The effects of subacute and subchronic oral exposure to cis-1,2-dichloroethylene in Sprague-Dawley rats.

Cis-1,2-dichloroethylene was administered daily by corn oil gavage to male and female Sprague-Dawley rats at the following dose levels: 1.0, 3.0, 10.0 and 22.0 mmol/kg/day for 14 days. Doses gavaged during the 90-day subchronic study were 0.33, 1.00, 3.00 and 9.00 mmol/kg/day. There were no compound-related deaths or histopathological changes demonstrated. Significant increases in relative liver weights were seen after 14- and 90-days of treatment in both sexes. This study demonstrates some indication of toxicity at subacute and subchronic exposure levels as low as 0.33 mmol/kg/day. Implications of liver abnormalities were demonstrated at an exposure level of 1 mmol/kg/day while kidney abnormalities (relative weights) were demonstrated at an exposure level of 0.33 mmol/kg/day.

The effects of subchronic chlorate exposure in Sprague-Dawley rats.

Male and female Sprague-Dawley rats were exposed to drinking water containing 3.0, 12.0 or 48.0 mM sodium chlorate. The mean drinking water consumption varied between exposure groups from 100-200 ml/kg/day. Female exposure groups consistently drank more water (23-42%) than male exposure groups thereby receiving more chlorate/kg/day at every exposure level. There were no compound related deaths; however, both males and females in the high exposure groups had significant weight loss during the 90-day exposure period. Also, in these same groups females had mild but significant decreases in the following relative organ weights; adrenals, thymus and spleen, while the relative brain weight was increased. In males, the heart, kidneys and liver were mildly decreased while the brain and testes were mildly increased. Red blood cell counts and percent hematocrit were decreased in both sexes in the high dose group. Pituitary gland (pars distalis) vacuolization and thyroid gland colloid depletion were prominent in both sexes in mid and/or high dose animals. A NOAEL of 0.36 mM chlorate/kg b.w./day in males and 0.50 mM chlorate/kg b.w./day in females were established.

Toxicity studies of 1,3-dichlorobenzene in Sprague-Dawley rats.

Male and female Sprague-Dawley rats received 1,3-dichlorobenzene daily by corn oil gavage for 10 or 90 consecutive days. The 10-day study doses were 0, 37, 147, 368 and 735 mg/kg; the 90-day study doses were 0, 9, 37, 147 and 588 mg/kg. In the 10-day study, there was a significant depression of body weight in both sexes at 735 mg/kg. Liver weights were significantly increased in both sexes at 368 and 735 mg/kg. Serum cholesterol levels were significantly elevated in both sexes at 368 and 735 mg/kg. Histopathological evaluation revealed centrolobular hepatocellular degeneration at 368 mg/kg in males and 735 mg/kg in females. In the 90-day study, body weights were significantly depressed in both sexes at 588 mg/kg. Normalization of food and water consumption by final body weight indicated that at 588 mg/kg both sexes had increased food and water consumption relative to controls. Absolute and relative liver weights were significantly increased in both sexes at 147 and 588 mg/kg. Relative kidney weights were significantly higher in both sexes at 588 mg/kg and in males at 147 mg/kg. Serum cholesterol and calcium levels were significantly elevated over controls in females at 37, 147, and 588 mg/kg, and in males at all dose levels. Histopathological evaluation at 147 and/or 588 mg/kg demonstrated liver and thyroid lesions in both sexes, and pituitary and kidney lesions in males. A NOAEL was not firmly established.

X-ray microanalysis of calcium, potassium, and phosphorus in liver mitochondria stressed by carbon tetrachloride.

Previous measurements of elemental concentrations in liver mitochondria have generally required homogenization and fractionation of liver tissue, a procedure in which it is difficult to rule out ion movement between subcellular units. New techniques involving cryoultramicrotomy of rapidly frozen tissue, high resolution scanning transmission electron microscopy, and X-ray microanalysis were used to measure those elements in rat liver mitochondria reported to have changed following oral administration of carbon tetrachloride (CCl4). Increases in liver mitochondrial calcium were found 24 hr following intoxication by CCl4. Significant early (2 hr) mitochondrial increases in potassium and phosphorus were found following administration of CCl4. The electron microscope technique using quick-frozen samples promises to allow measurement of intracellular ionic concentrations under virtually lifelike conditions.

