Potentiation of evoked adrenal catecholamine release by cyanide: possible role of calcium.

The effect of cyanide on release of catecholamines was evaluated in isolated bovine adrenal glands stimulated with 4 different agonists. Cyanide (0.1-1 mM) increased catecholamine release induced by barium or cadmium 2-3-fold. Acetylcholine or potassium induced secretion of adrenal catecholamines was also enhanced by cyanide, but only to the extent of 30-50%. These data suggest that cyanide acts by multiple mechanisms to enhance evoked catecholamine release. The above results may be partly explained by the fact that cyanide inhibited 45Ca efflux from stimulated bovine adrenals. Changes in plasma membrane permeability may be crucial in the alterations of ion flux and evoked catecholamine release caused by cyanide.

Effects of chlorphentermine and nitrogen dioxide on murine alveolar macrophages.

Male Swiss-Webster mice were treated daily for 14 days with either 120 mg/kg chlorphentermine (CP) to produce pulmonary lipidosis or an equal volume of water. Animals in each treatment group were then exposed by whole-body inhalation to either air or NO2 for 48 h. Immediately following exposure, alveolar macrophages (MPs) were collected from each animal by bronchoalveolar lavage. Assays performed on adherent viable MPs showed some changes in metabolic reduction, phagocytosis, and killing activity. 5'-Nucleotidase activity and yeast phagocytosis and killing assays suggested that CP elicited an increase in phagocytosis over control levels. Although the percentage metabolic reduction and microbicidal killing activities following CP were not increased when compared to controls, absolute reduction and killing (percentage values times total MPs) were significantly increased. These increased functions seemed to be highly dependent on the large increase in the total number of MPs induced by CP. It is possible that the large accumulation of MPs in the airways of the lipidotic lung may help protect the alveolar epithelium from NO2 by quenching free radicals produced during NO2-induced lipid peroxidation.

The effect of chlorphentermine pretreatment on the toxicity of nitrogen dioxide in mice.

Chlorphentermine HCl (CP) was used to induce preexisting alveolar alterations resembling a pulmonary lipidosis in mice to study these effects on the severity and duration of nitrogen dioxide (NO2) toxicity. Results indicated that a daily dose of 120 mg/kg for 14 days produced consistent histopathologic changes characterized by an accumulation of large foamy macrophages. Male Swiss-Webster mice were divided into a control and three treatment groups. Group 1 received 120 mg/kg CP po daily for 2 weeks followed by exposure to air for 48 hr. Group 2 received 20 ppm NO2 for 48 hr via whole-body inhalation, and group 3 received 120 mg/kg CP daily for 2 weeks followed by 20 ppm NO2 for 48 hr. The fourth group served as a nontreated control and received water in place of CP and air in place of NO2. All groups were compared by morphologic evaluation of pulmonary tissues at the light and electron microscopic levels at Days 0, 1, 3, 5, and 7 after the 48-hr exposure to air or NO2. In a second experiment using the same treatment groups, thin-section light microscopy was used to count the number of type I and type II cells and macrophages. NO2 exposure alone caused deaths in 20.8 and 18.5% of the mice in the two studies, but no deaths were seen in the combination groups from both experiments. Histopathologic evaluation showed a typical cellular response to the NO2 exposure, but differences were noted between the two groups receiving NO2 on this treatment. There was increased type II cell hyperplasia and terminal bronchiolitis on Days 0 and 1 but less on Days 3 to 7 in the combination group compared to the NO2 alone group. CP treatment prior to NO2 exposure caused less terminal bronchiolar epithelial hyperplasia and less pulmonary edema than was seen in the NO2 along group. The CP treatment appeared to protect against the lethal effects of NO2 at the concentration and time of exposure used and altered the cellular repair mechanism that occurs in response to NO2 toxicity. CP treatment prior to NO2 exposure caused significantly less loss of type I cells and less increase in type II cells due to NO2 damage. The combination treatment also caused an increase in macrophages greater than that seen in either individual treatment, and this number remained increased through 5 days post-NO2 exposure, whereas the NO2 alone caused a steady increase in macrophages following the exposure until Day 3.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative study of the pharmacokinetics of carbon tetrachloride in the rat following repeated inhalation exposures of 8 and 11.5 hr/day.

