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Vitamin D Metabolites in Serum from Hypoparathyroid Patients Treated with Vitamin D₂ and la-Hydroxyvitamin D₃^*

L. AKSNES and D. AARSKOG

Department of Pediatrics, University of Bergen N-5016 Haukeland sykehus, Norway

Vitamin D and its metabolites 25-hydroxyvitamin D (25OHD), 24,25-dihydroxyvitamin D [24,25-(OH)2D], 25,26-(OH)₂D, and 1,25-(OH)₂D were measured after separation on high pressure liquid chromatography in sera from two hypoparathyroid patients treated with high doses of vitamin D₂. Fractions with displacement activities in the competitive protein- binding assays were found which were not detectable in sera from controls not supplemented with vitamin D₂. These fractions, presumably representing vitamin D₂ metabolites, were quantitated separately from the vitamin D₃ metabolites.

After a change of treatment from milligram doses of vitamin D₂ to microgram doses of lOHD₃, the serum metabolites of vitamin D₂ and vitamin D₃ were followed from 8–13 months. During the first 2–3 months, there was an initial relatively rapid fall in serum vitamin D₂ levels and metabolites, followed by a slower decline. High levels of vitamin D₂ metabolites were still present after 13 months. Taking into account the marked preponderance of.25OHD₂ to 25OHD₃, the relative concentration of (OH)₂D₃ metabolites were higher than expected, which might indicate a preferential 25OHD.) hydroxylation or alternatively, a more rapid degradation of vitamin D₂ metabolites in these patients. The high and sustained release of vitamin D₂, presumably from fat stores, more than a year after vitamin D₂ ingestion was stopped has obvious clinical implications and should be considered in the long term follow-up of patients shifted from the traditional high doses of vitamin D to the newly synthesized lOHD₃ or 1,25(OH)2D₃.

^* This work was supported by grants from the Norwegian Research Council for Science and the Humanities, the J. P. Broegelmann Foundation, and the Nordisk Insulin Foundation.

To whom requests for reprints should be addressed.

Received November 28, 1979.