FACILITATED DIFFUSION BY IONTOPHORESIS OF VASOACTIVE AGENTS TO THE RAT INCISOR PULP

The use of iontophoresis for facilitated diffusion of vasoactive agent s into the dental pulp was investigated in lower incisor teeth of anae sthetized rats. Acetylcholine, carbachol and noradrenaline were iontop horesed with anodal and sodium nitroprusside with cathodal direct curr ent through a superficial dentin exposure. Pulpal blood flow was measu red with laser Doppler flowmetry. Current intensities below 100 mu A o f both polarities, using sodium chloride as a medium, caused no or min or 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 mu A. The vascular responses to the cholinergic and noradrenergic drugs appeared within a minute after the onset of current and they were abolished by systemi c administration of atropine and phenoxy benzamine, respectively. Iont ophoresis of acetylcholine (40-100 mu A 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 t hose seen in intact animals. None of the drugs used locally had any ef fect on systemic blood pressure. The results of this study indicate th at iontophoresis can be used for delivery of vasoactive agents from an exposed dentin surface into the pulp ill sufficient quantity to elici t drug-specific local vascular responses without causing systemic vasc ular effects.