Serotonin in rat oral tissues: role of 5-HT1 receptors in sympathetic vascular control.

In this study we examined whether the indoleamine, serotonin (5-hydroxytryptamine, 5-HT), is contained in the rat incisor pulp and gingiva as well as its possible role in regulation of blood flow in these tissues. Tissue biochemical analysis, by means of high performance liquid chromatography coupled to electrochemical detection, revealed the presence of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), as well as the catecholamine, dopamine, in both pulp and gingiva. Unilateral surgical sympathectomy or resection of the inferior alveolar nerve failed to affect 5-HT levels in either tissue while dopamine contents in the pulp and gingiva were diminished following sympathectomy. Electrical stimulation of the sympathetic trunk induced a frequency-dependent vasoconstriction in the pulp and gingiva as measured by laser Doppler flowmetry. This vasoconstriction was unaffected by infusion of 5-HT2 or 5-HT3 receptor antagonists or dopamine receptor antagonists but it was significantly reduced in both tissues after alpha 1-adrenoceptor blockade. During this blockade the remaining vasoconstriction induced by high frequency stimulation (16 Hz) was reduced in gingiva by the 5-HT1 receptor blocker, methiothepin. The results indicate an involvement of 5-HT1 receptors and alpha 1-adrenoceptors in the sympathetic vascular control in the gingiva.