Early damage indicators in the lung. III. Biochemical and cytological response of the lung to inhaled metals salts.

The validity of using the enzymatic and cytologic profile of airway fluids to indicate lung damage was tested in animals exposed by inhalation to either a known toxic metallic salt (CdCl₂) or a relatively innocuous salt (CrCl₃). The enzymatic and cytologic response of the airways was compared to histopathological evaluation of lung damage. Syrian hamsters were exposed to an aerosol of CdCl₂ (aerodynamic diameter = 1.7 μm, $\text{σ}{}_{\mathrm{g}}\text{? 1.7}$) to achieve an initial lung burden (ILB) of 0.6 ± 0.3 and 4.4 ± 1.2 μg of CdCl₂ or to an aerosol of CrCl₃ (count median diameter = 1.2 μm, $\text{σ}{}_{\mathrm{g}}\text{? 1.5}$) to achieve an ILB of 0.7 ± 0.2 or 20 ± 10 μg of CrCl₃. Animals were sacrificed at 2 hr, 1, 7, and 21 days after exposure. A sample of airay fluid was obtained by bronchopulmonary lavage and examined for the enzymatic profile of the cell-free fraction and the cytological profile of the cell fraction. Lung tissue enzyme activities were also measured and histopathologic evaluations were made on lung tissue from exposed, but nonlavaged, animals. In the lavage fluid from animals exposed to CdCl₂, the enzymatic and cytologic data demonstrated a dose-response pattern and the airway response preceded enzymatic changes in the lung tissue. Tissue morphological changes correlated well with the biochemical changes. The response of the lung to CrCl₃ was minimal by both morphological and biochemical evaluations. Airway enzymatic and cytologic responses were shown to be potentially useful as indicators of lung damage in toxicological screening programs.     

Lactate dehydrogenase isoenzymes in hamster lung lavage fluid after lung injury

Lactate dehydrogenase (LD) levels and isoenzyme patterns were determined in the cell-free supernatant fractions of lung lavage fluid from hamsters exposed to alpha-quartz, iron oxide, Triton X-100, 100% O₂, or 200 ppm SO₂. The isoenzyme patterns were compared to those derived from hamster lung homogenates, serum, polymorphonuclear neutrophils (PMNs), pulmonary macrophages, and red blood cells. The isoenzyme patterns from alpha-quartz- and iron oxide-exposed animals resembled each other and were similar to that of PMNs. In contrast, the pattern seen after Triton X-100 exposure was similar to those of whole lung homogenates and of red blood cells. A 96-hr exposure to 100% O₂ yielded an LD isoenzyme pattern in lung lavage fluid similar to that of serum. Exposure to SO₂ did not alter LD levels, showing that upper airways damage is not reflected by changes in LD in lung lavage fluid. We conclude that LD isoenzyme patterns of lung lavage fluid can be used to differentiate among types of pulmonary injury and may help identify the sites of injury.     

Early damage indicators in the lung I. Lactate dehydrogenase activity in the airways

The rapid determination of damage in the lung is important in developing screening methods for ranking the toxicity of inhalable pollutants. The presence of lactate dehydrogenase (LDH) activity in the airways was found to be a sensitive indicator of acute toxicity to lung cells. The airway content of LDH increased after bronchopulmonary lavage of Syrian hamsters with increasing amounts of Triton X-100, with a correlation coefficient of 0.98. No increase in iron content of the lavage fluid occurred, indicating that lysed erythrocytes were not the source of the LDH. The isoenzyme pattern of the LDH activity in the lavage fluid suggested the LDH was released from lung cells. The method of detecting early lung injury by the presence of LDH in the airways can be used in one of two ways: The toxic material to be tested may be introduced into the lung by pulmonary lavage and the released LDH may be measured in the same lavage fluid; or in animals exposed to toxicants in aersol form, a lavage can be performed after exposure to obtain a sample of the LDH in the airways.     

Toxicity of N-(phosphonomethyl)glycine to chick embryo

The LD₅₀ values, 12.88 $\text{mg}\text{100 g egg}$ and 13.22 $\text{mg}\text{100 g egg}$, obtained when the N-phosphonomethyl derivative of glycine was injected into the air sacs of White Rock and White Leghorn eggs respectively, were significantly lower (P < 0.01) than the values, (24.72 $\text{mg}\text{100 g egg}$ for White Rocks and 25.44 $\text{mg}\text{100 g egg}$ for White Leghorns) obtained by injection into the yolk sac. These findings suggest that the toxicity of N-(phosphonomethyl)glycine (PMG) to the chick embryo depends on the route of injection.     

