The Relationship of pK a and Acute Skin Irritation in Man

The relationship between pK _a and skin irritation in man is studied for a homologous series of benzoic acid derivatives, which permeate through human skin at comparable rates (15–88 µg/cm²/hr). Skin irritation and pK _a are correlated for pK _a 4. Laser Doppler velocimetric assessment of skin blood flow, color meter readings, erythema, edema, and the primary irritation index are all linearly correlated and related to pK _a, erythema at 24 hr appears to be the most sensitive parameter to variation in pK _a when pK _a 4.     

Relationships Between Histological and Functional Indices of Acute Chemically Induced Nephrotoxicity

Relationships Between Histological and Functional Indices ofAcute Chemically Induced Nephrotoxicity. Miyajima, H., Hewitt,W.R., Côté, M.G., and Plaa, G.L. (1983). Fundam.Appl. Toxicol. 3: 543–551. Acute renal injury was producedin rats with K₂Cr₂O₇ (5–40 mg/kg, sc) HgCl₂ (0.5–5.0mg/kg, sc) or cephaloridine (0.5–3.0 g/kg, sc). Histological(percentage of normal, degenerated or necrotic cells) and functionalindices (relative kidney weight, renal cortical slice accumulationof organic ions, and blood urea nitrogen content) were evaluated48 hours later. The relative sensitivity of each of these indiceswas determined for each nephrotoxicant. Renal cortical accumulationof organic ions appeared to be the most sensitive of the functionalparameters. A quantitative histological evaluation was foundto be as sensitive an indicator of nephrotoxicity as organicion accumulation. Alterations in each of the functional indiceswere significantly correlated with changes in renal histology.     

Subchronic Oral and Intravenous (iv) Safety Evaluation and Pharmacokinetics in Rats and Dogs of Ipazilide Fumarate (Win 54, 177-4), an Antiarrhythmic Agent

Ipazilide fumarate (Win 54,177-4) is a chemically novel antiarrhythmicagent that prolongs ventricular refractoriness and possessesantiectopic activity. Subchronic (29 days) nonclinical safetyevaluation of ipazilide was conducted following oral and ivadministration in Sprague-Dawley rats (20–320 mg/kg oraland 1.25–10 mg/kg iv) and 14 and 28 days in beagle dogs(3–30 mg/kg oral and 2.5–20 mg/kg iv). The pharmacokineticparameters of ipazilide indicate that ipazilide is absorbed(t_max 1 hr) in fasted rats and dogs following single and repeatedoral administrations. The apparent elimination half-life inthe two species is approximately 1 hr (except in rats at a dosageof 320 mg/kg), suggesting rapid clearance. Increases in liverweights (rats 320 mg/kg) accompanied by the observation of centrilobularhypertrophy of hepatocytes were considered an expression ofan adaptive metabolic response of the liver to ipazilide andmay be associated with the induction of microsomal enzymes.Duodenal villous atrophy and epithelial hyperplasia (rats, 80and 320 mg/kg) were interpreted to represent an irritant responseto the drug. Local irritation was also observed at the injectionsite in rats and dogs. Dogs tolerated the oral and the iv administrationof ipazilide at dosages of up to 30 and 20 mg/kg, respectively.Despite emesis (oral dogs), which was reduced in frequency followingrepeated treatment over several weeks, plasma levels in treateddogs (i.e., C_max 4–5 µg/ml) were approximately twicethat required to convert spontaneous arrhythmias in the conscious dog model 24 hr after myocardial infarction. Moreover,plasma levels (C_max 6–7 µg/ml) of iv-treated dogswere approximately three times higher than the efficacious levelsin the dog model and did not cause adverse effects except emesis.Electrocardiographic changes (i.e., increased P wave and QRSdurations, and T wave alterations) in dogs were transient andrepresented an extension of the pharmacological effects of ipazilide.In summary, since ipazilide, at multiple therapeutic dosages,was well tolerated in rats and dogs, it may be considered anappropriate drug for clinical evaluation of safety and efficacyin humans as a potential antiarrhythmic agent. The safety profileof ipazilide in clinical trials is currently ongoing.     

