17ß-Estradiol Concentration and Direct ß2-Adrenoceptor Inhibition Determine Estrogen-Mediated Reversal of Adrenergic Immunosuppression.

Background: Sympathetic innervation of lymphoid organs, and the presence of 17ß-estradiol (estrogen or E2) and adrenergic receptors (ARs) on lymphocytes, suggests that sympathetic stimulation and hormonal activation may influence immune functions. Purpose: Modeling and simulating these pathways may help to understand the dynamics of neuroendocrine-immune modulation at the cellular and molecular levels. Methods: Dose- and receptor-dependent effects of E2 and AR subtype-specific agonists were established in vitro on lymphocytes from young male Sprague-Dawley rats and were modeled in silico using the MATLAB Simbiology toolbox. Kinetic principles were assigned to define receptor-ligand dynamics, and concentration/time plots were obtained using Ode15s solvers at different time intervals for key regulatory molecules. Comparisons were drawn between in silico and in vitro data for validating the constructed model with sensitivity analysis of key regulatory molecules to assess their individual impacts on the dynamics of the system. Finally, docking studies were conducted with key ligands E2 and norepinephrine (NE) to understand the mechanistic principles underlying their interactions. Results: Adrenergic activation triggered proapoptotic signals, while E2 enhanced survival signals, showing opposing effects as observed in vitro. Treatment of lymphocytes with E2 shows a 10-fold increase in survival signals in a dose-dependent manner. Cyclic adenosine monophosphate (cAMP) activation is crucial for the activation of survival signals through extracellular signal-regulated kinase (p-ERK) and cAMP responsive element binding (p-CREB) protein. Docking studies showed the direct inhibition of ERK by NE and ß2-AR by E2 explaining how estrogen signaling overrides NE-mediated immunosuppression in vitro. Conclusion: The cross-talk between E2 and adrenergic signaling pathways determines lymphocyte functions in a receptor subtype and coactivation-dependent manner in health and disease.

BRCA1 regulation on ß-hCG: a mechanism for tumorigenicity in BRCA1 defective breast cancer.

Human chorionic gonadotropin ß (ß-hCG) has been implicated in breast tumorigenesis. However, the role of this hormone is highly controversial as certain studies suggest it has anti-tumor properties while others have found it to be pro-tumorigenic. To unveil the truth, we have analyzed the expression of ß-hCG in breast cancer. We identified for the first time that ß-hCG expression is linked to BRCA1 status and its overexpression is seen in BRCA1 mutated breast cancer cells, BRCA1 conditional knockout mouse breast cancer tissues and BRCA1 floxed basal cell carcinoma (BCC) tissues. An analysis of three large, transcriptomic data sets from TCGA (The Cancer Genome Atlas) expression profile confirmed the inverse correlation between BRCA1 and ß-hCG in human breast cancer. Using ChIP and luciferase assays, we also demonstrated that the cancer cells with wild-type but not mutant BRCA1 directly repress the expression of ß-hCG by binding to its promoter. Further, ß-hCG promotes migration and invasion predominantly in BRCA1 mutant breast cancer cells. Interestingly, stable overexpression of ß-hCG in BRCA1 mutant but not wild-type breast cancer cells results in the formation of spheres even on monolayer cultures. The cells of these spheres show high expression of both EMT and stem cell markers. Since ß-hCG belongs to a cysteine knot family of proteins like TGFß and TGFß signaling is deregulated in BRCA1 defective tumors, we checked whether ß-hCG can mediate signaling through TGFßRII in BRCA1 mutated cells. We found for the first time that ß-hCG can bind and phosphorylate TGFßRII, irrespective of LHCGR status and induce proliferation in BRCA1 defective cells. Our results confirmed that there exists a transcriptional regulation of BRCA1 on ß-hCG and BRCA1 mutation promotes ß-hCG mediated tumorigenesis through TGFßRII signaling. Thus inhibiting ß-hCG-TGFßRII could prove an effective treatment strategy for BRCA1 mutated tumors.

