抄録
A competitive protein binding assay for 25-OH-D and 24,25-(OH)_2-D has been described using the binding protein from rats fed a low calcium, vitamin D-deficient diet. As some vitamin D-metabolites which possess hydroxyl group at C-25 position interact with the binding protein, possible interference by these compounds in the assay has been overcome by preparative chromatography of serum extracts on Sephadex LH-20 and/or high pressure liquid chromatography (HPLC) prior to assay. The sensitivity of the assay for 24,25-(OH)_2-D significantly improved when used [^3H]-25-OH-D_3 with specific activity of 110 Ci/mmol as the tracer, and 1 ml of serum was enough for the assay. Ten blood samples were collected from healthy Japanese adult volunteers in July. The mean serum level of 25-OH-D was 32.5±4.5 ng/ml without any chromatographic preparation, 22.1±4.8 ng/ml with Sephadex LH-20, and 19.0±3.4 ng/ml with Sephadex LH-20 and HPLC, respectively. The concentration of 24,25-(OH)_2-D was 1.28±0.32 ng/ml (approximately 6% of the 25-OH-D level).