Cardiovascular Effects of Fumonisins in Swine

Fumonisins, mycotoxins produced by Fusarium moniliforme, inducehepatic damage and acute lethal pulmonary edema in swine. Weexamined the cardiovascular effects of short-term fumonisinexposure in anesthetized and conscious male cross-bred pigsweighing 30–36 kg. Culture material containing fumonisinsat 20 mg/kg/day (fumonisin B₁ and B₂ backbone) was added tothe feed of treated pigs (n = 5) for 7 days, while control pigs(n = 5) were fed a diet free of fumonisins. On Day 8, pigs wereanesthetized with halothane and instrumented with Swan-Ganzcatheters to facilitate hemodynamic measurements. Mean pulmonaryartery pressure, central venous pressure, heart rate, cardiacoutput, and electrocardiographic variables were recorded andstroke volume was calculated. All measurements were repeatedat least 18 hr after recovery from anesthesia. Pigs fed fumonisinshad a significant increase in mean pulmonary artery pressure,accompanied by decreased heart rate, cardiac output, and mixedvenous oxygen tension. The electrocardiogram was normal, andthere was no evidence of pulmonary edema formation either histologicallyor by altered lung wet/dry weights. This study suggests thatpulmonary hypertension caused by hypoxic vasoconstriction maybe associated with the pulmonary edema observed in fumonisintoxicity.     

Chloroform Hepatotoxicity in the Mongolian Gerbil

Chloroform Hepatotoxicity in the Mongolian Gerbil. EBEL, R.E., BARLOW, R., and MCGRATH, E. A. (1987). Fundam. Appl. Toxicol.8, 207–216. CHCl₃ hepatotoxicity was studied in the maleMongolian gerbil and compared to that in the male Sprague–Dawleystrain rat. Based on elevations in serum transaminase activitiesin response to CHCl₃ exposure, control gerbils were more sensitiveto CHCl₃ than were gerbils treated with phenobarbital, chlordecone,mirex, or 3-methylcholanthrene. The increased sensitivity ofthe control relative to the induced gerbil was consistent withearlier observations of CCl₄ hepatotoxicity (Ebel, R. E., andMcGrath, E. A., 1984, Toxicol. Lett., 22, 205–210). Microsomalenzyme concentrations or activities were not decreased in thecontrol or induced gerbils in response to CHCl₃ exposures ofup to 200 µl/kg. At a dose of 500 µl/kg, cytochromeP-450 and its reductase were decreased by about 25% in the chlordecone-inducedgerbil. In contrast, chlordecone- and phenobarbital-inducedrats were sensitive to CHCl₃ as evidenced by marked elevationsin serum transaminase activities, decreases in microsomal enzymeconcentrations or activities, and a transient decrease in hepaticnonprotein sulfhydryl groups. Control rats were insensitiveto CHCl₃. Histopathological changes in the livers of these animalswere consistent with alterations in the biochemical parametersmeasured. The relationship between sensitivity to the hepatotoxiceffects of CHCl₃ and CCl₄ was different for the gerbil and rat.     

Maternotoxicity and Fetotoxicity of an Angiotensin-Converting Enzyme Inhibitor, Enalapril, in Rabbits

Maternotoxicity and Fetotoxicity of an Angiotensin-ConvertingEnzyme Inhibitor, Enalapril, in Rabbits. MINSKER, D. H., BAGDON,W. J., MACDONALD, J. S., ROBERTSON, R. T., AND BOKELMAN, D.L. (1990). Fundam. Appl. Toxicol 14, 461–470. When enalapril,an angiotensin-converting enzyme (ACE) inhibitor, was orallyadministered to inseminated rabbits at dosages of 0.1 to 30mg/kg/day for 13 days in a range-finding study, nephrotoxicity,as measured by elevated serum urea nitrogen concentrations,occurred at 1 mg/kg/day and higher dosages and significant (p 0.05) increases in fetal wastage were observed at dosages aslow as 3 mg/kg/day. Saline supplementation during treatmentprevented this rise in urea nitrogen. Fetal wastage was significantly(p 0.05) increased in the absence of maternotoxicity when saline-supplementedfemales were treated with enalapril at 30 mg/kg/day. A developmentaltoxicity study of enalapril in saline-supplemented rabbits producedno evidence of teratogenicity at 3, 10, and 30 mg/kg/ day. Theperiod of sensitivity of fetuses to the toxic effects of enalaprilwas found to be limited to middle-to-late gestation (GestationalDays 14-27). A single oral dose of enalapril (30 mg/kg) on Day26 of gestation resulted in 100% fetal deaths. On the basisof the work done by Broughton Pipkin el al. [1982, J. Physiol.(London) 323, 415–422] and Broughton Pipkin and Wallace(1986, Brit. J. Pharmacol 87, 533–542), which demonstratedthat the sheep fetus becomes markedly hypotensive when the damis treated with captopril or enalapril during late pregnancy,we believe that the observed fetotoxicity of enalapril in rabbitsis also due to fetal hypotension. On the basis of publishedevidence indicating that the renin-angiotensin system in rabbitsand in humans is not developed until middle-to-late gestation,we believe our results support the premise that incidental exposureto enalapril early in human pregnancy is unlikely to be associatedwith an increased risk of fetotoxicity. However, our resultsand those cited above demonstrate that ACE inhibitors are fetotoxicin late gestation in rabbits and sheep, and should be givenin pregnancy only if the potential benefit justifies the potentialrisk to the fetus.     

