The stretching of mouse skin in vivo: effect on epidermal proliferation and thickness.

Small springs were implanted in the backskin of hairless mice to determine the effects of mechanical stretching on epidermal proliferation. The controls consisted of sham operated animals, in which the implanted springs did not exert any tension so as to identify any effect due to surgical trauma, and unoperated animals. There was a significant rise in the mitotic index after one day in both experimental and sham operated animals and a slight thinning of the stretched epidermis. After 2 days the mitotic index and thickness of the epidermis of the stretched skin were greater than that of the sham operated or unoperated control group, and these differences were maintained after 4 days and were significant. At this time the stretched epidermis showed a hyperplastic response with a thickening of all cell layers. It appears that tension due to stretching increases the mitotic activity of the epidermis leading to an increased progenitor cell population and subsequent tissue hyperplasia.