Twenty-five years of surveillance for contaminants in human breast milk.

To monitor the exposure of Canadian populations, Health Canada has carried out six major surveys of breast milk contaminants, beginning in 1967. In these national surveys, breast milk was collected from nursing mothers at various times in their nursing period, and the concentrations of chlorinated hydrocarbons were measured. There was a downward trend from 1967 to 1992, in the concentrations of organochlorine (OC) pesticides and polychorinated biphenyl hydrocarbons (PCBs). This regression was observed for samples across Canada, except for a sharp isolated increase in 1982 for the Quebec Province. As the disappearance curves of the chemicals surveyed follow the same pattern for both Ontario and Canada, a similar decline could be expected of OC concentrations in human breast milk in the Great Lakes Basin.

Hazard assessment of boric acid in toys.

Boric acid (H3BO3) has been used in a wide variety of applications--medication, pesticides, and household products. Reports of child poisoning by H3BO3 were common in the clinical literature before 1975. However, a decline in its use as a bacteriostatic agent coupled with increased regulatory control has almost eliminated poisonings by accidental ingestion. Schedule I (Part I, Item 8) of the Hazardous Products Act of Canada, proclaimed in the late 1960s, followed in the wake of concerns about accidental poisoning and prohibits its use in toys. Since that time, scientific knowledge has increased and has led to a reevaluation of the hazard associated with H3BO3. A maximum tolerated dose (MTD) was sought for children in the most susceptible age range, with a view to determine a maximum acceptable concentration (MAC) in toys. The effects of H3BO3 in a variety of exposure scenarios were evaluated. Precedence was given to clinical data in humans, particularly children, since there is no suitable animal model of boric acid intoxication. An extensive search of the pediatric literature was conducted to find a no-observed-adverse-effect level (NOAEL) or a lowest-observed-adverse-effect level (LOAEL). An analysis of the pivotal study to the present assessment resulted in the application of an uncertainty factor of 100 to account for variations in sensitivity among children and for the use of a LOAEL. Based on a pediatric LOAEL of 300 mg/kg body wt, we derived a MTD of 3 mg H3BO3/ kg body wt and a MAC of 9.1 mg H3BO3/g of toy. These results compared favorably with calculations from other human and animal NOAELs/LOAELs.

Structure-nephrotoxicity relationships of glutathione pathway intermediates derived from organic solvents.

The nephrotoxicity of glutathione (GSH) pathway metabolites derived from toluene (TOL), styrene (STYR), bromobenzene (BB), acrylonitrile (ACLN) and 2-chloroacrylonitrile (CACLN) were compared with that of dichlorovinylcysteine (DCVC), using renal brush border and basal-lateral uptake parameters as indices. Cysteine conjugates and mercapturates of ACLN did not alter p-aminohippurate (PAH) uptake by renal tubule suspensions in contrast to its chlorinated homologue. O-, m- and p-conjugates of BB inhibited PAH uptake by 43-82%, the mercapturates showing more potency than corresponding cysteine conjugates. The TOL derivatives N-acetylbenzylcysteine curtailed PAH uptake but benzylcysteine was more effective. The GSH conjugate and mercapturate synthesized from STYR oxide were also active inhibitors but not its cysteine conjugate. Among all GSH pathway metabolites studied, only DCVC and phenylhydroxyethylglutathione, derived from STYR oxide, impeded the renal basal-lateral uptake of [14C]tetraethylammonium (TEA) while DCVC was the sole inhibitor of brush border transport events such as the uptakes of [3H]glutamate and [14C]alpha-methyl-D-glucoside. These data indicate that GSH conjugation represents a non-nephrotoxic detoxication pathway for ACLN. In contrast, GSH conjugation with 2-chloroacrylonitrile and with aromatic solvents like TOL, STYR, BB gives rise to nephrotoxic mercapturates which may be less potent but show more specificity for the organic anion transport system than DCVC.

Toxicologic aspects of voodoo in Haiti.

