Effect of phenobarbital on cephaloridine toxicity and accumulation in rabbit and rat kidneys

Cephaloridine causes necrosis of renal proximal tubules in humans and laboratory animals. This antibiotic nephrotoxicity in rats has been shown to be reduced by mixed-function oxidase (MFO) inhibitors such as piperonyl butoxide and cobaltous chloride. The purpose of this study was to determine the effect of phenobarbital, a MFO inducer, on cephaloridine nephrotoxicity in rats and rabbits. Phenobarbital induced rabbit renal MFO activities and also potentiated cephaloridine toxicity in rabbit kidneys. In contrast, a similar treatment with phenobarbital produced little effect on rat renal MFO activities and did not alter cephaloridine nephrotoxicity in rats. These results suggested that cephaloridine may have to be bioactivated within the kidney prior to producing toxicity. However, a higher renal cortical concentration of cephaloridine was detected in phenobarbital-treated rabbits. This higher concentration appeared to be due to a greater ability of renal cortical cells to accumulate cephaloridine. Therefore, rather than as a result of enzyme induction, the potentiating effect of phenobarbital on cephaloridine nephrotoxicity might be due to the increased renal cortical accumulation of the parent drug, cephaloridine.     

Reproductive toxicity of dimethyl methyl phosphonate (DMMP) in the male Fischer 344 rat

Dimethyl methyl phosphonate (DMMP) has been considered for use by the U.S. Armed Forces as a nerve gas simulant in a variety of experimental situations to simulate the physical properties of nerve gases, but not the neurotoxic properties. Dimethyl methyl phosphonate is also used as a flame retardant for urethane foams and polyester resins. This study was conducted to determine the reproductive toxicity of DMMP after subchronic dosing. DMMP was administered to male Fischer 344 rats by gavage 5 days/week for 90 days at dosages of 0, 250, 500, 1000, and 2000 mg/kg, and all animals survived this dosing schedule. At Day 84, the rats were mated to untreated female Fischer 344 rats. There was a dose-related decrease in sperm count, sperm motility, and the male fertility index. The male fertility index was 70, 75, 60, 40, and 0% in the 0, 250, 500, 1000, and 2000 mg/kg dose groups. DMMP acted as a dominant lethal mutagen as demonstrated by an increase in the number of resorptions with increasing doses of the drug. The percentage of resorptions in the control group was 6.1% and increased to 14.9, 37.8, and 79.1% in the 250, 500, and 1000 mg/kg groups, respectively. The testes of the male rats were examined histologically to determine the relationship between reproductive function and pathologic abnormalities. DMMP altered reproductive function at all dose levels, while histologic abnormalities of the testis were seen only in the high-dose group. Changes in the testes of the high-dose animals were characterized by lack of spermatogenesis or by degeneration, vacuolization, and necrosis of cells in the spermatogenic tubules. Histopathologic abnormalities of the kidney were seen in some animals from each of the dosed groups and microscopic changes of the prostate were seen in some of the high-dose animals.     

Drug-nitrite interactions: the lack of toxicity of a N-nitroso derivative of tripelennamine formed in the rat.

[Benzyl-¹⁴C]-tripelennamine (100 mg/kg, 100 μCi/kg) and sodium nitrite (100 mg/kg) were administered orally to 24-hr fasted rats. After 1 hr, the rats were sacrificed and the stomach contents were analyzed for the N-nitroso derivative of tripelennamine with the aid of preparative thin-layer chromatography (tlc) and mass spectrometry. About 6% conversion of the administered drug to its N-nitroso derivative was found to occur in the rat stomach during the first hour. The N-nitroso compound was also detected in the 24- and 48-hr urine samples from rats to which tripelennamine and nitrite were coadministered. The N-nitroso derivative failed to produce any definitive hepatic or kidney necrosis in rats during acute and short-term toxicity studies, and it was found to be devoid of the central nervous system (CNS) activity of the parent drug.     

