Inhibition of N-2-fluorenylacetamide-induced mammary tumorigenesis in rats by dietary polybrominated biphenyls.

Female SD rats were maintained for approximately 1 year on diets containing 300 ppm N-2-fluorenylacetamide (2-FAA), 50 ppm polybrominated biphenyls (PBB), or a combination of these chemicals (PBB + 2-FAA). Ingestion of 2-FAA significantly reduced the average survival time of the rats; this effect was virtually blocked by the simultaneous ingestion of PBB. Simultaneous ingestion of PBB also significantly reduced the overall incidence of 2-FAA-induced tumors during the examination period. The lower incidence of tumorigenesis was accompanied by an increase in the latency time for tumor induction; tumors were found in 100% of the animals given 2-FAA after 29 weeks of carcinogen ingestion, whereas only 50% of the PBB + 2-FAA-fed animals had tumors at the end of the experiment (53 wk of carcinogen ingestion). PBB significantly reduced the incidence of 2-FAA-induced tumors at nonhepatic locations (mammary gland and ear duct) but did not affect the incidence of hepatic tumors to a statistically significant extent. PBB ingestion did not significantly increase the incidence of tumors when compared with controls; 1 tumor was found in 1 of 12 rats fed 50 ppm PBB for 57 weeks, and no tumors were detected in 8 controls.

Carcinogenic potential of phthalic acid esters and related compounds: structure-activity relationships.

Chronic toxicity and carcinogenicity studies of several phthalic acid esters (PAEs) and compounds containing a 2-ethylhexyl moiety were conducted in Fischer 344 rats and B6C3F1 (hybrid) mice. The compounds studied were phthalic anhydride, di(2-ethylhexyl) phthalate, butyl benzyl phthalate, diallyl phthalate, di(2-ethylhexyl) adipate, tris(2-ethylhexyl) phosphate, and 2-ethylhexyl sulfate (sodium salt). Estimated maximum tolerable doses and fractionally lower doses of each compound were administered to groups of 50 male and 50 female rats and mice for 2 years, followed by sacrifice, necropsy, and histopathological examination of major organs and tissues. The low toxic potencies of most of the compounds allowed for relatively high doses to be given during the chronic studies. In general, the toxic manifestations of the PAEs were closely correlated with their ester substituents. Although many of the PAEs possessed some carcinogenic activity, target sites for such effects were dissimilar, suggesting the absence of a common mode of action. In contrast, all of the 2-ethylhexyl-containing compounds studied possessed some hepatocarcinogenic activity, indicating that this moiety may have a propensity for causing hepatocarcinogenesis in mice, particularly those of the female sex. The 2-ethylhexyl compound that caused the greatest hepatocarcinogenic response in mice, di(2-ethylhexyl) phthalate, was also hepatocarcinogenic in rats. Similarly, those with a relatively greater effect in female mice were also active in male mice. Thus, sex and species differences in 2-ethylhexyl-induced hepatocarcinogenesis in rodents are probably quantitative rather than qualitative in nature.

Overview of phthalate ester pharmacokinetics in mammalian species.

Phthalic acid esters, or phthalate esters, are generally well absorbed from the gastrointestinal tract following oral administration. Hydrolysis to the corresponding monoester metabolite, with release of an alcoholic substituent, largely occurs prior to intestinal absorption of the longer-chain alkyl derivatives such as di(2-ethylhexyl) phthalate (DEHP). Phthalate esters are widely distributed in the body, with the liver being the major, initial repository organ. Clearance from the body is rapid and there is only a slight cumulative potential. Short-chain dialkyl phthalates, such as dimethyl phthalate, can be excreted in an unchanged form or following complete hydrolysis to phthalic acid. Longer-chain compounds such as DEHP, however, are converted principally to polar derivatives of the monoesters by oxidative metabolism prior to excretion. A marked species difference in DEHP metabolism exists: primates (man, monkey, some rodent species) glucuronidate DEHP at the carboxylate moiety following hydrolysis of a single ester linkage, whereas rats appear to be unable to glucuronidate the monoester metabolite and oxidize the residual alkyl chain instead to various ketone and carboxylate derivatives. The major route of phthalate ester elimination from the body is urinary excretion. Certain phthalate esters are excreted in the bile but undergo enterohepatic circulation. The relationships of phthalate ester pharmacokinetics to their toxicological actions are unknown at the present time, largely due to a lack of elucidated mechanisms of toxic action.