Voodoo is a folk religion that emerged from the interaction of West African ethnotheologies with European Christian rituals. Haitian Voodoo priests control two major practices which might be of interest to toxicologists: healing and poisoning. Intoxications arising from therapeutic activities pertaining to this cult are of the same kind as those encountered in the practice of Modern Medicine. Remedies used in Voodoo originate generally from plants, as do most prescription drugs; however, the poisons are extracted from both plant and animal tissues, then administered to intended victims as a means of punishment established by a clandestine justice system. The present paper reviews recent attempts at analyzing some of the most lethal Voodoo poisons which appear to induce catalepsy. Although tetrodotoxin was singled out as the probable active ingredient, chromatographic analyses of such poisons as well as the presence of yet unidentified neurotoxicants in Caribbean fish and amphibians familiar to Voodoo practitioners suggest otherwise. To gain more insight into this problem, it is proposed that chemical analyses and toxicological studies be carried out on each ingredient individually, then on combinations of ingredients contained in these Voodoo potions. Such a strategy could help discriminate between active and inactive components and focus on the real toxic elements.

Segmental and intracellular distribution of lead in rat kidney and salivary glands.

The segmental and intracellular distribution of lead (Pb) was studied in the kidney and salivary gland of Sprague-Dawley rats. Lead acetate was administered i.v. in a single dose (10 or 65 mg/kg body wt) or multiple biweekly doses (subchronic: 7 X 10 mg/kg over 3 months; chronic: 13 X 10 mg/kg over 6 months). Segments of cortical nephrons and salivary glands were separated following tissue slicing, incubation with collagenase and centrifugation on a Percoll density gradient medium. Subcellular fractions were obtained by differential centrifugation of renal and salivary tissue homogenates. Lead was predominantly localized in the renal proximal tubules, which contained at least twice as much of the metal as the distal tubules. Segment populations prepared from salivary tissues contained far less Pb than the renal fractions and showed no clear differences among themselves in their affinity for the metal. Intracellular Pb distribution was as follows: kidney nuclei (Nu) greater than mitochondria (Mt) greater than cytosol (Cy) greater than microsomes (Mc); salivary gland Cy greater than Mc greater than Mt greater than Nu. In most cases, 45Ca followed the same intracellular distribution as lead. Our data suggest that the proximal tubular segment may be the most likely renal target of chronic lead toxicity. The results point also to a much greater retention of Pb by the kidney than by salivary glands. The ability of the kidney to accumulate a great deal of lead to be released into tubular fluid over long periods, makes urinary lead a poor indicator of duration and frequency of exposure. On the other hand, the inability of salivary glands to retain this metal makes saliva lead concentration a potential indicator of current exposure.

Lead flux through the kidney and salivary glands of rats.

The blood disappearance curve of lead injected intravenously into rats and its appearance curve in the saliva reflect a three-compartment open model. Urinary elimination rate showed many fluctuations in the first 10 days but decreased progressively afterward. In clearance experiments, with low lead infusion (4 micrograms/min), renal reabsorption accounted for nearly all the filtered lead load, and salivary secretion was on the order of 1 ng/min. Experiments with renal and salivary tissue fragments indicated maximal accumulation in both tissues. Contrary to salivary tissue uptake, renal accumulation of lead decreased in the presence of KCN and 2,4-dinitrophenol, and in Na+-deficient media. Renal lead uptake contains, therefore, an important energy-dependent component. In vitro evidence that the lead transport mechanisms of the kidney and salivary glands are fundamentally different is consistent with the results of the pharmacokinetic study. The resemblance between the early profile of salivary lead secretion and its disappearance from the blood indicates that salivary glands represent diffusion barriers for the metal, in contrast to the kidney where lead uptake may be influenced by energy- and metabolism-dependent mechanisms.

Metabolic machinery of the alligator kidney.

