The biological speciation and toxicokinetics of aluminum

This review discusses recent literature on the chemical and physiological factors that influence the absorption, distribution, and excretion of aluminum in mammals, with particular regard to gastrointestinal absorption and speciation in plasma. Humans encounter aluminum, a ubiquitous yet highly insoluble element in most forms, in foods, drinking water, and pharmaceuticals. Exposure also occurs by inhalation of dust and aerosols, particularly in occupational settings. Absorption from the gut depends largely on pH and the presence of complexing ligands, particularly carboxylic acids, with which the metal can form absorbable neutral aluminum species. Uremic animals and humans experience higher than normal body burdens of aluminum despite increased urinary clearance of the metal. In plasma, 80-90% of aluminum binds to transferrin, an iron-transport protein for which receptors exist in many tissue. The remaining fraction of plasma aluminum takes the form of small-molecule hydroxy species and small complexes with carboxylic acids, phosphate, and, to a much lesser degree, amino acids. Most of these species have not been observed in vivo but are predicted from equilibrium models derived from potentiometric methods and NMR investigations. These models predict that the major small-molecule aluminum species under plasma conditions are charged and hence unavailable for uptake into tissues.

Pharmacokinetics of aluminum 3-hydroxypyridin-4-one complexes: implications for aluminum redistribution subsequent to chelation therapy

The pharmacokinetics of selected aluminum-hydroxypyridinone (Al-HP complexes were determined in rats to better understand the relationship between their disposition and elimination parameters and the safety of HPs in the chelation therapy of Al intoxication. Five complexes were administered as i.v. bolus doses of Al-HP (0.25 mmol/kg Al-0.75 mmol/kg HP). The Al-HP steady state volumes of distribution ranged from 220 to 871 ml/kg, suggesting that each complex distributed out of the vascular compartment (which should have been approximately 65 ml/kg). Systemic clearances ranged from 189 to 906 ml/h per kg. Elimination half-lives (t1/2) and mean residence times ranged from 0.36 to 0.84 and 0.52 to 1.20 h, respectively. The Al-CP20 complex had a short t1/2 and a midrange volume of distribution. It demonstrated no apparent toxicity, whereas myoclonic seizures were observed after Al-CP22, Al-CP24 and Al-CP94 administration. The most appropriate choice for Al chelation among the HPs tested may be CP20. Characterization of the distribution and elimination of Al-HP complexes improves the understanding of potential toxicity that may be associated with HP therapy of Al intoxication.

Aluminum chelation: chemistry, clinical, and experimental studies and the search for alternatives to desferrioxamine

This review focuses on aluminum (Al) chelation, its chemistry and biology. The toxicology and biology of Al in mammalian organisms are briefly reviewed to introduce the problems associated with excessive Al exposure and accumulation and the challenges facing an effective Al chelator. The basics of Al chelation chemistry are considered to help the reader understand the Al chelation chemical literature. The chemical properties of Al enable prediction of effective functional groups for Al chelation. A compilation of distribution coefficients between octanol and aqueous phases (Do/a) for chelators and their complexes with Al shows the effect of complexation on lipophilicity. A compilation of stability constants for Al.chelator complexes illustrates the role of oxygen in ligands that form stable complexes. The history of clinical Al chelation therapy is reviewed, with emphasis on desferrioxamine (DFO), which has been extensively used since 1980. The beneficial and adverse effects and limitations of DFO use in end-stage renal-diseased patients, in patients with neurodegenerative disorders, including Alzheimer's disease, and in animal models of Al intoxication are presented. The methods to evaluate potential Al chelators in vitro, in vivo, and using computer modeling are discussed. The Al chelation literature is reviewed by the chemical class of chelators, including fluoride, carboxylic acids, amino acids, catechols, polyamino carboxylic acids, phenyl carboxylic acids, the hydroxypyridinones, and hydroxamic acids.

Application of electron energy loss spectroscopy and electron spectroscopic imaging to aluminum determination in biological tissue

Electron energy loss spectroscopy (EELS) is a high spatial resolution electron microscopic technique with the potential to quantify elements at the subcellular level. The presence of each element is demonstrated by the electron energy loss edge at the energy characteristic of that element. The area of the edge may indicate the quantity of element present. Electron spectroscopic imaging (ESI) is a similar technique generating graphic images of elemental localization in the specimens. An ESI of an aluminum (Al)-loaded rabbit hippocampus showed Al only in pyramidal cell lysosomes, but no EELS edge could be obtained. To determine the sensitivity of EELS for Al and to be able to adjust the instrument to optimal operating conditions, standards containing 50-5000 ppm Al were produced. An Al-chloride: dicyclohexano-18-crown-6 (Al: crown) complex was synthesized. The purity of the complex was confirmed by nuclear magnetic resonance (NMR) spectroscopy and the percentage of Al in the complex was determined by electrothermal atomic absorption spectroscopy (ETAAS). The complex was introduced into a biological tissue embedding resin (Spurr medium) and appeared to be compatible with the resin at Al concentrations < or = 500 ppm. EELS signals from the Al K edge could be obtained at a spatial resolution of 3.3 nm in a 30-nm thick section from 2.78 x 10(-21) g of Al, representing a sample concentration of 1% Al.

Pharmacokinetics of representative 3-hydroxypyridin-4-ones in rabbits: CP20 and CP94

Selected 3-hydroxypyridin-4-ones (HPs) are under clinical investigation as iron chelators. Representative HPs have been shown to be potential aluminum chelators by use of in vitro test systems. This study was conducted to determine systemic availability of representative HPs in rabbits prior to studies of their oral efficacy as aluminum chelators. Each of 12 rabbits was administered 0.45 mmol/kg 1,2-dimethyl- (CP20; L1) and of 1,2-diethyl-3-hydroxypyridin-4-one (CP94; EL1NEt) by gastric lavage and by injection into a lateral ear vein. Each rabbit received both compounds via both routes with at least 7 days between doses. Blood samples (1.5 ml) were collected up to 24 hr after dosing. The HPs were extracted, then analyzed by HPLC with a column packed with graphitized carbon. The mean (+/- SD) systemic clearance, steady-state volume of distribution, mean residence time, mean oral absorption time, and systemic availability for CP20 and CP94 were 0.8 +/- 0.3 and 2.1 +/- 1.4 liter/hr/kg; 1.2 +/- 0.5 and 1.2 +/- 0.5 liter/kg; 1.7 +/- 0.7 and 0.7 +/- 0.3 hr; 0.9 +/- 1.6 and 0.6 +/- 0.5 hr; and 72 +/- 20 and 57 +/- 27%, respectively. Rabbits demonstrated fairly good absorption and rapid elimination of 1,2-dimethyl- and 1,2-diethyl-3-hydroxypyridin-4-one.

