26-Hydroxylation of 1alpha,25-dihydroxyvitamin D3 does not occur under physiological conditions.
The 26-hydroxylation of 1alpha,25-dihydroxyvitamin D3 in rats in vitro and in vivo was studied under physiological conditions. Incubation of 1alpha,25-dihydroxy-[26,27-3H]vitamin D3 with rat kidney or rat liver homogenate showed formation of a metabolite that was identified as 1alpha,25(S),26-trihydroxy-[26,27-3H]vitamin D3 by comigration on three different HPLC systems and a periodate cleavage reaction. This metabolite was not generated by hydroxylation of 1alpha,25-dihydroxy-[26,27-3H]vitamin D3 itself but by an enzymatic conversion of a precursor that was formed nonenzymatically in substantial amounts upon storage of 1alpha,25-dihydroxy-[26,27-3H]vitamin D3 in ethanol at -20 degrees C under argon for more than three weeks. An in vivo metabolism study in rats dosed with a physiological dose of 1alpha,25-dihydroxy-[26,27-3H]vitamin D3 confirmed the absence of 26-hydroxylation of the hormone. As expected at 6 h postinjection of purified 1alpha,25-dihydroxy-[26,27-3H]vitamin D3, 1alpha,24(R),25-trihydroxy-[26,27-3H]vitamin D3, as well as traces of (23S,25R)-1alpha,25-dihydroxy-[3H]vitamin D3-lactone were detected and identified on straight phase and reverse phase HPLC in serum, kidney, and liver.
Endres
B
B
Department of Biochemistry, University of Wisconsin-Madison, 53706, USA.
DeLuca
H F
HF
D000818:Animals; D002117:Calcitriol / Q000097:blood / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D006900:Hydroxylation; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D010504:Periodic Acid / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D010504:Periodic Acid; C009288:metaperiodate; D002117:Calcitriol