Regulation of the vitamin D endocrine system located in the kidney.

During the past decade, it has been clearly established that the kidney is an endocrine organ which converts 25-hydroxyvitamin D to the active hormone 1,25-dihydroxyvitamin D. The kidney and intestine are the sites of an alternative hydroxylation which places an 24 hydroxyl in the R position on either 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D. The production of 1,25-dihydroxyvitamin D is stimulated by hypocalcemia through the parathyroid gland, hypophosphatemia, the sex hormones and the peptide hormones insulin and prolactin. This vitamin D based endocrine system is of central importance in regulating calcium and phosphorus metabolism and its disturbances result in a variety of pathological conditions.