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 p arathyroid glands from patients and animals with chronic renal failure has been implicated in the pathogenesis of secondary hyperparathyroid ism. In these studies, we examined the regulation of VDR by 1,25-dihyd roxyvitamin D-3 (1,25-D-3) and 22-oxacalcitriol (OCT) in parathyroid g lands 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). Treatm ent with either 1,25-D-3 or OCT prevented the decrease in VDR. We conc lude 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 th e development of secondary hyperparathyroidism.