The role of isocyanates in the toxicity of antitumour haloalkylnitrosoureas

The cytotoxicity of the antitumour nitrosoureas BCNU and CCNU and the isocyanates which they liberate (chloroethylisocyanate and cyclohexylisocyanate respectively) has been measured utilising an in vitro-in vivo bioassay. Lines of the TLX5 lymphoma and L1210 leukaemia were used which were either sensitive or resistant to nitrosoureas in vivo. An estimated logarithmic cell kill produced by each compound in vitro (before injecting the cells into animals) was calculated by reference to assays of the survival time of animals given from 2 × 10⁵ to 2 × 10⁰ cells of each line. Resistance to both BCNU and CCNU was observed in vitro in the cell lines of the TLX5 lymphoma made resistant to either BCNU or a dimethyltriazene in vivo. The latter tumour was cross-resistant in vivo to nitrosoureas. Resistance in vitro to nitrosoureas was also observed in a line of L1210 leukaemia which had had resistance to BCNU induced in vivo. The nitrosourea resistant TLX5 lymphomas were cross-resistant in vitro to both cyclohexylisocyanate and chloroethylisocyanate whereas the nitrosourea resistant L1210 line showed no cross-resistance to cyclohexylisocyanate and marginal cross-resistance to chloroethylisocyanate. The results suggest that the TLX5 lymphoma, which is naturally resistant to alkylating agents of the 2-chloroethylamine type, may be sensitive in vivo to nitrosoureas as a consequence of the intracellular release of isocyanates. This hypothesis was supported by the finding that the resistant TLX5 lymphoma showed no cross-resistance to other electrophilic agents, for example formaldehyde, monomethyltriazene or HN2. The transport of nitrosoureas into the sensitive and resistant cell lines was similar in profile and there was no difference in the concentration of non-protein thiols.     

Alkyldiol antidotes to ethylene glycol toxicity in mice.

A series of alkyldiols were compared to ethanol or pyrazole as antidotes in ethylene glycol toxicity. Mouse liver alcohol dehydrogenase oxidized ethanol and a series of alkyldiols. The K_m values in millimoles per liter determined from the assays were 0.4 with ethanol, 53 with ethylene glycol, 14 with propylene glycol, 5.4 with 1,3-propanediol, 3.8 with 1,2-butanediol, 1.5 with 1,3-butanediol, 0.5 with 1,4-butanediol, 56 with 2,3-butanediol, 0.23 with 1,5-pentanediol, and 0.031 with 1,6-hexanediol. These data indicated that ethanol and the alkyldiols, with the exception of 2,3-butanediol, had higher affinities for mouse liver alcohol dehydrogenase than ethylene glycol. Propylene glycol (27.2 mmol/kg), 1,2-butanediol (11.2 mmol/kg), and 1,3-butanediol (22.3 mmol/kg) were the only alkyldiols found to protect mice. Acute and delayed toxicity and hexobarbital sleeping time studies indicated that the alkyldiols which protected the mice were, in general, the least toxic and least hypnotic of the alkyldiols. Therapeutic ratios found by dividing the 144 hr LD50 of an antidote by the dose which produced the maximum antidotal effect were 3.17 for ethanol, 2.56 for pyrazole, 6.16 for propylene glycol, 4.15 for 1.2-butanediol, and 5.11 for 1,3-butanediol. These data suggest that the alkyldiol antidotes are effective and may be safter than either ethanol or pyrazole.     

Effect of papain on bee venom toxicity

The use of Adolph's Meat Tenderizer, which contains the enzyme papain, has been recommended for the treatment of bee stings, although no controlled animal or clinical data existed to support this treatment. Using mice as the test animals, we could find no evidence for antagonism of bee venom lethality or intradermal lesions by papain or Adolph's Meat Tenderizer administered following the venom. It therefore can be tentatively concluded that no positive effect would be expected by the application of these preparations in the usual clinical situation. Inactivation of bee venom only occurred when the venom and papain were mixed together prior to injection. In contrast, hydrocortisone ointment 0.5% was highly effective in decreasing the size of lesions produced by the prior intradermal injection of bee venom.     

