Effect of freezing on iontophoretic transport through hairless rat skin.

The influence of frozen storage of hairless rat skin on the constant-current iontophoretic transport of a model weak acid, salicylic acid, was examined. Nearly a threefold increase was observed in the steady-state flux of salicylic acid through previously frozen skin (217.1 nmol h-1 cm-2) when compared with fresh, excised skin (72.3 nmol h-1 cm-2). The iontophoretic permeability of skin to salicylic acid was also found to be dependent upon the length of time skin samples remained in the frozen state. Differential scanning calorimetry studies revealed distinct differences in the thermograms for fresh and frozen skin. These results suggest that storage of skin samples in the frozen state may contribute to physical or chemical changes in skin structure.