Potentiation of hepatic and renal toxicity of various compounds by prior exposure to polybrominated biphenyls.

Mice ingesting a standard rodent diet supplemented with polybrominated biphenyls (PBBs) were more susceptible to chlorinated hydrocarbon solvent-induced renal and hepatic damage, as well as the lethal effects of CHCl3 and CCl4, than were mice consuming control diet. As little as 0.025 ml/kg CHCl3 caused a significant increase in serum glutamic oxaloacetic transaminase (SGOT) and blood urea nitrogen (BUN) and a significant decrease in renal cortical slices accumulation of p-aminohippurate (PAH) in PBB-pretreated but not control mice. SGOT and serum glutamic pyruvate transaminase (SGPT) were greater in PBB-pretreated mice than in control mice after 0.125 and 0.005 ml/kg CCl4, respectively. Renal cortical PAH accumulation was greatly reduced in PBB-pretreated but not control mice aftter 0.125 ml/kg CCl4. The solvent-induced decrease in PAH accumulation was also greater in PBB-pretreated mice than in control mice following administration of 1.0 ml/kg trichloroethylene (TRI) and 0.15 ml/kg 1,1,2-trichloroethane (TCE).

Effects of di(2-ethylhexyl) phthalate on the gonadal pathophysiology, sperm morphology, and reproductive performance of male rats.

Dietary exposure of adult male F344 rats to 0, 320, 1250, 5000, or 20,000 ppm DEHP for 60 consecutive days resulted in a dose-dependent reduction in total body, testis, epididymis, and prostate weights at 5000 and 20,000 ppm. Degenerative changes were observed in testis, along with decreased testicular zinc content, reduced epididymal sperm density and motility, and increased occurrence of abnormal sperm at 20,000 ppm. There was a trend towards reduced testosterone and increased luteinizing hormone and follicle stimulating hormone in serum at 5000 and 20,000 ppm. The mean percentage of fertile animals was unchanged and reduction in fertility parameters, although not marked in severity, were correlated with gonadal effects. Average litter size was reduced at 20,000 ppm, but initial pup weights and growth were unaffected. There were no grossly observed abnormalities in the offspring and the rate of neonatal deaths was similar in control and DEHP treated groups. Characteristic toxicity manifestations of DEHP included dose-dependent enlargement of liver and reduced sperm triglycerides and cholesterol. Additionally, serum albumin and total proteins were dose dependently increased upon treatment with DEHP. Cessation of exposure to DEHP initiated partial to complete recovery from toxicity in most cases. The magnitude of recovery were variable with that of the gonads being slower than other systems. These data suggest a lack of reproductive dysfunction in F344 male rats at DEHP doses below 20,000 ppm which produced measurable testicular degeneration and afflicted epididymal sperm morphology under the present experimental conditions.

Effects of polybrominated biphenyls on kidney function and activity of renal microsomal enzymes.

Polybrominated biphenyls (PBBs) cause hepatic microsomal enzyme stimulation and histopathological alterations in several organs, including kidney. Concern about effects of PBBs on the health of newborns has increased after the discovery of PBBs in milk of nursing mothers. Therefore, it was of interest to investigate the effects of PBBs on kidney function and the activity of renal microsomal enzymes in adult and immature animals. Seven and eleven day old pups were treated with a single IP injection of either peanut oil or 150 mg/kg PBBs (FireMaster BP-6) in peanut oil. Adult virgin rats were fed diet containing 0 or 100 ppm PBBs for 30 or 90 days. Treatment with PBBs only retarded weight gain after 90 days exposure. Kidney-to-body weight ratio was not altered by PBBs. Arylhydrocarbon hydroxylase activity was increased while epoxide hydratase activity was decreased (adults) or not affected (immature rats) in kidney following treatment with PBBs. Administration of PBBs had no effect on blood urea nitrogen, the clearance of inulin, p-aminohippurate (PAH), or fractional sodium excretion. Similarly, the in vitro accumulation of PAH and N-methylnicotinamide (NMN) by thin renal cortical slices and ammoniagenesis and gluconeogenesis in renal cortical slices were not affected by PBBs. In conclusion, treatment with PBBs resulted in modification of the activity of renal microsomal enzyme activities but had no detectable effect on renal function.

