EFFECTS OF SILICON, CITRATE AND THE FASTING STATE ON THE INTESTINAL-ABSORPTION OF ALUMINUM IN RATS

1. The effect of silicon (Si) contained in drinking water and solid fo od on the intestinal absorption of aluminium (Al) remains a matter of debate, The present study was designed to readdress this issue in the experimental animal, and to examine concomitantly the effects of citra te and the fasting state, respectively. 2. Three groups of young, non- fasted rats (n = 8 per group) were gavaged by solutions containing 3.8 ng of Al-26, 63 ng of Al-27, and either distilled water (< 0.1 mg/l S i) or commercial mineral water with a medium (6 mg/l) or high (14 mg/l ) Si concentration. 3. Two other groups of eight non-fasted rats each received the same distilled water or high-Si gavage solution, respecti vely, together with a high citrate concentration (62 g/l), In each cas e the animals had free access to drinking water for 5 days before and 2 days after the gavage, containing the same Si concentration as in th e gavage solution, A sixth group of eight rats was gavaged by low-Si, Al and distilled water in the fasted state. 4. The animals were killed 48 h after gavage, and blood, tissue and urine samples were collected for Al-26 measurements by accelerator mass spectrometry. 5. We found that the fraction of absorbed Al-26 retained in the skeleton (0.025-0. 030%) was of the same order of magnitude as the fraction excreted in t he 48 h urine (0.035-0.037%), High Si concentrations in the drinking w ater failed to depress the Al-26 fraction absorbed, as estimated on th e basis of skeletal accumulation and urinary excretion. 6. The adminis tration of citrate-containing fluid enhanced Al-26 absorption 5- to 10 -fold (P<0.005), but again the Si content of drinking water did not in terfere, Finally, the intestinal absorption of Al-26 was approximately 15 times higher in the fasted than in the non-fasted state. 7. In con clusion, the provision of large amounts of Si in the drinking water fa iled to modify physiological intestinal Al absorption under basal cond itions or after its stimulation by citrate, However, a prolonged fast greatly enhanced Al absorption, compared with the non-fasted state.