Short-term regulation of the renal vitamin D receptor in rats by 1,25-dihydroxycholecalciferol is calcium insensitive.

Acute regulation of the vitamin D receptor in kidney by 1,25-dihydroxycholecalciferol and dietary calcium was investigated using vitamin D-deficient rats. 1,25-Dihydroxycholecalciferol administered to normocalcemic, vitamin D-deficient rats increased the renal receptor level, whereas serum calcium and phosphorus concentrations remained nearly constant. In hypocalcemic, vitamin D-deficient rats, 1,25-dihydroxycholecalciferol caused a sharp response at 4 h, which remained elevated for the remaining 20 h. Serum calcium rose gradually over 24 h, whereas serum phosphorus remained fairly constant. When hypocalcemic, vitamin D-deficient rats were fed a high calcium diet following 14 h without food, the serum calcium concentration increased and serum phosphorus concentration decreased, whereas renal receptor levels were unchanged. These data indicate that 1,25-dihydroxycholecalciferol rapidly regulates the renal vitamin D receptor, independent of serum calcium and phosphorus, but requires an adequate serum calcium concentration to sustain a prolonged effect.