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) su bstance P-induced vasodilation in the pulp, lip, oral mucosa and subma ndibular gland was investigated in anaesthetized rats by means of lase r 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. Electrica l stimulation of the inferior alveolar nerve, in the presence of pheno xybenzamine, 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 eff ects. Administration of the enantiomer (D-NAME) did not exert any effe ct on basal blood flow and on antidromic vasodilation. Infusion of sub stance P resulted in a transient vasodilation in all of the oral tissu es studied. L-NAME reduced this vasodilation in the submandibular glan d (only the lower doses) but it potentiated the responses in the pulp and oral mucosa. Pretreatment with L-arginine prevented the potentiate d responses in the pulp and those induced by the lower doses of substa nce P in the oral mucosa. Thus, nitric oxide appears to differentially regulate the basal blood flow and the antidromic or substance P-induc ed vasodilation in the microvasculature of the lip and dental pulp.