Kinetics of epidermal production during epidermal regeneration following abrasion in mice.

A technique is presented which allows us to measure total increases in epidermal wet weight on the back of a mouse during epidermal regeneration, thus for the first time permitting us to determine the kinetics of increase of epidermal mass during epidermal regeneration. Within 2 days after removal of the epidermis by abrasion with an emery wheel, in mice in the resting phase of the hair growth cycle, the epidermis begins to be regenerated from the cells of the underlying resting hair follicles. By Day 3 epidermal wet weight is 70% of normal. By Day 4 it is 1.97 times normal and reaches its peak of 3.8 times normal by 5 days. Associated with this increase in epidermal wet weight is a two times increase in the number of epidermal cells per millimeter of interfollicular epidermis. However, the change in the number of cells is not uniform for all types of epidermal cells. Suprabasal cells increase 4.6 times by 7 days, whereas the basal cells actually decrease to 60% of normal levels. Colchicine mitotic count is increased almost 18-fold by Day 3 and remains above control levels for the rest of the experimental period. Many mitoses appear in the suprabasal layers.