Skin Tumorigenic Potential of Crude and Refined Coal Liquids and Analogous Petroleum Products

Skin Tumorigenic Potential of Crude and Refined Coal Liquidsand Analogous Petroleum Products. WITSCHI, H. P., SMITH, L.H., FROME, E. L., PECQUET-GOAD, M. E., GRIEST, W. H., HO. C.-H.,AND GUERIN, M. R. (1987). Fundam. Appl. Toxicol 9, 297–303.The skin tumorigenic potential of seven complex hydrocarbonmixtures was determined: a coal-derived raw blend composed oflight and heavy oils, a low- and high-severity hydrotreatedproduct of that blend, and naphthas and fuel oils from the rawblend or from natural petroleum. Male and female C3H/Bd_f micewere exposed three times per week to each test mixture by dermalapplication of 50 µl of neat, 50, or 25% (w/v) preparations.Room, vehicle, and benzo[a] control groups were run concurrently.The raw blend produced an almost 100% incidence of skin tumorsat all three doses while tuniorigenicity was considerably decreasedby hydrotreating the blend both in terms of incidence and onset.The tumongenicities of the naphthas and fuel oils derived fromthe raw blend or from petroleums were low relative to that ofthe parent mixture. Although tumorigens in the raw blend weremuch reduced by hydrotreatment, tumori genicity of the otheragents did not parallel the content of polycyclic aromatic hydrocarbonsknown to be good tumor initiators.     

In Vivo Percutaneous Absorption of Boric Acid, Borax, and Disodium Octaborate Tetrahydrate in Humans Compared to in Vitro Absorption in Human Skin from Infinite and Finite Doses

Literature from the first half of this century report concernfor toxicity from topical use of boric acid, but assessmentof percutaneous absorption has been impaired by lack of analyticalsensitivity. Analytical methods in this study included inductivelycoupled plasma-mass spectrometry which now allows quantitationof percutaneous absorption of ¹⁰B in ¹⁰B-enriched boric acid,borax, and disodium octaborate tetrahydrate (DOT) in biologicalmatrices. This made it possible, in the presence of comparativelylarge natural dietary boron intakes for the in vivo segmentof this study, to quantify the boron passing through skin. Humanvolunteers were dosed with ¹⁰B-enriched boric acid, 5.0%, borax,5.0%, or disodium octaborate tetrahydrate, 10%, in aqueous solutions.Urinalysis, for boron and changes in boron isotope ratios, wasused to measure absorption. Boric acid in vivo percutaneousabsorption was 0.226 (SD = 0.125) mean percentage dose, withflux and permeability constant (K_p) calculated at 0.009 µg/cm²/hand 1.9 x 10^–7 cm/h, respectively. Borax absorption was0.210 (SD = 0.194) mean percentage of dose, with flux; and K_pcalculated at 0.009 µg/cm²/h and 1.8 x 10^–7 cm/h,respectively. DOT absorption was 0.122 (SD = 0.108) mean percentage,with flux and K_p calculated at 0.01 µg/cm²/h and 1.0 x10^–7 cm/h, respectively. Pretreatment with the potentialskin irritant 2% sodium lauryl sulfate had no effect on boronskin absorption. In vitro human skin percentage of doses ofboric acid absorbed were 1.2 for a 0.05% solution, 0.28 fora 0.5% solution, and 0.70 for a 5.0% solution. These absorptionamounts translated into flux values of, respectively, 0.25,0.58, and 14.58     