4-Trimethylammonium antipyrine: a quaternary ammonium nonradionuclide marker for blood-brain barrier integrity during in vivo microdialysis

The well-controlled microdialysis (MD) study of substance permeation into brain extracellular fluid (ECF) and cerebrospinal fluid requires consideration of blood-brain barrier (BBB) integrity, which might be compromised by microdialysis probe implantation. Others have assessed BBB integrity with radionuclide markers. A nonradionuclide marker may be desirable in many studies. A charged antipyrine analogue may be useful to determine BBB integrity with concomitant antipyrine characterization of probe efficiency (Yokel et al., 1992, J Pharmacol Toxicol Methods 27:135-142), and may not require another analytical technique. We synthesized, validated, and evaluated 4-trimethylammonium antipyrine (4TMA-AP) as a BBB integrity marker. BBB permeation was determined by calculation of a BBB integrity percentage (Pi) from brain/blood concentrations. The PiS of Evan's blue, which does not permeate the intact BBB, and 4TMA-AP were not significantly different in rats without known BBB disruption, suggesting a lack of 4TMA-AP permeation through the intact BBB. When MD probes were slowly implanted into the frontal cortex, 4TMA-AP PiS were usually zero. Intracarotid oleic acid injection to open the BBB significantly increased 4TMA-AP PiS, suggesting that 4TMA-AP entered brain ECF when the BBB was compromised. Rapid probe implantation produced increased 4TMA-AP PiS, suggesting BBB disruption. The predicted appearance of 4TMA-AP in brain ECF suggests that it is a BBB integrity marker.

Antipyrine as a dialyzable reference to correct differences in efficiency among and within sampling devices during in vivo microdialysis

Antipyrine was investigated as a dialyzable substance that could be used to quantitate relative differences in the efficiency of dialysis among multiple microdialysis probes and by a single probe over time. The contribution of effective membrane surface area to recovery variability was tested by the introduction of air into microdialysis probes. Reduction of effective membrane surface area reduced antipyrine recovery. Dialysates from probes implanted in the jugular vein, brain, and liver of rats receiving antipyrine demonstrated differences in antipyrine concentration among probes within the same rat. These results suggest dissimilar efficiencies of the probes to recover antipyrine, which should be uniformly distributed throughout body water. Dialysates from blood, brain, and liver probes in rats that received both antipyrine and tritiated water (3H2O) showed differences in antipyrine and 3H2O concentrations among probes. Variability of antipyrine and 3H2O concentrations over time within a probe were positively correlated, suggesting that the cause(s) of temporal variability affected both of these markers of body water. Correction of antipyrine tissue/blood ratios, using 3H2O blood/tissue ratios from the same sampling period, reduced the variability in antipyrine tissue/blood ratios, producing ratios closer to the expected value of 1. Differences in probe efficiency contributing to the variability of antipyrine and 3H2O recovery would also be expected to influence the recovery of other substances during microdialysis. The administration of antipyrine during microdialysis experiments is suggested to enable reduction of temporal and site-related differences in substance recovery that are due to differences in probe efficiency. Other methods are necessary to determine the actual extracellular concentration of dialyzed substances and the integrity of the blood-brain barrier.

Dissimilar aluminum and gallium permeation of the blood-brain barrier demonstrated by in vivo microdialysis

Aluminum (Al) and gallium (Ga) permeations of the blood-brain barrier (BBB) were assessed in rats. Unbound extracellular Al and Ga concentrations were ascertained at the two potential sites of BBB permeation, cerebral capillaries and choroid plexuses, by implantation of microdialysis probes in the frontal cortex and lateral ventricle, respectively. A microdialysis probe implanted in the jugular vein revealed unbound blood Al or Ga concentrations. Al or 67Ga citrate was administered via the femoral vein. Peak Al and Ga concentrations were seen within the first 10 min at all three sites. Area under the curve (concentration vs. time to final sample) values were calculated using RSTRIP. Within-rat overall frontal cortical/blood and lateral ventricular/blood ratios [brain/blood ratios (oBBRs)] were calculated from area under the curve values. Aluminum frontal cortical oBBRs were significantly higher than those for the lateral ventricle. Ga oBBRs were not significantly different between the two sites. Al and Ga oBBRs were significantly different in the lateral ventricle. These results suggest that the primary site of A1 permeation across the BBB is at cerebral capillaries, whereas Ga permeation across the BBB does not significantly differ between cerebral capillaries and choroid plexuses. The use of Ga as a model to study Al pharmacokinetics may not be appropriate in the elucidation of the site or mechanism of Al entry into the brain.

Aluminum inhibits glutamate release from transverse rat hippocampal slices: role of G proteins, Ca channels and protein kinase C

Aluminum (Al) has been shown to produce deficits in learning and memory. The present experiments tested the hypothesis that Al-induced inhibition of learning may be due to its effect on glutamate release secondary to changes in calcium channel function and/or intracellular events triggering glutamate release. Calcium-dependent potassium (K)-evoked [14C]-glutamate release from 400 microns transverse rat hippocampal slices was inhibited by Al in a concentration dependent manner (IC50 = 40 microM). Aluminum (30, 100 microM) noncompetitively inhibited Bay K 8644-evoked glutamate release. 4-Aminopyridine (30, 1000 microM) noncompetitively attenuated the Al inhibition of glutamate release, suggesting an Al-induced alteration of Ca channel function. Activation of the Gi protein by R(-)phenylisopropyladenosine (PIA; 1 microM) reduced K-evoked glutamate release 69%, whereas 300 microM Al produced an 84% reduction. These effects were prevented by the Gi protein inhibitor N-ethylmaleimide (NEM; 100 microM), suggesting an effect of Al on the Gi protein to inhibit glutamate release. Phorbol myristate acetate (0.16 microM)-induced glutamate release was inhibited by 300 microM Al and 80 microM polymyxin B, suggesting an Al modulation of protein kinase C (PKC)-evoked glutamate release. These results demonstrate an Al inhibition of glutamate release that may be mediated by multiple, but interconnected mechanisms (e.g., via interactions with Ca systems), providing multiple targets for an Al-induced alteration of neuronal function.

