INCREASED INTERSTITIAL HISTAMINE CONCENTRATION IN THE PSORIATIC PLAQUE

The psoriatic plaque contains an increased number of mast cells that a re thought to have an important role in the initiation and maintenance of psoriatic lesions through the release of mediators such as histami ne, proteoglycans, lipid mediators, and cytokines. It is not known, ho wever, whether the interstitial concentration of histamine (and other mediators) is truly increased in the psoriatic plaque. The aim of the present study was to examine histamine concentration and histamine rel ease front involved and uninvolved skin of psoriatic patients, Intracu taneous microdialysis was performed in lesional and nonlesional skin o f 23 psoriatic subjects. The relative recovery of histamine was assess ed after calibration in situ to approximate to 76% in both lesional an d nonlesional skin. The interstitial histamine concentration was 32 +/ - 3 nmol per liter in lesional skin and 13 +/- 1 nmol per liter in non lesional skin (mean +/- SEM) (p < 0,001), Dermal histamine release was estimated according to the Fick principle after measurements of the a rterialized venous plasma histamine concentration (3 +/- 1 nmol per li ter) and blood flow and was found to be 10-fold increased in lesional compared with nonlesional skin, The results are compatible with the hy pothesis that mast cells in lesional skin secrete an increased amount of histamine that may contribute to the immunostimulation and inflamma tion in the psoriatic plaque.