Effect of u.v. rays on 7-dehydrocholesterol content in rat skin.

Long-term exposure of rat to ultraviolet irradiation affected the cholesterol metabolism in the skin. The 7-dehydrocholesterol content was increased to 1.6 times of non-irradiated rat. However, the cholesterol content was not altered. Ultraviolet-induced precholecalciferol and cholecalciferol bound with an activator protein of delta 5,7 sterol-delta 7-reductase. This observation suggested that precholecalciferol and cholecalciferol bound with an activator protein of delta 5,7 sterol-delta 7-reductase. This observation suggested that precholecalciferol and cholecalciferol inhibit the conversion of 7-dehydrocholesterol to cholesterol and accumulate 7-dehydrocholesterol. The action of ultraviolet rays on the cholesterol metabolism in the skin may be explained as the action of ultraviolet-induced precholecalciferol and cholecalciferol.