Toxicity studies on clove cigarette smoke and constituents of clove: determination of the LD50 of eugenol by intratracheal instillation in rats and hamsters

Eugenol, eugenol acetate, -caryophyllene, and -humulene are constituents of clove and clove cigarette smoke. The toxicity of these compounds was evaluated by intratracheal instillation in male F-344 rats. Eugenol was most toxic in this assay. The LD₅₀ of eugenol was 11 mg/ kg in male F-344 rats and 17 mg/kg in male Syrian golden hamsters. Congestion of the lung with interstitial hemorrhages, acute emphysema, and acute pulmonary edema were among the macroscopic and histologic findings observed in the animals after intratracheal administration of eugenol. Similar effects were not observed with male Syrian golden hamsters exposed to clove cigarette smoke. The estimated daily intake of eugenol for those hamsters exposed to clove cigarette smoke was below 2 mg/kg.     

Studies on the respiratory uptake and excretion and the skin absorption of methyl n-butyl ketone in humans and dogs

Methyl n-butyl ketone (MnBK) has produced peripheral neuropathy in experimental animals and is implicated in an occupationally produced neuropathy. Since occupational exposure to MnBK is by inhalation or skin contact, both the absorption and elimination of MnBK vapor and its absorption through skin were investigated. Studies were carried out first with male beagle dogs and subsequently with human volunteers. Humans exposed for 7.5 hours to 10 or 50 ppm or for 4 hr to 100 ppm of MnBK vapor absorbed between 75 and 92% of the inhaled vapor. Unchanged MnBK was not eliminated extensively in the postexposure breath or in urine. 2,5-Hexanedione, a metabolite of MnBK known to be neurotoxic in rats, was found in the serum of humans exposed to either 50 or 100 ppm of MnBK. The absorption and elimination of MnBK in dogs was similar to that observed in humans. The skin absorption of [1-¹⁴C]MnBK or a $\text{9}\text{1}$ ($\text{v}\text{v}$) mixture of methyl ethyl ketone $\text{(MEK)}\text{[1-}{}^{14}\text{C]MnBK}$ was determined by excretion analysis. Two volunteers exposed by skin contact to [1-¹⁴C]MnBK absorbed 4.8 μg min^?1 cm^?2 and 8.0 μg min^?1 cm^?2, respectively. Skin exposure to $\text{MEK}\text{[1-}{}^{14}\text{C]MnBK}$ resulted in the respective absorption of 4.2 and 5.6 μg min^?1 cm^?2 by two individuals. Two volunteers given an oral dose of [1-¹⁴C]MnBK (2 μCi; 0.1 mg/kg) excreted 49.9 and 29.0% of the dose, respectively, as respiratory ¹⁴CO₂ within 3 to 5 days and 27.6 and 25.0% of the dose, respectively, in urine within 8 days. Both [1-¹⁴C]MnBK and $\text{MEK}\text{[1-}{}^{14}\text{C]MnBK}$ were absorbed through the skin of dogs. These findings show that MnBK is readily absorbed by the lungs, the gastrointestinal tract, and through the skin, is not eliminated extensively unchanged in breath or urine, and is metabolized to CO₂ and 2,5-hexanedione. Radioactivity derived from [1-¹⁴C]MnBK was excreted slowly by man, suggesting that repeated daily exposure to high concentrations of MnBK may lead to a prolonged exposure to neurotoxic metabolites.     

