INFLUENCE OF VITAMIN-D3 ON INTESTINAL CALCIUM-ABSORPTION AND ON MINERAL METABOLISM IN PATIENTS WITH CHRONIC-RENAL-FAILURE AND HEMODIALYSIS

Impairment of intestinal calcium-absorption (Ca) can be observed already in early stage of renal failure. An investigation of 68 healthy control-persons and of patients with glomerulonephritis and pyelonephritis showed a deterioration of Ca-absorption with increasing renal insufficiency. These alterations are due to impairment of vitamin D3-metabolism. The lack of active metabolites of vitamin D, especially 1,25 (OH)2D3, leads to a decreased synthesis of Ca-binding proteine, calmodulin and other different systems of enzymes in the mucosal cells. These are factors which are considered to be relevant for Ca-absorption. Although these reactions according to receptor specificity are dependent of 1,25(OH)2D3-level, they can also be influenced by vitamin D2 and vitamin D3. In 29 patients, - 16 with chronic renal failure and 13 undergoing hemodialysis - 47 Ca-absorption-rate was markedly improved by daily application of 40000 IU vitamin D2 or vitamin D3 over 4 weeks: vitamin D2-group: fR (absorption-rate): 6.8 --> 16.9. - vitamin D3-group: fR (absorption-rate): 23.9 --> 27.4. Increment of the vitamin D-dosage to 80000 IU per day yielded no further benefit. Parallel to the improved intestinal Ca-absorption serum-Ca tot and serum-Ca ion normalized. The impairment of Ca-metabolismus could be better influenced by vitamin D3 than vitamin D2. In 9 patients with chronic renal failure the parameters of mineral-metabolism were normalized (serum Ca ion: 0.98 +/- 0.01 - 1.10 +/- 0.03 under longterm application of 20000 IU vitamin D3 per day over 6 months. In 11 hemodialysis patients-despite of increase of serum-Ca (Ca ion.: 1.02 +/- 0.01 --> 1.17 + 0.03 mmol/l) and increase of serum 25-(OH)D3 (28.9 + 18.2 --> 147.2 + 124.7-mu-g/ml) the hyperparathyroidism was not suppressed effectively: Enhanced PTH, alkaline phosphatase and hydroxyproline-excretion could not be corrected. As a consequence of knowledge about the impaired intestinal Ca-absorption in chronic renal failure the necessity of vitamin D-therapy is given. It should be started in an early stage of renal failure; once the stage of dialysis is reached, there is no effective control of the complex disorder of regulation by these vitamin D-agents any more.