Vitamin D nutrition increases skin tyrosinase response to exposure to ultraviolet radiation.

The influence of vitamin D nutrition on melanogenesis in skin induced by UV radiation was studied in pigmented adult rats. Melanogenesis, assessed by the activity of skin tyrosinase (radiometric assay), was studied in vitamin-D-deficient and vitamin-D-fed rats exposed to UV (0.1 J/cm2, 290-320 nm). The tyrosinase activity in skin was not significantly changed by vitamin D treatment alone. In contrast, the induction of tyrosinase activity provoked by UV radiation was greater in vitamin-D-fed than in vitamin-D-deficient rats. The increase in skin tyrosinase activity in response to UV was preceded by an increase in skin cAMP levels. This rise in cAMP was greater in vitamin-D-treated rats than in vitamin-D-deficient rats. The pretreatment of rats with phosphodiesterase inhibitor potentiated the effect of vitamin D on skin tyrosinase activity. The low serum calcium levels in the vitamin-D-deficient group were evidently not responsible for the lower UV induction of skin tyrosinase activity because the vitamin-D-deficient rats with normal serum calcium levels (supplemented with 20% lactose and 2% calcium in the diet) were also unable to show maximal induction of skin tyrosinase activity in response to UV radiation requires the presence of adequate vitamin D. cAMP may be involved in the mediation of this effect. The relationship observed between the vitamin D status of animals and tyrosinase activity of skin could provide an effective feed-back control for protection against UV and vitamin D intoxication.