Acute Lung Injury Following Inhalation Exposure to Nerve Agent VX in Guinea Pigs

A microinstillation technique of inhalation exposure was utilized to assess lung injury following chemical warfare nerve agent VX [methylphosphonothioic acid S-(2-[bis(1-methylethyl)amino]ethyl) O-ethyl ester] exposure in guinea pigs. Animals were anesthetized using Telazol-meditomidine, gently intubated, and VX was aerosolized using a microcatheter placed 2 cm above the bifurcation of the trachea. Different doses (50.4 μg/m³, 70.4 μ g/m^m3, 90.4 μg/m^m3) of VX were administered at 40 pulses/min for 5 min. Dosing of VX was calculated by the volume of aerosol produced per 200 pulses and diluting the agent accordingly. Although the survival rate of animals exposed to different doses of VX was similar to the controls, nearly a 20% weight reduction was observed in exposed animals. After 24 h of recovery, the animals were euthanized and bronchoalveolar lavage (BAL) was performed with oxygen free saline. BAL was centrifuged and separated into BAL fluid (BALF) and BAL cells (BALC) and analyzed for indication of lung injury. The edema by dry/wet weight ratio of the accessory lobe increased 11% in VX-treated animals. BAL cell number was increased in VX-treated animals compared to controls, independent of dosage. Trypan blue viability assay indicated an increase in BAL cell death in 70.4 μg/m^m3 and 90.4 μg/m^m3 VX-exposed animals. Differential cell counting of BALC indicated a decrease in macrophage/monocytes in VX-exposed animals. The total amount of BAL protein increased gradually with the exposed dose of VX and was highest in animals exposed to 90.4 μg/m^m3, indicating that this dose of VX caused lung injury that persisted at 24 h. In addition, histopathology results also suggest that inhalation exposure to VX induces acute lung injury.     

Benzene disposition in the rat after exposure by inhalation.

Little information is available on benzene disposition after exposure by inhalation despite the importance of this route in man. Benzene metabolites as a group have been measured in bone marrow, but quantitation of individual metabolites in this target tissue has not been reported. Male Fischer-344 rats were exposed to 500 ppm benzene in air and the uptake and elimination was followed in several tissues. Concentrations of free phenol, catechol, and hydroquinone in blood and bone marrow were also measured. Steady-state concentrations of benzene (11.5, 37.0, and 164.0 μg/g in blood, bone marrow, and fat, respectively) were achieved within 6 hr in all tissues studied. Benzene half-lives during the first 9 hr were similar in all tissues (0.8 hr). A plot of amount of benzene remaining to be excreted in the expired air was biphasic with $\text{t}\text{1}\text{2}$ values for the α and β phases of 0.7 and 13.1 hr, respectively. Phenol was the main metabolite in bone marrow at early times (peak concentration, 19.4 μg/g). Catechol and hydroquinone predominated later (peak concentrations, 13.0 and 70.4 μg/g, respectively). Concentrations of these two metabolites declined very slowly during the first 9 hr. These data indicate that free catechol and hydroquinone persist in bone marrow longer than benzene or free phenol.     

The lack of effects of pretreatment with phenobarbital and chlorpromazine on the acute toxicity of benzene in rats

Female CD rats were injected ip daily for 3 days with either phenobarbital (75 mg/kg) or chlorpromazine (15 mg/kg). On the fourth morning the animals were either subjected to a 4-hr inhalation exposure of benzene or given an ip injection of 50% ($\text{v}\text{v}$) of benzene and mineral oil. Animals were injected with doses of 1, 2, 3 and 4 g benzene/kg body weight. In the inhalation studies, animals were exposed to 6 levels of benzene ranging from 11,500 to 15,500 ppm. The LD50 for animals injected with benzene and the LC50 for animals inhaling benzene were calculated for control groups and those pretreated with either phenobarbital or chlorpromazine. Neither the LD50 or the LC50 were affected by any of the treatment protocols. In order to determine that the pretreatment was stimulating benzene metabolism, a method for measuring benzene metabolism has been developed using [¹⁴C]benzene. These studies have shown that phenobarbital and 3-MC do induce benzene metabolism in the liver, that chlorpromazine slightly induces benzene metabolism in the lung, and that pretreatment by these compounds does not affect the acute inhalation toxicity or the ip toxicity of benzene.     

Influence of elastase-induced emphysema and the inhalation of an irritant aerosol on deposition and retention of an inhaled insoluble aerosol in Fischer-344 rats

The purpose of this study was to assess the effects of elastase-induced pulmonary emphysema and the inhalation of an irritant aerosol (Triton X-100, a nonionic surfactant similar to those used in a number of pressurized consumer products) on pulmonary deposition and retention of an insoluble test aerosol, 59Fe-labeled Fe2O3. Untreated rats or rats pretreated by intratracheal instillation with elastase were exposed to an aerosol of 59Fe-labeled Fe2O3 either 18 hr or 7 days after exposure to aerosolized Triton X-100 which was administered in doses of 20, 100, or 200 micrograms/g of lung. Rats pretreated with elastase had significantly lower pulmonary deposition of 59Fe than the untreated controls (p less than 0.005). Pulmonary deposition of Fe2O3 was unaffected by pretreatment with Triton X-100. Elastase treatment alone had no effect on retention of Fe2O3. Triton X-100 administered 18 hr prior to exposure of rats to Fe2O3 aerosol resulted in dose-related increases in whole-body retention of 59Fe. When rats were exposed to Triton X-100 7 days before exposure to Fe2O3, increased retention of 59Fe was noted only in those treated at the highest Triton X-100 dose level (200 micrograms/g).     

