Abstract
Using a cDNA probe for rat renal 24-hydroxylase, expression of its mRNA was compared in the rat kidney and intestine. Vitamin D-deficient rats received a single injection of 1 alpha,25-dihydroxyvitamin D3. Expression of 24-hydroxylase mRNA was first detected in the kidney at 3-h post-injection and increased thereafter. Similarly, 24-hydroxylase mRNA was expressed in the intestine after 1 alpha,25-dihydroxyvitamin D3 injection. However, the dose level of 1 alpha,25-dihydroxyvitamin D3 required to induce the intestinal 24-hydroxylase mRNA expression was only 1/100 the amount required to induce renal 24-hydroxylase mRNA. Induction of intestinal 24-hydroxylase mRNA expression by 1 alpha,25-dihydroxyvitamin D3 was far more rapid than that of renal 24-hydroxylase mRNA. Thyroparathyroidectomy shortened the time required to induce expression of renal, but not intestinal, 24-hydroxylase mRNA. Administration of either parathyroid hormone or cAMP to vitamin D-deficient rats greatly reduced the expression of 24-hydroxylase mRNA in the kidney but not in the intestine. When rats were fed a vitamin D-repleted diet containing 0.7% (adequate) or 0.03% (low) calcium for 2 weeks, intestinal expression of 24-hydroxylase mRNA could be induced only in the low calcium group. In contrast, renal mRNA expression was preferentially stimulated in the adequate calcium group. These results clearly demonstrate that the expression of 24-hydroxylase mRNA is down-regulated by parathyroid hormone in the kidney but not in the intestine.
Highlights
Parathyroid Hormone Inhibits 25-Hydroxyvitamin D3-24Hydroxylase mRNA Expression Stimulated by la,25Dihydroxyvitamin D3 in RatKidney butNot in Intestine*
Vitamin D-deficient rats received been demonstrated tobe the active form of vitamin D3 [1,2,3]. a singleinjection of la,25-dihydroxyvitamin Ds
Vitamin D metabolism hasbeen examined mainly in termsof Expression of 24-hydroxylase mRNA was first de- enzyme activity
Summary
Parathyroid Hormone Inhibits 25-Hydroxyvitamin D3-24Hydroxylase mRNA Expression Stimulated by la,25Dihydroxyvitamin D3 in RatKidney butNot in Intestine*. Administration of la,25-(OH)2D3 to vitamin D-deficient rats dose-dependently stimulated theexpression of 24-hydroxylase mRNA in both the kidney and the intestine, but expression was far more sensitive in the latter.
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