To evaluate whether exposure to inhaled vapors for periods longer than 8 hr/day could affect the rates and routes of elimination, male Sprague-Dawley rats were repeatedly exposed to 100 ppm of radiolabeled carbon tetrachloride (14CCl4) in a closed-loop chamber. One group was exposed for 8 hr/day for 5 days and another group for 11.5 hr/day for 4 days. Two other groups were exposed for either 8 hr/day for 10 of 12 consecutive days or 11.5 hr/day for 7 of 10 days. The elimination of 14C activity was measured in the expired air, urine, and feces for up to 100 hr following exposure and the pharmacokinetic parameters were determined. Following 2 weeks of exposure to the 8-hr/day schedule, 14CCl4 in the breath and 14C activity in the feces comprised 45 and 48% of the total 14C excreted, respectively. Following 2 weeks of exposure to the 11.5-hr/day schedule, the values were 32 and 62%, respectively, indicating that repeated exposure to the longer schedule altered the route of elimination of CCl4. Regardless of the period of exposure, less than 8% of the inhaled 14CCl4 was excreted in the urine and less than 2% was exhaled in the breath as the 14CO2 metabolite. Approximately 97-98% of the 14C activity in the expired air was 14CCl4. The quantities of 14C noted in the feces and urine suggest that more than 60% of the inhaled CCl4 was metabolized. Elimination of 14CCl4 and 14CO2 in the breath followed a two-compartment, first-order pharmacokinetic model (r2 = 0.98). For rats exposed 8 hr/day and 11.5 hr/day for 2 weeks, the average half-lives for elimination of 14CCl4 in the breath for the fast (alpha) and slow (beta) phases averaged 96 and 455 min, and 89 and 568 min, respectively. The average alpha and beta half-lives for elimination of 14CO2 in the breath of rats exposed to the 11.5-hr/day schedule were 455 and 1824 min, and these were significantly longer than for the 8-hr/day groups, 305 and 829 min. The longer half-lives of elimination for 14CO2 and 14CCl4 which were observed for the groups exposed to the 11.5-hr/day schedule suggest that the 3.5 additional hr of daily exposure places a relatively greater percentage of the absorbed dose into poorly perfused lipophilic depots such as the fat.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of an 11.5-hr/day exposure schedule on the distribution and toxicity of inhaled carbon tetrachloride in the rat.

This study evaluated the differences in toxicity and tissue distribution for 16 groups of male rats repeatedly exposed to 100 ppm of 14CCl4 vapors for 8 or 11.5 hr/day for periods of 1 to 10 days. Serum sorbitol dehydrogenase (SDH) was also evaluated for its sensitivity at detecting CCl4-induced hepatotoxicity. Following 1, 2, 3, 4, 5, 7, 11, and 14 days, one group of rats from each exposure schedule was sacrificed and 14C activity in seven tissues and serum SDH levels were measured. To compare the effects of CCl4 on the liver and kidney following repeated exposure to the two schedules, one group of rats was exposed for 8 hr/day for 10 of 12 consecutive days and another for 11.5 hr/day for 7 of 12 consecutive days so that each group received essentially the same dose (8000 ppm-hr) of CCl4. The 11.5-hr/day exposure schedule, compared to rats exposed 8-hr/day, produced minor changes in the distribution and concentration of 14C (CCl4 equivalents) in various tissues. Following 1 and 2 weeks of exposure to either schedule, the fat, liver, lungs, and adrenals had the highest concentration of CCl4 equivalents. There were no significant differences in CCl4-induced hepatotoxicity or nephrotoxicity between rats exposed to the two schedules following either 1 or 2 weeks of exposure as measured by histopathology. In contrast, rats exposed 11.5 hr/day had significantly higher SDH levels than those exposed to the 8-hr/day schedule; thus suggesting that the 11.5-hr schedule did produce a measurably greater degree of hepatotoxicity, although it was too subtle to detect pathologically. Rats exposed for a fourth and fifth day during the second week of the 11.5-hr schedule had a significantly greater concentration of 14C activity in the fat than rats exposed to the 8-hr/day schedule as well as severe fatty infiltration of the liver and higher serum SDH activity. This study demonstrated that SDH is a very useful assay for detecting subtle changes in liver injury as compared to histopathology. It was also shown that even at relatively low vapor concentrations, modest changes in dosage regimen, like those involving unusual (e.g., 10- or 12-hr/day) work schedules, can have a measurable effect on the distribution of the chemical and the degree of toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Method for quantitative operant response measurement during inhalation exposure.

A method for pharmacologic and toxicologic investigation of operant responses during inhalation exposure has been developed. The method was tested with rats. Toluene was utilized as a reference chemical. Toluene has been reported to cause significant increases in response rates of animals responding under operant schedules. A fixed interval schedule (F1-120 sec) was used. A significant increase in response rate was observed. Thus, the results indicated that the method was reliable and allowed operant schedule data to be obtained. The significance of this method lies in its versatility to allow an integrative study of operant response, inhalation kinetics, and pharmacologic action. Potential practical applications of the method include studies of the actions of drugs and chemicals administered via inhalation exposure.

Effects of toluene inhalation on brain biogenic amines in the rat.

The effects of toluene exposure on the biogenic amine concentrations in the central nervous system were investigated in the rat. Toluene was administered via inhalation to groups of rats at concentrations of 0, l00, 300, or 1000 ppm. After an 8-h continuous exposure, animals were sacrificed and whole brain concentrations of dopamine (DA), norepinephrine (NE), and 5-hydroxytryptamine (5-HT) were determined. The data indicated a significant increase in whole brain concentrations of DA following the 100-ppm exposure. A regional analysis of DA, NE, and 5-HT concentrations in rats exposed to 1000 ppm of toluene for 8-h indicated a significant increase in DA concentration in the striatum. A significant increase in NE concentrations was detected in the medulla and midbrain while 5-HT concentrations were significantly increase in the cerebellum, medulla, and striatum. The results indicate that toluene action results in elevated concentrations of behaviorally significant neuro-transmitters.

