title: Evidence for extrarenal production of 1 alpha ,25-dihydroxyvitamin D in man.
abstract: Recent studies provide evidence for extrarenal production of 1 alpha ,25-dihydroxyvitamin D [1 alpha ,25(OH)2D]. To  investigate this possibility, serum vitamin D, 25-hydroxyvitamin D (25-OHD), 24,25-dihydroxyvitamin D [24,25(OH)2D], and 1 alpha ,25(OH)2D were measured in eight adult anephric subjects. All were undergoing hemodialysis and three of them were receiving vitamin D, 50,000 or 100,000 U/d. Serum vitamin D was elevated in two of the patients given vitamin D and was abnormally low in the others. Mean serum 25-OHD was increased in patients given vitamin D (94.0 +/- 7.6 ng/ml) and was normal in the others (16.4 +/- 0.9 ng/ml, P less than 0.001). Mean serum 24,25(OH)2D was normal in patients given vitamin D (1.38 +/- 0.27 ng/ml) and was low in the others (0.25 +/- 0.08 ng/ml, P less than 0.001). Serum 24,25(OH)2D correlated significantly with serum 25-OHD (r = 0.848, P less than 0.01). Mean serum 1 alpha ,25(OH)2D determined by receptor assay was 5.8 +/- 1.9 pg/ml in patients who were not given vitamin D and was 14.1 +/- 0.6 in those who were given vitamin D (P less than 0.001). Serum 1 alpha ,25(OH)2D correlated significantly with serum 25-OHD (r = 0.911, P less than 0.01). Mean serum 1 alpha ,25(OH)2D, measured by bioassay, was 8.3 +/- 1.9 pg/ml in patients who were given vitamin D and was 15.9 +/- 2.4 pg/ml in those who were given vitamin D (P less than 0.05). There was a significant correlation between the values for serum 1 alpha ,25(OH)2D obtained with the two methods (r = 0.728, P less than 0.01). The results (a) provide evidence in man for extrarenal production of both 24,25(OH)2D and, by two independent assays, of 1 alpha , 25(OH)2D, and (b) indicate that serum values of the two dihydroxy metabolites of vitamin D in anephric subjects vary with the serum concentration of the precursor 25-OHD.
mesh_terms: D000328:Adult; D002117:Calcitriol / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D003404:Creatinine / Q000097:blood; D004100:Dihydroxycholecalciferols / Q000097:blood; D005260:Female; D006801:Humans; D007668:Kidney / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009392:Nephrectomy; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood; D006435:Renal Dialysis; D014807:Vitamin D / Q000097:blood / Q000627:therapeutic use
chemical_list: D004100:Dihydroxycholecalciferols; D010281:Parathyroid Hormone; D014807:Vitamin D; D010758:Phosphorus; D003404:Creatinine; D002117:Calcitriol; D002118:Calcium