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

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.

To examine the influence of UVB irradiation of the eye or ear on the pigmentation of mouse epidermis and intestine.

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.

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.

These results suggest that the UVB-induced pigmentation in the epidermis and the intestine is related to increased levels of α-MSH and MC1R.