Increase in dopa-positive melanocytes in the mouse intestine in response to ultraviolet B rays via the eyes.

ABSTRACT

BACKGROUND: Irradiation by ultraviolet (UV) initiates pigmentation of skin; however, it is not known whether changes in intestinal pigmentation are also induced by UVB irradiation of the eye. AIM: To examine the influence of UVB irradiation of the eye or ear on the pigmentation of mouse epidermis and intestine. METHODS: DBA/2 male mice were locally exposed to UVB (280-320 nm) using a 20SE sunlamp directed at the eye or ear. The irradiation was given over 3 days, at a dosage of 2.5 kJ/m(2) per day. Five days after irradiation, samples were taken from the skin and intestine. Melanocytes in both epidermis and intestine were stained for dopa and expression of melanocortin-1 receptor (MC1R). Levels of plasma α-melanocyte-stimulating hormone (α-MSH) were measured using ELISA. RESULTS: Ultraviolet B irradiation of either the eye or ear in increased the number of dopa-positive melanocytes in the skin and the intestine (jejunum and colon). Irradiation of the eye caused a much greater increase in dopa than did irradiation of the ear. Both eye and ear irradiation increased blood α-MSH level to a similar extent, but only irradiation to the eye increased MC1R expression in the intestine. CONCLUSIONS: These results suggest that the UVB-induced pigmentation in the epidermis and the intestine is related to increased levels of α-MSH and MC1R.