Regulation of vitamin D: an evolutionary view.

The regulation of vitamin D metabolism by the kidney is now known to be multifactorial. Three regulatory factors are discussed: 1,25(OH)2D3 itself; parathyroid hormone, and phospate. The influence of 1,25(OH)2D3 probably depends on new protein synthesis, while the mode of action of phosphate is unknown. Parathyroid hormone is not essential for regulation but may have an important biological role. The direction of its effect varies, perhaps due to a complex interrelation of changes in calcium and phosphorus metabolism and the level of kidney adenyl cyclase activity.