Mucosal injury and gamma-irradiation produce persistent gastric ulcers in the rabbit. Evaluation of antiulcer drug binding to experimental ulcer sites

A method producing persistent gastric ulcers in the rhesus monkey by combined mucosal injury and gamma-irradiation was modified and evaluated in the rabbit. gamma-Irradiation (800-1000 cGy) immediately after removal of 2-mm-diameter sections of antral mucosa resulted in ulcer craters 5-7 days later. Ulcer sites were characterized by loss of the mucosa, muscularis mucosa, and much of the submucosa. The exposed submucosa was coated with fibrin and necrotic debris infiltrated with heterophils, the rabbit equivalent of neutrophils. These ulcers strongly resemble human chronic gastric ulcers. Binding of Carafate (sucralfate; Marion Laboratories, Inc., Kansas City, MO) and Maalox (magnesia-alumina oral suspension; Wm. H. Rorer, Inc., Ft. Washington, PA) to ulcer and nearby nonulcer sites in the antrum was assessed 1 hour after drug dosing. Drug binding was determined by aluminum quantitation of stomach wall punch biopsies at necropsy. Both drugs significantly increased aluminum bound to the stomach wall compared with vehicle treatment. Significantly more antiulcer drug was bound to ulcer sites than to nearby nonulcer sites only after sucralfate administration. This model of persistent gastric ulcer should be useful to further study gastric ulcer pathogenesis and treatment.

Evaluation of potential aluminum chelators in vitro by aluminum solubilization ability, aluminum mobilization from transferrin and the octanol/aqueous distribution of the chelators and their complexes with aluminum

Representative amino acids, carboxylic acids, a ketone, hydroxamic acids, 3-hydroxypyridinones and a linear catecholcarboxyamide were tested in vitro to estimate their aluminum (Al) chelation potential. Their ability to solubilize Al from insoluble Al borate in a previously described octanol/aqueous (o/a) system was tested. Salicylhydroxamic acid, rhodotorulic acid, the 3-hydroxypyridin-4-ones and a sulfonated linear polycatecholcarboxamide significantly increased solubilized Al, suggesting Al chelation potential. Some of the above compounds and some compounds previously shown to solubilize Al in the o/a system were tested for their ability to mobilize Al from the Al plasma binding protein transferrin. Chelators solubilizing Al in the o/a system were comparably effective in mobilizing Al from transferrin, supporting the utility of the o/a system as a screening method. The o/a distribution coefficient of each chelator was determined, when possible, to assess its hydrophilicity. When compared with the suggested desirable hydrophilicity of effective chelators, the o/a distribution coefficient of many of the 3-hydroxypyridin-4-ones and a sulfonated linear polycatecholcarboxamide suggest that they might be able to chelate intracellular Al. The o/a distribution coefficient of each Al-chelator complex was determined, when possible, to predict the likelihood of redistribution within or excretion from the intact animal of this complex. Complexation of chelators with Al usually increased chelator hydrophilicity. The results suggest several compounds that warrant further investigation as potential alternatives to desferrioxamine in the treatment of Al accumulation and toxicity.

Aluminum mobilization by desferrioxamine assessed by microdialysis of the blood, liver and brain

Aluminum (Al) mobilization by i.v. desferrioxamine (DFO) into blood and into brain and liver extracellular space was followed in the Al-loaded rat using microdialysis probes. Dialyzable extracellular liver Al peaked at an estimated 1360 microgram/l whereas dialyzable blood and extracellular brain Al peaked at 860 and 155-175 microgram/l, respectively. Estimated Al concentrations were derived from dialysate Al from microdialysis probes which was corrected for probe efficiency. Liver Al after DFO was generally greater than blood Al. Both declined over time. The rapid increase in extracellular liver Al above blood Al suggests the ability of DFO to rapidly distribute out of the vascular compartment to mobilize Al from hepatocytes. Presumably an Al-DFO complex was formed and released into blood, from which it was eliminated. Extracellular brain Al and DFO was less than blood Al and did not decline during 5 h. After an i.v. Al-DFO injection to non-Al-loaded rats, blood Al was greater than liver much greater than brain Al, suggesting Al-DFO diffusion down a concentration gradient and demonstrating the ability of Al-DFO to permeate vascular membranes and the blood-brain barrier. The lack of decline of brain extracellular Al after DFO was presumably due to its inability to diffuse into the blood against the concentration gradient. The DFO-induced mobilization of Al in the brain may explain the reports of sudden onset or worsening of encephalopathy associated with DFO treatment of Al-loaded humans.

Aluminum distribution into brain and liver of rats and rabbits following intravenous aluminum lactate or citrate: a microdialysis study

Microdialysis probes were utilized to follow the appearance and disappearance of dialyzable aluminum (Al) in rat and rabbit brain and liver extracellular fluid compared to blood after iv Al lactate or Al citrate injection. Dialyzable Al was assumed to be the fraction not protein bound or self-associated into complexes greater than the molecular weight cutoff of the dialysis membrane. Aluminum concentrations peaked in brain frontal cortex and ventral hippocampus and in the liver in the first 20-min dialysis sample, indicating rapid Al penetration into the extracellular space of these organs. In vitro recovery experiments conducted with microdialysis probes at room temperature revealed an average dialysis efficiency of about 10% for both Al lactate and citrate. At 37 degrees C Al recovery increased for both Al lactate and citrate. In vivo Al recovery from rabbit blood averaged 5.15% for Al lactate and 3.25% for Al citrate. These observations are consistent with results from recovery studies of other substances showing an increased recovery with increased temperature but an overestimate of recovery by in vitro methods. Tissue/blood Al ratios (TBR; representing dialyzable extracellular tissue Al divided by dialyzable blood plasma Al) for liver were approximately 1, suggesting unhindered diffusion of Al between blood and liver. In contrast, brain TBR were less than 1, demonstrating a partial blood-brain barrier to Al. The brain TBR for Al lactate was greater than TBR for Al citrate, suggesting that Al citrate did not preferentially penetrate the blood-brain barrier. Higher TBR were seen in the rabbit than the rat, perhaps contributing to the greater susceptibility of the rabbit to Al-induced neurobehavioral toxicity. Metals can be repetitively sampled in the extracellular space using microdialysis, enabling metal toxicokinetic determinations in these compartments.

