Metabolites of vitamin D in normal and X-linked hypophosphatemic mice

Hyp mice are a model for human X-linked hypophosphatemia (vitamin D-resistant rickets.) To determine whether an abnormality of vitamin D metabolism exists in this disease, the profiles of the metabolites of vitamin D were determined in normal and Hyp mouse plasma. Hyp and normal mice were fed a vitamin D-deficient diet and received 1,2 3H-vitamin D3 at 16 Ci/mmol by stomach tube at 5 ng/g body weight (0.21 microCi/g b.w.) on alternate days for 14 days. The dose of vitamin D given maintained near normal plasma 25-OH-vitamin D. Thus the mice were in a vitamin D-replete state with all metabolite pools labeled with 3H. Plasma was collected from 4 normal and 4 Hyp mice. The plasma was extracted, and the extracts were chromatographed separately for each mouse on an LH-20 column. Each major peak of radioactivity was rechromatographed using high performance liquid chromatography on a Zorbax-Sil column using solvent systems known to resolve several vitamin D metabolites. Twenty-one radio-active peaks were identified. The disintegrations per minute of 3H in each peak were quantified and converted to plasma concentration using the known specific activity of the administered vitamin D. The 25-OH-vitamin D accounted for 55% of the circulating radioactivity, and 24,25-(OH)2-vitamin D accounted for 22%. The plasma levels of 24,25-(OH)2-vitamin D were similar to levels previously reported by us using protein binding assays. No peaks of radioactivity were missing in the plasma extracts of the Hyp mice.(ABSTRACT TRUNCATED AT 250 WORDS)