Carcinogenicity testing of phthalate esters and related compounds by the National Toxicology Program and the National Cancer Institute.

Five phthalate ester and related compounds (phthalic anhydride, phthalamide, di(2-ethylhexyl) phthalate, di(2-ethylhexyl) adipate and butyl benzyl phthalate) have been tested for carcinogenic effects in standard lifetime rodent feeding studies. Groups of 50 male and female rats and mice were fed diets containing various concentrations of the test chemicals for 102-106 consecutive weeks. The dietary concentrations were estimated to be maximally tolerated doses and half maximally tolerated doses. All animals that died during the study and all survivors at the end of two years were examined grossly and microscopically for the presence of tumors. The incidences of animals with tumors at a specific anatomic site in the treated groups and the controls were compared statistically. Neither phthalamide nor phthalic anhydride increased tumor incidences in rats or mice. Di(2-ethylhexyl) phthalate increased the incidences of liver tumors in rats and mice of both sexes, while di(2-ethylhexyl) adipate caused liver tumors in male and female mice, only. Butyl benzyl phthalate did not cause tumors in male or female mice, but the incidence of myelomonocytic leukemia in butyl benzyl phthalate-treated female rats was significantly greater than that in the controls. Chemically induced early deaths in the butyl benzyl phthalate-treated male rats precluded an evaluation of carcinogenic potential in this sex. Under the conditions of these tests, di(2-ethylhexyl) adipate was considered to be carcinogenic in both rats and mice and di(2-ethylhexyl) adipate was considered to be carcinogenic in mice. The evidence for carcinogenic effects of butyl benzyl phthalate in female rats was judged to be equivocal because of the variable nature of the incidence of myelomonocytic leukemia in Fischer 344 rats. Phthalamide and phthalic anhydride did not exhibit carcinogenic effects in these studies.

Chemical modulation of 1,2-dibromo-3-chloropropane toxicity.

Single subcutaneous injections of 1,2-dibromo-3-chloropropane (DBCP) produced dose-dependent injury to the kidney, testis, epididymis and liver of male, Fischer 344 rats. Pretreatment with the enzyme inducer phenobarbital reduced the nephrotoxic potency of DBCP. Serum creatinine and urea nitrogen concentrations were lower, and renal proximal tubular necrosis was less severe in phenobarbital pretreated than in non-pretreated rats subsequently injected with various amounts of DBCP. 3-Methylcholanthrene (3-MC) or cobaltous chloride (CoCl2) pretreatments enhanced the dose-dependent necrogenic effects of DBCP on the kidney and, in general, potentiated the DBCP-induced elevations of serum creatinine and urea nitrogen concentrations. Pre- and post-treatment with the enzyme inhibitor piperonyl butoxide had no discernable effect on the nephrotoxic potency of DBCP. The hepatotoxic potency of DBCP, as measured by elevations in the serum activities of glutamic pyruvic transaminase (GPT) and sorbitol dehydrogenase (SDH), and by histological analysis of the severity of centro lobular necrosis, was prevented or quantitatively reduced by phenobarbital pretreatment. 3-MC, CoCl2 or piperonyl butoxide pretreatments had no consistent effect on DBCP hepatotoxicity. The dose-dependent seminiferous tubular atrophy induced in rats by DBCP was enhanced by CoCl2 and reduced by phenobarbital. Cobalt chloride pretreatment also enhanced the DBCP-induced degeneration of the epithelium of the caput (head) epididymis, while phenobarbital blocked or reduced this effect. Neither 3-MC nor piperonyl butoxide consistently altered the gonadotoxic potency of DBCP. Cobalt chloride also enhanced, while phenobarbital reduced, the acute lethal potency of DBCP. Single-treatment, subcutaneous LD50 values for DBCP were 102 mg/kg in non-pretreated and 128 mg/kg in phenobarbital pretreated rats. The potency ratio (0.796; confidence interval, 0.728-0.871) was statistically significant (P less than 0.05). The modulating effects of CoCl2 and phenobarbital could not be ascribed simply to changes in tissue concentrations of the protective conjugation substrate glutathione, since CoCl2 increased and phenobarbital did not alter renal and hepatic non-protein sulfhydryl concentrations. These data indicate a complex role of metabolism in determining dose-dependent toxic response to DBCP administration.