Hematin toxicity in rats

The toxicity of intravenously administered hematin (3.4 and 6 $\text{mg}\text{100 g}$) was investigated in rats, where an LD₅₀ of 4.32 $\text{mg}\text{100 g}$ was computed, with 95% confidence limits of 5.40 and 3.46 $\text{mg}\text{100 g}$. At toxic levels (4 $\text{mg}\text{100 g}$) the rats showed a drop of blood pressure, hemorrhages and renal failure, whereas lower doses were well tolerated. This study indicates a possibly wide therapeutic margin of safety, when compared to the therapeutic use of hematin on porphyric patients.     

Pleural dosimetry and pathobiological responses in rats and hamsters exposed subchronically to MMVF 10a fiberglass.

Interspecies differences in pulmonary and pleural responses to the inhalation of natural mineral and synthetic vitreous fibers have been observed in chronic and subchronic studies. However, the reasons for these differences are not clearly understood. There are also fiber-specific differences in the outcome of chronic inhalation exposure to natural mineral and synthetic vitreous fibers. Whether these differences are dependent upon the ability of these fibers to translocate to the pleural space is unknown. The present study was conducted to compare retained fiber burdens and selected pathological responses in the pleural compartments of rats and hamsters following subchronic inhalation of MMVF 10a fiberglass, a fiber negative for tumorigenesis or fibrosis in chronic studies. Fischer 344 rats and Syrian golden hamsters were exposed for 4 or 12 weeks by nose-only inhalation at nominal aerosol mass concentrations of 45 mg/m3 (610 WHO fibers/cc). Pulmonary fiber burdens and pulmonary inflammatory responses were greater in rats than in hamsters. The total number of fibers in the lung was approximately three orders of magnitude greater than in the pleural compartment. Pleural burdens in the hamster (160 fibers/cm2 surface area) were significantly greater than burdens in similarly exposed rats (60 fibers/cm2 surface area) following 12 weeks of exposure. With time postexposure, pleural burdens decreased in hamsters but were essentially unchanged in rats. Pleural inflammatory responses in both species were minimal. In rats, pleural inflammation was characterized by increased numbers of macrophages and increases in mesothelial cell replication during the period of fiber exposure. In contrast, hamsters had increased numbers of macrophages and lymphocytes, and mesothelial-cell replication indices were elevated on the parietal pleura of the costal wall and diaphragm, with some of these responses persisting through 12 weeks of postexposure recovery. Taken together, the results suggest that differences among rodent species in pleural responses to inhaled fibers are due to a delivered dose of fibers and to the biological responses to the presence of the fibers.     

Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in C57B1/6 mice

Three-month-old male $\text{C57B1}\text{6}$ mice were given single oral doses of 0, 100, 150, or 200 μg of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg. The LD50 was 114 μ/kgg. In mice that died, depletion of the thymus and spleen were consistently found and edema and terminal hemorrhages occurred frequently. In a second experiment, 4-month-old male mice were dosed po with 0, 0.2, 1.0, 5.0 or 25 μg/kg, once a week for 2 or 6 weeks. Some deaths and growth retardation occurred in the 25 μg/kg dose group. Significantly increased liver and decreased thymus weights were found in the 1, 5 and 25 μg/kg dose groups. Total neutrophils were increased significantly, whereas hemoglobin values and mean corpuscular hemoglobin concentrations were decreased significantly after 6 doses of 25 μg/kg. Total serum protein and α-, β-, and γ-globulins were significantly decreased. TCDD was porphyrogenic. The hepatic porphyria was probably associated with liver damage. Degenerative and necrotic changes in the liver were essentially centrilobular and were accompanied by cellular infiltrates and ceroid pigment deposition. Proliferation of bile duct and bile duct epithelial cells occurred. Lipid accumulation was centrilobulary localized in the mice receiving 0.2 μg/kg, was more pronounced in the mice of the intermediate dose levels, and involved hepatocytes throughout the lobule in the 25 μg/kg dose group.     

