Metabolism of Vitamin D3in Nephrectomized Pigs Given Pharmacological Amounts of Vitamin D3

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Abstract
The metabolism of vitamin D3 was studied in bilaterally nephrectomized pigs and control pigs maintained for 8–10 days by daily peritoneal dialysis. Two or three pharmacological doses of vitamin D3 were given im, one on day 0 and the others on days 4, 6, or 7 of the 8- to 10-day experimental periods. Nephrectomized pigs had extremely high plasma concentrations of 24,25-dihydroxyvitarnin D3 [24,25-(OH)2D3] and 25,26- (OH)2D3 at the end of the 8- to 10-day periods; similar levels were present in control pigs. However, nephrectomized pigs had no detectable increase in plasma 25-hydroxyvitamin D3 (250HD3)-26,23-lactone concentrations throughout the experiment, in contrast with the high plasma concentrations of 25OHD3-26,23-lactone in the control pigs. Much higher plasma 25OHD3 concentrations were present in the nephrectomized pigs than in the control pigs. Plasma 1,25-(OH)2D concentrations in nephrectomized and control pigs were similar during most of the experiment, except the anephric pigs usually had significantly higher plasma 1,25-(OH)2D concentrations for several days after the vitamin D3 injections. These studies demonstrate extrarenal production of 24,25-(OH)2D3, 25,26-(OH)2D3, and possibly 1,25- (OH)2D, and kidney-dependent synthesis of 25OHD3-26,23-lactone in the pigs.