Histamine release from rat peritoneal mast cells exposed to ultraviolet light

After irradiation with ultraviolet light, rat peritoneal mast cells incubated with the histamine liberator compound 48/80 were found to have reduced capacity to release histamine. The action spectrum for histamine release inhibition seemed to be in the wavelength region of UVB. UV-light per se did not induce histamine liberation other than for dosages greater than or equal to 1.45 J/cm2. No such release was observed with the doses of UVA studied (3.4-20.5 J/cm2). The metabolic inhibitor 2.4-dinitrophenol (DNP), which almost completely inhibited compound 48/80-elicited histamine release, did not influence the UV-induced histamine release, indicating that the latter was not a secretory process but due to cytotoxic leakage of histamine from the cells. These results suggest that inhibition of histamine-releasing capacity or reduction of skin histamine due to photolysis of mast cells may explain the beneficial effect of UV in pruritic disorders where histamine release from mast cells is involved.