Impaired 24,25-Dihydroxyvitamin D Production in Anephric Human and Pig

Open Access
Publisher Website
Google Scholar
Abstract
Plasma 25-hydroxyvitamin D and 24, 25-dihydroxy-vitamin D [24,25-(OH)2D] concentrations were measured in normal and chronically dialyzed anephric humans and pigs. Measurement of the 24, 25-(OH)2D was preceded by three purification steps involving one Sephadex LH-20 column and two high-pressure liquid chromatographic columns. The final high-pressure liquid chromatography step involved resolution of 25-hydroxy-vitamin D3-26,23 lactone and 25,26-dihydroxy-vitamin D2 from 24,25-dihydroxyvitamin D2 and 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3]. The total 25-hydroxyvitamin D [25-hydroxyvitamin D2 plus 25-hydroxyvitamin D3 (25-OHD3)] was 31.7±3.6 ng/ml in the plasma of eight anephric human subjects and 40.1±3.7 ng/ml in five normal human subjects. Six of the eight anephric patients had undetectable (2D concentrations. Two of the eight patients had very low (0.51 and 0.41 ng/ml), but detectable, 24,25-dihydroxyvitamin D2. The normal human volunteers had plasma 24,25-(OH)2D concentrations of 2.8±0.7 ng/ml. Chronically dialyzed anephric and normal pigs were given intramuscular injections of massive amounts (5 × 106 IU) of vitamin D3 immediately after surgery (day 0) and again on day 7. In anephric pigs, plasma 25-OHD3 progressively rose from 12±4 ng/ml on day 0 to 705±62 ng/ml on day 10. The 25-OHD3 concentrations in normal pigs rose from 8±2 ng/ml on day 0 to 439±64 ng/ml on day 10. Plasma 25-OHD3 was higher in anephrics throughout the experiment, and concentrations were significantly higher (P < 0.05) on days 9 and 10. Plasma 24,25-(OH)2D3 concentrations declined progressively in anephric pigs from 3.6±0.6 ng/ml on day 0 to 3.2±0.7 ng/ml on day 2. During days 4-10, plasma 24,25-(OH)2D3 was not apparent until plasma 25-OHD3 was >400 ng/ml. In control pigs, plasma 24,25-(OH)2D3 was elevated from 4.3±0.6 ng/ml on day 0 to 178±2.7 ng/ml on day 3. Plasma 24,25-(OH)2D3 was significantly higher (P < 0.05) in controls on days 1-8. At the end of the experiment (day 10), 24,25-(OH)2D3 concentrations were similar and not significantly different in both groups (87.0±18.4 ng/ml in anephric and 110.3±32.1 ng/ml in normal pigs). The identity of the 24,25-(OH)2D3 isolated from anephric pig plasma was confirmed by mass spectroscopy. Our data suggest that anephric humans receiving normal dietary levels of vitamin D3 have little or no ability to produce 24,25-(OH)2D. However, we have shown that pigs produce 24,25-(OH)2D3 when plasma 25-OHD3 is extremely high (>400 ng/ml).