Modification of some of the toxic effects of daunomycin (NSC-82,151) by pretreatment with the antineoplastic agent ICRF 159 (NSC-129,943)

Daunomycin (50 mg/kg) was lethal to Syrian golden hamsters ($\text{10}\text{10}$) within 2–3 days, however, when this same dose was given 30 min after 100 mg/kg of 2,6-piperazinedione, 4,4′-propylenedi-, [±]-(ICRF 159) half of the animals ($\text{5}\text{10}$) survived over 21 days. Between 40 and 51% of the total dose of daunomycin (50 mg/kg) could be recovered unchanged from hamster serum, urine, heart, lung, liver, kidney and spleen. The amount of unchanged daunomycin recovered from these tissues was higher (44–69%) in animals pretreated with ICRF 159. The amount of daunomycinone, a metabolite of daunomycin, recovered from the various tissues was less at all intervals in animals pretreated with ICRF 159 (0–3% of the total daunomycin dose) when compared with 4–9% recovered from the saline-pretreated hamsters. The iv administration of daunomycin (50 mg/kg) in the rhesus monkey produced hyperglycemia (140%) within 15 min, followed by a secondary hypoglycemia after 1–3 hr. Pretreatment with ICRF 159 (100 mg/kg) blocked the initial increase, but not the secondary decrease, in blood sugar over a 3-hr period. Daunomycin increased creatine phosphokinase and glutamic-oxaloacetic transaminase serum enzyme activities 13 and 4.5 times, respectively. Smaller increases were detected in serum enzyme activities of glutamic-pyruvic transaminase (3.5 times) and lactic acid dehydrogenase (2.5 times). The increases in serum enzyme activities were attenuated in animals pretreated with ICRF 159. In the present experiments, a decrease in production of daunomycinone may be an important factor in the reduction of daunomycin toxicity.     

Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the Golden Syrian hamster

Lethality, pathology, and various clinical chemical parameters were assessed in the hamster following a single ip or po treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). A single dose, 50-day LD₅₀ of greater than 3000 μg TCDD/kg, ip, was obtained for male and female hamsters while the LD₅₀ of orally administered TCDD was found to be 1157 μg/kg. Thus, the hamster appears to be the least sensitive mammalian species to the lethal effect of TCDD that has yet been investigated. TCDD treatment generally reduced the rate of body weight gain, with orally treated hamsters exhibiting the greatest reduction in rate. Thymic atrophy was the most consistent pathologic finding in TCDD treated hamsters. No histopathological changes were seen in the liver, spleen, kidneys, adrenals, or heart. Moderate to severe ileitis and peritonitis were found in many of the hamsters which died following oral treatment with TCDD. This lesion usually affects the distal ileum and consists of a marked hyperplasia of the mucosal epithelium with mild to severe hemorrhaging and necrosis. The intestinal lesion probably contributed in part to the greater lethality of TCDD in orally treated hamsters. A significant increase in serum alkaline phosphatase, bilirubin, protein, iron, cholesterol, and a decrease in serum albumin, chloride, urea nitrogen, and triglycerides were found in hamsters following both ip and po treatment with TCDD.     

Chronic morphine administration alters epinephrine uptake in rat adrenal storage vesicles.

Chronic administration of morphine in rats altered the kinetics of epinephrine uptake into adrenal medullary storage vesicles measured in vitro. In controls, the Michaelis constant for epinephrine was $\text{50.5 ± 2.9 μ}\text{m}$ and maximal uptake was 16.5 ± 0.9 nmol/100 μg of endogenous catecholamines; after chronic morphine, the Michaelis constant was $\text{92.2 ± 7.5 μ}\text{m}$ and maximal uptake was 21.1 ± l.6 nmol/100 μg of endogenous catecholamines. These data suggest that morphine alters the storage vesicle membrane transport system as well as affecting intravesicular binding of amines.     

Influence of intracerebroventricular injections of N6, O2'-dibutyryl adenosine 3':5'-cyclic monophosphate on sodium pentobarbital-induced narcosis in rats.