Evaluation of unscheduled DNA synthesis (UDS) and replicative DNA synthesis (RDS) following treatment of rats and mice with p-dichlorobenzene.

p-Dichlorobenzene (PDCB) has been reported to produce tumors in the male and female mouse liver and in the male rat kidney in 2-year gavage studies (NPT, 1987). To elucidate the possible mechanisms of carcinogenicity more fully, UDS and RDS were evaluated in B6C3F1 mouse hepatocytes and F-344 rat kidney cells by autoradiography following in vivo administration of PDCB. All corn oil gavage doses of PDCB (300, 600, and 1,000 mg/kg) and the negative control resulted in < 0 net grains/nucleus (NG) in the mouse liver and rat kidney, indicating that PDCB does not induce UDS in either tissue. Compared to controls with < or = 0.29% hepatocytes in S-phase (%S), treatment of mice induced 0.46, 1.90, and 1.52 %S (males) and 2.61, 1.18, and 4.45 %S (females), which indicates that PDCB acts as an inducer of cell proliferation in the liver. In male rat kidney cells, the same doses produced 0.87, 0.67, and 1.01 %S (0.38% in controls) and in females 0.48, 0.43, and 0.32 %S (0.52% in controls), indicating that PDCB induces cell replication in the male but not the female rat kidney. Therefore, these data demonstrate that PDCB is not genotoxic in the mouse liver or rat kidney at single oral doses comparable to the daily doses given in the National Toxicology Program (NTP) bioassay (NTP, 1987). Furthermore, the increases in RDS support the hypotheses that mouse liver tumor formation occurs via stimulation of hepatocyte proliferation and male rat kidney carcinogenesis via increased renal cell proliferation.

Evaluation of lymphopenia among workers with low-level benzene exposure and the utility of routine data collection.

Whether low-level benzene exposure produces health effects is controversial. We used routinely collected data from our medical/industrial hygiene system to study 387 workers with daily 8-hour time-weighted exposures averaging 0.55 ppm. The cross-sectional repeated survey design included 553 unexposed workers. Lymphopenia is considered to be the earliest and most sensitive indicator of benzene toxicity. We found no increase in the prevalence of lymphopenia among benzene-exposed workers (odds ratio, 0.6; 95% confidence interval, 0.2 to 1.8), taking into account smoking, age, and sex. There also was no increase in risk among workers exposed 5 or more years (odds ratio, 0.6; 95% confidence interval, 0.2 to 1.9). Examination of other measures of hematotoxicity, including mean corpuscular volume and counts of total white blood cells, red blood cells, hemoglobin, and platelets, produced similar results. We conclude that risk of lymphopenia and other early indicators of hematotoxicity are not increased among workers in this study who were exposed to low levels of benzene.

Mixture risk assessment: a case study of Monsanto experiences.

Monsanto employs several pragmatic approaches for evaluating the toxicity of mixtures. These approaches are similar to those recommended by many national and international agencies. When conducting hazard and risk assessments, priority is always given to using data collected directly on the mixture of concern. To provide an example of the first tier of evaluation, actual data on acute respiratory irritation studies on mixtures were evaluated to determine whether the principle of additivity was applicable to the mixture evaluated. If actual data on the mixture are unavailable, extrapolation across similar mixtures is considered. Because many formulations are quite similar in composition, the toxicity data from one mixture can be extended to a closely related mixture in a scientifically justifiable manner. An example of a family of products where such extrapolations have been made is presented to exemplify this second approach. Lastly, if data on similar mixtures are unavailable, data on component fractions are used to predict the toxicity of the mixture. In this third approach, process knowledge and scientific judgement are used to determine how the known toxicological properties of the individual fractions affect toxicity of the mixture. Three examples of plant effluents where toxicological data on fractions were used to predict the toxicity of the mixture are discussed. The results of the analysis are used to discuss the predictive value of each of the above mentioned toxicological approaches for evaluating chemical mixtures.

Biochemical toxicology and disposition of Therminol 66 heat transfer fluid after inhalation or after dietary administration to male Sprague-Dawley rats.