Tissue levels of saccharin in the rat during two-generation feeding studies

A single oral dose of [³H]saccharin was given to female rats in late pregnancy. The concentrations of ³H in the tissues of fetal rats 6 to 12 hr after the dose were lower than those in the mother. However, the concentrations in fetal tissues, including bladder wall, decreased more slowly, so that by 48 hr they exceeded the corresponding values obtained for maternal tissues, suggesting the possibility of accumulation during chronic intake. Despite this, the steady-state concentrations of saccharin in the liver and kidneys of fetuses from mothers fed a 5% saccharin diet ad libitum were lower than the corresponding materal values, while the concentrations in the fetal bladder were similar or slightly higher. The concentrations of saccharin in the tissues of rats in utero were not markedly higher than those found in adult F₁ animals. The turnover of saccharin in the fetuses of animals maintained on 5% saccharin diet was similar to that seen after a single dose. The results showed no evidence of excessive accumulation in the bladder wall or other tissues of male rats during in utero exposure or during lactation, which could explain the reported sex and generation specificity of the tumorigenic response.     

A comparison of xenobiotic metabolism in cells isolated from rat liver and small intestinal mucosa.

The metabolism of several foreign compounds has been investigated in viable isolated liver and intestinal mucosal cells. Glucuronic acid and sulphate conjugation was observed in both cell preparations with respect to phenol. Conjugation of 1-naphthol was also observed in isolated intestinal cells. Acetanilide was the only metabolic product of aniline observed with intestinal cells. N-Acetylation was also found to be the major pathway of aniline metabolism in liver cells but p-hydroxylation followed by O-conjugation were also important reactions. Intestinal cells thus appear to be generally effective in conjugation reactions. However, in contrast to hepatocytes the intestinal cells were unable to form glycine conjugates from benzoic acid. The metabolism of 7-ethoxycoumarin and 7-hydroxycoumarin was investigated in isolated intestinal cells from control, 3-methylcholanthrene and phenobarbitone pretreated rats. Glucuronic acid and sulphate conjugation rates of 7-hydroxycoumarin appeared to be unaffected by these pretreatments whereas increases in 7-ethoxycoumarin O-deethylation were observed.     

The effect of dietary restriction and altered sodium intake on the cardiopulmonary toxicity of monocrotaline pyrrole

Monocrotaline pyrrole (MCTP) is a reactive metabolite of the plant toxin monocrotaline (MCT), which produces pulmonary vascular injury and right ventricular hypertrophy in rats. In this study, the influence of diet restriction on the cardiopulmonary toxicity of MCTP was examined. In rats fed ad libitum, MCTP treatment resulted in increased lung weight, in elevated lactate dehydrogenase (LDH) activity and protein concentration in cell-free bronchopulmonary lavage fluid, and in right ventricular enlargement. Restriction of feed intake to 40% of normal attenuated the increases in lung weight and lavage protein concentration in MCTP-treated rats and abolished the right ventricular enlargement but did not affect the increased lavage LDH activity. In a study of the effect of diet restriction on the survival of MCTP-treated rats, the percentage of diet-restricted animals surviving was significantly higher than that of surviving animals which ate ad libitum through Day 28, but thereafter there was no significant difference between the two groups. Alterations in dietary sodium intake alone did not affect MCTP-induced toxicity. These results indicate that diet restriction partially protects against the cardiopulmonary toxicity due to MCTP, and that this protective effect cannot be explained by changes in salt intake.     

