Ultrasensitive analysis of the intestinal absorption and compartmentalization of aluminium in uraemic rats: a 26Al tracer study employing accelerator mass spectrometry

BACKGROUND: Developments in accelerator mass spectrometry (AMS) now permitthe determination of femtogram amounts of 26Al in blood and in varioustissues with good precision and free of external contamination. METHODS: Inthe present study we used trace quantities of 26Al to investigate theintestinal absorption and compartmentalization of aluminium in rats withrenal failure (Nx, 5/6 nephrectomy) and in pair- fed controls (C). Singleoral doses of 20 ng 26Al were administered to six animals in each groupand, subsequently, 24-h post-load 26Al was analysed in serum, urine, bone,liver, and spleen by means of AMS. RESULTS: Serum concentrations of 26Alwere significantly lower in uraemic rats compared to controls, whereasurinary excretion was comparable (Nx, 7.11 +/- 5.78 pg/day vs C, 9.46 +/-6.10 pg/day), suggesting a higher fraction of ultrafiltrable serum 26Al inuraemia. The target tissues of cellular transferrin-mediated 26Al uptake,liver and spleen, tended to show a larger degree of aluminium accumulationin controls (0.26 +/- 0.31 pg/g vs Nx, 0.14 +/- 0.10 pg/g and 0.37 +/- 0.27pg/g vs Nx, 0.25 +/- 0.27 pg/g respectively). In contrast, in bone, a siteof extracellular aluminium deposition, 26Al concentrations were moreelevated in uraemia (1.22 +/- 0.59 pg/g vs C: 0.68 +/- 0.30 pg/g).Estimated total 26Al accumulation in all measured target tissues wassignificantly higher in uraemic rats (28.15 +/- 9.90 pg vs C: 17.03 +/-7.03 pg) and total recovery of 26Al from tissue and urine was 26.58 +/-6.74 pg in controls and 35.75 +/- 7.03 pg in uraemic animals, suggesting afractional absorption of 0.133% and 0.175% respectively. CONCLUSIONS: Ourdata suggest that fractional absorption from a dietary level dose of 26Alis about 0.13%. Compartmentalization occurs in transferrin-dependent targettissues such as liver and spleen; however, in quantitative termsextracellular deposition in bone is more important. Uraemia has asignificant effect on the intestinal absorption and compartmentalization ofaluminium. It enhances fractional absorption and increases subsequentextracellular deposition of aluminium in bone. However, at the same timeuraemia does not increase transferrin-dependent cellular accumulation ofaluminium in liver and spleen.