The Effects of Select Neurotoxic Chemicals on Synaptosomal Monoamine Uptake and K+-Dependent Phosphatase

The Effects of Select Neurotoxic Chemicals on Synaptosomal MonoamineUptake and K⁺-Dependent Phosphatase. Bracken, William M., Sharma,Raghubir P. and Kleinschuster, Stephen J. (1981). Fundam. Appl.Toxicol. 1:432–436. The in vitro inhibition of norepinephrine(NE) and serotonin (5-HT) uptake into rat brain synaptosomesby a diverse group of neurotoxic chemicals was studied. Thetest chemicals included CH₃HgCl, Hg(NO₃)₂, CdCl₂, diisopropylfluorophosphate(DFP), paraoxon, acrylamide and Kepone while chlorpromazineand ouabain were used as reference chemicals. Methylmercuricchloride, Hg(NO₃)₂ and Kepone inhibited the NE and 5-HT uptakewith IC₅₀'s (concentration of chemical inhibiting 50% of uptake)between 10^–4 to 10^–3 M for both amines. Maximalinhibition was 60–100% at 10 3 M. Cadmium chloride, paraoxon,DFP and acrylamide were not inhibitory. The influence of thetest chemicals on synaptosomal K⁺-dependent phosphatase wasstudied. Methylmercuric chloride, Hg(NO₃)₂, CdCl₂ and Keponewere inhibitors of the phosphatase with 50% inhibition (I₅₀)at micromolar concentrations. The phosphatase was most sensitiveto Hg(NO₃)₂ inhibition with an I₅₀ of 0.03 /M. The inhibitoryconcentrations for these chemicals ranged from 10^–7 to10^–3 M. A correlation of the phosphatase and monoamineuptake inhibitions was not suggested from the data. The lowaffinity inhibition (IC₅₀ greater than 10(^–5 M) of theNE and 5-HT uptake by CH₃HgCl, Hg(NO₃)₂ and Kepone suggestedthat this is not a biologically important phenomena. The apparenthigh affinity inhibition (I₅₀ less than 10^–5 M) of thephosphatase demonstrated the specific influences the test compoundscan have on enzymatic processes. Such enzymatic inhibition wouldbe of critical importance if these neurotoxicants were ableto penetrate the synaptic or neuronal membrane.     

Kinetic Studies and Structure--Activity Relationships of Bispyridinium Oximes as Reactivators of Acetylcholinesterase Inhibited by Organophosphorus Compounds

Kinetic Studies and Structure-Activity Relationships of BispyridiniumOximes as Reactivators of Acetylcholinesterase Inhibited byOrganophosphorus Compounds. SU, C-T., WANG, P-H., LIU, R-F.,SHIH, J-H., MA, C., LIN, C-H., LIU, C-Y., AND WU, M-T. (1986).Fundam. Appl. Toxicol. 6,506–514. The kinetics of thereactivation of acetylcholinesterase inhibited by isopropylmethylphosphonofluoridate was studied. The reactivators usedinclude nine bispyridinium monooximes and three bispyridiniumdioximes. The dissociation constant (K₁). and the rate constant(K₂) of dephosphonylation of the complex formed from the organophosphorusacetylcholinesterase (OP-AChE) and the oxime were measured.The reactivation parameters obtained from the in vitro kineticstudies were used to elucidate the structure—activityrelationships. The hydrophobic property of a nonoxime substituentat the 3-position on the pyridinium ring can exert a positiveeffect on their binding affinity to OP-AChE. However, the rateconstants (K₂) of the nucleophiic displacement of OP-AChE byoximes depend negatively on these physical and structural factorsof the oximes. The correlations of the in vivo antidotal efficacy(ED50) of these bispyridinium oximes have been analyzed withtheir pharmacological properties, e.g., reactivation potency,antimuscarinic activities, and antinicotinic activities. However,no satisfactory correlations were observed. It may be concludedthat the detoxication mechanism of poisoning by isopropyl methylphosphonofluoridateis different from those of pinacolyl methylphosphonofluoridateand paraoxon.     

