Differential effects of nitric oxide synthesis inhibition on basal blood flow and antidromic vasodilation in rat oral tissues.

The role of nitric oxide in the mediation of (a) antidromic and (b) substance P-induced vasodilation in the pulp, lip, oral mucosa and submandibular gland was investigated in anaesthetized rats by means of laser Doppler flowmetry. Bolus or continuous infusion of N omega-nitro-L-arginine methyl ester (L-NAME) increased mean arterial blood pressure and reduced basal blood flow in the pulp but not in the lip. Electrical stimulation of the inferior alveolar nerve, in the presence of phenoxybenzamine, resulted in a long lasting vasodilation in lower lip and incisor pulp. Infusion of L-NAME enhanced the antidromic vasodilation in both lip and pulp. Pretreatment with L-arginine prevented these effects. Administration of the enantiomer (D-NAME) did not exert any effect on basal blood flow and on antidromic vasodilation. Infusion of substance P resulted in a transient vasodilation in all of the oral tissues studied. L-NAME reduced this vasodilation in the submandibular gland (only the lower doses) but it potentiated the responses in the pulp and oral mucosa. Pretreatment with L-arginine prevented the potentiated responses in the pulp and those induced by the lower doses of substance P in the oral mucosa. Thus, nitric oxide appears to differentially regulate the basal blood flow and the antidromic or substance P-induced vasodilation in the microvasculature of the lip and dental pulp.