Interactions of chlorpheniramine ethanol combinations: acute toxicity and antihistaminic activity

Significant toxicologic and pharmacologic interactions occurred between chlorpheniramine maleate and 25% $\text{v}\text{v}$ ethanol at several dosage combinations. Conditions of both independence and antagonism of acute toxicity were observed in LD50 determinations of chlorpheniramine-ethanol combinations in mice, and confirmed expected results based on the toxicologic pattern of the agents when administered singly. Enhancement of the antihistaminic action of chlorpheniramine by ethanol was demonstrated during histamine-aerosol challenge studies in guinea pigs.     

Neuropharmacology of the afferent projections from the lateral habenula and substantia nigra to the anterior raphe in the rat

Previous neuroanatomical studies have demonstrated the existence of major afferent projections to the nucleus raphe dorsalis originating in the lateral habenula and substantia nigra. These projections have a predominantly suppressive effect on raphe unit activity. The present acute electrophysiological study in anesthetized rats evaluated: (a) the effects of pharmacological blockade of GABAergic transmission on the suppression of activity of units in the nuclei raphe dorsalis and raphe medianus by stimulation of the lateral habenula, and (b) the effects of pharmacological blockade of GABA, dopamine, acetylcholine, glycine, opiates, serotonin, norepinephrine and histamine on the suppression of raphe activity by electrical stimulation of the substantia nigra. Results showed that the GABA bloeker, picrotoxin, attenuated the effects of lateral habenula stimulation on unit activity in the raphe dorsalis and medianus and that GABA may exert a tonic inhibitory influence on spontaneous unit activity in the raphe. The effects of stimulation in the nigra on raphe dorsalis and medianus neuronal activity were not blocked by any of the 10 drugs tested. Indirect evidence was obtained, however, that norepinephrine and possibly histamine exerted an excitatory effect on raphe units since drugs which block these transmitters tended to enhance the suppressive effects of nigral stimulation. The present results do not permit identification of the neurotransmitter which mediates the marked suppression of unit activity in the anterior raphe produced by electrical stimulation of the substantia nigra.     

Acute toxicity of polyethylene glycol p-isooctylphenol ether in Syrian hamsters exposed by inhalation or bronchopulmonary lavage

Dose-response studies were conducted with Syrian hamsters exposed to polyethylene glycol p-isooctylphenyl ether (Triton X-100) via inhalation or bronchopulmonary lavage. Syrian hamsters were exposed to an aerosol of Triton X-100 with a mass median aerodynamic diameter of 1.5 μm and a concentration of 3.0 mg/liter. Estimated initial lung burdens of Triton X-100 ranged from 800 to 3100 μg. Hamsters were lavaged with concentrations of Triton X-100 ranging from 0.01 to 0.10% in isotonic saline resulting in initial lung burdens of Triton X-100 that ranged from 300 to 3200 μg. The $\text{LD}\text{50}\text{7}$ values were 1700 μg (1300–2100 μg, 95% confidence limits) for the inhalation study and 2100 (1900–2700) μg for the lavage study. The difference between the $\text{LD}\text{50}\text{7}$ values for the two methods of exposure was not significant. However histopathological examination revealed differences in the nature and distribution of pathologic changes observed in animals exposed by the two routes of administration. Animals exposed by inhalation died as a result of ulcerative laryngitis and laryngeal edema with only minimal pulmonary pathologic alterations. Animals exposed by lavage, where the larynx was not exposed to Triton X-100, died from pulmonary edema and acute exudative pneumonia, these results demonstrate the need for careful selection of exposure methods to meet the specific objectives of a toxicology study.     

Involvement of 5-hydroxytryptamine in the central control of respiration, blood pressure and heart rate in the anaesthetized rat.

