title: Stimulation of 1,25-dihydroxyvitamin D3 production by 1,25-dihydroxyvitamin D3 in the hypocalcaemic rat.
abstract: Serum 1,25-dihydroxyvitamin D3 concentration and renal 25-hydroxyvitamin D 1 alpha-hydroxylase activity were measured in rats fed various levels of calcium, phosphorus and vitamin D3. Both calcium deprivation and phosphorus deprivation greatly increased circulating levels of 1,25-dihydroxyvitamin D3. The circulating level of 1,25-dihydroxyvitamin D3 in rats on a low-calcium diet increased with increasing doses of vitamin D3, whereas it did not change in rats on a low-phosphorus diet given increasing doses of vitamin D3. In concert with these results, the 25-hydroxyvitamin D 1 alpha-hydroxylase activity was markedly increased by vitamin D3 administration to rats on a low-calcium diet, whereas the same treatment of rats on a low-phosphorus diet had no effect and actually suppressed the 1 alpha-hydroxylase in rats fed an adequate-calcium/adequate-phosphorus diet. The administration of 1,25-dihydroxyvitamin D3 to vitamin D-deficient rats on a low-calcium diet also increased the renal 25-hydroxy-vitamin D 1 alpha-hydroxylase activity. These results demonstrate that the regulatory action of 1,25-dihydroxyvitamin D3 on the renal 25-hydroxyvitamin D3 1 alpha-hydroxylase is complex and not simply a suppressant of this system.
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D000818:Animals; D002117:Calcitriol / Q000097:blood / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D002136:Calcium, Dietary / Q000008:administration & dosage; D002762:Cholecalciferol / Q000494:pharmacology; D006996:Hypocalcemia / Q000097:blood / Q000201:enzymology / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008297:Male; D010710:Phosphates / Q000097:blood; D010758:Phosphorus / Q000008:administration & dosage; D051381:Rats; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013268:Stimulation, Chemical; D014808:Vitamin D Deficiency / Q000097:blood
chemical_list: D002136:Calcium, Dietary; D010710:Phosphates; D002762:Cholecalciferol; D010758:Phosphorus; D013250:Steroid Hydroxylases; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol; D002118:Calcium