Modulation of Pulmonary Eicosanoid Metabolism following Exposure to Sulfuric Acid

Modulation of Pulmonary Eicosanoid Metabolism following Exposureto Sulfuric Acid. SCHLESINGER, R. B., GUNNISON, A. F., AND ZELIKOFF,J. T. (1990). Fundam. Appl. Toxicol. 15, 151–162. Eicosanoids(arachidonic acid metabolites) are potent biological mediators.Modulation of their metabolism by air pollutants may be a possiblefactor in the pathogenesis of environmentally related lung disease.Sulfuric acid (H₂SO₄) aerosols are components of ambient airin many areas. Rabbits were exposed to H₂SO₄ (0.3 µm)at 250, 500, or 1000 µg/m³ for 1 hr/ day for 5 days. Theywere then euthanized, the lungs lavaged, and eicosanoid analysesperformed by radioimmunoassay of acellular lavage fluid. Anexposure-concentration-dependent decrease in levels of prostaglandinsE₂ and F₂ and thromboxane B₂ was found; no change in leukotrieneB₄ was observed. Tracheal explants exposed to acidic environmentsin vitro also showed reduced production of PGE₂, PGF₂, and TxB₂.Incubation with sodium sulfate (Na₂SO₄ showed no effect of thesulfate ion (SO₄^2–). This study, the first to examineeicosanoid production after in vivo exposure to pure H₂SO₄ droplets,indicates that such exposure can modulate arachidonic acid metabolism,and that this is likely due to the deposition of hydrogen ion(H⁺ on target issue.     

Pharmacokinetic Fate of14C-Labeled Deoxynivalenol in Swine

Pharmacokinetic Fate of ¹⁴C-Labeled Deoxynivalenol in Swine.PRELUSKY, D. B., HARTIN, K. E., TRENHOLM, H. L., AND MILLER,J. D. (1988). Fundam. Appl Toxicol. 10,276-286. The pharmacokineticsof the trichothecene mycotoxin deoxynivalenol (DON) was investigatedin swine following intravenous (0.30 mg, 0.35 µCi/kg)and intragastric (0.60 mg, 0.60 µCi/kg) administrationof the ¹⁴C-labeled toxin. After iv dosing, plasma concentrationdata favored a three-compartment open model with half-life valuesfor the rapid distribution (), slower distribution (ß),and terminal elimination () phases of 5.8, 96.7, and 510.0 min,respectively. The apparent volume of distribution (V') was 1.34liter/kg, the volume of the central compartment (K_c) was 0.166liter/kg, and the plasma clearance was 1.81 ml/min/kg. DON wasrapidly cleared essentially unchanged (>95%), and was excretedprimarily in unne (86–104%), with minor elimination inbile (3–5%). Following intragastric dosing DON was veryrapidly absorbed, reaching near peak plasma levels within 15–30min. Levels remained elevated (63-325 ng/ml) for approximately9 hr, and began declining slowly (t ß= 7.1 hr) thereafter.The calculated systemic bioavailability (F) was between 48 and65%, although urinary and biliary recoveries indicated marginallygreater absorption actually occurred (54–85%). Overall,although DON was eliminated rapidly and completely within 24hr following a single iv or intragastric dose, data suggestthat residues may undergo temporary sequestration in a tissuedepot.     

Estimation of Octanol-Water Partition Coefficients and Correlation with Dermal Absorption for Several Polyhalogenated Aromatic Hydrocarbons

n-Octanol-Water partition coefficients (K_ow)were experimentallyestimated for: 2,3,7,8-tetrachloro- and 2,3,7,8-tetrabromodibenzo-p-dioxin;2,3,7,8-tetrachloro-, 2,3,7,8-tetrabromo-, and 1,2,7,8- tetrabromodibenzofuran;1,2,3,7,8- pentachioro-, 1,2,3,7,8-pentabromo-, 2,3,4,7,8-pentachloro-,and 2,3,4,7,8- pentabromodibenzofuran; 1,2,4,6,8,9-hexachlorodibenzofuran(HxCDF), and 3,4,3',4'-tetrachlorobiphenyl (3,4,3',4'-TCB).The method involved correlation of literature K_ow with reversephasehigh-performance liquid chromotography (RP-HPLC) retention timefor a series of 23 calibration standards and estimation of K_owfor test compounds from measured RP-HPLC retention. Retentiontimes for all standards and test chemicals were measured induplicate on the same octadecasilane (C₁₈ reverse-phase columnwith an isocratic 85:15 methanol:water mobile phase; soluteswere detected by uv absorbance (254 nm). Literature log K_owvalues used for the calibration standards had been measuredexclusively by the generator column method. Log K_ow estimatesfor the test compounds in the present study ranged from 5.45for 3,4,3',4'-TCB to 6.81 for HxCDF. K_ow estimates were thenplotted against laboratory data for the in vivo 3-day dermalabsorption of single equimolar doses (200 pmol and 20 nmol,or 1 nmol/kg and 0.1 µmol/kg) of selected test compoundsin male F344 rats. Strong inverse correlations were found betweenoctanol-water partition coefficient estimates and single-dosedermal absorption for most of the compounds studied. In addition,RP-HPLC retention time itself appeared to be as equally suitedas K_ow to such correlations with dermal absorption. The structure-activityrelationships suggested in this study were sought in order toexplain observed differences in the dermal absorption of polyhalogenateddibenzo-p-dioxin, dibenzofuran, and biphenyl congeners differingin number, position, and/or type (Cl or Br) of halogen substituents.Moreover, these results should be of predictive value in therisk assessment of dermal exposure to polychlorinated dibenzo-p-dioxins,dibenzofurans, biphenyls, and their brominated analogues.     

