The role of aluminum in the development of hypercalcemia in the rat

Effects of aluminum on phosphate metabolism in rats: a possible interaction with vitamin D3 renal production

The effect of chronic aluminum (Al) administration on the phosphorous (Pi) metabolism of different target tissues was studied. Male Wistar rats received aluminum lactate for 3 months (5.75 mg/kg bodyweight of Al, i.p., three times per week). The animals were studied at the end of the 1st, 2nd and 3rd month of treatment. They were housed individually in metabolic cages for 4 days to study Pi and calcium (Ca) balance. Daily food and water intakes were recorded for all animals and urine and feces were collected for Pi and calcium assays. After 3 months the Pi intestinal absorption and the Pi deposition in bone were studied using 32Pi. Another group of rats was treated daily for 7 days with calcitriol (0.08 microg/kg body weight in sesame oil, i.p.) and the Pi balance was studied for the last 4 days. The results indicated that chronic administration of Al affected simultaneously the Pi and calcium balance, with a significant diminution of calcium and increased Pi accretion in bones, together with a diminution in the intestinal absorption of Pi. The treatment of the rats with calcitriol promoted a normalized Pi balance in Al treated rats. These findings suggest that Al could modify the Pi metabolism acting directly on intestine, kidney and bone, or indirectly through possible changes in the levels of vitamin D3.

Element variations in pregnant and nonpregnant female rats orally intoxicated by aluminum lactate

Pregnant or nonpregnant female rats were orally intoxicated by aluminum lactate (400 mg Al/kg/d) from d 0-19 of gestation to determine the treatment's influence on element variations in the females and their fetuses. The aluminum levels of plasma, liver, spleen, and kidneys were significantly higher in treated pregnant rats than non-pregnant female rats. Differences of P, Ca, Cu, Zn, or Mg levels were observed among the four groups of female rats in the tissues and plasma. The aluminum content of the 20-d-old fetuses did not significantly differ between the treated and control groups. On the contrary, calcium and magnesium levels in the whole fetuses from treated or nontreated dams are significantly different.

Mechanism of Alzheimer's disease: arguments for a neurotransmitter-aluminium complex implication

The authors are convinced that in Alzheimer's disease, as in Down's syndrome and Guam-Parkinson dementia, one may find an alteration in blood brain barrier transfer and a resultant imbalance in mineral metabolism. Metals, such as aluminium, which in vivo yield stable complexes with aspartic and glutamic acids act as previously been clearly shown with glutamic acid; they cross the blood brain barrier, and are deposited in the brain. The authors explain how amyloid protein or neurofibrillary tangles could well be produced by aluminium complex formation. Within the brain, in the form precisely of aluminium complex, L-glutamic acid is consequently unable to detoxify ammonia from neurons and to produce L-glutamin. Accumulation of ammonia is subsequently responsible for the neuronal death, affecting each and every neurotransmitter system.

Direct inhibitory effect of calcitriol on parathyroid function (sigmoidal curve) in dialysis

The effect of intravenous calcitriol on parathyroid function was evaluated in nine chronic hemodialysis patients with secondary hyperparathyroidism. Two micrograms of calcitriol were administered intravenously after dialysis thrice weekly for ten weeks. Parathyroid function was assessed by inducing hypo- and hypercalcemia with low calcium (1.0 mEq/liter) and high calcium (4.0 mEq/liter) dialyses before and after ten weeks of intravenous calcitriol therapy. To avoid hypercalcemia during calcitriol administration, the dialysate calcium was reduced to 2.5 mEq/liter. Parathyroid hormone (PTH) values (pg/ml) from dialysis-induced hypo- and hypercalcemia were plotted against serum ionized calcium, and the sigmoidal relationship between PTH and calcium was evaluated. Basal PTH levels fell from 902 +/- 126 pg/ml to 466 +/- 152 pg/ml (P less than 0.01) after therapy without a significant change in the serum total calcium concentration. The ionized calcium-PTH sigmoidal curve shifted to the left and downward after calcitriol therapy. The maximal PTH response during hypocalcemia decreased after calcitriol from 1661 +/- 485 pg/ml before calcitriol to 1031 +/- 280 pg/ml afterward (P less than 0.05). The PTH level at maximal inhibition due to hypercalcemia decreased from 281 +/- 76 pg/ml before calcitriol to 192 +/- 48 pg/ml afterward (P less than 0.05). The slope of the sigmoidal curve changed from -2125 +/- 487 to -1563 +/- 385 (P less than 0.05). The set point of ionized calcium (4.60 +/- .11 mg/dl before vs. 4.44 +/- .07 mg/dl after) did not change significantly with calcitriol therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Desferrioxamine therapy in hemodialysis patients with aluminum-associated bone disease

Aluminum toxicity in dialysis patients is associated with decreased bone turnover and a relative parathyroid hormone (PTH) deficiency. Desferrioxamine (DFO), a chelating agent, has been reported to improve bone histology in aluminum associated, low turnover bone disease in dialysis patients not subjected to parathyroidectomy. Information on the effect of DFO therapy on parathyroid gland function is lacking. In the present study, in addition to changes in bone histology, parathyroid gland function was evaluated in 18 hemodialysis patients with aluminum associated, low turnover bone disease (osteomalacia and aplastic bone disease) before and after one year of DFO treatment (1 to 6 g/week). Parathyroid gland function was assessed by using a calcium free and high calcium (3.5 to 4 mEq/liter) hemodialysis bath.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Aluminum intoxication in vitamin D-deficient rats: studies of bone aluminum localization and histomorphometry before and after vitamin D repletion

Aluminum accumulation by both dialysis patients and nonuremic patients, requiring chronic total parenteral nutrition, may be an etiological factor in the development of severe osteomalacia. To study the role of aluminum toxicity in bone, further experiments have been conducted in the nonuremic, vitamin D-deficient rat. Weanling rats were raised on vitamin D-deficient diets, and half received parenteral aluminum (5 mg/wk), for 30 days. In the first experiment low doses of 25-OH cholecalciferol (500 ng/week) were given subcutaneously for a further 30 days. Control rats were maintained on a similar protocol, but were supplemented with cholecalciferol (5 micrograms/week) from the outset until sacrifice at 60 days. In the second experiment a single bolus of cholecalciferol (5 micrograms) was given to study short-term changes in serum biochemistry and bone histology at 96 hr. Quantitative bone histomorphometric analyses of the proximal tibial metaphysis were made in all experimental groups. In the experimental vitamin D-deficient group, with the highest bone aluminum content (as assessed by extraction of whole bone aluminum), X-ray microanalysis was performed to determine the distribution of aluminum in bone tissue and bone cell organelles. The results showed that control rats treated with prolonged aluminum therapy (30 mg over 60 days) had evidence of both reduced osteoid matrix synthesis and mineralization. However, in vitamin D-deficient rats, there was no evidence that aluminum exacerbated the osteomalacic lesion, even though there was histochemical evidence of aluminum deposition at the bone-osteoid interface.(ABSTRACT TRUNCATED AT 250 WORDS)