The objectives of this study were to determine the disposition of Therminol 66 in rats and to determine the effects of this heat-transfer fluid on liver and kidney microsomal drug-metabolizing enzymes. Therminol 66 was administered to male Sprague-Dawley rats at various doses as either a single oral administration at 0, 100, or 300 mg/kg, or as a single 6-h inhalation exposure at 0 or 350 mg/m3. Animals were killed 48 h after gavage or after termination of inhalation exposure. Additional groups of animals were exposed to Therminol 66 via the diet at 0, 100, 500, or 5000 ppm for 14 d, or via repeated inhalation exposure at 0, 25, 250, or 1200 mg/m3 for 6 h/d for 14 d. These exposure scenarios represent approximately equivalent doses of Therminol 66 by the different routes of administration. No change in body weight was observed after acute oral or inhalation exposure, and little change in body weight was observed in animals administered Therminol 66 via the diet except at the highest dose. There was no change in kidney weight, and liver weights were increased only at the higher doses of Therminol 66. The body weight gain of animals exposed to Therminol 66 via inhalation decreased in a dose-dependent manner over the 2-wk exposure period. Results from the disposition study indicated that Therminol 66 did not appear to accumulate in the tissues examined and did not appear to be extensively absorbed after a single oral dose of 300 mg/kg. The whole-body elimination half-life was approximately 14 h and occurred primarily via the feces. There was no significant induction of hepatic aryl hydrocarbon hydroxylase (AHH) activity after single oral or inhalation exposures to Therminol 66. Ethoxycoumarin O-deethylase (ECOD) was significantly induced only in animals exposed to 350 mg/m3 via inhalation. Repeated dietary and inhalation exposures resulted in AHH and ECOD induction only at the highest doses, and the kidney appeared to be less sensitive than the liver. Animals exposed via inhalation demonstrated a greater hepatic inductive effect than did animals exposed via the diet, which may be due to absorption differences.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicity of calcium sodium metaphosphate fiber. II. Chronic inhalation and oncogenicity study.

Male and female Fischer 344 rats (80/sex/group) were exposed to CSM fiber 6 hr/day, 5 days/week at target-exposure levels of 0, 1, 5, or 25 mg/m3 for 24 months, corresponding to 0, 27, 80, and 513 fibers/cc, respectively. Number and size of the airborne fibers were determined during the course of the study. At 3 and 12 months, 10 rats/sex/group were euthanized and at 18 and 24 months 5 rats/sex/group were euthanized. In addition, 5 rats/sex/group were removed from exposure at 18 months and maintained for a 6-month recovery period. All animals surviving at the completion of the exposure period were maintained in a clean environment for up to 5 additional months. Clinical laboratory examinations were performed on 10 animals/sex/group at 3, 12, and 24 months. The number of fibers in the lung were also determined at 3, 12, 18, and 24 months. Body weight and survival did not appear to be affected by treatment. There were no biologically significant effects on clinical parameters. There was a dose-related increase in lung weight during the exposure period which was generally reversible during the recovery periods. There also was a dose-related increase in the number of fibers/milligram of lung, but no increase in lung fiber burden after the first 3 months. The number of fibers in the lungs of animals exposed to CSM fiber for 18 months and allowed 6-month recovery period showed a decrease especially at the high dose. No increase in tumors (benign or malignant) was observed in this study. Microscopic changes considered reflective of an irritant response were observed in the nasal turbinates notably at the 5 and 25 mg/m3 levels. Histological changes were also observed in the lungs at the 5 and 25 mg/m3 levels. The incidence and/or severity of histopathological changes in the 1 mg/m3 group was considered to be essentially comparable to controls.

Toxicity of calcium sodium metaphosphate fiber. I. In vitro and in vivo degradation and clearance studies.

