ALTERATIONS IN MESSENGER-RNA EXPRESSION OF DUODENAL 1,25-DIHYDROXYVITAMIN-D(3) RECEPTOR AND VITAMIN-D-DEPENDENT CALCIUM-BINDING PROTEIN IN AGED WISTAR RATS

Previously, we reported that uptake of calcium into isolated duodenal cells and duodenal brush border membrane vesicles decreased in senesce nce. Decreases in duodenal 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] rec eptor number and 9k vitamin D-dependent calcium binding protein (CaBP) were also observed in aged rats. In this study, we examined the stead y state mRNA levels of duodenal 1,25-(OH)2D3 receptor and CaBP in both adult (6-month-old) and old (24-month-old) rats. We identified one ma jor band of 4.4 kb for 1,25-(OH)2D3 receptor mRNA. The size of the tra nscript was not affected by age. The content of 1,25-(OH)2D3 receptor mRNA (normalized with poly(A)+RNA) decreased 23% in the aged rat as co mpared to the adult rat. The expression of CaBP was also examined. A s ingle band of 0.6 kb was observed for CaBP mRNA. The size of CaBP mRNA was not altered with age. However, the abundance of CaBP mRNA (normal ized with poly(A)+RNA) was reduced 20% in the senescent rat. Thus, the results in the present study were consistent with our previous findin gs that the number of 1,25-(OH)2D3 receptors and the level of CaBP dec lined in the aged rat. However, the precise mechanism leading to the a ge-related deficit in mRNA expression remains to be elucidated.