1. Until recently studies of intestinal aluminium absorption used pharmacological amounts of stable 27Al.

2. To examine the intestinal absorption of trace amounts of different chemical compounds of aluminium, in the present study we have employed the long half-life isotope of aluminium, 26Al, and accelerator mass spectrometry. Trace amounts of 26Al (2.7–12.1 ng) as the hydroxide, citrate, citrate plus 1 mmol/kg sodium citrate, or maltolate respectively, were administered to four groups of rats (n = 9 per group) by gavage. Blood and urine samples were collected for 5 h and the 26Al content (as a percentage of the administered dose) determined by accelerator mass spectrometry.

3. The 5 h urinary 26Al excretion amounted to 0.1 ± 0.02, 0.7 ± 0.2, 5.1 ± 1.5 and 0.1 ± 0.1% of administered dose in the four groups respectively. There was a strong positive correlation between peak plasma 26Al (r = 0.98) and urinary 26Al excretion in individual animals (P < 0.001).

4. We conclude that the fractional intestinal absorption of trace oral doses of aluminium hydroxide is at least 0.1% (compared with the previous estimate of 0.01% using large 27Al oral loads). Absorption of aluminium citrate given alone is significantly greater (0.7%) and is further increased to 5% by the accompanying sodium citrate, consistent with an enhancing effect of added citrate upon mucosal aluminium permeability. Aluminium maltolate absorption approximates that of aluminium hydroxide (0.1%).

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