Hypochlorite-serum reaction products inhibit porcine vascular endothelial cell growth in culture.

In vitro toxicity studies wer initiated in order to determine if chlorination affects vascular endothelial cells. Twelfth to twentieth passage porcine aortic vascular endothelial cells (PAE) were grown to confluency and replated in the presence of complete media (Eagle's minimum essential media supplemented with 20% fetal bovine serum) which had been preincubated for 30 minutes with 15.0 mg/liter chlorine. During a 72-hour exposure period, control PAE cells grew to confluency, an increase of approximately 9 fold in the number of cells/plate. Those cells exposed to media preincubated with 15.0 mg/liter chlorine derived from sodium hypochlorite increased only 6 fold. There was no sign of cell killing, but an apparent inhibition of cell division. No effect was seen when either the amino acid or vitamin component of the complete media was reacted at the 15.0 mg dose level. However, when the serum component was preincubated with 15.0 mg chlorine/liter as sodium hypochlorite, an inhibition in growth rate similar to the complete media occurred.

Dimethyltin dichloride: investigations into its gastrointestinal absorption and transplacental transfer.

Dimethyltin dichloride (DMDC) is commonly used as a stabilizer in PVC pipe used for transport of potable water. Learning deficiencies have been observed postnatally in pups from DMDC-treated dams. Studies were conducted with female Sprague-Dawley rats to determine whether DMDC was absorbed by the dam and transferred across the placenta to fetal blood and brain tissue. This was accomplished in three phases: (1) a comparison of absorption of organic and inorganic tin from drinking water, (2) a comparison of prenatal and postnatal levels of tin in the pups in cross-fostering studies, and (3) a [14C]dimethyltin dichloride tracer study to determine whether organic tin passed to the pup intact. Major findings include: (1) DMDC is absorbed in the gastrointestinal tract of the dam much more rapidly than Sn2+; (2) the more rapid absorption of DMDC results in higher concentration of tin in fetal blood and brain; and (3) in fetuses that receive tin as DMDC, both tin and the methyl carbon are absorbed by the dam and transferred to the blood and brain of the fetuses.

Barium bioavailability as the chloride, sulfate, or carbonate salt in the rat.

This study was conducted to determine how the bioavailability of a low concentration of barium (Ba) in drinking water is affected by the anion. Male Sprague Dawley rats weighing 250-300 grams were maintained on a diet of less than 1 mg Ba/kg of food for at least 1 month prior to experimentation. Rats were given 10.0 mg 131Ba/liter as sulfate (SO4), chloride (Cl), or carbonate (CO3) at pH 7.0. Animals were sacrificed at 2, 5, 10, 20, 30, 60, and 120 minutes and 24 hours after intubation. When 131Ba was administered, as Cl, 131Ba in blood rose linearly for 10 minutes and then less rapidly until the highest number of counts was measured at 60 minutes. At 24 hours 131Ba was still at 90% of peak levels. Five tissues were tested 24 hours after dosing for 131Ba. In decreasing order of 131Ba concentration they were heart, eye, skeletal muscle, kidney, and liver. 131Ba in the heart reached 8x that observed in blood 24 hours after dosing. In the eye, 131Ba increased linearly for 1 hour. Isotope concentrations in the eye eventually reached 2.5x that observed in blood. When 131Ba was administered as SO4 or CO3, 131Ba in blood was respectively 85% or 45% of levels, of 131Ba from 131BaCl2. Initial uptake of 131Ba and deposition in the eye were not different when administered as Cl or SO4.

The effects of lead on the developing central nervous system of the rat.

