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Plasma 24,25‐dihydroxyvitamin D 3 concentrations in x‐linked hypophosphatemic mice: Studies using mass fragmentographic and radioreceptor assays
Author(s) -
Cunningham John,
Coldwell Ruth D.,
Trafford David J. H.,
Makin Hugh L. J.,
Jones Glenville,
Tenenhouse Harriet S.
Publication year - 1990
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650050211
Subject(s) - chemistry , endocrinology , medicine , hypophosphatemia , plasma concentration , biochemistry
Previous studies have suggested that both plasma 24,25‐dihydroxyvitamin D [24,25‐(OH) 2 D] concentrations and renal 25‐hydroxyvitamin D‐24‐hydroxylase activity are increased in mice with X‐linked hypophosphatemia ( Hyp mice). However, because the plasma levels of 24,25‐(OH) 2 D seemed surprisingly high, we repeated these assays using two different techniques. Mass fragmentographic and radioreceptor assays were employed to compare the plasma concentrations of 25‐hydroxyvitamin D (25‐OHD) and 24,25‐(OH) 2 D in normal mice with those in Hyp mice. These assays yielded 24,25‐(OH) 2 D concentrations much lower than previously reported in mice (both normal and Hyp ). The concentrations of 25‐OHD 3 , and 24,25‐(OH) 2 D 3 , determined by mass fragmentography, were lower in Hyp mice than in controls [25‐OHD 3 , 9.7 ± 0.4 versus 14.6 ± 0.6 ng/ml, p < 0.01; 24,25‐(OH) 2 D 3 , 7.1 ± 0.3 versus 10.4 ± 0.4 ng/ml, p < 0.01]. Plasma 25‐OHD concentration was the main determinant of plasma 24,25‐(OH) 2 D, and the ratio of 25‐OHD 3 to 24,25‐(OH) 2 D 3 obtained from mass fragmentographic measurements did not differ between the two groups (1.40 ± 0.05 versus 1.36 ± 0.03 ng/ml, NS in normal and Hyp groups, respectively). Separate measurement of plasma 25‐OHD, 24,25‐(OH) 2 D, and 25‐OHD 3 ‐26,23‐lactone by radioreceptor assay showed no difference between either plasma 24,25‐(OH) 2 D, or the ratio of 25‐OHD concentration to 24,25‐(OH) 2 D concentration among Hyp and control animals. In neither study was plasma phosphate concentration related to the 25‐OHD 3 : 24,25‐(OH) 2 D 3 ratio. We conclude that previous estimations of plasma 24,25‐(OH) 2 D 3 concentrations in mice were erroneously high and, further, that in fact this metabolite is not present in increased concentration in Hyp mice