title: Quantification and kinetics of 25-hydroxyvitamin D3 by isotope dilution liquid chromatography/thermospray mass spectrometry.
abstract: A liquid chromatography/thermospray mass spectrometry method has been developed and used to measure the plasma levels and half-life of 25-hydroxyvitamin D3 in adults. The mean plasma levels of 25-hydroxyvitamin D3 averaged 40 ng ml-1 (n = 4) in summer and 30 ng ml-1 (n = 6) in winter. The method was also used to determine the half-life of serum 25-hydroxyvitamin D3 in subjects maintained on either high or low-fiber diets who had been given an intravenous infusion of (6,19,19-2H3)25-hydroxyvitamin D3 sufficient to label 5% of their estimated body pools. The half-life was determined to be 10.4 days (n = 4), which is approximately 50% of the currently accepted value of 19 days, determined using radiolabeled methods. This difference may be due to kinetic isotope effects arising as a result of the tritiated compounds being labeled at sites that undergo Cyt-P450-catalyzed oxidations.
authors.affiliation: Section on Metabolic Analysis and Mass Spectrometry, NIH, Bethesda, Maryland 20892.
authors.forename: D
authors.initials: D
authors.lastname: Vicchio
authors.forename: A
authors.initials: A
authors.lastname: Yergey
authors.forename: K
authors.initials: K
authors.lastname: O'Brien
authors.forename: L
authors.initials: L
authors.lastname: Allen
authors.forename: R
authors.initials: R
authors.lastname: Ray
authors.forename: M
authors.initials: M
authors.lastname: Holick
mesh_terms: D000328:Adult; D002112:Calcifediol / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D002853:Chromatography, Liquid; D006207:Half-Life; D006801:Humans; D007700:Kinetics; D013058:Mass Spectrometry
chemical_list: D002112:Calcifediol