EPR PERSISTENCE MEASUREMENTS OF UV-INDUCED MELANIN FREE-RADICALS IN WHOLE SKIN

Electron paramagnetic resonance is used to detect the formation of fre e radicals caused by exposure to ultraviolet radiation in chemically u ntreated rabbit skin. A fast jump in EPR signal level, occurring over a few seconds, is observed immediately after a skin sample is exposed to UV. This is followed by a slower increase toward an elevated steady -state signal over a period of hours as the skin is continuously expos ed to a UV light source. Upon cessation of UV light exposure, EPR sign al levels undergo an abrupt drop followed by a slower decay toward nat ural levels. Elevated free radical concentrations following UV exposur e are found to persist for several hours in whole skin. These results are consistent with time-resolved EPR measurements of photoinduced rad icals in various natural melanins.