A 6-month dietary toxicity study of acidic sodium aluminium phosphate in beagle dogs.

Sodium aluminium phosphate [NaAl3H14(PO4)8. 4H2O], a leavening acid, was administered to groups of six male and six female beagle dogs at dietary concentrations of 0, 0.3, 1.0 or 3.0% for 6 months. No adverse treatment-related clinical signs were observed. There were no statistically significant differences in mean body weights between test and control groups at any of the weekly determinations. Weekly mean food consumption values of all male treated groups did not differ significantly from those of the control group at any stage of the study. Statistically significant reductions in food consumption occurred sporadically in all treated groups of female dogs. No significant absolute or relative organ-weight differences were found between any of the treated groups and their respective controls. Haematological, blood chemistry and urinalysis data showed no toxicologically significant trends. Histopathological examination revealed no changes considered to be related to treatment. Thus dietary administration of sodium aluminum phosphate for 6 months at concentrations of 3% or lower caused no significant toxicological effects in beagle dogs.

Fate of silvex following oral administration to humans.

The fate of silvex [2-(2,4,5-trichlorophenoxy)propionic acid] was defined in seven men and in one woman following oral administration of 1 mg/kg. No adverse effects were observed. Samples of blood plasma, urine, and feces were collected at designated time intervals through 168 hr. Plasma samples were analyzed for silvex only, while samples of urine and feces were analyzed for silvex, silvex conjugate(s), 2,4,5-trichlorophenol, and 2,4,5-trichlorophenol conjugate(s). Apparent first-order kinetics described the biphasic clearance of silvex from plasma and excretion in urine. The half-life values for clearance of silvex from plasma were 4.0 +/- 1.9 and 16.5 +/- 7.3 hr for the initial and terminal phases, respectively. Peak plasma levels of silvex occurred within 2-4 hr after dosage. Within 24 hr after administration, 65% of the administered dose had been excreted in urine. Silvex was excreted in urine as silvex and silvex conjugate(s). The half-life values for excretion of silvex per se in urine were 5.0 +/- 1.8 and 25.9 +/- 6.3 hr for the two phases, respectively. Small amounts (3.2% or less) of silvex and/or silvex conjugate(s) were eliminated in feces. Recovery of silvex and its conjugate(s) in urine and feces through 168 hr ranged from 66.6 to 95.1% of the administered dose, with a mean value and standard deviation of 80.3 +/- 10.5%. In humans, silvex is readily absorbed after ingestion and subsequently readily excreted, predominantly via the urine.

The fate of 2,4-dichlorophenoxyacetic acid (2,4-D) following oral administration to man.

The pharmacokinetic profile of 2,4-D is defined in man. Five male human volunteers ingested a single dose of 5 mg/kg 2,4-D without detectable clinical effects. Concentration of 2,4-D were determined in plasma in 3 of 5 subjects and in urine in all subjects at intervals after ingestion. The elimination of 2,4-D from plasma in all subjects occurred by an apparent first-order rate process with an average half-life (t1/2) of 11.6 h. All subjects excreted 2,4-D in the urine with an average t1/2 of 17.7 h. Excretion occurred mainly as 2,4-D (82.3%) with smaller amounts excreted as a 2,4-D conjugate (12.8%). Essentially all of the 2,4-D was absorbed from the gastrointestinal tract in man. Clearance of 2,4-D from the plasma and excretion from the body are first-order rate processes. There was no evidence that 2,4-D would accumulate following repeated administration.

Dose-dependent pharmacokinetic profile of silvex following intravenous administration in rats.

The pharmacokinetic profile of silvex was defined in rats after single intravenous doses of 5 and 50 mg/kg 14C ring-labeles silvex. Clearance of silvex from plasma at the 5 mg/kg dose was linear with a half-life of 16.2 hr, while clearance at the 50 mg/kg dose was nonlinear. Activities of 14C recovered in excreta were 94.1 and 95.1% of the administered doses at 5 and 50 mg/kg, respectively. Excreta was collected for 192 hr at 5 mg/kg and 216 hr at 50 mg/kg. Urinary excretion of 14C activity accounted for 80.5 and 68.7% of the administered dose at 5 and 50 mg/kg, respectively; fecal excretion accounted for 13.7 and 26.4% of the administered dose at 5 and 50 mg/kg, respectively. Urinary excretion of silvex is saturated at the 50 mg/kg dose. Significant amounts of silvex are excreted in bile and undergo enterohepatic circulation. Concentrations of silvex in liver and kidney are higher than those in fat, brain, and muscle 8 and 216 hr after administration. In a companion oral study, silvex was extensively if not completely absorbed. The pharmacokinetic data presented indicate that statistical projection of experimental results with large doses of silvex to predict the hazard of exposure to small amounts is not justified because the capability to excrete silvex in urine has been saturated.

