Influence of Ultraviolet Rays on alpha-MSH Plasmaconcentration. Ultraviolet total-body irradiation induces changes of alpha-MSH plasmaconcentration dependent on wave-length of the source of radiation as well as skin type of the volunteers. Following UV-A total-body irradiation, we observed a significant increase of the proteohormone alpha-MSH, whereas UV-B rays did not change the plasma concentration. With regard to persons showing skin type I or II, we found low alpha-MSH basic values which were significantly increased 1 hour after UV-A irradiation; in contrast, more pigmented volunteers (skin type III or VI) showed far higher basic values but only little increase after UV-A irradiation.