Introduction It is generally accepted that calcitriol (1,251hydroxycholecalciferol) represents the biologically active metabolite of vitamin D3 (1), while the function of (24A)-hydroxycalcidiol is still controversial. Human pharmacokinetics of (24/?)-hydroxycalcidiol have been studied (2 -- 5), but only one of these studies yielded reliable estimates for its clearance and proEur. J. Ctin. Chem. Clin. Biochem. / Vol. 31,1993 / No. 7 duction rate (5). In vitro and in vivo studies have demonstrated that the activity of rat 24-hydroxylase is modulated by parathyroid hormone (parathyrin) (6-8), calcitriol (7-11), dietary calcium (7, 10-13), and phosphorus (7, 10). Hence, production rate or clearance of (24/?)-hydroxycalcidiol may be determined by these factors and may reflect abnormalities of calcium and vitamin D3 metabolism. Leeuwenkamp et al.: Human pharmacokinetics of (24 A)-hydroxycalcidiol Aliquots of these pooled samples were chromatographed on the Chromatographie system used in our assay procedure (15), the (24-K)-hydroxycalcidiol fractions were collected, the eluent evaporated under a stream of nitrogen and the residue dissolved in 480 of ethanol. Of this solution 350 were used to determine (24A)-hydroxycalcidiol; 100 were rechromatographed on a 30-cm d8 column (Spherisorb ODS 2) with 95 : 5 methanol-water as eluent (1.0 ml/miri), the (24^)-hydroxycalcidiol fractions were collected (recovery
Clinical Chemistry and Laboratory Medicine – de Gruyter
Published: Jan 1, 1993
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