Ferguson Gary W, Gehrmann William H, Karsten Kristopher B, Hammack Stephen H, McRae Michele, Chen Tai C, Lung Nancy P, Holick Michael F
Department of Biology, Texas Christian University, Fort Worth, TX 76129, USA.
Physiol Biochem Zool. 2003 Jan-Feb;76(1):52-9. doi: 10.1086/374276.
Basking by ectothermic vertebrates is thought to have evolved for thermoregulation. However, another beneficial effect of sunlight exposure, specifically the ultraviolet B (UV-B) component, includes endogenous production of vitamin D(3). In the laboratory, panther chameleons exhibited a positive phototaxis to greater visible, ultraviolet A (UV-A) and UV-B light. However, with equivalent high irradiances of UV-A or UV-B, their response to UV-B was significantly greater than it was to UV-A. Exposure of in vitro skin patches of panther chameleons to high UV-B (90 microW/cm(2)) for 1 h significantly enhanced vitamin D(3) concentration. Voluntary exposure to higher UV-B irradiance (70 vs. 1 microW/cm(2)) resulted in greater circulating 25-hydroxyvitamin D(3) in female panther chameleons (604 vs. 92 ng/mL). Depending on dietary intake of vitamin D(3), chameleons adjusted their exposure time to UV-B irradiation as if regulating their endogenous production of this vital hormone. When dietary intake was low (1-3 IU/g), they exposed themselves to significantly more UV-producing light; when intake was high (9-129 IU/g), they exposed themselves to less. Vitamin D(3) photoregulation seems to be an important additional component of the function of basking.
变温脊椎动物晒太阳被认为是为了体温调节而进化而来。然而，阳光照射的另一个有益效果，特别是紫外线B（UV-B）成分，包括内源性维生素D(3)的产生。在实验室中，豹变色龙对更强的可见光、紫外线A（UV-A）和UV-B光表现出正向趋光性。然而，在UV-A或UV-B的同等高辐照度下，它们对UV-B的反应明显大于对UV-A的反应。将豹变色龙的体外皮肤贴片暴露于高UV-B（90微瓦/平方厘米）1小时可显著提高维生素D(3)浓度。雌性豹变色龙自愿暴露于更高的UV-B辐照度（70与1微瓦/平方厘米）下，其循环中的25-羟基维生素D(3)水平更高（604与92纳克/毫升）。根据维生素D(3)的饮食摄入量，变色龙会调整它们对UV-B照射的暴露时间，就好像在调节这种重要激素的内源性产生一样。当饮食摄入量较低（1-3国际单位/克）时，它们会让自己暴露在更多产生紫外线的光线下；当摄入量较高（9-129国际单位/克）时，它们暴露的时间则较少。维生素D(3)的光调节似乎是晒太阳功能的一个重要附加组成部分。
