Pruritic and vascular responses induced by serotonin in patients with atopic dermatitis and in healthy controls.

Atopic dermatitis (AD) is a chronic inflammatory skin disease with often severe itch. The aim of this study was to determine the pruritogenic and vascular effect of serotonin (5-hydroxytryptamine; 5-HT) in patients with AD and in healthy controls. A 50 µg dose of 5-HT was injected intradermally into non-lesional skin of 25 patients with AD and 25 healthy control individuals, and the effect compared with 0.2 µg histamine as a positive control, and buffer as a negative control. Pruritus was recorded by the subjects, using a computerized visual analogue scale, while flare and wheal were recorded by the investigator. There was no qualitative or quantitative difference in 5-HT-induced itch between patients and control subjects, or between males and females. However, reduced flare and wheal were found in the patient group for 5-HT. There were no correlations between clinical findings (i.e. eczema severity, clinical pruritus) and recorded experimental itch, or flare or wheal responses for 5-HT, in the patients with AD. In both groups a shorter itch latency was found for 5-HT compared with histamine. Through the use of intradermal injections, making it possible to calculate the dose of substance delivered, a lower vascular response to 5-HT was shown in patients with AD compared with healthy controls. In addition to confirming a pruritogenic role of 5-HT in both patients with AD and healthy controls, we found a shorter itch latency for 5-HT compared with histamine in both groups. The short itch latency time may indicate a direct effect of 5-HT on itch receptors.