Parenteral aluminum administration in the dog: I. Plasma kinetics, tissue levels, calcium metabolism, and parathyroid hormone

Interactions between aluminum and the actions and metabolism of vitamin D3 in the chick

The effects of intraperitoneal injections of aluminum chloride were tested on the intestinal calcium absorption and bone calcium mobilization responses to vitamin D3 and 1,25(OH)2D3, as measured by bioassay in chicks. Aluminum at 5 mg/kg given 5 days before the bioassay in vitamin D-deficient chicks, partially blocked the intestinal calcium absorption response to low (0.65 and 3.2 nmol), but not to higher (32 nmol) doses of vitamin D3. The responses to all doses (0.32-2.1 nmol) of 1,25(OH)2D3 were partially blocked by aluminum treatment. Serum calcium values were elevated in vitamin D-deficient chicks by aluminum administration, but no consistent effects of the treatment on bone calcium mobilization in response to vitamin D3 or 1,25(OH)2D3 were noted. Aluminum treatment in vivo led to decreased 25-OH-D3-1-hydroxylase activity subsequently measured in renal homogenates; under a variety of conditions, no direct effect of aluminum on 25-OH-D3 metabolism by primary cultures of chick kidney cells was observed. The results suggest that the ability of the intestine to respond normally to 1,25(OH)2D3 may be compromised by exposure to high levels of aluminum and that the effect of this element on 25-OH-D3 metabolism observed in vivo may not be exerted by direct action on the renal cell.

Aluminum bioavailability and disposition in adult and immature rabbits

Prolonged aluminum (Al) exposure produces neurobehavioral and skeletal toxicity. To further characterize the risk from Al exposure, lactating rabbits were administered iv (40 or 80 mumol/kg), po (4 or 20 mmol/kg), and sc (400 mumol/kg) doses of Al lactate on Days 10, 15, and 20 of lactation. Baseline pretreatment Al concentration averaged 138 ng/ml in serum and 710 ng/ml in milk. Individual baseline values were subtracted from posttreatment samples, and pharmacokinetic analysis was performed on these residual values. The high and low doses did not produce statistically significant differences in systemic clearance, half-life, or the apparent volume of distribution. The amount of aluminum in milk 24 hr after injection was estimated to be 2.4% of the iv and 3.3% of the absorbed sc dose. Systemic bioavailability of Al after low- (0.7 +/- 0.5% means +/- SD) and high-dose po Al (1.9 +/- 1.7%) was not significantly different. Bioavailability of sc Al was 27 +/- 7%. Rabbits receiving daily sc Al injections (400 mumol/kg) for 28 consecutive days demonstrated nonlinear kinetics. Preinjection serum Al concentrations and the area under the curves associated with the 7th dose were considerably greater than with the 1st dose. Further increases were seen with the 28th dose. Seven days after the last Al injection, 12% of the total Al injected was still in the region of the injections, indicating prolonged absorption. The bioavailability and disposition of Al were determined in 17- to 24-day old suckling rabbit offspring after iv (40 mumol/kg) and po (4 mmol/kg in water or milk) doses of Al lactate. Baseline pretreatment serum Al concentration averaged 119 ng/ml. Mean systemic clearance was comparable in offspring and adults, although the apparent volume of distribution was greater in offspring producing a longer half-life in the offspring. The limited distribution of Al into milk and poor GI absorption of Al support the observation that there is little risk of Al toxicity in suckling offspring of Al exposed nursing females.

Parenteral aluminum administration in the dog: II. Induction of osteomalacia and effect on vitamin D metabolism

There is an association between bone aluminum (Al) accumulation and dialysis-associated osteomalacia (OM). To study whether Al is pathogenic in OM, quantitative bone histomorphometry was done in six dogs before (Bx 1) and after (Bx 2) 3 to 5 weeks of intravenous Al administration (1 mg Al /kg/day). Bone Al was determined by histochemical and chemical methods. The percent osteoid rose from 2.8 +/- 0.8 to 7.0 +/- 4.3% (mean +/- SD), P less than 0.05, and osteoid width increased from 5.7 +/- 0.6 to 8.0 +/- 1.2 mu, P less than 0.01, after Al. Bone Al rose from 1.3 +/- 1.6 to 94.0 +/- 19.0 mg/kg after Al, and the severity of OM, expressed as either percent forming surface or percent osteoid, correlated with bone Al measured histochemically and expressed as either percent surface or percent area of trabecular bone staining for Al (r = 0.85 - 0.90, P less than 0.01). Poor tetracycline uptake (six dogs), which indicates impaired mineralization, and little or no separation of tetracycline labels (four dogs) were noted at Bx 2; thus, bone apposition and formation rates were below the limits of detection. Resorptive surface did not change but trabecular volume, expressed as percent of tissue volume, fell from 22.1 +/- 3.0 to 17.1 +/- 1.4%, P less than 0.05. Serum levels of 1,25(OH)2D fell from 26.8 +/- 9.1 to 4.5 +/- 5.5 pg/ml after 17 days of Al; serum 25(OH)D levels were unchanged. These data indicate that Al can cause OM and that its severity correlates with the bone Al content.2 +