Facilitated diffusion by iontophoresis of vasoactive agents to the rat incisor pulp

The use of iontophoresis for facilitated diffusion of vasoactive agents into the dental pulp was investigated in lower incisor teeth of anaesthetized rats. Acetylcholine, carbachol and noradrenaline were iontophoresed with anodal and sodium nitroprusside with cathodal direct current through a superficial dentin exposure. Pulpal blood flow was measured with laser Doppler flowmetry. Current intensities below 100 microA of both polarities, using sodium chloride as a medium, caused no or minor afferent nerve-induced vasodilation, but excited sympathetic fibres of the pulp in a current-dependent manner. The current threshold for facilitated diffusion of acetylcholine was about 20 microA. The vascular responses to the cholinergic and noradrenergic drugs appeared within a minute after the onset of current and they were abolished by systemic administration of atropine and phenoxy benzamine, respectively. Iontophoresis of acetylcholine (40-100 microA for 20-120 s) caused a 3-fold increase of pulpal blood flow which was not dose-dependent; carbachol provoked a high-magnitude, long-lasting vasodilation and so did sodium nitroprusside. Noradrenaline caused a long-lasting vasoconstriction. In denervated rats iontophoresis of carbachol had effects similar to those seen in intact animals. None of the drugs used locally had any effect on systemic blood pressure. The results of this study indicate that iontophoresis can be used for delivery of vasoactive agents from an exposed dentin surface into the pulp in sufficient quantity to elicit drug-specific local vascular responses without causing systemic vascular effects.