| Popis: |
Serum Ca must be maintained at about 10 mg/100 ml for the proper function of nerve, muscle, and bone. Serum Ca is maintained through the action of vitamin D metabolites and parathyroid hormone (PTH) on intestine, kidney, and bone (DeLuca, 1988; Minghetti and Norman, 1988) (Figure 1). Vitamin D3 (cholecalciferol) itself has very little biological activity. It must first be hydroxylated in the liver to from 25-hydroxyvitamin D3 (25[OH]D), which has some biological activity. However, the major activation takes place in the kidnev. Where 25 (OH)D is hydroxulated to 1,25-dihydroxyvitamin D3 (1,25[OH])2D)the metabolite of vitamin D with the most biological activity. 1,25(OH)2D is then inactivated by the 24-(OHases) in various target tissues. The charactristics of these vitamin D hydroxylases (OHases) and their regulation in health and diseasse are the subject of this review. |
