Alterations in mRNA expression of duodenal 1,25-dihydroxyvitamin D3 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 senescence. Decreases in duodenal 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] receptor number and 9k vitamin D-dependent calcium binding protein (CaBP) were also observed in aged rats. In this study, we examined the steady 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 major band of 4.4 kb for 1,25-(OH)2D3 receptor mRNA. The size of the transcript 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 compared to the adult rat. The expression of CaBP was also examined. A single 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 (normalized with poly(A)+RNA) was reduced 20% in the senescent rat. Thus, the results in the present study were consistent with our previous findings that the number of 1,25-(OH)2D3 receptors and the level of CaBP declined in the aged rat. However, the precise mechanism leading to the age-related deficit in mRNA expression remains to be elucidated.