Renal accumulation and urinary excretion of cisplatin in diabetic rats

Previous work has demonstrated that cisplatin nephrotoxicity was attenuated in streptozotocin (STZ)-induced diabetic rats. The following studies investigated the hypothesis that renal cisplatin accumulation was reduced in diabetic rats. Male Fischer 344 (F344) rats were injected with 32 mg/kg STZ (i.p.) or citrate buffer. Renal platinum (Pt) accumulation was quantitated 0-96 h after the administration of 5 mg/kg cisplatin (i.p.) to normoglycemic and diabetic rats (greater than or equal to 4/group). Total renal Pt accumulation was decreased (P less than 0.05) in the diabetic rats, when compared to the normoglycemic group, 6-48 h after cisplatin injection. Further studies were also conducted to examine if urinary cisplatin excretion was enhanced in diabetic relative to normoglycemic groups. Urinary Pt excretion was quantitated 0-96 h following cisplatin (5 mg/kg, i.p.) administration. Pt excretion was increased in the diabetic group relative to the normoglycemics when comparisons were made on the basis of Pt excreted per hour or cumulative Pt excretion. Differences were also detected in urinary Pt concentration. The diabetic group had a lower urinary concentration of the metal 12-96 h after cisplatin injection. These findings suggest that the reduction in nephrotoxicity in diabetic rats may be at least partially due to decreased renal accumulation as well as altered renal excretion.

Relationship of dietary aluminum, phosphorus, and calcium to phosphorus and calcium metabolism and growth performance of broiler chicks

Dietary treatments providing three levels of added Al (0, .196, or .392%) as aluminum sulfate and of available phosphorus (Pav) .45, .68, or .78%) in a factorial arrangement were administered to day-old chicks in Experiment 1. Plasma inorganic phosphorus (Pi) was significantly (P less than .05) elevated by increasing Pav and was decreased by Al. Body weight gain, feed intake, and the gain:feed ratio at Day 21 were significantly decreased by increased concentrations of Al, but were unaffected by the Pav concentrations. Decreases of 39 and 73% in weight gain and of 34 and 66% in feed intake resulted from feeding .196 and .392% Al, respectively. In Experiment 2, day-old chicks were fed diets supplemented with 0 or .392% Al in combination with .9% Ca plus .45% Pav, .9% Ca plus .78% Pav, 1.8% Ca plus .45% Pav, or 1.8% Ca plus .9% Pav. After 21 days, the supplemental Al resulted in: 1) significantly poorer growth performance; 2) decreased plasma Pi, total Ca, Zn, and Mg; and 3) decreased tibia weight and breaking strength. Elevating Pav improved growth performance, plasma Pi, and tibia weight and strength, and decreased plasma total Ca. Increasing dietary Ca significantly decreased plasma Pi and increased plasma total Ca without affecting other parameters. Increasing Pav alleviated the negative effect of Al on plasma Pi without correcting the negative effect of Al on growth performance.

Effect of dietary aluminum sulfate on calcium and phosphorus metabolism of broiler chicks

The effect of dietary aluminum sulfate on Ca and P metabolism was studied using 1-day-old male broiler chicks. In Experiment 1, practical diets providing .90% Ca plus .45% available P (Pav), .90% Ca plus .78% Pav, 1.80% Ca plus .45% Pav, or 1.80% Ca plus .90% Pav were fed with 0 or .392% A1 as aluminum sulfate for 21 days. The control diet (.90% Ca plus .45% Pav) without added A1 was fed to all chicks during Days 22 to 49. In general, A1 significantly (P less than .05) decreased BW gain, feed intake, gain:feed ratio, plasma inorganic P (Pi), tibia breaking strength, tibia weight, percentage of tibia ash, and plasma Zn, measured at Day 21. Elevating Pav increased BW gain, feed intake, gain:feed ratio, tibia weight and plasma Zn, and decreased plasma total Ca in the presence of .392% A1 plus 1.80% Ca. Plasma Pi, tibia breaking strength, and percentage of tibia ash were increased by raising dietary Pav in the presence of .392% A1 with either level of Ca. Negative effects of dietary A1 on feed intake and BW persisted through Day 49. In Experiment 2, a control diet (.90% Ca, .45% Pav) was fed for ad libitum access either alone or supplemented with .2% A1 as aluminum sulfate or with an equivalent amount of sulfate provided by potassium sulfate. The control diet was also pair-fed to chicks given .2% A1. Dietary A1 significantly depressed weight gain, feed intake, gain:feed ratio, and plasma Pi.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigating aluminium citrate speciation by high performance liquid chromatography

The toxicity of aluminium (Al) is dependent on its chemical form or species. However, there are no current techniques available to separate small molecular weight toxic Al complexes. In the present study, HPLC separation was combined with atomic absorption spectroscopic detection of Al in an attempt to determine the potential for this analytical method to separate Al citrate from other Al species. A total of nine different HPLC stationary phase supports along with numerous mobile phases were examined. Promising results were obtained with the Cyclobond I and Cyclobond III columns containing the beta- and alpha-cyclodextrin stationary phases, respectively and the cyano column. Using a mobile phase of methanol:water (1:1; v/v) containing 0.1 M triethylamine (TEA) and glacial acetic acid (pH = 4.0), Al was reproducibly retained for approximately 9 minutes following the injection of Al citrate onto the Cyclobond III column. Injection of other simple Al complexes showed no demonstrable recovery of Al under these same conditions. However, the more stable Al desferrioxamine complex was retained, but with a retention time that was only 3-4.5 minutes. Unfortunately, the retention characteristics and recovery of Al were not reproducible or sufficient with either of the cyclobond columns for routine quantitation of Al citrate in biological samples. The cyano column did provide better recovery of Al citrate (up to 65%) than could be obtained with the cyclobond column (up to 58%). However, manipulation of the retention time for Al citrate on the cyano column was limited to a period of only 3-4.5 minutes. Under similar conditions, Al desferrioxamine could be retained for over 10 minutes on this same column.(ABSTRACT TRUNCATED AT 250 WORDS)

Benefit vs. risk of oral aluminum forms: antacid and phosphate binding vs. absorption

Oral consumption of aluminum (Al) compounds to neutralize stomach acid and bind phosphate can result in Al absorption and potential Al accumulation and toxicity. Selecting an effective antacid/phosphate binder would optimize the benefit/risk of therapy. It has been suggested that Al solubilization would predict oral Al bioavailability, and therefore risk. The acid neutralizing and phosphate binding capacity of eight representative Al forms was determined. The results were compared to the oral bioavailability, solubility and octanol/water partitioning coefficient of each compound. The results fail to confirm Al solubilization as an indicator of Al absorption, and presumably, Al toxicity. Acid neutralizing and phosphate binding capacities did not correlate with bioavailability, solubility or the partitioning coefficient. Determination of acid neutralization and phosphate binding in vitro and Al absorption and/or toxicity in vivo may be more predictive measures to establish the benefit/risk ratio of Al-containing products.