In an experiment to ascertain the degradability of calcium sodium metaphosphate (CSM) fiber in vitro, 32P-labeled CSM fiber was incubated in media with or without rat lung epithelial cells (LEC) or rat alveolar macrophages (RAM). The amount of radioactivity appearing in the filtrate of the media in the presence of cells minus the radioactivity in the media in the absence of cells was considered to reflect cell-aided dissolution of the fiber. LEC and RAM cells increased the degree of dissolution two- and sevenfold, respectively, compared to their respective media controls in a 7-day time period. In a separate experiment, male Fischer rats were given 32P-labeled CSM fiber either by intraperitoneal injection or by intratracheal instillation and the amount of radioactivity appearing in the urine and feces was measured over a period of 60 days. Selected animals from this experiment were also subjected to whole-body autoradiography 0, 1, 5, 15, 30, and 60 days postexposure. After intraperitoneal injection, approximately 0.9% of the administered dose appeared in the urine. A similar percentage of the dose was eliminated in the urine when the fibers were administered by intratracheal instillation; however, the amount of radioactivity in the feces after intratracheal instillation, i.e., 11.6% of the administered dose, was much higher than that after intraperitoneal dose, i.e., 0.24% of the administered dose. Whole-body autoradiographs showed a time-related increase in radioactivity at a site other than the site of administration, and the location of this radioactivity appeared to be exclusively associated with mineralized tissue. The clearance of nonradiolabeled CSM fiber (approximately 200,000 fibers) from rat lung after intratracheal inhalation (IH) and intratracheal instillation (IT) was monitored. Approximately 93% of the initial fiber load after IH and approximately 84% of the initial fiber load after IT was cleared from the lung in 6 months. Histological and biochemical evaluation of the rat lungs did not reveal any indication of fibrosis up to a period of 6 months. All the studies discussed indicate that CSM is degradable in biological systems and is cleared from the lung after IT and IH administration. These attributes of CSM fiber should reduce the potential for chronic adverse effects in the lung after inhalation.

The genotoxic potential of linear alkylbenzene mixtures in a short-term test battery.

Alkylate 215 (A-215), Alkylate 225 (A-225), and Alkylate 230 (A-230) are mixtures of C10-C14 linear alkylbenzenes used as intermediates for the manufacture of detergents. These products were evaluated for genotoxic activity in the Ames bacterial mutagenesis assay (strains TA98, 100, 1535, and 1537), the CHO/HGPRT mammalian cell forward gene mutation assay, and the in vivo rat bone marrow chromosome assay. The Ames and CHO/HGPRT assays were conducted both with and without the addition of Aroclor-induced rat liver S9. The maximum concentrations evaluated were 10 mg/plate (A-215) and 3 mg/plate (A-225 and A-230) for the Ames test, and 1.5 mg/ml (A-215 and A-225) and 2.0 mg/ml (A-230) for the CHO/HGPRT assay. In each case, the highest concentrations produced evidence of either toxicity or insolubility. The highest dose in the bone marrow cytogenetics assay was 12,700 mg/kg, a level which produced significant weight loss. The results of all tests were negative, indicating a lack of genotoxic activity as measured by the battery of tests used.

Subchronic rat inhalation study with Skydrol 500B-4 fire resistant hydraulic fluid.

Skydrol 500B-4 fire resistant hydraulic fluid, a proprietary phosphate ester mixture composed principally of dibutyl phenyl phosphate (DBPP) and tributyl phosphate (TBP) and used as a commercial airline hydraulic fluid, was evaluated in an inhalation toxicity study of Sprague-Dawley rats. Target exposure levels used in the study were 0, 5, 100, and 300 mg/m3, and exposures were maintained for 6 hr/day, 5 days/week. Mass median aerodynamic diameters determined for particles in the mid- and high-exposure inhalation chambers were 2.85 microns and 3.31 microns, with geometric standard deviations of 1.99 microns and 1.92 microns, respectively. The percentage of particles less than 10 microns in diameter were 96.4% in the mid-exposure chamber and 95.5% in the high-exposure chamber. After 6 weeks of Skydrol exposure, 10 rats/sex/group were euthanized and then assessed for indications of possible chemical toxicity. Another 15 rats/sex/group were studied for a total of 13 weeks of exposure. The only clinical sign of chemical toxicity was the observation of a reddish nasal discharge with accompanying oral salivation in mid- and high-exposure animals of both sexes, indicative of an irritant response. Statistically significant reduced body weights; increased absolute and relative liver weights; and decreased erythrocyte counts, hemoglobin levels, and hematocrit values were observed in high-exposure female rats euthanized after 13 weeks of Skydrol exposure. High-exposure male rats also had increased absolute and relative liver weights and decreased hematocrit values after 13 weeks. Plasma cholinesterase levels were decreased in high-exposure female rats both 6 and 13 weeks after the study was initiated.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of teratogenic potential of N-formylpiperidine in rats.

