SPECIFIC RADIOASSAY OF 24,25 DIHYDROXYVITAMIN D (24,25(OH)₂D) IN SERA OF NEWBORNS, CHILDREN AND ADOLESCENTS

Abstract

To further evaluate vitamin D metabolism in children, serum concentrations of 24,25(OH)₂D, a metabolite produced by the renal 25OHD-24 hydroxylase system, were measured by a competitive radioassay utilizing normal rat serum as binding protein, ³H-25OHD as tracer and reference 24, 25(OH)₂D³ as standard. Blosynthesized ³H-24, 25(OH)₂D³ was used to monitor recoveries. The 24, 25(OH)₂D and 25OHD from serum lipid extracts were isolated by chromatography on 24 × 0.5 cm columns of Sephadex LH20. Mean (±S.D.) serum 24, 25(OH)₂D in children (age 2-17 yrs, N=20) was significantly (p < .01) higher (3.3±1.3 ng/ml) than in newborns (N=14, 1.87±0.6 ng/ml). Mean radioassayable serum 25OHD was also significantly (p < .01) higher (31.3±11 ng/ml) in children than in newborns (14.4±3.4 ng/ml). No significant difference in serum concentrations of 24, 25(OH)₂D was found between term (N=7) and preterm (N=7) neonates (2.0±0.5 vs 1.7±0.7 ng/ml) nor between prepubertal (N=9) and pubertal (N=11) children (3.8±1.4 vs 2.9±1.1 ng/ml). A significant positive correlation (r=0.87, p<.01) was found between serum 25OHD and 24.25OHD concentrations in children. However, no such relationship was found among newborns. Conclusions: 1) Radioassay of 24, 25(OH)₂D will provide further data concerning the specific metabolism of vitamin D in normal and abnormal subjects; 2) Synthesis of 24, 25(OH)₂D in neonates is apparently independent of the levels of its precursor, 25OHD; 3) Utilization of column chromatography is essential for measurement of absolute levels of 24, 25(OH)₂D and 25OHD.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD