Vitamin D Endocrinology

Abstract

The current status of understanding of the metabolism of vitamin D and its implications in metabolic bone disease is reviewed. The details of metabolism of vitamin D3 to 25-hydroxyvitamin D3 in the liver and its further conversion in the kidney to either 1,25-dihydroxyvitamin D3 or 24,25-dihydroxyvitamin D3 are presented. The latter conversions are regulated by the vitamin D status, serum Ca through the parathyroid gland system and serum inorganic P concentration. The 1,25-dihydroxyvitamin D3 can now be regarded as a Ca- and a phosphate-mobilizing hormone and must be considered as 1 of the most important serum Ca-regulating hormones. Disruption of the vitamin D metabolic sequence or the signal system for 1,25-dihydroxyvitamin D3 results in several bone and Ca metabolism disorders such as renal osteodystrophy, hypoparathyroidism, pseudohypoparathyroidism and vitamin D-dependency rickets. The use of the synthetic analogs of 1,25-dihydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 itself in the management of these [human] disease states is discussed. [Other organisms discussed include chickens, rats and cows].