CITRIC-ACID CONCENTRATION COMPARED TO SERUM PARATHYROID-HORMONE, 1,25(OH)2D3 AND CALCITONIN DURING DIETARY CA DEFICIENCY AND REHABILITATIONENHANCED WITH XYLITOL IN RATS

Young male Wistar rats were fed on a Ca-deficient diet for 3 weeks, af ter which dietary Ca was restored with either CaCO3 or CaCO3 + xylitol (5% per weight). Citric acid, Ca, Mg, Zn and P were determined in the tibia and femur at the beginning and after 2 and 4 weeks of rehabilit ation, and serum and urinary citric acid and serum 1,25(OH)2D3, parath yroid hormone (PTH) and calcitonin were measured at the same points in time. The diminished bone Ca (p < 0.001) after 3 weeks of deficiency did not reduce the bone citric acid concentration, although serum citr ate increased markedly. Simultaneously the serum 1,25(OH)2D3 concentra tion more than doubled and PTH increased (p < 0.01). Rehabilitation wi th CaCO3 + xylitol reduced the 1,25(OH)2D3 concentration to below the control level (p < 0.05), while serum citric acid remained elevated. C aCO3 alone normalized the elevated hormone and citric acid levels in t he serum. Dietary CaCO3 and CaCO3 + xylitol normalized the PTH concent ration equally well. The gain in bone Ca after 4 weeks of rehabilitati on was significantly greater when xylitol was added compared with CaCO 3 alone (p < 0.05). Only the 4-week CaCO3 + xylitol group attained the bone Ca concentration of the controls. Xylitol supplementation seems to affect the serum citric acid concentration independent of 1,25(OH)2 D3 and PTH concentrations. The elevated citric acid concentration coul d be associated with increasing bone Ca.