Enhancement of 24,25-dihydroxyvitamin D levels in patients treated with continuous ambulatory peritoneal dialysis

We measured 24,25-dihydroxyvitamin D [24,25(OH)2D] levels in patients treated with chronic ambulatory peritoneal dialysis (CAPD), before and after receiving vitamin D2 or 1 alpha-hydroxyvitamin D3 (1 alpha-OH-D3). Vitamin D2 administration led to an increase in 25-hydroxyvitamin D (25-OH-D) and a concomitant rise in 24,25(OH)2D. No change was observed in 1,25-dihydroxyvitamin D [1,25(OH)2D]. Administration of 1 alpha-OH-D3 resulted in an increase in 1,25(OH)2D3, and a concomitant rise in 24,25(OH)2D, but no change in 25-OH-D3. Thus, 24,25(OH)2D levels may be increased in CAPD patients by raising 25-OH-D levels, or by raising 1,25(OH)2D3 levels. Since the latter enhances specifically the renal 24-hydroxylase enzyme, we conclude that this enzyme is present in CAPD patients with kidneys in situ, and may be stimulated by adequate 1,25(OH)2D3 levels. Thus, administration of 1 alpha-OH-D3 to CAPD patients with kidneys in situ seems to be sufficient to obtain normal levels of 1,25(OH)2D3 and 24,25(OH)2D3. However, anephric patients require vitamin D2 in addition as a source of 25-OH-D, the substrate for extrarenal production of 24,25(OH)2D.