The teratogenic potential of a versatile solvent, N-formylpiperidine (NFP), was evaluated in the rat. Three groups of 25 mated female Sprague-Dawley rats were given 110, 220, or 440 mg/kg/day NFP in distilled water by gavage on Days 6 through 20 of gestation. A control group of 25 animals received distilled water on a comparable regimen. Maternal animals were observed daily for signs of toxicity; body weights and food consumption were measured at regular intervals throughout the study. All animals were euthanized on Gestation Day 21 and the fetuses examined for cleft palate and external abnormalities. One-half of the fetuses in each litter were examined for visceral anomalies while the remaining fetuses were examined for skeletal malformations after appropriate staining. One female in the high dosage group died on Gestation Day 12. Clinical signs of toxicity, observed in 6 females in the high dosage group, included tremors, convulsive movements, and an apparent weakness of the legs. Maternal toxicity, in terms of significantly decreased body weight and food consumption, was observed in the mid and high dosage groups. Food consumption was also significantly depressed for the first 4 days of dosing in the low dosage group. There was a significant increase in number of resorptions in the high dosage group when compared to controls. No effects were observed on other reproductive parameters. Mean fetal body weight was significantly lower in the high dosage group when compared to controls. While the incidence of fetal malformations on a litter basis was higher in the high dosage group, this change was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of the hematologic effects of chronic low-level exposure to benzene.

A study of 200 persons working with benzene showed no differences in commonly measured hematologic outcomes when compared with 268 nonbenzene workers in the same plant. Exposures ranged from 0.01 ppm to a high of 1.40 ppm 8-hour time weighted average over a 10-year period. Several other factors (age, sex, race, and smoking), however, were associated with these outcomes, indicating the importance of considering confounding factors when comparing hematology results. Exposure to low levels of benzene does not appear to produce an increased level of abnormal hematology measures detectable in routine medical surveillance.

Subchronic and reproduction studies with dibutyl phenyl phosphate in Sprague-Dawley rats.

Dibutyl phenyl phosphate (DBPP) was administered to male and female Sprague-Dawley rats in their diets in separate subchronic (91-day) and two-generation reproduction studies. Dose levels of DBPP were 5, 50, and 250 mg/kg/day in both studies. In the reproduction study, cross-fostering was performed between some high-exposure and control litter offspring and dams following a second mating of F0 animals. Compared to control animals, body weights were consistently lower in high-exposure adult animals in both studies; this observation was less consistent in mid-exposure adult rats. High-exposure rats in the subchronic study had decreased erythrocyte counts and hematocrit and hemoglobin levels. They also had increased absolute and/or relative liver weights with concomitant decreased hepatocytic vacuolation and increased fatty accumulation. In the reproduction study, mating and fertility indices were comparable among the parental animals in both generations, but survivability among high-exposure pups reared by control dams appeared to be decreased. Urinary bladder histopathologic changes, consisting of mononuclear cell infiltration and transitional epithelial hyperplasia, were noted in mid- and high-exposure rats from both studies. The no observable adverse effect level in both of these studies was 5 mg/kg/day.

Chronic toxicity, oncogenic potential, and reproductive toxicity of p-nitroaniline in rats.

