INFLUENCE OF DIETARY CALCIUM-PHOSPHATE ON THE DISPOSITION OF BILIRUBIN IN RATS WITH UNCONJUGATED HYPERBILIRUBINEMIA

The aim of this study was to test a possible form of therapy that coul d be used in the management of unconjugated hyperbilirubinemia. We hyp othesized that unconjugated bilirubin (UCB) can permeate the intestina l wall and can thus be secreted with the feces. We have previously obs erved that UCB binds to amorphous calcium phosphate in vitro, Orally i ngested amorphous calcium phosphate may act as a trapping agent for bi lirubin in the intestine, thereby preventing back-diffusion across the intestinal wall, In this study, we tested whether feeding calcium pho sphate leads to enhanced excretion of unconjugated bilirubin in Gunn r ats. When a purified control diet was substituted by a high calcium ph osphate diet, a decrease in bilirubin levels of 30% to 50% in male Gun n rats and of 23% in female rats was observed, The fecal output of bil irubin was more than doubled in Gunn rats in the first 3 days after th e normal diet had been replaced by the high calcium-phosphate diet, Th e biological half-life of H-3-labeled bilirubin in blood was 89.8 +/- 17.2 hours in rats fed the purified control diet and 50.9 +/- 1.4 hour s in rats fed the high calcium phosphate diet (P = .004). After 30 wee ks, plasma bilirubin levels were still significantly lower in Gunn rat s fed a high calcium phosphate diet, No differences were found in plas ma concentrations of calcium, magnesium, phosphate, urea, and creatini ne in both Gunn rats and Wistar rats on control or high calcium phosph ate diets, This therapy might be useful in the management of Crigler-N ajjar patients, for example, as an adjunct to phototherapy.