The Increase of Epidermal Imidazoleacrylic Acid Following Insolation

It has been confirmed, by electron microscopy, that suction blisters detach the epidermis at the dermo-epidermal junction. Inter- and intracellular vacuolization was observed in some of the specimens. On the basis of a study comprising 15 subjects (12 males and 3 females), it was concluded that urocanic acid in the epidermis (suction blister skin) of the upper arm increased 9–11 days following insolation in comparison with specimens situated at an exactly symmetrical site of the control (non-irradiated) arm. This difference was significant in terms of μg urocanic acid per mg dry weight at a 95% level of probability and in terms of μg per cm2 of blister base at a 99% level (t-test for paired values). In two of the subjects other time intervals after insolation were also studied and an increase of epidermal urocanic acid level was noted. Dry weights of epidermis (mg per cm2) on the irradiated and control side (9–11 days following insolation) did not differ significantly in the group of 15 subjects. Significant increase due to insolation was only demonstrated when the values were divided by control values obtained for the respective arms 2 months before the experiment. Histidine ammonia-lyase activity was estimated in 8 subjects. The increase on the irradiated side on the 9–11th day after unilateral insolation was not significant.