Blood flow increase in the human lip after high-intensity tooth stimulation is not based on cholinergic mechanisms

The purpose of this study was to investigate whether parasympathetic cholinergic pathways are involved in the regulation of orofacial blood flow. The effect of atropin (1 mg, iv.) on blood flow responses in the lower lip, nose and hand during painful tooth stimulation was studied in healthy human subjects (n=8). In all subjects, tooth stimulation caused a long lasting vasodilatation in the lower lip. During stimulation there was a transient elevation in heart rate (HR) and blood pressure (BP) concomitantly with a blood flow decrease in the finger and nose. With atropin, the pain-induced HR and BP elevations and blood flow reductions in the nose and finger were decreased. However, the pain-induced blood flow increase in the lip was not changed. This study indicates that the tooth stimulation-induced vasodilatation in the lip is not based on parasympathetic cholinergic mechanisms.