[en] Recent interest is centred on the development of improved assays for 1,25-dihydroxycholecalciferol (1,25-(OH)₂D₃) the hormonal form of vitamin D. Because radioimmunoassays have been successful when applied to the measurement of steroid hormones it seemed reasonable to use this approach to assay 1,25-(OH)₂D₃. These techniques have now been developed and applied to clinical studies. Clearly, the radioimmunoassay using tritium as label, is proving to be a versatile tool in the clinical study of the production and disposition of the hydroxylated vitamin D metabolites. This technique has a distinct practical advantage over existing radioreceptor assays in that antibodies provide a continuous supply of stable binding reagent whereas radioreceptor assays require preparation of intestinal binding protein from vitamin D deficient chickens. Moreover, with the radioimmunoasay approach there is considerable potential for further development. For example, by immunizing more animals with the same or different immunogens it may be possible to produce antisera with even higher affinity and with greatest structural specificity. These possibilities are now being investigated. (Auth.)

[en] 1α,25-Dihydroxy-25-hemisuccinate cholecalciferol has been synthesized and conjugated to bovine serum albumin. This conjugate is immunogenic; when injected into rabbits antibodies of high affinity for 1α,25-dihydroxy-cholecalciferol were obtained. Vitamin D metabolites lacking the 1α-hydroxy group were of lower cross-reactivity with the antibodies. By using these antibodies and 1α,25-[23,24-³H]dihydroxycholecalciferol as tracer a sensitive radioimmunoassay has been developed capable of detecting 20 pg of 1α,25-dihydroxycholecalciferol. (author)

[en] 1,25-dihydroxycholecalciferol (1,25-(OH)₂D₃) has been measured on human serum by radioimmunoassay. The assay uses a high titre antiserum raised in sheep against 1,25-(OH)₂D₃-25-hemisuccinate, conjugated to bovine serum albumin. The sensitivity of the assay is 10 pg/tube. Other hydroxylated forms of vitamin D₃ cross react with the antiserum and are therefore removed from serum extracts by chromatography on Sephadex LH 20 followed by high pressure liquid chromatography. The mean (+-SEM) serum 1,25-(OH)₂D₃ concentration for a group of healthy adult subjects was 41 +- 2.5 pg/ml. None was detected in anephric patients and the concentration was low or undetectable in patients with chronic renal failure. (author)

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