Biochemical and structural development of the cerebral cortex of rat pups is delayed by low levels of lead administered in the dam's drinking water during gestation and suckling periods. These changes in brain development coincide with delays in the development of exploratory and locomotor activity and impaired learning. Subsequent cross-fostering experiments have shown that delays in synaptogenesis and in the development of exploratory behavior were attributed entirely to the prenatal, as opposed to the postnatal, exposure to lead at the low dose levels utilized. Examination of the variations in blood lead concentrations in pups and dams during gestation and until weaning at 21 days of postnatal age indicated that a substantial increase in blood lead concentrations occurred late in pregnancy. At 200 mg of Pb/liter of drinking water, peak blood Pb concentrations were observed to be approximately 60 micrograms/dl in dams and 80 micrograms/dl in pups on the 20th day of gestation. By the 10th postnatal day blood Pb concentrations had decreased to 35 micrograms/dl in dams and 40 microgram/dl in pups despite an increased consumption of drinking water containing the same concentration of Pb during this period. (Delays in cerebral cortical development were observed after 10 days of postnatal age). Tracer studies utilizing 203Pb indicate that the rate of Pb absorption was substantially increased in the pregnant, relative to the non-pregnant, dam. Although a similar increase in 45Ca absorption was also observed during pregnancy, increases in Pb absorption were enhanced by Pb-pretreatment, whereas Ca absorption was independent of Pb-pretreatment. From this data it is concluded that the apparently greater sensitivity of postnatal development on prenatal Pb exposure is secondary to enhanced Pb absorption in the pregnant rat. In vitro metabolic studies in isolated cerebral cortex slices taken from 15 day old rat pups exposed to Pb revealed increased glucose and oxygen consumption in response to elevations in the potassium concentration of the incubation media. This evidence of metabolic uncoupling in the immature rat cerebral cortex may be causally related to the measured delays in brain development.

The effect of prenatal and postnatal lead exposure on neonatal synaptogenesis in rat cerebral cortex.

Pregnant rats were exposed to drinking water with lead (Pb) concentrations of 0, 30, or 200 mg/l. The resultant pups were sacrificed at 11, 15, and 21 d of postnatal age for the determination of synapses/mm3 in parietal cortex. Synaptic counts from electron micrographs of ethanol phosphotungstic acid stained cortical slices were counted by four observers who were blinded as to treatment (control or 200 mg Pb/l drinking water). A greater than fourfold increase in synaptic counts was observed in layers I, II, and III of rat pups parietal cortex between 11 and 21 d of age. Pb treatment depressed synaptic counts maximally at 15 d of age. However, Pb-exposed pups displayed essentially the same synaptic counts as controls by 21 d of age. In a cross-fostering design, it was shown that prenatal exposure to Pb completely accounted for the delays in synaptogenesis. No significant depression of synaptic counts was observed in pups exposed only during the postnatal period. Blood lead concentrations (Pb X B) were determined during gestation and suckling in both mother and offspring. A dramatic peripartum (partum plus and minus 4 d) peak in Pb X B was seen in mother and pup. Pup Pb X B peaked at 80 micrograms/dl at exposures of 200 mg Pb/l drinking water. In addition to being dose-dependent, blood Pb levels resulting from the same concentration of Pb in drinking water displayed a significant dependence on litter at time-points between birth and 1 yr of age. These data indicate that the substantially elevated blood Pb concentrations that are evident at partum in pups prenatally exposed to Pb might be responsible for the postnatally observed delay in synaptogenesis.

Experimental approaches to evaluating the role of environmental factors in the development of cardiovascular disease.

Epidemiologic studies have suggested factors in drinking water influence on the human cardiovascular system. A clear identification of the factors involved requires more invasive techniques and more strict experimental controls than can usually be applied in epidemiologic studies. Consequently laboratory animals are often used to expand and support epidemiologic data. For laboratory purposes cardiovascular toxicology must be broken down to effects on the myocardium, the vasculature and the kidney. Further division may be necessary to take into account the influence of the neuroendocrine system or other systems that influence the function of the cardiovascular system. Since environmental influences upon the cardiovascular disease are relatively subtle (versus the acute effects of some drugs) it is assumed that major difficulties are chronic in nature. Accordingly, it is suggested that laboratory experimentation focus on either chronic toxin exposure or short-term exposure to stressed or genetically susceptible animals. A variety of in vivo and in vitro tests may be necessary to relate the toxicity realized in animals to what might be expected in man. Wide species differences with respect to the susceptibility of particular target tissues must be taken into account to clearly apply the results to man. Similarly, special characteristics of stressed and genetically susceptible animals must be understood to avoid deceptive results.