5-Hydroxytryptamine (5-HT, 1 ng-25 μg) injected into the cerebral ventricles of urethananaesthetized rats produced a rise in blood pressure, a biphasic change in heart rate and a decrease in ventilation. Responses were largest after injections into the 3rd ventricle. Lateral ventricle injections produced smaller responses while 4th ventricle injections produced the least response. The cardiovascular responses were prevented or reduced by prior intraventricular injection of bromolysergic acid diethylamide. The pressor response was not blocked by hexamethonium (10 mg/kg i.v.) and was only partly reduced by pretreatment with either 6-hydroxydopamine (3 × 100 mg/kg i.v.) or atropine methonitrate (10 mg/kg i.v.). The pressor response was prevented by spinal transection at C1 or C3 but only slightly reduced by transection at C5 or C7. In animals curarized and artificially respired with air, the blood pressure response was reduced. It is conjectured that the rise in blood pressure may involve a direct effect of hypoxia or hypercapnia resulting from a decrease in respiratory activity which is in turn mediated by a direct action of 5-HT on structures lining the 3rd ventricles. There appears to be little or no involvement of the autonomic nervous system in the response. The fall in heart rate is mediated sympathetically.     

Disposition of 1,2,3-trichloropropane in the Fischer 344 rat: conventional and physiological pharmacokinetics

To investigate the disposition of 1,2,3-trichloropropane (TCP), [14C]-TCP was administered iv to male Fischer 344 rats. Unchanged TCP and total radiolabel were determined in tissues and excreta at varying intervals after administration. The compound was distributed and eliminated rapidly. Initial and terminal half-lives of unchanged TCP in the blood were 0.29 and 23 hr. Adipose tissue accumulated 37% of the dose within 15 min and retained more of the dose than any other tissue until 4 hr; most (69%) of the radiolabel in adipose tissue through 4 hr was unchanged TCP. After 4 hr, the liver contained the largest fraction of the dose, primarily as metabolites. Thus TCP disappeared from adipose tissue while metabolites appeared in liver and other tissues. Excretion was nearly complete (90% of the dose) in 24 hr and was predominantly via the urine (47% of the dose). Expiration was the only route by which unchanged TCP (5% of the dose) was excreted. In addition, 25% of the dose was expired as carbon dioxide. There were numerous other metabolites, none accounting for more than 10% of the dose. Nonvolatile metabolites were longer lived than the parent compound. On the basis of high water solubility, reaction with 2,4-dinitrofluorobenzene, and diminished radiolabel in bile of glycidol-treated rats, glutathione conjugation is suggested as an important metabolic route for TCP. A physiological pharmacokinetic model was developed to describe the time course of trichloropropane concentration in tissues. The model demonstrates the possibility of using physiological and pharmacokinetic data to predict concentration-time relations for toxic compounds.     

Potentiation of duodenal ulcerogenic action of acrylonitrile by PCB or phenobarbital in the rat

Pretreatment of rats with the polychlorinated biphenyl (PCB) Aroclor 1254 or phenobarbital markedly increased the duodenal ulcerogenic action of acrylonitrile. The extent of forestomach and hepatic lesions in these rats, on the other hand, was not modified. The duodenal ulcers produced by Aroclor 1254 and acrylonitrile morphologically resembled the ulcers induced in other animal models of the human duodenal ulcer disease. The possible mechanisms of this potentiation of acrylonitrile action are discussed.     

Toxicity of free and liposome-encapsulated adriamycin following large volume,short-term intraperitoneal exposure in the rat

The effect of liposome encapsulation on toxicity of the anticancer drug adriamycin (ADR) was studied using large volume intraperitoneal (ip) administration. Concebtrations of 5, 20, and 75 μg/ml of free ADR, ADR encapsulated within lipid vesicles, or ADR in the presence of empty lipid vesicles were tested. The most prominent toxic effect was peritonitis, characterized by accumulation of peritoneal fluid, abdominal adhesions, and histologic evidence of inflammation. Two days after treatment, peritonitis was marginally less with encapsulated than with free ADR. Fourteen days after treatment, peritonitis was generally more severe in the encapsulated 20 μg/ml group than in the free ADR group. At 75 μg/ml the effects of encapsulation on local toxicity were mixed, although the systemic effects were less severe with encapsulation. A generalized hyperlipidemia (Day 14) and elevated LDH levels (Day 2) produced by the highest dose of free ADR were not observed in rats receiving encapsulated ADR. It is concluded that at the concentrations tested, encapsulation appears to offer minimal advantage in reducing local toxicity, but that it may be of benefit in reducing the incidence and severity of systemic toxicity resulting from large volume ip administration of ADR.     