Effects of ClO2 on the Absorption and Distribution of Dietary Iodide in the Rat

Effects of ClO₂ on the Absorption and Distribution of DietaryIodide in the Rat HARRINGTON, R. M., SHERTZER, H. G., AND BERCZ,J. P. (1985). Fundam. Appl. Toxicol. 5, 672–678. Aqueouschlorine dioxide (ClO₂g), an alternative disinfectant for drinkingwater, was found to decrease gastrointestinal (GI) bioavailabilityof dietary iodide. It has been previously reported that subchronicexposure to ClO₂ decreases thyroxine (T₄) levels in nonhumanprimates. In this study in vitro experiments with animal feed,isolated rat stomachs, as well as in vivo studies with intactrats, showed that ClO₂ in drinking water (at in situ concentrationsas low as 2 ppm) oxidizes iodide to its reactive elemental (radical)state, binding it to organic substances present in the GI tract.A single instance of acute exposure to ClO₂, however, did notdecrease blood iodide levels, or thyroid glandular uptake ofiodine     

Effects of Chlorpyrifos on High-Affinity Choline Uptake and [3H]Hemicholinium-3 Binding in Rat Brain

High, subcutaneous doses of the organophosphorus insecticidechlorpyrifos (CPF) in adult male rats can be well-tolerateddespite extensive and persistent acetylcholinesterase (AChE)inhibition. We propose that changes in acetylcholine synthesiscould modulate the toxicity associated with extensive AChE inhibitionfollowing CPF exposure. High-affinity choline uptake (HACU,the rate-limiting step in acetylcholine synthesis) and bindingto [³H]-hemicholinium-3 (HC-3, a specific ligand for the cholinetransporter) were chosen as indicators of acetylcholine synthesis.Female, Sprague-Dawley rats (220–280 g) were treated witheither vehicle (peanut oil, 2 ml/kg, sc) or CPF (280 mg/kg,2 ml/kg, sc), examined daily for clinical signs of toxicity,and sacrificed 1, 2, or 7 days later for neurochemical measurements{AChE inhibition, muscarinic receptor binding using [³H]quinuclidinylbenzilate (QNB) and [³H]cis-methyldioxolane (CD) as ligands,HACU and [³H]HC-3 binding} in frontal cortex. Despite extensiveAChE inhibition (90–93%) at all time points, relativelyminor degrees of overt toxicity were noted in CPF-treated rats.Binding to the non-selective muscarinic antagonist [³H]QNB wasreduced (10–34%), whereas binding to the putative m2-selectiveagonist [³H]CD was increased (15–23%) at all three timepoints. HACU was reduced (20%) in crude synaptosomes preparedfrom CPF-treated rats 1 day following exposure but no significantchanges were noted at 2 or 7 days after treatment. CPF-oxon,the active oxidative metabolite of CPF, was a weak inhibitorof HACU in vitro (IC₅₀>200 µM). Binding to [³H]HC-3was reduced in a dose-related manner 1 day after CPF exposure.Kinetic analyses of [³H]HC-3 binding 1 day after CPF (280 mg/kg)indicated a significant reduction in density {B_max: control,187±18 fmol/mg protein; CPF, 104±12 fmol/mg protein)with no apparent change in binding affinity (K_d: control, 25±3nM; CPF, 19±3 nM). These results suggest that a reductionin HACU/acetylcholine synthesis may contribute, along with compensatorychanges in cholinergic receptors, to the diminished toxicityfollowing extensive AChE inhibition by CPF.     

