Ethanol aggravates itch-related scratching in hairless mice developing atopic dermatitis

In patients with atopic dermatitis, alcoholic beverages can sometimes trigger or enhance itching. We have previously reported that HR-1 hairless mice fed a commercial special diet, HR-AD, but not a normal diet, develop atopic dermatitis-like skin inflammation with prolonged spontaneous scratching, and that skin barrier dysfunction is involved in the basal scratching. In the present study, the effects of ethanol on itch-related scratching were examined in this mouse model. When ethanol (30%, 10 ml/kg) was given orally to HR-AD-fed mice, scratching with long duration was further markedly increased, while oral ethanol administration had little effect on the scratching response in normal diet-fed mice. The scratching response after oral ethanol administration in HR-AD-fed mice (ethanol-induced scratching) was attenuated by antagonism of the μ-opioid receptor or local skin anesthesia, as in human itching. Ethanol-induced scratching was also suppressed by improvement of skin barrier function by an application of petrolatum ointment, while ethanol administration itself did not affect the function. This suggests that ethanol indirectly aggravates the basal scratching. Although antagonism of the transient receptor potential vanilloid-1 did not affect ethanol-induced scratching, blockade of ethanol actions in the central nervous system (CNS), including γ-aminobutyric acid type A receptor antagonism and N-methyl-d-aspartate receptor activation, inhibited it. Taken together, the present study demonstrates that orally administered ethanol markedly aggravates itch-related scratching in HR-AD-fed mice developing atopic dermatitis, and suggests that the CNS depressant actions of ethanol play an important role in the aggravation.