Effects of all-trans-retinoic acid on the dermis of hairless mice.

The marked degradative changes induced in human and animal dermis by chronic ultraviolet radiation are thought to be irreversible. We have shown in studies with hairless mice that a new normal dermis formed subepidermally after irradiation ceased. Because retinoids stimulate wound repair, we evaluated the ability of all-trans-retinoic acid (RA) to enhance the repair of ultraviolet damage. To produce mild dermal damage, hairless mice were irradiated for 10 weeks with FS20 sunlamps. The mice were then treated topically with various concentrations of RA for either 5 or 10 weeks. The skin was examined by light and electron microscopic techniques. The subepidermal repair zone in RA-treated mice was significantly wider than that in the untreated control group. The greater repair appeared to be retinoid specific and was dose dependent. The collagen was both histochemically and ultrastructurally normal; fibroblasts were numerous and morphologically hyperactive. In addition, topical RA increased dermal vascularity.