Fetal toxicity of cadmium in the rat: Decreased utero-placental blood flow

Previous studies have shown that fetuses can tolerate direct injections of CdCl₂ in amounts greater than those which cross the placenta following maternal injections. Thus, fetal death is not the result of direct effects of cadmium on the fetus. Alterations in utero-placental blood flow were investigated as a possible mechanism of fetal toxicity. Organ blood flow was measured using the microsphere technique. Utero-placental blood flow was unchanged from control values 8–10 hr following 40 μmol/kg CdCl₂ on Day 18 but was reduced 40 and 73% from control values at 12–16 and 18–24 hr, respectively. Fetal death increased from 5 to 20 to 60% during the same time periods. Blood flow to maternal organs was unchanged from control values with the exception of the adrenal after 12–16 hr and myometrium at 18–24 hr. Histologic examination of placentae indicated that the placental necrosis, fetal death, and utero-placental blood flow alterations occurred over a similar time period. Thus, a decrease in placental blood flow was associated with placental necrosis and fetal death. However, it is not apparent whether placental necrosis was a cause or an effect of the decrease in utero-placental blood flow.     

Sulfate absorption from the airways of the isolated perfused rat lung.

The kinetics of sulfate absorption from the airways of the isolated perfused rat lung are presented. Absorption of sulfate ion appears to be by simple diffusion and to be enhanced in the presence of ammonium ion at low concentrations. The $\text{t}\text{1}\text{2}$ for the initial rate was 11.9 ± 1.4 min. The administration of 1 μmol of (NH₄)₂SO₄ intratracheally led to a rapid decrease in the respiratory volume of the lung, an effect which could be blocked by prior perfusion with mepyramine maleate (10^?5m). Ammonium sulfate caused a rapid release of a large portion of the histamine stores into the lung perfusate. The results suggest that sulfate compounds are absorbed rapidly by the lung and that histamine release may occur during absorption. The biological effects of sulfate-containing aerosols may be related to the liberation of histamine reserves.     

Evidence for the nonenzymatic and irreversible binding of cytembena to rat liver microsomes in vitro

Characteristics of the irreversible binding of cytembena (CYT) to rat liver microsomal proteins have been investigated in vitro. Binding of [¹⁴C]CYT to rat liver microsomal proteins remained unchanged in the presence of SKF-525A or after heat denaturation and was not dependent upon the presence of pyridine nucleotide (NADPH or NADH). Ethacrynic acid, cysteine, dithiothreitol, and lysine were found to block the irreversible binding of [¹⁴C]CYT to microsomal proteins in a dose-dependent manner. The rank order of effectiveness as inhibitors of CYT binding was ethacrynic acid > cysteine > dithiothreitol > lysine. In other studies, CYT was shown to preferentially form adducts with cysteine rather than lysine or glycine. Using structural analogs and metabolites of CYT, it was found that 4-methoxybenzoylacrylic acid and β-benzoylacrylic acid were effective competitors of [¹⁴C]CYT binding to liver microsomal proteins. By contrast, 4-methoxybenzoylpropionic acid, 5-(4-methoxyphenyl)dihydro-2(3H)furanone and 4-hydroxy-4-(4-methoxyphenyl)butyric acid were ineffective as inhibitors of the irreversible binding of CYT. These data suggest that sulfhydryl groups are involved in the nonenzymatic binding of CYT and that the presence of a carbon-carbon double bond in CYT, in debrominated metabolites or structural analogs, is requisite for an interference of the binding of CYT to microsomal proteins.