Elevated aluminum persists in serum and tissues of rabbits after a six-hour infusion

The half-life of aluminum was estimated in selected tissues and fluids in a representative mammal, the rabbit. After a single iv aluminum infusion, half-lives were determined by serial killing of rabbits and aluminum quantitation in selected tissues and fluids by electrothermal atomic absorption spectroscopy. Tissues and fluids demonstrating a significant increase 4 hr after the 200 mumol/kg aluminum dose were the bile, kidney, liver, lung, serum, and spleen. Aluminum concentration did not significantly increase above control in the adrenal gland, bone, heart, muscle, testis, thyroid gland, or selected central nervous system regions. Biliary aluminum concentration returned to control within 12 hr after infusion. Estimated half-lives were 113 days in spleen, 74 days in liver, 44 days in lung, 42 days in serum, 4.2 days in kidney cortex, and 2.3 days in kidney medulla. The kidney also demonstrated another half-life greatly exceeding 100 days. The results demonstrate that aluminum persists in various tissues and fluids for different lengths of time. The calculated half-life of aluminum in these tissues is substantially longer than previously estimated half-lives based on serum aluminum determination. The persistence of aluminum in the liver and other tissues may serve as a source of continuous aluminum exposure for sensitive target organs such as the brain. These calculated half-lives establish the normal rate of aluminum elimination from tissues. Future studies could determine the influence of factors such as uremia or chelation therapy on the rate of aluminum elimination from storage sites as well as serum.

Aluminum produces age related behavioral toxicity in the rabbit

Two- to 3.4-year-old, retired breeder, rabbits received repeated aluminum (Al) lactate or sodium (Na) lactate injections. All six rabbits receiving twenty 400 mumol Al/kg SC injections died, demonstrating much higher mortality than previously seen in younger rabbits. Subsequent rabbits receiving Al were dosed with 200 mumole/kg injections. Aluminum injections inhibited body weight gain. Renal function, as measured by creatinine clearance, in these rabbits was inferior to younger rabbits, perhaps contributing to the Al induced toxicity. Renal function decreased during Al injections suggesting a nephrotoxic effect of Al. Rabbits were tested for their ability to acquire, retain and extinguish a classically conditioned reflex, nictitating membrane extension. Rabbits which received Al acquired and retained the conditioned response less well than Na lactate injected rabbits. Impaired acquisition was evidenced by lower percent conditioned responses, more trials to 1 to 10 consecutive conditioned responses and longer conditioned response latencies. Aluminum injections produced significant elevations in tissue Al concentration in frontal gray and hippocampal brain as well as most peripheral tissues studied. Aluminum induced behavioral toxicity is greater in adult and aged rabbits than in young rabbits. Aged rabbits are more susceptible to Al induced mortality than adult or young rabbits.

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.

The influence of dietary calcium reduction on aluminum absorption and kinetics in the rabbit

There is considerable evidence of an aluminum (Al)-calcium (Ca) interaction, including potentiation of Al accumulation and toxicity by Ca deficiency. To elucidate the influence of dietary Ca on Al absorption, rabbits were maintained on a low-Ca (0.024%) or a Ca-replete (0.83%) diet for 2 wk prior to testing. Once weekly, Al hydroxide, nitrate, citrate, or lactate or sucralfate was given orally, or Al lactate was given intravenously (iv). Oral Al bioavailability was determined by comparison of the area under the Al concentration-time curve to that obtained after iv Al. Neither oral Al bioavailability nor the pharmacokinetic parameters of iv Al lactate was significantly affected by dietary Ca concentration. When measured before the weekly Al treatments, total serum Ca of rabbits fed the low-Ca diet averaged 88% of rabbits fed the Ca-replete diet. Total serum Ca 1-72 h after Al treatment decreased from 1% (Al hydroxide) to 15% (Al citrate) below pretreatment concentrations.

Influence of renal impairment, chemical form, and serum protein binding on intravenous and oral aluminum kinetics in the rabbit

The influence of renal impairment on the intravenous kinetics of aluminum (Al) lactate and the oral absorption of eight representative Al forms was determined. The serum protein binding of Al was assessed. Creatinine clearance in renally impaired rabbits was 23% of controls. Systemic clearance of Al was less in renally impaired rabbits (39 vs. 53 ml/hr/kg), as were the steady-state volume of distribution (516 vs. 1175 ml/kg), the half-life of elimination (14 vs. 27 hr), and the mean residence time of Al (14 vs. 25 hr). The shorter Al half-life and mean residence time in renally impaired rabbits were due to a diminished volume of Al distribution. Oral bioavailability of Al in renally intact rabbits ranged from 0.3 to 2.2% (Al borate less than glycinate less than hydroxide less than chloride less than sucralfate less than lactate less than nitrate less than citrate). Renal impairment had little influence on oral bioavailability of most Al forms, although it increased Al citrate absorption to 4.6%. In vitro and in vivo determination of Al ultrafilterability (less than 30,000 D) as an estimate of serum protein binding suggested a greater percentage of ultrafilterable Al species in renally impaired rabbit serum than in control rabbit serum. The increase in ultrafilterable Al species produced the less than expected reduction in Al clearance in renally impaired rabbits. The ultrafilterability of various Al concentrations was greater for citrate greater than lactate greater than nitrate greater than chloride, perhaps partially explaining the similar rank order of oral absorption of these Al forms. The physicochemistry of the eight Al forms was further characterized by determination of their octanol/water partitioning coefficients and their water solubility. There was a significant correlation between the percentage absorbed and the log of the octanol/water partition coefficient. Knowledge of the physicochemistry of Al aids in the understanding of Al pharmacokinetics.

Aluminum uptake by the in situ rat gut preparation

An in situ rat gut preparation was used to elucidate the mechanisms of gastrointestinal aluminum (Al) absorption. Al uptake rate at the mucosal surface was decreased by the paracellular pathway blockers kinetin (1 mM) and 2,4,6-triaminopyrimidinium (10 mM), by sodium removal with choline substitution and by treatment with amiloride (1 mM), an epithelial sodium transport blocker. The rate of Al uptake was unchanged by 2,4-dinitrophenol (0.1 mM), 4-aminopyridine (0.1 mM, 0.5 mM) and verapamil (0.1 mM). The rate of Al uptake was increased from a medium containing no added calcium, a treatment which decreases resistance to flux in the paracellular pathway. These results suggest that gastrointestinal Al uptake occurs by an energy-independent, sodium-dependent, paracellular pathway-mediated process.

