A method of studying the intestinal absorption of aluminium in the rat

Absorption of bismuth from several bismuth compounds during in vivo perfusion of rat small intestine

Evaluation of the amount of bismuth (Bi) absorbed from the gastrointestinal tract is important for assessment of the possible risks associated with the use of Bi compounds in the treatment of gastrointestinal disorders. We compared the absorption of Bi from media containing the equivalent of 1 g of elemental Bi from either Bi subnitrate (BSN), Bi subsalicylate (BSS), colloidal Bi subcitrate (CBS), Bi chloride (BiCl3), or Bi citrate (BCit) by an in vivo perfusion system of rat small intestine. The intestinal absorption was < 1% for all compounds, but higher from BCit and CBS than from BSN, BSS, and BiCl3. The dose dependency of Bi absorption from both CBS and BiCl3 in citrate buffer showed a nonlinear relationship between the concentration of Bi in perfusate and the concentration of Bi in blood after 60 min.

The transport of aluminum and water across the rat small intestine

Aluminum transport across the epithelium of the rat small intestine has been investigated to determine factors affecting its absorption and its effect on the transport of other substances across the membrane. The intestines were attached to a perfusion apparatus and perfused with Krebs-Ringer-bicarbonate buffer containing aluminum. The transport of aluminum and buffer ions across the small intestine were measured. Phosphate transport was found to be the most satisfactory marker for viability. It is impossible to accurately measure the aluminum transport across a biological membrane unless the aluminum concentration of the solution is stable over the period of measurement. Hence, the solutions were stabilized with citrate ions which made them stable over a period of at least two hours. The velocity of transport of aluminum across the epithelium increased steadily and only became constant after about one hour. The steady state value of 0.12 micrograms atom of Al/hr/mg dry tissue compares well with that reported in the literature for stable aluminum solutions. Aluminum inhibited the transport of water across the membrane, but the inhibition took about two hours to reach a steady state of about 50% of the control value. This indicates that aluminum-containing medications and foods are able to interfere with the absorption of nutrients from the gut. Aluminum salts may therefore be useful to prevent rapid dehydration in the treatment of certain diseases such as cholera.

Kinetics and mechanism of uptake of platinum-based pharmaceuticals by the rat small intestine

The absorption of two platinum-based pharmaceuticals, cisplatin and carboplatin, was studied using in vitro and in situ models. By utilizing everted rat small intestine, it was found that absorption of both drugs was linear with time up to 60 min and was not saturable up to a concentration of 1.0 mM. Moreover, uptake against a concentration gradient could not be demonstrated and absorption was not reduced by metabolic inhibition or anoxic conditions. These results indicate the lack of involvement of an active transport mechanism for cisplatin and carboplatin and imply that absorption across the gastrointestinal tract is by passive diffusion. Cisplatin was absorbed more readily than carboplatin, both in vitro and in situ. In situ both drugs were found to disappear from the intestinal lumen following first-order kinetics. The results of in situ studies indicate that a decrease in pH of the perfusion medium leads to an increase in absorption of carboplatin into the systemic blood. This report establishes the fact that both cisplatin and carboplatin are absorbed across the gastro-intestinal tract and indicates that preclinical trials involving oral administration of platinum-based pharmaceuticals could be justified.

Aluminum speciation studies in biological fluids. Part 3. Quantitative investigation of aluminum-phosphate complexes and assessment of their potential significance in vivo

Following the discovery that specific health disorders affecting patients with renal disease were due to their excessive body accumulation of aluminum, it was established that aluminum toxicity was mainly due to the ingestion of aluminum-containing phosphate binders. Suspicion of toxicity was thus cast on aluminum-containing antacids, and subsequent tests held on healthy subjects did reveal that aluminum hydroxide gels were also potential oral sources of aluminum, especially in the presence of citric acid. Nevertheless, authors of these tests concluded that there was only marginal absorption of aluminum phosphate. In contrast with these clinical conclusions, it has recently been contended on theoretical grounds that aluminum phosphate represents a serious health hazard. To help elucidate this issue, this paper first deals with a quantitative investigation of aluminum-phosphate equilibria under physiological conditions. Then appropriate computer simulations based on corresponding results are used to assess the actual extent to which phosphate can influence aluminum bioavailability. These simulations confirm that aluminum phosphate is not expected to induce absorption of high amounts of aluminum when administered by itself. Nevertheless, this result may no longer apply in the presence of food, whose various acidic components are likely to modify the involved chemical equilibria. Moreover, it is shown that rising blood plasma phosphate levels should tend to increase aluminum tissue penetration and hence favor its potential toxicity.

Intestinal absorption of aluminum in rats: stimulation by citric acid and inhibition by dinitrophenol

The effects of citric acid and dinitrophenol on the mucosal uptake of aluminum (Al) and its appearance in the portal and systemic blood were investigated to establish the energy dependence of these processes. Therefore, the rat small intestine was perfused in situ with media containing 20 mmol Al/liter, with or without 5 mmol citric acid/liter, and with or without 0.1 mmol/liter of the metabolic inhibitor DNP. It is concluded that (1) the appearance of Al in systemic blood depends on the mucosal Al uptake after perfusion and the systemic blood level before perfusion and (2) citric acid stimulates and DNP inhibits both mucosal uptake and Al absorption in situ.

