Oxalate absorption and postprandial urine supersaturation in an experimental human model of absorptive hypercalciuria.
The effect of 1.25-dihydroxyvitamin D [1,25-(OH)2D] on dietary oxalate absorption and postprandial urine supersaturation with calcium oxalate was determined in 11 normal subjects. 1,25-(OH)2D increased the urinary excretion of orally administered [14C]oxalate in the 8 h period after a liquid meal containing 1.875 mmol of calcium and 0.83 mmol of oxalate (P less than 0.01), and during a 48 h period when the subjects ingested a diet containing 25 mmol of calcium and 3.3 mmol of oxalate/day (P less than 0.01); however, 1,25-(OH)2D administration had no effect on [14C]oxalate excretion when calcium was removed from the liquid meal. 1.25-(OH)2D increased 24 h urinary oxalate excretion from 28.7 +/- 2.1 mmol/mol of creatinine to 36.8 +/- 2.6 mmol/mol of creatinine (P less than 0.05) on the 10 mmol/day calcium diet and from 26.4 +/- 2.9 to 33.2 +/- 2.2 mmol/mol of creatinine (P less than 0.1) on the 25 mmol/day calcium diet. A linear correlation (r = 0.72) was found between plasma 1,25-(OH)2D levels and urinary [14C]oxalate excretion after the liquid meal. 1,25-(OH)2D administration produced postprandial supersaturation of urine with calcium oxalate and calcium oxalate crystalluria. These studies suggest that 1,25-(OH)2D increases oxalate absorption (and urinary excretion) by increasing calcium absorption, which results in less binding of calcium to oxalate in the intestine; therefore more oxalate is available for absorption. The combined effect of increased calcium and oxalate absorption results in postprandial supersaturation of urine with calcium oxalate, with resultant crystalluria.
D000328:Adult; D002117:Calcitriol; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism*; D002128:Calcium Metabolism Disorders / Q000139:chemically induced; D002129:Calcium Oxalate / Q000652:urine*; D003460:Crystallization; D005215:Fasting; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects; D008297:Male; D009994:Osmolar Concentration; D010070:Oxalates / Q000378:metabolism*; D019815:Oxalic Acid
D010070:Oxalates; D002129:Calcium Oxalate; D019815:Oxalic Acid; D002117:Calcitriol; D002118:Calcium