Premedication with dibutyryl cyclic AMP (225 μg, i.c.v.) decreased the responsiveness of the central nervous system and lethality to sodium pentobarbital in the rat. The LD₅₀ of sodium pentobarbital was increased (79.9–116 $\text{solmg}\text{kg}$ i.p.) and the sleep time was decreased from 120min to 76 min in dibutyryl cyclic AMP pretreated animals. The brain and plasma pentobarbital concentrations at the time of awakening were higher in the dibutyryl cyclic AMP group as compared to saline pretreated rats. The threshold dose level of sodium pentobarbital as determined from the dose—response curves and the dose of intravenous infused pentobarbital necessary to suppress EEG activity was increased after administration of the cyclic nucleotide. Pretreatment with gradient doses of dibutyryl cyclic AMP produced a biphasic dose-response of pentobarbital sleep time with the shortest duration observed at 225 μg of dibutyryl cyclic AMP and a progressive increase in duration of sleep time from 250 and 275 μg was produced. Doses of dibutyryl cyclic AMP greater than 275 μg produced death in all animals. The cardiovascular depressant action of pentobarbital was antagonized by dibutyryl cyclic AMP. However, the hypothermic action of pentobarbital was not reversed. The results suggest dibutyryl cyclic AMP produces a generalized stimulation of the CNS and does not specifically antagonize barbiturate-induced toxicity.     

EEG-synchronizing effect of gamma-hydroxybutyrate and 1-hydroxy-3-amino-pyrrolidone-2 (HA-966) in relation to dopaminergic brain function.

The earlier finding that γ-hydroxybutyrate and HA-966-induced depression of the central nervous system was associated with the increase of dopamine concentration and block of its release, prompted this study of the influence which the monoaminergic system may have upon the electrocorticogram in rats.The synchronization induced by α-methyl-p-tyrosine began earlier than the decrease of the duration of arousal, indicating different sensitivities to the depressive drug action of structures responsible for synchronizing and for arousal.Five $\text{mg}\text{kg}$ HA-966 in diethyldithiocarbamate desynchronized animals increased the amplitude but the duration of arousal was unchanged. p-Chlorophenylalanine treatment of rats did not influence the synchronizing effect of HA-966 (10–20 $\text{mg}\text{kg}$) or the inhibitory effect upon the duration of arousal. Haloperidol (100 μg-4 $\text{mg}\text{kg}$) potentiated the synchronizing effect of y-hydroxybutyrate and HA-966. The number of phasic discharges in the electrocorticogram induced by treatment with anaesthetic doses of γ-hydroxybutyrate were increased by the low dose of haloperidol (100 $\text{μg}\text{kg}$), while the higher dose (4 $\text{mg}\text{kg}$) was ineffective.Animals with intact and lesioned substantia nigra compacta responded equally to the synchronizing activity of HA-966 and γ-hydroxybutyrate. Therefore, it is concluded that their effect is not due to the accumulation of dopamine in the nigrostriatal system.     

Effects of thiamin antagonists on drug hydroxylation and properties of cytochrome P-450 in the rat

The administration of small amounts of thiamin (0.3 $\text{μg}\text{day}$ or more, i.p., for 21 days) depressed musomal cytochrome P-450 content and the V_max of aniline hydroxylase when compared to values obtained from rats fed a thiamin-deficient diet (approximately 0.1 μg of thiamine/day in basal diet). The concurrent administration of neopyrithiamin (50 $\text{μg}\text{day}$, i.p.) eliminated the depressant effect of 10.0 μig of thiamin/ day, but was without significant effect in rats receiving more than 100 μg of thiamin/ day. In contrast, 100 μg of oxythiamin/day had no thiamin-opposing effect on cytochrome P-450 content and only partially counteracted the effects of 1 μg of thiamin/day on aniline hydroxylase activity. These treatments were without significant effect on the K_m for this reaction. Using ethyl isocyanide as the ligand, there appears to be a qualitative change induced in the cytochrome P-450 from thiamin-deficient rats. The absorption peak height ratios indicate that cytochrome P₁-450 is increased in a manner analogous to that produced by the administration of 3-methylcholanthrene. This was supported by the fact that aniline binding, as evidenced by increased ΔA_max, is enchanced in musomes from thiamin-deficient animals, whereas the hexobarbital spectral shift was unaltered.     

Antagonism of cadmium-induced pulmonary toxicity by WR2721

Rats exposed to aerosols of cadmium oxide (? 60 $\text{μg}\text{l}$ for 30 min) develop severe and frequently fatal pulmonary edema. Electron muscopic examination of lung tissue revealed a progressive destruction of type I alveolar epithelial cells preceding death due to edema. Pre-exposure treatment of rats with a radioprotective agent, WR2721 (S-2-aminopropylamino)ethyl phosphorothioic acid hydrate) reduced edema formation, as measured by leakage of serum protein into the air spaces, and acute mortality.