Cellular and subcellular localization of 1,25-(OH)2-vitamin D3 in rat kidney: comparison with localization of parathyroid hormone and estradiol.

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Abstract
Results of thaw-mount autoradiographic studies of kidney obtained 1-3 h after a single injection of 1,25-(OH)2-[3H]vitamin D3 to rats showed strong nuclear concentration of radioactivity in podocytes and cells of distal tubules, including the pars convoluta, macula densa and pars recta. Intermediate nuclear concentration was found in cells of the thin limb of Henle''s loops, whereas weak or no nuclear uptake was seen in cells of the proximal tubules. In contrast, after injection of 3H-labeled parathyroid hormone [PTH] or [3H]estradiol [E2], mainly cells of the proximal tubules were labeled; after 3H-labeled PTH, apical cytoplasmic uptake of radioactivity was seen most strongly in the proximal part of the proximal tubules, whereas after [3H]E2, weak nuclear concentration was seen in cells throughout the proximal tubules. Synthesis of 1,25-(OH)2-vitamin D3 apparently occurs in the proximal tubules under stimulation of PTH or E2 (or other hormones) and the major site of action of 1,25-(OH)2-vitamin D3 is in the distal tubules.