Figure 3.

LC-MS/MS-based vitamin D metabolic profiles of serum extracts of VDR null mice (4-mo-old mice as indicated in Tables 1 and 2) fed high-calcium/high-lactose rescue diet. Vitamin D metabolites are extracted, derivatized with DMEQ-TAD, and then subjected to LC-MS/MS as described in Materials and Methods. Depicted are selected MRMs representing (A) the dihydroxyvitamin D₃ daughter fragments at m/z 762→468 and (B) the 25-OH-D₃-26,23-lactone daughter fragment at m/z 762→468. Note that each vitamin D metabolite generates 2 adduct peaks when derivatized with DMEQ-TAD; the peaks can be resolved on the LC column. Retention times of metabolites, based upon authentic standards, are provided in the text.