Crocodilians such as caimans and alligators are uricotelic and ammoniotelic animals. They are carnivorous but they excrete ammonium ions in an alkaline urine. The metabolic organization of the kidney of the Mississippi alligator was studied by measuring the renal metabolite profile, the activities of enzymes, and the behavior of kidney tubules in vitro. The liver and tail muscle were also studied. Both awake and anesthetized animals were in a state of low plasma bicarbonate and low blood pH with high plasma lactate concentration. This did not prevent the excretion of an alkaline urine (pH 7.76). alpha-Ketoglutarate was low in all three tissues and lactate was high. Glutamate concentration and glutamate dehydrogenase activity were highest in the kidney with a low equilibrium constant for alanine aminotransferase (KGPT). Glutaminase I was found only in the kidney. It could not be detected in liver or muscle. Glutamine synthetase was found only in the liver. Phosphoenolpyruvate carboxykinase (PEPCK) was present in both liver and kidney. Alanine aminotransferase and malic enzyme showed high activity in the kidney but were inconspicuous in liver and muscle. Malate dehydrogenase and lactate dehydrogenase were present in all three tissues. Renal tubules incubated with glutamine and alanine were ammoniagenic and gluconeogenic. Lactate was gluconeogenic. Enzyme activities were measured at both 30 and 37 degrees C. The studies on renal tubules were also performed at these two temperatures. Temperature had little effect on the data including acid-base values in the blood. Our findings demonstrate that the kidney of the alligator is perfectly equipped for various metabolic functions and especially for ammoniagenesis and gluconeogenesis.

Metabolism and transport of L-glutamine and L-alanine by renal tubules of chickens.

The metabolism and cellular transport of 1 and 5 mM glutamine (Gln) and alanine (Ala) and the metabolism of lactate (Lac) by renal tubular fragments of normal and chronically acidotic chickens were studied. The tubules were prepared by the collagenase digestion procedure and incubated for 0-60 min with or without substrates. Acidosis increased 1 mM Gln utilization from 1.14 to 1.74 and 1 mM Ala from 1.55 to 2.92 mumol X min-1 X g wet wt-1. Gluconeogenesis increased from 0.29 to 0.59 (Gln) and 0.44 to 1.06 (Ala), while ammoniagenesis rose from 2.19 to 3.24 (Gln) and 1.54 to 2.56 (Ala) mumol X min-1 X g-1. In contrast, Lac uptake (2.71 mumol X min-1 X g-1) and gluconeogenesis from Lac (1.05 mumol X min-1 X g-1), which equalled or exceeded the values observed with Gln or Ala in normal rats, were unchanged by acidosis. These data suggest 1) that acidosis increases gluconeogenesis from Gln and Ala by accelerating the glutamate deamination process, and 2) that the glutamate originating from glutamine and alanine are segregated in two different pools within the mitochondria with different access to glutamate dehydrogenase activity. Net cellular uptake of Gln was greater in acidotic chicken tubules, establishing an intracellular concentration of 4.5 in acidotic vs. 3.0 mM in normal chickens when 1 mM Gln was used in the incubation medium. In contrast, 1 mM alanine uptake was not modified by acidosis, greater intracellular metabolism lowering the cellular concentration of this amino acid. These observations suggest that the cellular transport of glutamine but not that of alanine is increased in tubular fragments of acidotic chickens.

The kidney of chicken adapts to chronic metabolic acidosis: in vivo and in vitro studies.

Renal adaptation to chronic metabolic acidosis was studies in Arbor Acre hens receiving ammonium chloride by stomach tube 0.75 g/kg/day during 6 days. During a 14-day study, it was shown that the animals could excrete as much as 60% of the acid load during ammonium chloride administration. At the same time urate excretion fell markedly but the renal contribution to urate excretion (14%) did not change. During acidosis, blood glutamine increased twofold and the tissue concentration of glutamine rose in both liver and kidney. Infusion of L-glutamine led to increased ammonia excretion and more so in acidotic animals. Glutaminase I, glutamate dehydrogenase, alanine aminotransferase (GPT), and malic enzyme activities increased in the kidney during acidosis but phosphoenolpyruvate carboxykinase (PEPCK) activity did not change. Glutaminase I was not found in the liver, but hepatic glutamine synthetase rose markedly during acidosis. Glutamine synthetase was not found in the kidney. Renal tubules incubated with glutamine and alanine were ammoniagenic and gluconeogenic to the same degree as rat tubules with the same increments in acidosis. Lactate was gluconeogenic without increment during acidosis. The present study indicates that the avian kidney adapts to chronic metabolic acidosis with similarities and differences when compared to dog and rat. Glutamine originating from the liver appears to be the major ammoniagenic substrate. Our data also support the hypothesis that hepatic urate synthesis is decreased during acidosis.

