ROLE OF MAST-CELL HISTAMINE IN THE FORMATION OF RAT PAW EDEMA - A MICRODIALYSIS STUDY

We determined the endogenous histamine concentration in the subplantar space of rat hind paws using an in vivo microdialysis technique. A mi crodialysis probe was implanted into the rat hind paw and the histamin e content in dialysates was measured by high performance liquid chroma tography-fluorometry. In wild type (+/+) rats, the histamine output (b asal level 25.7 +/- 0.9 pmol/ml) increased 115-, 199- and 426-fold rap idly after subplantar injection of compound 48/80 at doses of 0.5, 5 a nd 50 mu g/paw, respectively. In genetically mast cell-deficient (Ws/W s) rats, the basal level of histamine was one third of that obtained f rom +/+ rats, and was not increased by compound 48/80 injection, With this treatment, marked, dose dependent, but relatively gradual develop ment of the paw edema was found in +/+ rats. However, no edema formati on was observed in Ws/Ws rats. Histological observations showed neithe r mast cells nor edema to be present in the paw skin of Ws/Ws rats. Th ese findings indicate the critical role of histamine as a trigger for the development of edema in vivo. in addition, Ws/Ws rats will provide important information as to the roles of mast cells in the inflammato ry response. (C) 1997 Elsevier Science B.V.