Influence of calcium on aluminum accumulation by the rat jejunal slice

The isolated rat jejunal slice was used to determine if aluminum (Al) interacts with the gastrointestinal (GI) calcium (Ca) transporting system. Al uptake by the rat jejunal slice was reduced by Ca channel blockers (verapamil, nifedipine, diltiazem-10 microM) and a medium containing no added Ca. Conversely, Al uptake was increased by Ca channel activators (4-aminopyridine, .05mM, .1mM; Bay k 8644, 1, 10 microM) and by 5mM Ca. Al uptake was saturable and energy dependent but yielded a low activation energy (Ea = 3.9 +/- 0.3 kcal/mole). Al uptake was increased by vanadate (100 microM), an inhibitor of both the active Ca pump and Na/K-ATPase. These results suggest that Al does interact with the GI Ca transporting system. This interaction may form the basis for its accumulation and toxicity in different tissues which contain similar processes for handling Ca.

Murine lung response to kaolin conveyed by cigarette smoke

The effects of chronic (3 to 8.5 months) smoke inhalation from cigarettes laced with 0.1, 1.0 and 10.0 mg kaolin (hydrated aluminum silicate) per gram of tobacco on the morphological integrity of lungs and the pulmonary macrophage population were evaluated in young and old male C57BL/6 mice. Lacing procedures, monitored by determining aluminum content in acid-digested aliquots of tobacco via atomic absorption spectrometry (AAS), proved to be uniform. Amounts of aluminum in right lungs of young mice evaluated by AAS and of kaolin assessed by electron diffraction and polarizing light microscopy were larger in mice which inhaled smoke from cigarettes laced with more kaolin. A more pronounced increase in lung parenchymal tissue and decrease of alveolar space was observed in old mice subjected to smoke from cigarettes containing higher doses of kaolin than in similarly treated young animals. Concomitant with the above, the lung macrophage population did not increase as markedly in response to smoke inhalation in old mice nor did it increase in as clear a dose-response fashion to kaolin as it did in young animals. Further, the degree of ultrastructural alteration of the phagocytes in the old mice suggested impaired cell function. Plate-like material resembling kaolin crystals was most conspicuous in lung macrophages of mice which inhaled largest amounts of kaolin. Manifestations of abnormal aggregates of lymphocytes and macrophages correlated with kaolin dose inhaled in old mice but not in young animals. The reported observations indicate that 1) kaolin gains access to lungs via cigarette smoke inhalation, 2) macrophages are important in maintaining pulmonary homeostasis and 3) the inorganic compound kaolin appears to impede macrophage function, resulting in potentiation of lung abnormalities.

Accumulation of aluminum by rabbit renal cortex

Aluminum is a ubiquitous metal with significant toxic potential for humans. It is eliminated principally by the kidney, however the mechanisms involved remain obscure. The purpose of this study was to define and quantify the uptake process for aluminum by incubated slices of rabbit kidney cortex. Time-course experiments demonstrated that aluminum uptake was progressive and substantial, with a slice-to-medium ratio (S/M) exceeding 20 after four hours of incubation of slices in the presence of 0.01 mM aluminum (as the lactate). Concentration-dependent uptake studies suggested that the process was of limited capacity with maximal tissue uptake of approximately 24 micrograms/gm wet wt. Incubation of slices with aluminum in the presence of metabolic inhibitors (NaCN, 2,4-DNP) demonstrated that about 20-35% of the uptake could be attributed to an energy-dependent component. The calcium channel blockers verapamil, diltiazem and lanthanum decreased S/M aluminum by 65-73% compared to control, suggesting that a calcium dependent process plays a role in aluminum accumulation in renal cortex. Aluminum was not acutely toxic to the renal tubular cells even at a medium concentration of 1.0 mM.

Assessment of potential aluminum chelators in an octanol/aqueous system and in the aluminum-loaded rabbit

Aluminum (Al) solubilization from Al borate and its distribution in an octanol/aqueous system (Do/w) were determined in the absence and presence of 12 potential Al chelators. Citrate, N,N'-bis-(2-hydroxybenzyl)ethylenediamine- N,N'-diacetic acid (HBED), cyclohexane-1,2-diaminotetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), desferrioxamine, and ethylenediamine-N,N'-bis(2-dihydroxyphenylacetic acid) (EDDHA) were 55 to over 100% efficient in solubilizing equimolar amounts of Al. Tetracycline, EDTA, and 2,3-dihydroxybenzoic acid (DHBA) were less than 20% efficient. 1,4-Dioxane and fluoride were ineffective. The Do/w of Al averaged 0.005. The Do/w of the Al.chelator complex was generally less than that of Al, except for HBED and tetracycline (0.04 and 0.96, respectively). The Do/w of DHBA, desferrioxamine, EDDHA, and HBED were not influenced by Al, but tetracycline became more lipophilic. These compounds were tested for their ability to increase urinary Al excretion in Al-loaded rabbits. Chelators were given po weekly beginning 2 weeks after Al loading. Urine was obtained hourly from 3 hr prior to 6 hr after chelator administration and analyzed for Al. Fluoride and tetracycline (450 and 4500 mumol/kg) and citrate, NTA, EDTA, CDTA, DTPA, DHBA, HBED, and 1,4-dioxane (150 and 1500 mumol/kg) were ineffective. Following HBED administration, some of the Al-loaded rabbits died, presumably due to redistribution of Al within the rabbit. Following DTPA administration, some of the Al-loaded rabbits died, presumably due to DTPA. Oral EDDHA (1500 mumol/kg) significantly increased urinary Al excretion. EDDHA and desferrioxamine (150 mumol/kg) were administered by po, sc, and iv routes and were found to have comparable potency. The in vitro results may explain some of the in vivo findings. The in vitro methods may be useful to screen out compounds with no chelation potential. EDDHA-like compounds may have potential as alternatives to desferrioxamine in the prevention or treatment of Al accumulation and Al-induced toxicity.

