THE LATE PHASE OF HEMATOPORPHYRIN DERIVATIVE‐INDUCED PHOTOTOXICITY IN MICE: RELEASE OF HISTAMINE and HISTOLOGIC CHANGES

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Abstract
—: This study was designed to directly examine the role of mast cells and the histologic changes in the late phase (4–48 h) of hematoporphyrin derivative‐induced phototoxicity. BALB/c mice were rendered phototoxic by intraperitoneal injection of HpD, followed by exposure to 1.59 kj/m2 of 396–406 nm radiation. Immediately before radiation, and at 4, 8, 12, 18, 24 and 48 h after radiation, the ear thickness, serum histamine levels and histologic changes of ears were examined. A maximal net increase in ear thickness of 33.5 ±0.3 times 10‐2 mm (mean ± SE) was noted at 12 h, associated with a maximal net increase of serum histamine (43.3 ± 11.6 ng/ml, mean ± SE), and a maximal mast cell degranulation. Other histologic changes consisted of mild epidermal spongiosis at 18–24 h, and a predominant neutrophilic infiltrate, which peaked at 24 h (211.6 ± 0.4 cells/mm2). No significant alteration was observed in control mice. These data indicated that mast cells participate in the late phase of HpD‐induced phototoxicity in mice.