15 V, 2 ms, 10 Hz for 30 s or 5 min). Blood flow changes in the lower lip and incisor pulp were recorded by laser Doppler flowmetry. Increased vascular permeability in the lip, gingiva and pulp was indirectly determined by means of the Evans blue dye method and spectrophotometric analysis. Stimulation of the inferior alveolar nerve for 30 s, in the presence of the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), increased blood flow in the lip by 172 +/- 16% and in the pulp by 38 +/- 5% as compared to basal blood flow. Intravenous (i.v.) adminstration of atropine (1 mg/kg), chlorisondamine (3 mg/kg), timolol (150 mug/kg), cimetidine plus mepyramine (3 mg/kg of each), methysergide (1 mg/kg) and diclofenac sodium (3 mg/kg) was without effect on this response. Acute pretreatment with capsaicin (1-3 mg/kg, i.v.), however, abolished the vasodilation in the pulp and reduced that in the lip by 58% (p < 0.05). In untreated animals, stimulation of the inferior alveolar nerve for 5 min increased the Evans blue content in the ipsilateral lip by 164% (p < 0.001), gingiva by 55% (p < 0.01) and pulp by 67% (p < 0.01). Pretreatment (i.v.) with a combination of cimetidine and mepyramine counteracted the dye extravasation only in the gingiva. Diclofenac abolished the stimulation-induced accumulation of Evans blue in the gingiva and pulp but not in the lip. These results demonstrate that while antidromic stimulation of the inferior alveolar nerve induces extravasation of plasma proteins in rat oral tissues including the dental pulp, the mechanisms involved in this reaction are not identical in the pulp, gingiva and lip.