Induction of ornithine decarboxylase activity in hairless rat epidermis as a pharmacological model: validation of the animal model.

We use a mutant hairless Sprague Dawley rat to evaluate the capacity of retinoids to inhibit the epidermal ornithine decarboxylase activity induced by sellotape stripping. In order to minimize the variability introduced by the animals in our model we decided to validate the hairless rats used. A number of animal parameters were examined using a single lot of 50 males and 50 females aged from 4 to 11 weeks and acclimatized to laboratory conditions. The body weight growth curves were established. Nude animals present two periods of hair growth, the first at 6-7 weeks and the second at about 10-11 weeks. Hair development is more pronounced in males. No histological change was observed in the stratum corneum but an increase in epidermal thickness was noted in males aged 9 weeks. Removal of the stratum corneum by sellotape stripping was more effective and reproducible in the females, as determined histologically. Sellotape-stripping induction of ornithine decarboxylase in the epidermis was higher in rats aged 5-6 weeks and reached a plateau in animals aged 6-12 weeks. Individual variations obtained were lower in females (about 5%-10% in females and 10%-20% in males). The present research suggests that female rats aged about 8 weeks provide maximum reproducibility of response and ease of use.