Displacement potency of vitamin D2 analogs in competitive protein-binding assays for 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, and 1,25-dihydroxyvitamin D3.
24(R),25-Dihydroxyergocalciferol [24,25-(OH)2-D2] is 1.7 times less potent than 24 (R), 25-(OH)2D3, 25-Hydroxyvitamin D2 (25OHD2), or 25OHD3 in the displacement of (3H)25OHD3 from rat serum binding proteins. 1,25-(OH)2D2 is 1.3 times less potent than 1,25-(OH)2D3 in the displacement of (3H)1,25-(OH)2D3 from a chick intestinal binding receptor. In light of binding affinity and chromatographic differences between vitamin D3 and its D2 analogs, it is our view that methods which purport to measure 1,25-(OH)2D and 24,25-(OH)2D probably understimate the contributions of D2 metabolites. This is particularly important in the case of plasma extracts from patients given large doses of vitamin D2.
D015650:24,25-Dihydroxyvitamin D 3; D000818:Animals; D001667:Binding, Competitive; D002112:Calcifediol; D002117:Calcitriol; D002352:Carrier Proteins / Q000097:blood; D002645:Chickens; D003600:Cytosol; D004100:Dihydroxycholecalciferols / Q000032:analysis* / Q000378:metabolism; D004872:Ergocalciferols / Q000031:analogs & derivatives*; D006887:Hydroxycholecalciferols / Q000032:analysis* / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011955:Receptors, Drug / Q000378:metabolism; D014809:Vitamin D-Binding Protein
D002352:Carrier Proteins; D004100:Dihydroxycholecalciferols; D004872:Ergocalciferols; D006887:Hydroxycholecalciferols; D011955:Receptors, Drug; D014809:Vitamin D-Binding Protein; D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol; D002112:Calcifediol