Capsaicin treatment induces histamine release and perfusion changes in psoriatic skin

To determine whether neurogenic factors may be of importance in the regulat ion of histamine release and blood flow in psoriatic plaque, the effect of capsaicin was studied in 22 psoriatic patients with active, untreated psori atic lesions. In each of 12 patients, one microdialysis fibre was placed in non-lesional skin and one was placed in lesional skin at depths of 0.7 and 0.9 mm, respectively. Dialysates were collected for the analysis of histam ine in the resting state and after 60 min of repetitive epicutaneous applic ation of 1% capsaicin above the microdialysis catheter. In 10 patients, top ical capsaicin and placebo were applied for 24 h to lesional/lesion-free sk in. Skin blood now and perfusion (evaluated using the (133)xenon clearance technique and scanning laser Doppler, respectively) were measured before th e application of capsaicin and after removal. After 60 min of capsaicin tre atment, both the perfusion and interstitial concentration of histamine, as well as the net release of histamine, were significantly increased in affec ted (from 38 +/- 6 to 45 +/- 6 nmol/L, mean +/- SEM) and unaffected (from 1 5 +/- 2 to 19 +/- 2 nmol/L) skin. Compared with placebo, 24 h of treatment with capsaicin caused a 15% decrease in perfusion in lesional skin. The res ults are compatible with the hypothesis that capsaicin-sensitive nerves may induce histamine release in non-lesional and lesional skin and that affere nt unmyelinated nerve fibres may contribute to the high blood flow in psori atic plaques.