Histamine-releasing factor(s) in sera of uraemic pruritus patients in a possible mechanism of UVB therapy.

Uraemic pruritus is poorly understood despite the high incidence among chronic renal failure (CRF) patients undergoing haemodialysis. Serum histamine levels have been shown to be elevated in CRF patients with itching, and ultraviolet B (UVB) therapy, even if applied to only part of the body surface, has been reported to be beneficial for the generalized relief of the pruritus. A local mechanism of UVB action is suggested by evidence that UVB radiation is able to suppress histamine release from mast cells. However, detailed systemic mechanism(s) remain obscure. Sera from patients with or without uraemic pruritus were incubated with purified rat peritoneal mast cells and the resulting histamine release was compared. A higher histamine release was obtained with sera from uraemic pruritus patients (44.60 +/- 6.32%, n = 9, P < 0.005) than with sera from patients without itching (19.71 +/- 3.14%, n = 5, P > 0.25) and with normal control sera (23.62 +/- 7.14%, n = 6). This increased histamine release was dose-dependently restored to spontaneous release levels in five of seven patients by pre-exposure of the sera to UVB in vitro. From these results, sera of CRF patients with uraemic pruritus were considered to contain some histamine releasing factor(s) which was depleted or diminished by UVB irradiation, suggesting a possible systemic mechanism of UVB action.