EFFECT OF DIETARY PHOSPHORUS LEVELS ON PORCINE RENAL 25-HYDROXYVITAMIN D-la-AND 24R-HYDROXYLASE ACTIVITI ES AND PLASMA 1,25-DIHYDROXYVITAMIN D3 CONCENTRATION 1'2

Summary Results of studies on the effect of dietary P deprivation on pig renal la- and 24-hydroxylase activities and on concentrations of plasma alkaline phosphatase, Ca, P and vitamin D metabolites are presented. Renal l~-hydroxylase activity was increased six- to eightfold and plasma 1,25-dihydroxyvitamin D 3 concentra- tion 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-hydroxy- vitamin 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 l~-hydroxylase activity in spite of the presence of a pronounced