Toxicity of aluminum exposure to the neonatal and immature rabbit

To assess aluminum toxicity to the neonatal and immature rabbit, rabbits received 20 sc Al lactate injections of 0 or 400 mumol Al/kg during the first month postpartum or 0, 25, 100, or 400 mumol Al/kg during the second month postpartum. Results were compared to studies in which pregnant, lactating, or adult rabbits received comparable Al injections. Aluminum injections to neonatal rabbits decreased milk consumption, but not as severely as seen in neonatal rabbits of does receiving Al during gestation or lactation. Reduction in body weight gain was greater in adult rabbits than in any group of rabbits exposed to Al at a younger age. Increased carpal joint width, suggestive of poor bone calcification, was observed in rabbits receiving 400 mumol Al injections during the second postnatal month, but not in any other Al-exposed group. Tissue Al accumulation, particularly in reticuloendothelial organs, the kidney and skeletal system, seems to be most pronounced in adult rabbits. Clearance of Al from these tissues is extremely slow. Learning and memory changes were not observed after Al treatment of neonatal and immature rabbits, compared to the biphasic effect (enhancement after low doses, attenuation after high doses) seen in gestationally exposed rabbits and the attenuation observed in adult rabbits. Taken together, these results demonstrate prolonged effects of reduced body weight, impairment of bone formation, and tissue Al accumulation following Al exposure that are not readily reversed with termination of exposure. The results show that the immature rabbit is most susceptible to Al-induced skeletal toxicity and the mature rabbit most susceptible to Al-induced behavioral toxicity.

Toxicity of gestational aluminum exposure to the maternal rabbit and offspring

To assess aluminum toxicity to the Al-exposed pregnant female and her developing offspring, pregnant rabbits received 20 sc Al lactate injections (0, 25, 100, or 400 mumol Al/kg/inj) between Days 2 and 27 of gestation. Fifty-eight percent perinatal mortality resulted from the highest dose. At 2 days postpartum litters were culled to six offspring. Three of the offspring of Al-treated does were cross-fostered to a non-Al-treated doe in exchange for three of the non-Al-treated doe's offspring. Tissue Al concentrations in 0- to 2-day-old offspring positively correlated with their does' Al exposure, but were lower than Al concentrations in placental tissue or in does 5 weeks postpartum, suggesting that the placenta partially protects the fetus from Al. Offspring of 25 mumol group does gained body weight faster than controls, whereas 400 mumol group does and their offspring gained weight less rapidly than controls. The weight of milk consumed by offspring inversely correlated with their does' Al exposure. Learning a classically conditioned reflex was facilitated by lower and impaired by higher Al exposure in offspring conditioned at 7 and 11 weeks of age. Offspring receiving higher Al exposure also showed impaired memory of the learned reflex. Aluminum appears to distribute into the developing fetus where it accumulates and can produce delayed effects which may be beneficial following lower but detrimental following higher exposure concentrations.

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.

Toxicity of aluminum exposure during lactation to the maternal and suckling rabbit

To assess aluminum toxicity to the A1-exposed lactating organism and her suckling offspring, lactating rabbits received 20, sc, A1 lactate injections (0, 25, 100, 400, or 800 mumol A1/kg/inj) between Days 4 and 29 postpartum. Offspring were weaned Day 30 postpartum. Weight gain in the first 12 postnatal weeks was slightly greater in 25 and 100 mumol offspring and somewhat less in 400 and 800 mumol offspring than in controls. Significant weight loss was seen in the 400 and 800 mumol group does. Does in the 800 mumol group died within 10 days after completion of the A1 injections. Every fifth day postpartum, after 24-hr isolation of the doe from her offspring, a milk sample was obtained and the weight of milk consumed by the offspring was determined. Does receiving higher A1 exposures had increased milk A1 concentration [e.g., 6.0 micrograms/g (220 microM)] in the 800 mumol group vs 1.3 micrograms/g in controls) and decreased milk production (105 g/day vs 219 g/day). Based on milk consumption and milk A1 concentration, no more than 2% of the A1 injected into the does in any of the treatment groups was found in the milk 24 hr later. During the 1 month postpartum, each suckling offspring of a 800-mumol group doe received a cumulative oral A1 exposure of about 300 mumol/kg, whereas each doe received a total of 16,000 mumol/kg, sc, and approximately 60,000 mumol/kg in her diet. When measured 1 week after weaning, offspring had no elevations in tissue A1 concentration, whereas their does had a considerable increase 5 and 9 weeks after weaning. Other than the decreased weight gain of 400 and 800 mumol offspring, probably caused by the decreased milk production of the does, no detrimental effects of the A1 treatment of lactating does were observed in the offspring. The lack of effects in the offspring is probably explained by their low levels of A1 exposure from milk compared to typical adult rabbit A1 intakes.

Effects of subchronic desferrioxamine infusion on aluminum toxicity in rabbits

The effects of subchronic desferrioxamine (DFO) infusion on aluminum (A1) loaded rabbits were studied. Rabbits received sc injections of A1 lactate (600 mumoles A1/kg) or Na lactate (1800 mumoles/kg) 5 days per week for 4 weeks. Beginning 2 weeks later rabbits received DFO by sc infusion at a rate of 3.85 mg/hour for 4 weeks (total dose = 2550 mg), or sham treatment. The treatment groups were: control, DFO-only, A1-only, and A1+DFO. A1-induced reductions in food consumption and efficiency of food utilization were not affected by DFO. A1-induced decreases in water consumption were enhanced by DFO. A1 levels were reduced in 10 of 12 organs and brain regions of A1+DFO vs. A1-only groups, but results were statistically significant in only 2 tissues. Subchronic DFO infusion appears to be beneficial in A1-loaded subjects but not without potential for further toxicity.

Persistent aluminum accumulation after prolonged systemic aluminum exposure

To determine the distribution of aluminum (A1) following systemic exposure, female New Zealand white rabbits were given 20 subcutaneous injections, over 4 weeks, of 0, 25, 50, 100, 200, or 400 μmol A1/kg/injection, as the lactate salt. They were sacrificed 5 weeks after completion of injections and selected tissues removed for graphite furnace atomic absorption analysis of tissue A1 content. Rabbits not receiving A1 injections had mean tissue A1 concentrations ranging from 1.5-7.4 μg/g. Bone was higher, 18.7 μg/g. All tissues, except for muscle, demonstrated an increase in A1 concentration correlating with the A1 exposure. After 400 μmol A1/kg/injection for 20 injections, tissue A1 concentrations were: bone 90, heart 12, kidney-cortex 1290, kidney-medulla 245, liver 246, lung 19, and spleen 465 μg A1/g. The average of the 5 central nervous system regions sampled (frontal grey, white, hippocampus, cerebellum, and spinal cord) rose 53% over controls. Determination of A1 in kidney, liver, or bone may be useful in diagnosis of A1 overload conditions in humans (dialysis encepthalopathy, dialysis osteomalacia, and parenteral nutrition-associated osteomalacia). The rabbit appears to be a useful model to further study A1 intoxication syndromes.

