Change in epidermal transmission due to UV-induced hyperplasia in hairless mice: a first approximation of the action spectrum.

UV-induced epidermal hyperplasia was investigated by measuring the optical transmission of the epidermis of hairless mice exposed daily to ultraviolet radiation. The effects of 2 different radiation sources were investigated: Philips TUV 40W, emitting mainly 254 nm radiation, and Philips TL01 40W, emitting radiation in a narrow band around 312 nm. With both lamps a number of groups of animals were used, each receiving a different daily dose. In the experiments with both types of lamps, hyperplasia appeared to be fully determined by the accumulated dose, irrespective of the daily dose administered. This implies reciprocity between the daily dose and the time elapsed since the first exposure. Moreover, the change of transmission with time and daily dose showed very characteristic behaviour. A simple mathematical model was used to describe these changes. In a previous study we used this model to describe the results of a similar experiment with Westinghouse FS40 sunlamps. The combined data from the present and the previous experiments were used to calculate a first approximation of the action spectrum for UV-induced hyperplasia. In addition, we calculated the dose-response relationship for UV-induced increase in tolerance against ultraviolet radiation for the 3 irradiation sources.