Reduced intestinal calcium and dietary calcium intake, increased aluminum absorption, and tissue concentration in the rat

To test the influence of calcium (Ca) on aluminum (Al) absorption, Ca was withheld from or added (1mM) to the perfusate of the in situ rat gut. The rats had been maintained on Purina Rat Chow. Ca addition significantly decreased (to 70%) the rate of Al disappearance from the gut and decreased (to 55%) the area under the curve of Al appearance in portal blood. To test the influence of Ca deficiency on Al absorption, rats were maintained on a low-Ca (0.008%) or a Ca-replete (0.5%) diet for 1-4 wk. The in situ gut was prepared, and a perfusate containing approximately 1 microM Ca was used. The rate of Al disappearance from the gut of low-Ca diet rats was significantly faster than from the gut of rats maintained on the Ca-replete diet, averaging 156% of the latter. Al appearance in portal blood was significantly greater (averaging 38%) in rats maintained on the low-Ca diet than in controls. To determine if Ca deficiency influences Al tissue distribution independent of gastrointestinal Al absorption, rats maintained on a low-Ca or a Ca-replete diet received 20 ip Al injections over 1 mo. Rats eating the low-Ca diet demonstrated enhanced tissue Al accumulation in all tissues studied, except for muscle and cerebral cortex. These results demonstrate enhanced Al absorption and tissue retention in the presence of reduced intestinal Ca concentration and reduced Ca intake.

Aluminum and chronic renal failure: sources, absorption, transport, and toxicity

In normal subjects the gastrointestinal tract is a relatively impermeable barrier to aluminum with a low fractional absorption rate for this metal ion. Aluminum absorbed from the gastrointestinal tract is normally excreted by the kidneys; in the presence of impaired renal function aluminum is retained and accumulates in body tissues. Aluminum-containing medications are given, by mouth, to patients with chronic renal failure as phosphate-binding agents for the therapeutic control of hyperphosphatemia. Patients with chronic renal failure are also exposed to aluminum in domestic tap-water supplies used either for drinking or, in those on dialysis treatment, in the preparation of their dialysate. In patients with end-stage chronic renal failure, particularly in those on treatment by hemodialysis, the accumulation of aluminum in bone, brain, and other tissues is associated with toxic sequelae. An increased brain content of aluminum appears to be the major etiological factor in the development of a neurological syndrome called either "dialysis encephalopathy" or "dialysis dementia"; an increased bone content causes a specific form of osteomalacia. An excess of aluminum also appears to be an etiological factor in a microcytic, hypochromic anemia that occurs in some patients with chronic renal failure on long-term treatment with hemodialysis. The various mechanisms involved in the toxic phenomena associated with the accumulation of aluminum in body tissues have not been clearly defined but are the subject of extensive investigations.

Serum aluminium concentrations in patients with rheumatoid arthritis

Aluminium (AlS) and zinc (ZnS) concentrations in serum were measured in patients with rheumatoid arthritis (RA) with and without Al-containing drugs and compared with levels in healthy controls. In RA patients without Al-containing antacids, the AlS levels did not differ from those of the healthy controls (mean 9.9, SEM 0.9 microgram/l and mean 8.6, SEM 0.5 microgram/l). However, the AlS levels in RA patients treated with Al-containing drugs were significantly (p less than 0.05) higher than in the other two groups (mean 14.1, SEM 1.1 microgram/l). Serum zinc (ZnS) levels in both RA groups were significantly (0.01 less than p less than 0.025) lower than in the healthy controls (mean 10.5, SEM 0.4 mumol/l and mean 10.2, SEM 0.4 mumol/l for the RA groups with and without Al-containing drugs, and in healthy volunteers mean 14.4, SEM 0.6 mumol/l). The difference in AlS levels might be due not only to the intestinal absorption of Al from Al-containing drugs, but also to a slightly impaired renal function, serum creatinine being slightly but significantly higher (p less than 0.05) in the Al-treated RA group than in non-Al-treated one. This difference in serum creatinine between the two RA groups might be explained by the more frequent use of cimetidine in the Al-treated RA group.

Intestinal absorption of aluminum in rats: effect of intraluminal pH and aluminum concentration

The intestinal absorption of aluminum (Al) was studied in an in situ perfusion system of rat small intestine in combination with systemic and portal blood sampling. The jejunum-ileum was perfused with media containing 4.63, 9.25 and 18.50 mmol l-1 Al chloride at pH 4.0 and 7.0. Both mucosal retention was not affected by pH but at lower pH more Al was released into the blood. The amount of Al which appeared in the blood was linearly related to the mucosal retention. The Al release into the blood was much less (mumol l-1) than the mucosal retention (mmol l-1). It is concluded that the intestinal absorption of Al is pH- and concentration-dependent.

Intestinal absorption of aluminium from antacids: a comparison between hydrotalcite and algeldrate

The intestinal absorption of aluminium (Al) from the antacid hydrotalcite (Ultacit) was compared with that from algeldrate (Algeldratum des-acidans) in 8 healthy human subjects in a cross-over study. The level of Al in serum (AlS) was increased in 7 out of 8 subjects 7 hr after intake of 6 g algeldrate while AlS did not rise after intake of 8 g hydrotalcite--a dose with at least comparable acid-neutralizing capacity--in any of the subjects.

Intestinal absorption of aluminium in rats

To study the mechanism of intestinal aluminium (Al) absorption, an experimental investigation into the uptake of Al from the rat gut was undertaken. The small intestine was perfused in situ for 60 min with isotonic media containing 4.63, 9.25, and 18.50 mmol/l Al chloride at pH 4.0 and 7.0. Portal and systemic blood were sampled and analysed for its Al content by flameless atomic absorption spectrophotometry. It was found that the intestinal absorption of Al in rats is concentration and pH dependent.