Toxicological evaluation and pharmacokinetic profile of beta-hydroxypropionitrile in rats.

Beta-hydroxypropionitrile (beta-HPN) was incorporated in the drinking water of rats in order to define the toxicological effects associated with repeated daily exposure to this compound. Parameters evaluated were appearance and demeanor, mortality, body weight, food consumption, water consumption, hematology, terminal organ weights and organ to body weight ratio, and gross and microscopic pathology of tissues. No untoward effects were associated with the ingestion of beta-HPN at the dose levels utilized.

Animal models of human disease: severe and mild lead encephalopathy in the neonatal rat.

Inorganic lead produces cerebral dysfunction and clinically definable encephalopathies in man. To date there have been few studies on the biochemical changes in brain following exposure to inorganic lead. Studies correlating toxicity with behavioral and brain neurochemical changes following lead exposure have been hindered because adult laboratory animals are resistant to the central nervous system effects of lead poisoning. Such studies have been impeded by lack of suitable experimental models until Pentschew and Garro showed that brain lesions develop in neonatal rats when a pregnant rat newly delivered of her litter is placed on a 4% lead carbonate containing diet. Lead passes into the developing sucklings via maternal milk. Lead-poisoned new-borns have pronounced retardation of growth and during the fourth week of ilfe develop the severe signs of lead encephalopathy, namely, extensive histological lesions of the cerebellum, brain edema, and paraplegia. There is an approximate 85-fold increase in the lead concentration of both the cerebellum and cerebral cortex relative to controls, but edema and gross vascular changes are confined to the cerebellum. Ingested lead had little effect on RNA, DNA, and protein concentrations of developing rat cerebellum and cerebral cortex. However, there was a reduction of between 10 and 20% in the DNA content of the cerebellum around 3 weeks of age in the lead-exposed sucklings. This suggests a failure of cell multiplication in this part of the brain.A critical evaluation of this experimental approach indicated that under similar dietary conditions experimental lactating rats eat 30% less food than controls resulting in: (a) sustained loss in body weight of nursing mothers and that (b) offsprings who develop paraplegia and cerebellar damage do so after gaining access to lead containing diet. We have studied mothers' food consumption and body weight changes and blood, milk, and brain lead content; and newborns' body and brain weight changes, blood and brain lead content, and brain serotonin (5HT), norepinephrine (NE), dopamine (DA), and gamma-aminobutyric acid (GABA). We have found that a lactating mother rat eating 5% lead acetate (2.73% Pb) produced milk containing 25 ppm lead. When the mothers' diet is changed at day 16 from 5% PbAc to one containing 25 ppm Pb, and neonates allowed free access to the solid diet, the sucklings still have retarded body growth but do not develop paraplegia or grossly apparent vascular damage of the cerebellum. However, during the fourth week these animals exhibit a less severe form of "encephalopathy" consisting of hyperactivity, tremors, and stereotype behavior. Pair-fed controls coetaneous to experimental groups do not display such activities. There was no change in brain 5HT, GABA, or NE, but a 15-20% decrease in brain DA. Change in DA relative to other monoamines suggests a relationship between CNS dysfunction due to lead and DA metabolism in the brain.The experimental design as discribed provides a model of CNS dysfunction due to lead exposure without debilitating histopathologies. It is possible that our findings on increased motor activity and changes in brain dopamine may correspond to early responses to lead exposure before recognized overt signs of toxicity.

Hyperactivity and brain catecholamines in lead-exposed developing rats.

Newborn rats that suckled mothers eating a diet containing 4 percent lead carbonate display hyperactivity, aggressiveness, and excessive stereotyped behavior starting at 4 weeks of age. There is an eightfold increase in the concentration of lead in brain, no change in norepinephrine, but a 20 percent decrease in dopamine relative to coetaneous controls. This suggests a relationship between central nervous system dysfunction due to lead and dopamine metabolism in brain.