title: Rat renal 25-hydroxyvitamin D3 1- and 24-hydroxylases: their in vivo regulation.
abstract: The effects of thyroparathyroidectomy, parathyroid hormone, 1,25-dihydroxyvitamin D3, dietary calcium, dietary phosphorus, age, and sex on the renal 25-hydroxyvitamin D3 1- and 24-hydroxylases measured in vitro in rats have been studied. Thyroparathyroidectomy of vitamin D-deficient rats abolishes 25-hydroxyvitamin D3 1-hydroxylase activity, and administration of bovine parathyroid extract to the thyroparathyroidectomized rat restores diminished 1-hydroxylase activity. Both suppression and restoration of the enzyme activities require many hours (18-24 h) independent of rapid changes in serum calcium and inorganic phosphorus levels in response to these manipulations. Administration of 1,25-dihydroxyvitamin D3 to vitamin D-deficient rats suppresses 25-hydroxyvitamin D3 1-hydroxylase activity and stimulates 25-hydroxyvitamin D3 24-hydroxylase activity within 48 h. Rats maintained on a low-calcium or a low-phosphorus diet with a daily supplement of 20 IU vitamin D3 show high 25-hydroxyvitamin D3 1-hydroxylase activity and low 24-hydroxylase activity as compared with rats similarly treated but fed a diet containing adequate calcium or adequate phosphorus. When vitamin D-sufficient rats having suppressed renal 25-hydroxyvitamin D3 1-hydroxylase activity are placed on a low-calcium vitamin D-deficient diet for 7 days, the 1-hydroxylase activity is greatly stimulated in 6-wk-old rats but much less so in rats with advancing age.
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D000367:Age Factors; D000818:Animals; D002136:Calcium, Dietary / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System; D007668:Kidney / Q000201:enzymology*; D008297:Male; D010280:Parathyroid Glands / Q000502:physiology; D010281:Parathyroid Hormone / Q000494:pharmacology; D010758:Phosphorus / Q000494:pharmacology; D051381:Rats; D012737:Sex Factors; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013961:Thyroid Gland / Q000502:physiology; D014808:Vitamin D Deficiency / Q000201:enzymology; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D010758:Phosphorus; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase