1,25-dihydroxyvitamin D-3 and 22-oxacalcitriol prevent the decrease in vitamin D receptor content in the parathyroid glands of uremic rats

Decreased content of the 1,25-dihydroxyvitamin D-3 receptor (VDR) in parathyroid glands from patients and animals with chronic renal failure has been implicated in the pathogenesis of secondary hyperparathyroidism. In these studies, we examined the regulation of VDR by 1,25-dihydroxyvitamin D-3 (1,25-D-3) and 22-oxacalcitriol (OCT) in parathyroid glands of uremic rats. After eight weeks of renal failure, VDR content in parathyroid glands of uremic rats was decreased (400 +/- 42 vs. 729 +/- 47 fmol/mg protein in normal control rats, P < 0.05) and strongly correlated with serum 1,25-D-3 levels (r = 0.829, P = 0.0001). Treatment with either 1,25-D-3 or OCT prevented the decrease in VDR. We conclude that low serum 1,25-D-3 levels, at least in part, account for the decrease in VDR content in parathyroid glands of uremic rats and that treatment with 1,25-D-3 or OCT prevents this decrease ameliorating the development of secondary hyperparathyroidism.