Vitamin D and the parathyroid

Vitamin D's biologically active metabolite, 1,25(OH)(2)D-3 has important effects upon the parathyroid cell that are relevant to both the physiology of mineral metabolism and the regulation of the secondary hyperparathyroidism of chronic renal failure. 1,25(OH)(2)D-3 markedly decreases parathyroid hormone (PTH) gene transcription and thus PTH synthesis and secretion. It also acts to decrease parathyroid cell proliferation. Non-hypercalemic analogs of 1,25(OH)(2)D-3 are being developed that may have a wider therapeutic window than 1,25(OH)(2)D-3 itself. In the situations of chronic hypocalcemia and hypophosphatemia, there are interesting interrelationships between 1,25(OH)(2)D-3 and the posttranscriptional regulation of the PTH gene. In nodular secondary hyperparathyroidism, there is down-regulation of the vitamin D receptor in the parathyroid, Different vitamin D receptor genotypes may be associated with higher levels of serum PTH and a predisposition to autonomous hyperplasia.