INTESTINAL CALCIUM ABSORPTION--EFFECT OF AGE

描述（改编自申请人摘要）：有临床 证据表明，1，25二羟基维生素D [1，25（OH）2D 3]的能力， 维生素D的活性代谢物，刺激肠道钙吸收 随着年龄的增长而下降。 雄性Fischer 344大鼠将用于回答 问题“为什么有一个年龄相关的减少肠道 对1，25（OH）2D 3的反应与钙离子吸收有关？". 的 1，25（OH）2D 3增加特定成分表达的能力 研究了Ca 2+的转运机制。 这些组件包括 钙结合蛋白是一种参与细胞内Ca 2+运动的蛋白质， 以及肠钙泵，将钙泵出肠外 吸收细胞 肠道24 OHase，降解1，25（OH）2D 3 并可调节1，25（OH）_2D_3在肠道中的作用， 也被研究。将使用2、6、12和27月龄的大鼠 研究1，25（OH）2D 3在成熟期、成年期和 衰老 为了回答这个关键问题，将测试三个假设：a）在 减少了对Ca 2+吸收的刺激， 1，25（OH）2D 3对关键肠蛋白的诱导作用随年龄增长而增加。 的 钙结合蛋白、钙泵和24 Ohase蛋白的诱导 将使用免疫学方法测量1，25（OH）2D 3。 的能力 每个年龄组的肠道mRNA被翻译成特定的 将在体外测量蛋白质。 肠道容量 每个年龄组的核糖体合成特定的蛋白质， 测定; B）对Ca 2+吸收的刺激减少，因为 肠道蛋白质的功能发生了改变， 1，25（OH）2D 3随年龄增长。 钙结合蛋白结合Ca ~（2+）的能力， Ca 2+泵泵送Ca 2+的能力，以及24 Ohase的能力 羟基化1，25（OH）2D 3的能力。 维生素D受体结合在每个年龄组之前和之后 将测量1，25（OH）2D 3治疗;以及c） 刺激Ca 2+吸收，因为存在与年龄相关的变化， 肠组织本身。 使用培养的肠段， 每个年龄组，1，25（OH）2D 3对关键转运蛋白的诱导 将在体外进行研究。 研究了1，25（OH）_2D_3对细胞凋亡的影响。 还将研究Ca 2+泵的磷酸化。 最后， 已知的1，25（OH）2D 3作用的刺激剂如佛波醇的作用 酯和酮康唑，将从每个年龄段确定 组 这些研究可能提示增加Ca 2+吸收的方法 因此，改善钙平衡和维持骨量， 老人

DESCRIPTION (Adapted from the Applicant's Abstract): There is clinical evidence that the capacity of 1,25 dihydroxy vitamin D [1,25(OH)2D3], the active metabolite of vitamin D, to stimulate intestinal Ca2+ absorption declines with age. Male Fischer 344 rats will be used to answer the question "Why is there an age related decrease in intestinal responsiveness to 1,25(OH)2D3 with regard to Ca2+ absorption?". The capacity of 1,25(OH)2D3 to increase expression of specific components of the Ca2+ transport mechanism will be studied. These components include calbindin, which is a protein involved in Ca2+ movement across the cell, and the intestinal Ca2+ pump, which pumps Ca2+ out of the intestinal absorptive cell. The intestinal 24 OHase, which degrades 1,25(OH)2D3 and which may regulate the action of 1,25(OH)2D3 in the intestine, will also be studied. Rats which are 2, 6, 12, and 27 months old will be used to study 1,25(OH)2D3 action during maturation, adulthood, and senescence. To answer the key question, three hypotheses will be tested: a) there is decreased stimulation of Ca2+ absorption because there is decreased induction of key intestinal proteins by 1,25(OH)2D3 with age. The induction of calbindin, the Ca2+ pump, and the 24 Ohase protein by 1,25(OH)2D3 will be measured using immunological methods. The capacity of intestinal MRNA from each age group to be translated into specific proteins will be measured in vitro. The capacity of intestinal ribosomes from each age group to synthesize specific proteins will be determined; b) there is decreased stimulation of Ca2+ absorption because there is altered function of the intestinal proteins induced by 1,25(OH)2D3 with age. The capacity of calbindin to bind Ca2+, the capacity of the Ca2+ pump to pump Ca2+, and the capacity of the 24 Ohase to hydroxylate 1,25(OH)2D3 will be determined for each age group. Vitamin D receptor binding in each age group before and after 1,25(OH)2D3 treatment will be measured; and c) there is decreased stimulation of Ca2+ absorption because there are age related changes in the intestinal tissue itself. Using cultured intestinal segments from each age group, the induction of key transport proteins by 1,25(OH)2D3 will be studied in vitro. The effect of 1,25(OH)2D3 on the phosphorylation of the Ca2+ pump will also be investigated. Finally, the effects of known stimulators of 1,25(OH)2D3 action, such as phorbol ester and ketoconazole, will be determined in segments from each age group. These studies may suggest ways of increasing Ca2+ absorption and, thus, improving Ca2+ balance and maintaining bone mass in the elderly.