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 1α-hydroxyvitamin D₃ (1α-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 1α-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 1α-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.