Effect of different methods of sunlight exposure and vitamin D supplement on vitamin D receptor expression and bone mineral addition rate in rats

Objective To study the influence of ultraviolet intensity from different sun exposure and vitamin D supplement on vitamin D receptor(VDR) expression and bone mineral addition rate(MAR) in rats.Methods Seventytwo 21-day-old male Wistar rats were divided into six groups randomly,direct sunlight exposure+VitD,direct sunlight exposure-VitD,indoors sunlight exposure+VitD,indoors sunlight exposure-VitD,and without sunlight exposure+VitD,without sunlight exposure-VitD.UVB was measured by ZQJ-254 ultraviolet rays detector.VDR mRNA expression in kidney and bone MAR were measured after 60 days.Results The mean intensity of outdoor UVB was 0.0429w/m2.After passing through double-ply glass,about 85.1% UVB intensity was lost and the indoor UVB was only 0.0064w/m2.Without vitamin D supplement,the VDR expression between direct sunlight exposure group(0.56±0.14) and indoor sunlight exposure group(0.56±0.08) was not significantly different,P=0.910.Without sunlight exposure,the VDR expression between vitamin D supplement group(0.46±0.07) and non-vitamin D supplement group(0.47±0.08) was not significantly different,P=0.828.Without vitamin D supplement,the mean MAR between direct sunlight exposure group(0.91±0.23 μm/d) and indoor sunlight exposure group(0.72±0.18μm/d) was not significantly different,P=0.091.Without sunlight exposure,the mean MAR between vitamin D supplement group(0.71±0.19 μm/d) and nonvitamin D supplement group(0.64±0.21 μm/d) was not significantly different,P=0.563.Meanwhile,the mean MAR between direct sunlight exposure+VitD group(1.24±0.26 μm/d) and direct sunlight exposure-VitD group(0.91±0.23 μm/d) was significantly different,P=0.004.Conclusions Sunlight exposure is one of the main interference factors in VDR mRNA expression and MAR in rats.Although 85.1% UVB in sunlight is lost after passing through double-ply glass,the indoor sunlight exposure almost has the same effect on VDR mRNA expression and MAR as direct sunlight exposure after the long time exposure in rats.Vitamin D plays a role of cooperator with sunlight exposure in MAR.