Metabolism of 25-hydroxyvitamin D3 in anephric rats: a new active metabolite.

After the injection of radioactive 25-hydroxyvitamin D(3) into rats given a normal diet, two metabolites can be detected on Sephadex LH-20 chromatography modified to reveal polar metabolites. The first is designated peak Va, which by means of periodate cleavage has been identified as 24,25-dihydroxyvitamin D(3). The second more polar metabolite has been designated peak X(1) and is only partially sensitive to periodate. This metabolite appears in serum, bone, intestine, and liver and does not chromatograph on any system like any of the previously identified metabolites. Nephrectomy, especially in the animals given large doses of 25-hydroxyvitamin D(3), does not abolish production of either peak Va or X(1), revealing that both metabolites can be made in extra-renal tissue. Peak X(1) has marked ability to elevate serum calcium of rats on a vitamin D-deficient, low calcium diet, but requires the presence of kidneys to carry out this function.