不同紫外线暴露强度及方式与生长期大鼠25羟维生素D及骨代谢的关系

背景:北方冬季日照时间短,婴幼儿易维生素D缺乏.最新教科书及中华医学会指南均认为玻璃遮挡紫外线,室内暴露对人类无意义.前期研究已经证明隔玻璃日光暴露对大鼠具有意义,但难以准确量化,且大鼠户外暴露难以继续进行.实验采用B波段紫外线,乃是日光中影响维生素D代谢的波长部分,且便于进一步深入研究.目的:观察实验室内中波紫外线对生长期大鼠血清25羟维生素D(25-hydroxy vitamin D,25-OHD)及骨代谢的影响.设计、时间及地点:采用随机同期对照动物实验,于2007-07在解放军总医院动物中心完成.材料:21d龄雄性Wistar大鼠40只.钙迪生人工光照补钙仪提供人工紫外线光源(波长280-350μm,照射强度5.5μW/cm~2).方法:将40只Wistar生长期大鼠用随机表随机分为4组,暴露于不同强度的紫外线下:直接照射组直接暴露20min,暴露剂量4.2mJ/(cm~2·d);间接暴露60min组及120min组暴露通过普通玻璃分别照射60min及120min,暴露剂量0.36,0.72 mJ/(cm~2·d);非暴露组,无紫外线暴露.直接暴露组将人工光照补钙仪置于笼上,间接暴露组以厚度为3mm无色普通玻璃覆盖笼上,置于人工光照补钙仪下,暴露组为连续暴露,实验期20d.主要观察指标:第21天检测大鼠血清25-OHD、骨碱性磷酸酶(bone alkaline phosphatase,BALP)及骨密度(bone mineral density,BMD).结果:各暴露组25-OHD显著高于非暴露组(P＜0.001),但暴露组间无显著性差异.各暴露组BALP显著低于非暴露组(P＜0.001),间接暴露组120min组BALP显著低于间接暴露60min组(P=0.022).血清25-OHD及BALP间存在负相关(r=-0.569,P=0.002),但各组的BMD无统计学差异.暴露剂量与25-OHD存在正相关关系(r=0.555,P=0.002),暴露剂量与骨碱性磷酸酶间存在负相关关系(r=-0.595,P=0.001)但暴露剂量存在阈值现象,当0.36mJ/(cm~2·d)达到后,血清25-OHD不再随暴露剂量增加而升高,BALP也不再随暴露剂量增加而下降.结论:中波紫外线通过玻璃照射引起生长期大鼠血清25(OH)D升高及BAP下降,且与直接暴露无明显差异.B波段紫外线暴露存在阈值现象,较小剂量并延长暴露时间,同样可以达到阈值暴露效果.

Effect of ultraviolet irradiation dose and style on 25-hydroxyvitamin D and bone metabolism in growing rats

BACKGROUND:Sunshine time in northem region is short in winter,the infants and young children are vulnerable to lack of vitamin D. Up-to-date textbooks and the guidelines formulated by Chinese Medical Association account that glass block ultraviolet and indoor exposure to human is meaningless. Early studies have shown that sunlight exposure through glass had meaning in rats,but it was difficult to accurately quantify,while outdoor exposure in rats is difficult to continue. This expedment uses B-band ultraviolet rays,which has the impact on vitamin D metabolism in some wavelengths,to facilitate further study.OBJECTIVE:To study the effect of ultraviolet B exposure in laboratory on 25-hydroxy vitamin D(25-OHD)level and bone metabolism in the serum of growing rats.DESIGN,TIME AND SETTING:A randomized controlled animal experiment was performed in June 2007 in the ExperimantalAnimal Center of Chinese PLA General Hospital.MATERIALS:Forty male 21-day-old Wistar rats were employed in this study. Ultraviolet waves were sourced from an artificial UV light instrument(wavelength 280-350 μm,irradiation intensity 5.5μW/cm~2).METHODS:Forty Wistar rats were divided into four groups by random sampling table,exposed to different doses of ultraviolet Bwave. Direct exposure group:direct exposure for 20 minutes at an irradiation dose of 4.2 mJ/(cm~2·d);Indirect exposure 60 and 120 min groups:exposure through a single pane of glass for 60 and 120 minutes at an irradiation dose of 0.36 and 0.72 mJ/(cm~2·d).Control group:no exposure was given. For the direct exposure group,the lamp was placed above the cage. A 3-mm-thick pane of glass(common window glass) was placed underneath the lamp in the indirect exposure groups. Exposure groups were given irradiation for successive 20 days.MAIN OUTCOME MEASURES:Serum 25-OHD,bone alkaline phosphatase (BALP),and bone mineral density (BMD) were measured on day 21.RESULTS:25-OHD was significantly higher in all exposure groups compared with the control group (P＜0.001),but there was no difference between the direct exposure group and two indirect exposure groups. BALP was significantly lower in the exposure groups than control group (P＜0.001),it was also significantly lower in the 120-min indirect group than in the 60-min indirect group (P=0.022). There was a positive correlation between exposure dose and 25-OHD (r=0.555,P=0.002) and a negative correlation between exposure dose and BALP (r=0.595,P=0.001),also a negative correlation between 25-OHD and BALP (r=0.569,P=0.002),but there were no differences between groups for BMD. Exposure dose exhibited a threshold,serum 25-OHD and BALP no longer increased or decreased when it was 0.36 mJ/(cm~2·d).CONCLUSION:Midwave ultraviolet rays might affect serum 25-OHD and BALP levels in the growing rats through glass exposure,with no significant difference compared to direct exposure. The B-band ultraviolet exposure dose may play an important role in serum 25-OHD synthesis,but there is a threshold dose for the synthesis. Low-dose and prolonged exposure time also achieve threshold exposure.