Renal 25-hydroxyvitamin D3-1-hydroxylase in patients with renal disease

Renal 25-hydroxyvitamin D3-1-hydroxylase (1-hydroxylase) activity has been measured in 20 patients with renal disease using the remaining portion of needle renal biopsy specimens taken for diagnostic purposes and in five patients using kidney tissue removed during transplantation. The 1-hydroxylase activity of 12 patients with asymptomatic proteinuria and/or hematuria (group A) measured 83.2 +/- 37.7 pg/mg tissue/20 min. Since these 12 patients did not show impaired mineral metabolism or pathological changes in the renal tubules, we have presumed that these results indicate normal activity in man. We also measured the 1-hydroxylase activity in four patients treated with prednisolone (group B). The 1-hydroxylase activity (81.1 +/- 27.1 pg/mg tissue/20 min) of group B did not differ from that of group A. However, the urinary excretion of calcium (ratio of calcium/creatinine) was increased (0.18 +/- 0.07 vs. 0.07 +/- 0.03, P less than 0.01) by prednisolone therapy. These data suggest that glucocorticoid-induced changes in urinary calcium excretion are not the result of a direct effect of glucocorticoid on renal 1-hydroxylase. In the three patients with mild renal insufficiency (group C), the 1-hydroxylase activity (75.4 +/- 22.4 pg/mg tissue/20 min) did not differ from that of group A. However, in five patients with severe renal insufficiency (group D), the 1-hydroxylase activity (8.5 +/- 3.7 pg/mg tissue/20 min) was significantly decreased (P less than 0.01).