The pharmacokinetics of inhaled chlorobenzene in the rat.

Male rats were exposed for 8 hr/day to 100, 400, or 700 ppm of [14C]chlorobenzene vapor for either 1 or 5 days for the purpose of examining the dose dependency of parameters indicative of the toxicity process and the effect of repeated exposure. 14C burdens in the blood, liver, kidneys, lungs, and fat were measured at 0, 16, and 48 hr after exposure. The labeled material excreted in the urine and expired air was collected for 48 hr. Analysis was performed on both the rats and total amounts eliminated. The mercapturic acid percentage of the urinary metabolites excreted in the first 24 hr was measured. The 14C burdens of all tissues increased in proportion to increased exposure concentrations, except for adipose tissue burdens, which increased more than 30-fold between 100 and 700 ppm. Respiratory elimination of 14C also increased disproportionately. The urinary metabolite profile was altered, with a dose-dependent decreased in the mercapturic acid percentage from 68% at 100 ppm to 51% at 700 ppm. Changes due to multiple versus single exposures were higher tissue burdens 48 hr after exposure, less total excretion of label, a lesser percentage of the total excreted through respiration, and a change in the rate of respiratory excretion. The dose-dependent changes are postulated to be due to saturation of the metabolic elimination of chlorobenzene. The effect of multiple exposure is apparently some stimulation of metabolism.

A dynamic closed-loop recirculating inhalation chamber for conducting pharmacokinetic and short-term toxicity studies.

Tests for evaluating the hazard of inhalation exposure generally require large quantities of the chemical of interest. This paper describes an inhalation technique that involves a dynamic closed-loop recirculating system which uses only small amounts of toxicant since the test atmosphere to which the animals are exposed is recycled. Carbon dioxide and water are continually removed while the oxygen and test substance absorbed by the animals are replenished. The approach described is different from other closed-loop chambers since the test substance is continuously added to the chamber and the air concentration is continuously measured. The technique was successfully used to expose 20 adult rats for up to 12 consecutive hours to 100 ppm of 14C-carbon tetrachloride yet only 2-3 mL of test material were consumed. The inhalation chambers were fabricated from standard 40-liter cylindrical glass bell jars. A high number of air changes (35-40 equivalent chamber volumes per hour) permitted exposure of as many as five adult rats per 10 liters of chamber volume. This closed-loop approach should prove to be especially useful for evaluating the risk of exposure to very expensive materials or when only limited quantities of a test material are available. These systems may also be used to expose rats and other small animals to radioisotopes in studies which evaluate the uptake, distribution, metabolism, and excretion of volatile xenobiotics.

Interaction of digoxin and montmorillonite: mechanism of adsorption and degradation.

IR, X-ray diffraction, and absorption studies showed that digoxin is adsorbed onto montmorillonite by a reversible adsorption mechanism at pH 2 and 6. Degradation studies indicated abnormally high acid hydrolysis rates for digoxin interacted with montmorillonite. Accelerated digoxin degradation is attributed to the ability of the clay surface to concentrate both digoxin and protons. The effective pH at the clay surface appeared to be 1.5 pH unites lower than the bulk suspension pH. Bisdigoxigenin was the major adsorbed degradation product. A similar catalytic effect also may occur with other neutral drugs that degrade by acid hydrolysis and should be considered in the formulation of clay-containing drug products or their coadministration with other drugs.

Preferential localization of radiolabeled liposomes in liver.

Liposome formulations were studied to achieve an efficient entrapment procedure for the production of liposomes of 99mTc-pentetic acid. The entrapment efficiency was studied by separation of the product using column chromatography. The particle-size range of the prepared liposomes was evaluated using electron microscopy. Entrapment techniques and separation procedures led to a liposome preparation with particles in the colloidal size range (0.001-0.5 micron). Dramatic differences in the organ distribution of the liposome preparation in mice were produced when different particle-size ranges were injected. Liposomes eluted in the first fraction after the void volume led to a maximum uptake by the liver and spleen 10 min after intravenous injection. Liposomes from pooled fractions provided less than half of the activity in the liver, as did the narrow size range liposome preparation.

The maternal distribution and placental transfer of cadmium in zinc deficient rats.

Although a transitory maternal zinc deficiency has been shown to result in an increased cadmium-induced fetotoxicity, the results of the present investigation indicated that a maternal zinc deficiency apparently did not affect the placental transfer of cadmium. However, a zinc deficiency did alter the maternal distribution of cadmium. The increased cadmium fetotoxicity associated with a maternal zinc deficiency may be caused by a maternal alteration rather than a direct effect on the fetus. Further study is necessary prior to any definitive statement concerning the effects of a maternal zinc deficiency on cadmium fetotoxicity.