Effect of nitric oxide inhibition on capsaicin-elicited vasodilation in the rat oral circulation.

The effects of local application of capsaicin on the vascular conductance of the oral structures (upper gingiva, lower gingiva, tongue, right and left submandibular glands) were studied with and without pretreatment with NG-nitro-L-arginine methyl ester (L-NAME), a potent inhibitor of nitric oxide formation in rats. Alterations in tissue blood flow were measured by laser-Doppler-flowmetry; systemic blood pressure was monitored continuously during the experiments. Local application of increasing concentrations of capsaicin (1.0; 3.33; 10.0; 33.3 mM; in a volume of 5 microliters) resulted in a dose-dependent increase in the vascular conductance of all tissues investigated. There was a significant correlation between the values obtained for vascular conductance in the right and the left submandibular glands. Bolus intravenous injection of L-NAME (10 mg kg-1) elevated the mean systemic blood pressure significantly, by about 20%, with a rapid onset. This increase persisted until the end of the experiment. The augmentation of vascular conductance elicited by 10.0 mM capsaicin, locally administered, was significantly diminished in animals pretreated with L-NAME in all tissues tested. The results indicate that nitric oxide formation plays a significant role in the enhancement of vascular conductance produced in rat oral structures by local capsaicin administration.