Effect of dietary acid and calcium on 25-hydroxyvitamin D metabolism by chick kidney.
Studies of the effects of acidosis and dietary calcium on 25-hydroxyvitamin D3 (25OHD3) metabolism were conducted utilizing assays of mitochondrial 1-hydroxylase and 24-hydroxylase activity following 96 hours of acid loading. The results showed decreased 1-hydroxylase (206 +/- 6 vs. 132 +/- 22 fmol min-1 mg/mitochondrial protein-1, p less than 0.01), augmented 24-hydroxylase (48 +/- 14 vs. 180 +/- 30 fmol min-1 mg-1, p less than 0.001) and increments in plasma calcium and phosphate following acidosis. High calcium diet also increased 24-hydroxylase activity (48 +/- 14 vs. 160 +/- 24 fmol min-1 mg-1, p less than 0.001) and plasma calcium, but decreased plasma phosphate. The extramitochondrial concentrations of calcium, potassium, and phosphate which maximally stimulated the hydroxylases in vitro were not altered by the in vivo dietary perturbations. The increments in 1-hydroxylase and 24-hydroxylase resulting from the presence of calcium, potassium, or phosphate in optimal concentrations (10(-5) M, 100 mM, and 100 mM, respectively) were changed by both acid loading and high calcium diet, decreasing in the case of 1-hydroxylase and increasing in that of 24-hydroxylase. The data indicate that the suppression of 1-hydroxylase and augmentation of 24-hydroxylase following these dietary perturbations may depend on both changed total enzyme capacity and altered enzyme sensitivity to extramitochondrial ions and are consistent with mediation by calcium of the effects of acidosis.
Cunningham
J
J
Division of Bone and Mineral Metabolism, Washington University School of Medicine, St. Louis, MO 63110.
Bikle
D D
DD
Avioli
L V
LV
D000138:Acidosis / Q000139:chemically induced / Q000378:metabolism*; D000643:Ammonium Chloride / Q000008:administration & dosage; D000818:Animals; D002112:Calcifediol / Q000378:metabolism*; D002118:Calcium / Q000008:administration & dosage* / Q000097:blood; D002645:Chickens; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D000643:Ammonium Chloride; D013250:Steroid Hydroxylases; D002112:Calcifediol; D002118:Calcium