Application of normal hen intestinal cytosol for the radioreceptor assay of serum 1α,25-dihydroxycholecalciferol concentration

Not only intestinal mucosa cytosol from vitamin deficient chicks which were used by Eisman et al., but also that from normal 24 to 28 month old hens may be used in the radioreceptor assay for easy determination of the serum 1α,25-(OH)2-D3. The yield of intestinal cytosol protein from one normal hen was six times as high as that obtained from a vitamin D deficient chick. The binding affinity and capacity of the cytosol taken from normal hens to 1α, 25-(OH)2-D3 were nearly the same as those obtained from vitamin D deficient chicks. The measured values of 1α,25-(OH)2-D3 using normal hens showed linear relation to the measured values using chicks. The circulating level of 1α,25-(OH)2-D3 was determined to be 41 pg/ml in healthy individuals, whereas in patients with renal failure, the concentration was lower. Intestinal mucosa cytosol of normal hens would thus be a good source of the binding protein for the 1α,25-(OH)2-D3 assay. (Kaihara, S.)