The guinea pig as a model for predicting photoallergic contact dermatitis.

This report describes modifications in the techniques used for both the induction and elicitation of photoallergic contact dermatitis (PACD) in the guinea pig. These changes have improved the reliability of this animal as the model of choice for screening chemicals or products for their tendency to produce PACD. The induction period consists of 15 exposures of the test substance to shoulder skin that has been abraded with a nylon brush rotating at 13,000 rpm. One hour later, the test site is irradiated with broadband UVA from a source having some irradiance below 320 nm (UVA/b). The animals receive 450 J/cm2 of UVA during the three-week induction period. The elicitation (challenge) test is repeated for two consecutive days. Each day, the test material, if a liquid, is applied to two sites every 30 to 60 min for 6 h; then one of the sites receives 20 J/cm2 of UVA. These photo-induction and photo-induction and photo-elicitation procedures have demonstrated that low-level concentrations (0.25% range) of 6-methyl coumarin or musk ambrette will both induce and elicit PACD in the guinea pig. This report adds more evidence that the induction of PACD in the guinea pig is dependent on broadband UVA.