Uptake of Vinylidene Fluoride in Rats Simulated by a Physiological Model

Uptake of Vinylidene Fluoride in Rats Simulated by a PhysiologicalModel. Medinsky, M. A., Bechtold, W. E., Birnbaum, L. S., Chico,D. M., Gerlach, R. F., and Henderson, R. F. (1988). Fundam.Appl. Toxicol 11, 250–260. The purpose of this study wasto develop a physiological model to simulate the uptake of vinylidenefluoride (VDF), an important plastics monomer, in laboratoryanimals. Male Fischer 344/N rats were exposed nose-only for6 hr to concentrations of VDF ranging from 27 to 16,000 ppm.Tidal volume (mean, 1.51 ml/breath) and respiratory frequency(mean, 132 breaths/min) were not influenced by exposure concentration.Experimentally determined, steady-state blood levels of VDF,obtained by gas chromatog-raphy-head space analysis of samplesfrom rats with indwelling jugular cannulas, increased linearlywith increasing exposure concentration up to 16,000 ppm. VDFtissue/air partition coefficients were determined experimentallyto be 0.07,0.18,0.8, 1.0, and 0.29 for water, blood, liver,fat, and muscle, respectively. These values and calculated constantsfor total body elimination of VDF, K_m and V_max were incorporatedinto the physiological model. Model predictions agreed withthe experimentally determined data. Time to reach steady-stateblood levels of VDF was less than 15 min for all concentrations.After cessation of exposure, blood levels of VDF decreased to10% of steady-state levels by 1 hr. Simulation of the metabolismof VDF indicated that although blood levels of VDF increasedlinearly with increasing concentration the amount of VDF metabolizedper 6-hr exposure period approached a maximum at about 2000ppm VDF.     

Technical Grade but Not Recrystallized {alpha}-Naphthylthiourea Potentiates Superoxide Release by Rat Neutrophils Stimulated in Vitro by Phorbol Myristate Acetate

Technical Grade but Not Recrystallized -Naphthylthiourea PotentiatesSuperoxide Release by Rat Neutrophils Stimulated in VitrobyPhorbol Myristate Acetate. ROTH, R.A., AND BALL, T.M. (1986).Fundam. Appl. Toxicol. 7, 324–328. -Naphthylthiourea (ANTU)causes pulmonary edema and pleural effusion in rats. It hasbeen suggested that ANTU pneumotoxicity may be mediated by bloodneutrophils (PMNs) via the release of reactive oxygen species.Accordingly, we tested the effect of technical grade ANTU (tANTU)on the ability of rat peritoneal PMNs to release superoxide(O₂). tANTU did not itself stimulate O₂ production by PMNs,but it increased the O₂ released in response to PMN stimulationby phorbol myristate acetate (PMA). This effect was dependentupon the amount of tANTU added. In PMNs activated in vitro bya submaximal PMA stimulus, addition of 20 µg/ml tANTUdoubled superoxide release. When tANTU was recrystallized fromethanol, the purified ANTU was not effective in potentiatingthe effect of PMA on PMNs. This suggests that an impurity intechnical grade ANTU is capable of increasing O₂ release bystimulated PMNs. tANTU and recrystallized ANTU caused similarpneumotoxicity in rats in vivo, suggesting that the unidentifiedimpurity does not markedly influence the biologic effects ofANTU.     

Oral Toxicity of Carbon Tetrachioride: Acute, Subacute, and Subchronic Studies in Rats

