Effect of dietary phosphorus levels on porcine renal 25-hydroxyvitamin D-1 alpha- and 24R-hydroxylase activities and plasma 1,25-dihydroxyvitamin D3 concentration.

Results of studies on the effect of dietary P deprivation on pig renal 1 alpha- and 24-hydroxylase activities and on concentrations of plasma alkaline phosphatase, Ca, P and vitamin D metabolites are presented. Renal 1 alpha-hydroxylase activity was increased six- to eightfold and plasma 1,25-dihydroxyvitamin D3 concentration increased two- to threefold in pigs fed a low P diet (.085% P) compared with pigs fed a control diet (.6% P). In contrast, renal 24-hydroxylase activity and plasma 25-hydroxyvitamin D concentration did not differ between diet groups. Plasma alkaline phosphatase activity was two to four times higher in pigs fed the low P diet compared with pigs fed the control diet. The rate of gain by pigs fed the low P diet was less than pigs fed the control diet. The low P diet was associated with a prolonged elevation of renal 1 alpha-hydroxylase activity in spite of the presence of a pronounced hypercalcemia.