Nonparticipation of extracellular glutathione in renal transport of dibasic amino acids.

Microinjections of L-[14C]arginine (2.9 mM) and L-[14C]ornithine (3.4 mM) were made into renal proximal tubules of rats in the presence of methionine sulfoximine (MSO) (10, 20 mM), ATP (10 mM), and MgCl2 (20 mM) together. Absorption of both labelled amino acids dropped, respectively, by 31.1 and 49.1% compared with control microinjections. The MSO alone or ATP plus MgCl2 had no effect. These data suggest that the inhibition by MSO plus ATP plus MgCl2 is not due to direct competition between MSO and dibasic amino acids but rather to suppression of the renewal of intracellular glutathione. Such an effect is discussed in comparison with cycloleucine inhibition of dibasic amino acid transport. Addition of exogenous glutathione to microinjectates die not reverse either type of inhibition. This study shows that while intracellular glutathione may affect amino acid transport, extracellular glutathione has no effect.

Experimental cystinuria: the cycloleucine model. II. Amino acid efflux from intestinal and renal tissues.

Loading and unloading experiments using intestinal sacs and renal cortex slices were undertaken to ascertain the role of amino acid efflux in cycloleucine-induced amino-aciduria. The presence of cycloleucine, lysine, or valine on the luminal or antiluminal side of the intestine caused an increased leakage of [14C] cycloleucine, [14C] lysine, and [35S] cystine from the tissue. Similar results were obtained when using kidney cortex slices, except for cystine efflux. The latter phenomenon was inhibited by cycloleucine and lysine. Data, also obtained with renal cortex slices, suggest that cystine and cysteine are recognized by different transport sites although one (the oxidized form) may be typically extracellular and the other (the reduced form), intracellular. A comparison of these data with previous works done in our laboratory shows that cycloleucine affects efflux less than influx and further suggests that in rats given cycloleucine, renal transport is impaired only at the brush border level for cystine and at both luminal and antiluminal membranes for dibasic amino acids.

Experimental cystinuria: the cycloleucine model. I. Amino acid interactions in renal and intestinal epithelia.

The injection of cycloleucine (1-aminocyclopentanecarboxylic acid (ACPC) into rats produces a hyperexcretion of dibasic amino acids and cystine, an aberration resembling cystinuria. This may constitute a model of experimental cystinuria, and the transport of amino acids involved in this disease was studied with the techniques of everted intestinal sacs (in vitro) and microinjections into renal tubules (in vivo). In verted sacs from normal rats, there was a decrease in transfer and in accumulation of L-cystine (0.03 mM) and L-valine (0.065 mM) when ACPC was on the mucosal (luminal) side. Dibasic amino acids such as L-arginine and L-lysine caused a similar inhibition of the transport of L-cystine. However, when ACPC was on the serosal (antiluminal) side, a lesser effect was noted while arginine and lysine had no effect. Intestinal sacs from treated rats (ACPC, 300 mg/kg X 3 days) transferred and accumulated as much L-cystine as those from control rats. The interaction between cycloleucine and L-cystine was competitive at the luminal and non-competitive at the antiluminal side of the intestine. Cycloleucine inhibited L-lysine transport in a non-competitive fashion at either side of the intestine. L-Lysine also interacted in a non-competitive fashion with L-cystine transport at the luminal membrane. In proximal convoluted tubules, the presence of L-arginine or ACPC caused a decrease in the transport of L-cystine and L-lysine. L-Valine exerted no effect. Furthermore, L-lysine and ACPC did not impair the reabsorption of L-valine significantly. These results suggest a functional heterogeneity between luminal and antiluminal membranes of renal and intestinal epitehlia and the existence, at both membranes, of different transport sites for cystine and dibasic amino acids.