A safe method to acid digest small samples of biological tissues for graphite furnace atomic absorption analysis of aluminum

A method was developed to prepare small biological tissue samples (approximately 100 mg) for flameless atomic absorption analysis of aluminum (Al). Screw cap Teflon containers were used in which the samples were dried, acid digested, acid evaporated, and diluted for analysis, minimizing contamination and sample loss. A heatable, semiclosed system was developed in which the nitric and perchloric acids used in tissue digestion could be safely evaporated from the sample containers and collected. Several spectrophotometer operating conditions for Al determination were compared, and a suitable condition was adopted. Analyses for aluminum levels in acid digested samples were conducted at two absorption wavelengths (309.3 and 396.2 nm) and by two analytical procedures (comparison of sample absorbance to standard absorbance and the method of standard additions). The developed method is suitable for analysis of the low levels of aluminum found in biological tissues and probably other elements as well. The method incorporates procedures designed to minimize contamination and the hazards of acid tissue digestion.

Effect of the chelator desferrioxamine on aluminum elimination in rabbits

The effect of desferrioxamine (DFO) on the mobilization and elimination of aluminum (Al) in Al-loaded rabbits was studied. Six to 7 weeks after completion of 20 s.c. Al injections (600 mumoles/kg administered 5 days/week), sterile deionized water or DFO (32 mg/kg s.c. every 2 hours for 3 doses) was administered and serum [Al] and urinary Al output (UA10) were monitored. DFO treatment significantly increased serum [Al] and UA10 over control treatment, supporting its use in human Al overload conditions.

Repeated systemic aluminum exposure effects on classical conditioning of the rabbit

Excessive aluminum exposure and accumulation has been implicated as the cause of two disorders which display learning deficits (dialysis encephalopathy and Alzheimer's disease). To develop an animal model, rabbits were given 20 sc Al lactate injections (0, 25, 50, 100, 200 or 400 mumole/kg) over 4 weeks. Dose dependent weight reductions were observed. Two weeks later the baseline frequency of nictitating membrane extension (NME) was determined. Differential classical conditioning of the NME was then conducted. No treatment group differences were observed in frequency of baseline NME, amplitude of the response to shock, or shock threshold to produce NME, suggesting no aluminum effects on the subjects' ability to perform the response. All subjects developed the discrimination. The 200 and 400 group acquired the conditioned response less well than controls, as shown by a lower percent of conditioned responses in the second half of the conditioning sessions (80 and 74% of controls) and a greater latency to onset of the conditioned response (327 and 310 msec vs. 261 msec for controls). These results indicate that chronic systemic exposure of adult rabbits to 1 results in learning deficits not due to sensory or motor impairment of the learned response.

Hair as an indicator of excessive aluminum exposure

To determine if excessive systemic exposure to aluminum would be reflected in increased aluminum concentration in hair, rabbits were given a series of aluminum lactate injections. Hair was collected before the aluminum lactate administration from the site of injections and twice after the injections from this site as well as from an area adjoining the injection site. Aluminum was determined by flameless atomic absorption analysis of acid-digested samples. The concentration of aluminum in the hair increased after the injections in samples taken at both times from both sites. Considerable variability in hair aluminum was found before excessive exposure, as has been reported in humans, and in response to the exposure. The increase in hair aluminum did not correlate with the amount of hair produced. Nevertheless, because some subjects exposed to excessive aluminum showed a very large increase in hair aluminum, hair may be a useful indicator of aluminum body burden in such aluminum-induced conditions as dialysis encephalopathy.

Hair as an indicator of excessive aluminum exposure

To determine if excessive systemic exposure to aluminum would be reflected in increased aluminum concentration in hair, rabbits were given a series of aluminum lactate injections. Hair was collected before the aluminum lactate administration from the site of injections and twice after the injections from this site as well as from an area adjoining the injection site. Aluminum was determined by flameless atomic absorption analysis of acid-digested samples. The concentration of aluminum in the hair increased after the injections in samples taken at both times from both sites. Considerable variability in hair aluminum was found before excessive exposure, as has been reported in humans, and in response to the exposure. The increase in hair aluminum did not correlate with the amount of hair produced. Nevertheless, because some subjects exposed to excessive aluminum showed a very large increase in hair aluminum, hair may be a useful indicator of aluminum body burden in such aluminum-induced conditions as dialysis encephalopathy.

Acute toxicity of latex microspheres

The distribution and acute lethality of i.v. administered 3 micrometers latex spheres were determined in rats. The results extend previous studies demonstrating the similarity between dog and rat in the dynamics of microspheres in these species and the inverse relationship between sphere diameter and hemodynamic toxicity. The results suggest that 3 micrometers spheres may be safe imaging agents or drug delivery systems for spleen and liver when administered slowly. Acute hemodynamic toxicity appears to be a function of the total volume of the spheres injected.

Repeated naloxone administration for morphine overdose in a 1-month-old infant

Repeated injections of naloxone by hydrochloride, a pure narcotic antagonist, were administered to a 3,320-gm 4-week-old boy for treatment of an accidental morphine overdose. The infant received frequent naloxone hydrochloride injections (0.2 mg per injection) during the first 12 hours of therapy to reverse morphine-induced apnea, hypothermia, and flaccidity. A cumulative dose of 2.73 mg of naloxone hydrochloride (0.822 mg/kg) was administered over 27 hours without apparent adverse effect or evidence of toxicity.

Abuse and pulmonary complications of injecting pentazocine and tripelennamine tablets

A current practice among drug abusers in certain Midwestern and Eastern cities is the intravenous injection of aqueous mixtures prepared from tablets of pentazocine and tripelennamine. Patients present with acute hypoxic episodes and symptoms suggesting physical dependence to pentazocine. Two cases are presented illustrating acute respiratory distress with hypoxia. Available evidence indicates that the respiratory syndrome is produced by talc from the injected tablets. Respiratory support and short-term oxygen therapy have been effective in managing this syndrome. Approaches to the treatment of pentazocine dependence and the role of the antihistamine in potentiating the narcotic activity are also discussed. Physicians, drug abuse counselors, and others should be aware of the abuse potential and pulmonary damage which can result from the intravenous use of this drug combination.