Dose levels for these studies were selected mainly on the basis of subchronic studies, although consideration was also given to workplace exposure levels and proposed mechanism of tumor formation with structurally similar compounds. For the chronic study, groups of 60 male and 60 female Sprague-Dawley CD (Registered Trademark of Charles River Breeding Laboratories, Portage, MI) rats were given 0, 0.25, 1.5, or 9.0 mg/kg/day paranitroaniline (PNA) by gavage in corn oil for a period of 2 years. Parameters monitored included clinical observations, ophthalmoscopic exams, body weights, food consumption, hematology, clinical chemistry, and urinalysis at regular intervals throughout the study. All gross lesions and over 40 tissues were examined histologically for all control and high-dosage-level animals. Gross lesions, spleens, and livers of low- and mid-dosage groups were also examined histologically. For the reproduction study, groups of 15 male and 30 female rats, designated as F0 generation, were given PNA at the same levels as the chronic study for 14 weeks prior to mating and during mating, gestation, and lactation. Selected groups of 15 male and 30 female rats of the F1 generation received the same dose of PNA for 18 weeks prior to mating and during mating, gestation, and lactation. F2 pups were observed through weaning at which time they were euthanized. Observations made during the study included body weights, food consumption, mating and fertility indices, pup and litter survival indices, and histopathology of selected tissues. In the chronic study, except for a slight decrease in survival of high-dose male rats late in the study, survival in all treated groups was comparable to controls. Blood methemoglobin levels were elevated in the mid- and high-dosage groups, while slight anemia was observed in the high-dosage group also. Spleen weights were significantly increased in the high-dosage groups. An accumulation of brown pigment was observed in the cytoplasm of the sinusoidal macrophages or littoral cells of the liver and in the reticuloendothelial cells of the spleen. No treatment-related increase in tumor incidence was observed. In the reproduction study, no consistent pattern of effect from treatment between the F0 and F1 generation was seen in mating, pregnancy, or fertility indices. Thus, administration of PNA at levels which produced significant methemoglobinemia and low-level anemia in the rat and histological changes in the spleen produced no tumors or reproducible effects on reproductive performance.

Assessment of the delayed neurotoxicity of tributyl phosphate, tributoxyethyl phosphate, and dibutylphenyl phosphate.

There industrial organophosphorus compounds were tested for their ability to cause organophosphorus compound-induced delayed neurotoxicity (OPIDN) in the adult hen. The compounds tested were tributyl phosphate (TBP), tributoxyethyl phosphate (TBEP), and dibutylphenyl phosphate (DBPP). The acute oral LD50 of TBP and DBPP were estimated to be 1,863 and 1,500 mg/kg, respectively, and the dose equal to the LD50 was used as a test dose. The acute oral LD50 of TBEP was greater than 5,000 mg/kg and 5,000 mg/kg was used as a test dose. An oral dose of 750 mg tri-o-cresyl phosphate (TOCP) was used as a positive control. For the acute delayed neurotoxicity test, hens were given two test doses of the test materials 21 days apart and killed 21 days after the second dose. None of the hens given TBP, TBEP, or DBPP exhibited nerve damage or clinical signs which distinguished them from untreated control animals. A single dose of TOCP resulted in paralysis and a histopathological profile typical of a distal neuropathy. For the assay of the inhibition of esterases, hens were killed 24 hours after a single dose equal to the greater of either the LD50 or 5000 mg/kg. TOCP administration resulted in over 90% inhibition of brain neurotoxic esterase (NTE), but none of the other three compounds inhibited NTE to an extent (greater than 70%) which would be expected to result in OPIDN. Administration of TOCP, TBEP, or DBPP resulted in approximately a 70% decrease in plasma butyrylcholinesterase (BuChE) activity. TBP caused a 2-3 fold increase in BuChE activity. TBEP administration resulted in about 45% inhibition of acetycholinesterase (AChE) in brain. These results indicate that TBP, TBEP, and DBPP are all unlikely to cause OPIDN with any single sublethal dose.

Subchronic inhalation and oral toxicity of hydrogenated terphenyls in rats.

The subchronic toxicity of a commercial blend of partially hydrogenated terphenyl was evaluated in rats by inhalation and oral routes of exposure. Animals were exposed to target concentrations of 0, 10, 100, or 500 mg/m3 for 6 hr/day, 5 days/week or were offered diets daily with concentrations of 0, 50, 200, or 2000 ppm. Each study lasted approximately 14 weeks. The study designs included observations for clinical signs, body weights, ophthalmic exams, hematology and clinical chemistry, major organ weights, and gross and histopathology. No treatment-related effects were noted in the ophthalmic exams. Body weights were slightly depressed in high-dose males from the inhalation study and high-dose females in the dietary study. Liver and liver/body weights were increased in high-dose animals of both sexes and high- and mid-dose males in the dietary and inhalation studies, respectively. In the high-dose females of the dietary study, kidney and kidney/body weights were increased with increased adrenal and adrenal/body weights were also observed. No compound-related gross lesions nor pathological correlates to the organ weight changes were observed in either study. The no-adverse effect levels were considered to be 100 mg/m3 and 200 ppm (15.9 mg/kg) for the inhalation and dietary studies, respectively. These data indicate that a wide margin of safety exists for hydrogenated terphenyl workplace exposure.