Oral Toxicity of Carbon Tetrachloide: Acute, Subacute, and SubchronicStudies in Rats. BRUCKNER, J. V., MACKENZIE, W. F., MURALIDHARA,S., LUTHRA, R., KYLE, G. M., AND ACOSTA, D. (1986). Fundam.Appl. Toxicol. 6, 16–34. This investigation was conductedto characterize the acute, subacute, and subchronic toxic potencyof ingested carbon tetrachloride (CCl₄) In the first acute andsubacute toxicity study, male Sprague-Dawley rats of 300–350g were gavaged with 0, 20, 40, or 80 mg CCl₄/kg once daily for5 consecutive days, rested for 2 days, and dosed once dailyfor 4 additional days. Rats of 200–250 g were gavagedwith 0, 20, 80, or 160 mg CCl₄/kg according to the same dosageregimen in the second acute and subacute study. In the firstand second studies one group of rats at each dosage level wassacrificed for clinical chemistry and histopathological evaluationat 24 hr, 4 days, and 11 days after initiation of dosing. Single20- and 40-mg/kg doses had no apparent toxic effect at 24 hr,although 80 mg/kg caused mild hepatic centrilobular vacuolizationand significant increases in some serum enzyme levels. In general,there was progressively severe hepatic injury at each dosagelevel over the 11-day period. CCl₄ was more hepatotoxic to the200–250-g rats than to the 300–350-g rats. In thesubchronic study, rats initially 200–250 g were gavaged5 times weekly for 12 weeks with 0, 1, 10, or 33 mg CCl4/kgBody weight and clinical chemistry indices were monitored duringthe 12 weeks of dosing and 2 weeks after cessation of dosing,A dose of 1 mg/kg had no apparent adverse effect; 10 mg/kg producedslight, but statistically significant increases in sorbitoldehydrogenase activity and mild hepatic centrilobular vacuolization;33 mg/kg caused marked hepatotoxicity. Serum enzyme levels remainedelevated during the 12-week dosing period, but returned towardnormal within 13 days of cessation of CCl₄ exposure. Microscopicexamination of livers of the 33-mg/kg rats revealed cirrhosis,characterized by bile duct proliferation, fibrosis, lobulardistortion, parenchymal regeneration, hyperplastic nodules,and single-cell necrosis. The fibrosis was not reversed withinthe 13-day recovery period.     

Age-Dependent Effect of Ozone on Pulmonary Eicosanoid Metabolism in Rabbits and Rats

Age-Dependent Effect of Ozone on Pulmonary Eicosanoid Metabolismin Rabbits and Rats. GUNNISON, A. F., FINKELSTEIN, I., WEIDEMAN,P., SU, W.-Y., SOBO, M., AND SCHLESINGER, R. B. (1990). Fundam.Appl Toxicol. 15, 779–790. Acute exposures to ozone havepreviously been shown to cause quantitative changes in the spectrumof arachidonic acid (AA) metabolites in lung lavage fluid. Sinceage appears to be an important variable in the toxicity of inhaledozone, we investigated its effect on ozone-induced changes inpulmonary eicosanoid metabolism. Rats and rabbits ranging inage from neonates to young adults were exposed either to airor to 1 ppm ozone for 2 hr. Lung lavage fluid was collectedwithin 1 hr following exposure and analyzed for its contentof selected eicosanoids. In both species, there was a pronouncedeffect of age on ozone-induced pulmonary eicosanoid metabolism.Ozone-exposed animals at the youngest ages examined had severalfoldgreater amounts of two products of the cyclooxygenase pathway,prostaglandin E₂ (PGE₂) and prostaglandin F_2a (PGF_2a), thandid age-matched controls. This effect lessened and eventuallydisappeared as the animals grew toward adulthood. In rabbits,ozone also induced increases in 6-keto-prostaglandin F_1a andthromboxane B₂, but these changes were of lesser magnitude andevident only in the youngest rabbits exposed. There was no observedeffect of ozone on lung lavage content of leukothriene B₄. Indicesof nonspecific pulmonary damage, i.e., protein concentrationin lung lavage fluid and total number and viability of lavagedlung cells, were affected by ozone exposure, but not in an age-dependentmanner that correlated with changes in pulmonary eicosanoidmetabolism. In vitro ozone exposure of lung macrophages fromnaive rabbits of the same age range as those exposed in vivodemonstrated that ozone is capable of stimulating the elaborationof PGF_2a and especially PGE₂. However, the increase in lavagefluid PGE₂ and PGF_2a caused by ozone inhalation could not beattributed to macrophage metabolism conclusively since elaborationof PGE₂ and PGF_2a by cultured macrophages was not enhanced byprior in vivo ozone exposure. In an ancillary study it was shownthat 15-hydroxyprostaglandin dehydrogenase (PGDH) activity inrabbit lung homogenates was not affected by prior exposure toozone, indicating that the increase in lung lavage fluid eicosanoidsthat occurred in these animals could not be explained by inhibitionof PGDH.