The Molecular Nature of 1,25-(OH)2-D3-Induced Calcium-Binding Protein Biosynthesis in the Rat
Exogenous 1,25-(OH)2-D3, administered to vitamin D-replete animals on a high calcium diet, induces biosynthesis of the duodenal, cytosolic calcium-binding protein (CaBP) in less than 2 h. This process can be blocked by simultaneously administered cycloheximide, but not by actinomycin D. In vitamin D-replete animals on a low Ca diet, on the other hand, 1,25-(OH)2-D3 administration leads to new CaBP synthesis only after about 7 h; this process can be blocked by actinomycin D. In vitamin D-deficient animals on a high calcium diet who have no CaBP, treatment with 1,25-(OH)2-D3 induces CaBP formation in ≃ 8 h; this process is known to be blocked by actinomycin D. Thus in D-replete animals on a low calcium diet and in D-deficient animals, CaBP biosynthesis proceeds by a transcriptional route, whereas in D-replete animals on a high calcium diet the rapid response appears to be posttranscriptional. This finding points to the possibility of a more rapid regulatory action of vitamin D than previously reported and how vitamin D might function in the D-replete state.
KeywordsCalcium Diet Calcium Transport Other Hand High Calcium Diet High Phosphorus Diet
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