Effect of tetrachlorophthalic anhydride on hepatic microsomal metabolism in rats and mice.

The capacity for induction of microsomal metabolic enzymes by tetrachlorophthalic anhydride (TCPA) was evaluated in male Sprague-Dawley rats and male CD-1 mice. The rats were orally dosed for 7 d with TCPA suspended in corn oil at 25, 100, 250, or 500 mg/kg. Following this treatment a dose-dependent reduction in the zoxazolamine paralysis time occurred over the dose range 100-500 mg/kg in the rat. No effect on the hexobarbital sleep time was observed at any test level. TCPA was found to produce statistically significant increases in hepatic aminopyrine N-demethylase, aniline hydroxylase, and cytochrome P-450 in the rat at 500 mg per kg. In addition statistically significant increases were seen in aniline hydroxylase and cytochrome P-450 at 25 mg/kg. Mice were orally dosed with TCPA for 7 d at 250, 500, or 1000 mg/kg. There was no effect in the zoxazolamine paralysis time or the hexobarbital sleep time in this species. Hepatic microsomal enzyme levels were not measured in the mouse. These results suggest that following oral dosage TCPA is a weak inducer of microsomal enzymes in the rat. A similar effect was not observed in the mouse for the parameters tested.

A two-generation reproduction study with monochlorobenzene vapor in rats.

Groups of 30 male and 30 female Sprague-Dawley CD rats, designated as the F0 generation, were exposed to vapor of monochlorobenzene (MCB) at target concentrations of 0, 50, 150, or 450 ppm for 10 weeks prior to mating and during mating, gestation, and lactation. The progeny of the F0 generation was designated as the F1 generation and groups of 30 male and 30 female F1 animals were exposed to the same concentrations of MCB as the F0 parents. Exposure of F1 animals was initiated 1 week postweaning and lasted 11 weeks prior to mating and through mating, gestation, and lactation. All F2 pups were observed through weaning at which time they were killed. Observations made during the study included body weights, food consumption, mating and fertility indices, pup and litter survival indices, and histopathology of selected tissues. No mortality was observed during the course of this study. Body weights and food consumption for all treated groups were comparable to controls during the growth period. Maternal body weight data during gestation and lactation were also comparable between the control and treated groups. Mating and fertility indices for males and females for both generations appeared unaffected by treatment. Pup and litter survival indices for all treated groups were comparable to those of controls. Hepatocellular hypertrophy and renal changes (tubular dilation with eosinophilic material, interstitial nephritis, and foci of regenerative epithelium) were observed among F0 and F1 male rats exposed to 150 and 450 ppm MCB.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of toxicity of o-nitrochlorobenzene in rats following a 4-week inhalation exposure.

o-Nitrochlorobenzene (ONCB) is a chemical intermediate used for the synthesis of various industrial chemicals. To evaluate the subchronic toxicity of this compound, three groups of 15 male and 15 female Sprague-Dawley rats were exposed to ONCB vapor 6 hr/day, 5 days/week for 4 weeks at target concentrations of 10, 30, or 60 mg/m3. A control group of 15 animals/sex was exposed to room air in a separate inhalation chamber. Concentrations of ONCB in the chambers were determined at least three times a day using a uv spectrophotometer. Parameters monitored in this study included observation for signs of toxicity, body weights, ophthalmoscopic exam, hematology, and clinical chemistry. At necropsy, selected organ weights were recorded and over 35 tissues/animal were examined microscopically for all control and high-exposure level animals. No mortality was observed in this study. Mean body weights of all groups were comparable to controls. Animals exposed to the mid and high concentrations of ONCB showed a significant increase in blood methemoglobin and a significant decrease in hemoglobin, hematocrit, and red blood cell counts. Spleen and liver weights (absolute and relative to body weight) were significantly increased for these two groups. Microscopic changes, observed only in the spleen, included increased degree of extramedullary hematopoiesis and hemosiderosis. These data suggest that the toxicity of ONCB is comparable to that of its structural analog, p-nitrochlorobenzene. Thus these two compounds should have similar work-place exposure limits.