INCREASE OF CALCITRIOL DURING TREATMENT WITH PROTEIN-REDUCED DIET IN PATIENTS WITH RENAL-FAILURE

Vitamin D metabolites 25-OH-D3 (calcifediol) and 1,25-(OH)2-D3 (calcit riol) were measured in plasma in 16 patients with advanced chronic ren al failure during treatment with a protein-restricted diet for 6 month s. The glomerular filtration rate (GFR) decreased only marginally, fro m 8.3 to 7.9 ml/min, during the study while there was a significant de crease of serum urea levels after the initiation of the protein-reduce d diet. Calcitriol levels rose significantly (p < 0.05) after 3 months from 17.1 to 27.7 pg/ml but fell after another 3 months to nearly the ir initial values, 15.3 pg/ml. The serum phosphate levels changed duri ng the same periods from 1.99 to 1.67 to 1.93 mmol/l. There were signi ficant inverse correlations between the calcitriol and phosphate level s at the start and after 3 months but not after 6 months. There was al so a significant correlation between the changes in calcitriol and ini tial GFR. A subgroup of patients with decreased or unchanged calcitrio l concentrations during dietary treatment had significantly higher ser um phosphate and creatinine and significantly lower standard bicarbona te concentrations. Multivariate regression analysis for the pooled set of data with calcitriol as the dependent variable showed significant values for GFR (p < 0.02), body mass index (p < 0.02), and serum phosp hate concentrations (p < 0.04). These results show the importance of p hosphate control and renal function for the regulation of calcitriol s ynthesis.