INTESTINAL CALCIUM ABSORPTION--EFFECT OF AGE

描述(改编自申请者摘要)：有临床 证据表明，1，25二羟基维生素D[1，25(OH)2D3]的能力， 维生素D活性代谢物，促进肠道钙吸收 随着年龄的增长而下降。雄性费舍尔344只大鼠将被用来回答 问题：为什么肠道中存在与年龄相关的下降？ 1，25(OH)2D3对钙离子吸收的响应性？ 1，25(OH)2D3增加特定成分表达的能力 对钙离子的转运机制进行了研究。这些组件包括 钙结合蛋白是一种参与细胞内钙离子移动的蛋白质， 还有肠道钙泵，它将钙离子泵出肠道 吸收细胞。肠道24OHase，降解1，25(OH)2D3 它可以调节1，25(OH)2D3在肠道中的作用，将 也有待研究。将使用2个月、6个月、12个月和27个月大的老鼠 研究1，25(OH)2D3在成熟期、成年期和成年期的作用 衰老。 为了回答这个关键问题，将检验三个假设：a)有 减少对钙离子吸收的刺激是因为 1，25(OH)2D3对肠道关键蛋白的诱导作用。这个 钙结合蛋白、钙泵和24Ohase蛋白的诱导 将使用免疫学方法测量1，25(OH)2D3。容量 来自各个年龄段的肠道mRNA被翻译成特定的 蛋白质将在体外进行测量。肠道容量 来自每个年龄段的核糖体将合成特定的蛋白质 确定；b)由于以下原因，对钙离子吸收的刺激减少 肠道蛋白质的功能发生了改变 1，25(OH)2D3随年龄增长。钙结合蛋白结合钙离子的能力， Ca~(2+)泵对Ca~(2+)泵的能力，以及24Ohase的能力 对每个年龄段的1，25(OH)2D3进行了测定。 各年龄组维生素D受体结合前后的变化 将测量1，25(OH)2D3处理；以及c)减少 钙离子吸收的刺激是因为年龄相关的变化 肠道组织本身。使用培养的肠段 各年龄组，1，25(OH)2D3诱导的关键转运蛋白 将在体外进行研究。1，25(OH)2D3对细胞周期的影响 钙泵的磷酸化也将被研究。最后， 已知的1，25(OH)2D3激动剂的作用，如佛波醇 酯和酮康唑，将从每个年龄段进行测定 一群人。这些研究可能会提出增加钙离子吸收的方法。 从而改善钙平衡，维持骨量。 老年人。

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.