DEGREE OF ULTRAVIOLET-INDUCED TORTUOSITY OF ELASTIC FIBERS IN RAT SKIN IS AGE-DEPENDENT

To elucidate differential effects of ultraviolet (UV) exposure on thre e-dimensional networks of elastic fibers during maturation of rat skin , Sprague-Dawley rat hind limbs were irradiated with suberythemal dose s of UV light (WB, 130 mJ/cm(2), or UVA, 27 J/cm(2)) in three differen t time courses of exposure: 3-9 weeks old, 9-15 weeks old, and 3-15 we eks old. Three-dimensional arrangement with special reference to linea rity of elastic fibers was quantified by image analysis using a scanni ng electron microscope after a combination of intravascular resin inje ction and selective digestion technique using formic acid. Among the t hree irradiation groups, the group irradiated with UVB or UVA between 3 and 15 weeks old (UVB, three times per week; UVA, five times per wee k) elicited the most marked decrease in the linearity of elastic fiber s. Despite the same irradiation period, there was a significant differ ence in the decreased linearity between the two irradiation groups of 3-9 and 9-15 weeks old, with the former irradiation group exhibiting g reater loss of linearity than the latter irradiation group. The magnit ude of the decreased linearity was greater in the UVB-exposed groups t han in the UVA-exposed group. These findings indicate that the three-d imensional linearity of elastic fibers is more susceptible to disrupti on by UV exposures during the growth period than that after the growth period.