Comparative induction of xenobiotic metabolism in rodent kidney, testis and liver by commercial mixtures of polybrominated biphenyls and polychlorinated biphenyls, phenobarbital and 3-methylcholanthrene: absolute and temporal effects.

Male Fischer 344 rats were killed at various times after single or multiple treatments with polybrominated biphenyls (PBB), polychlorinated biphenyls (PCB), sodium phenobarbital (NaPB) or 3-methylcholanthrene (3MC). p-Chloro-N-methyl-aniline N-demethylase (PCNMA) and aryl hydrocarbon hydroxylase (AHH) activities were determined in the 14 000 g supernatant fraction (postmitochondrial supernate, PMS) of renal, testicular and hepatic homogenates. Cytochrome P-450 (p-450) concentrations were determined in the 100 000 g pellet fractions of the same homogenates and the effects of enzyme induction on the sensitivities of AHH in PMS to inhibition by alpha-napthoflavone (ANF) and metyrapone (MET) in vitro were determined. Single treatments with PBB or PCB induced hepatic P-450 only, while multiple treatments with PBB, PCB or 3MC induced both renal and hepatic P-450; NaPB induced only hepatic P-450, while testicular P-450 concentration was unaffected by the inducers. Treatments with PBB, PCB or 3MC shifted the Soret maxima of renal and hepatic dithionite-reduced P-450 difference spectra to shorter wavelengths. Multiple treatments with PBB, PCB or 3MC increased renal and hepatic AHH activities, but NaPB induced hepatic AHH only. Renal AHH activity was increased more rapidly than hepatic AHH after a single treatment with PBB, PCB or 3MC and returned more rapidly to control. The renal AHH induced by PBB and PCB, like that induced by 3MC, was more sensitive to inhibition by ANF in vitro than was renal AHH from naive rats. Hepatic AHH induced by PBB and PCB, unlike that induced by NaPB or 3MC, exhibited no net alterations in sensitivities to the inhibitory effects of ANF or MET. Testicular AHH activity was not induced by PBB, PCB , NaPB or 3MC. Multiple treatments with PBB, PCB or NaPB increased hepatic, but not renal or testicular PCNMA activities. The organ-specificity and time-dependency of the effects of PBB, PCB, NaPB and 3MC on P-450 concentrations and AHH activities suggest that drug metabolism in kidney, testis and liver are regulated by separate control mechanisms. It may be possible to exploit such differences in organ response to enzyme inducers as tools with which to discern the roles of local metabolism in renal and testicular chemical injury.

Toxicology and carcinogenesis studies of isophorone in F344 rats and B6C3F1 mice.

Toxicology and carcinogenesis studies of isophorone were conducted by administering 0, 250, or 500 mg/kg body weight per day by gavage in corn oil to groups of 50 F344/N rats and 50 B6C3F1 mice of each sex, 5 days/week, for 103 weeks. Dosed male rats developed proliferative lesions of the kidney including hyperplasia, adenoma, and adenocarcinoma of the renal tubule, and epithelial hyperplasia of the renal pelvis. Non-proliferative kidney lesions observed in dosed male rats included mineralization, and a more severe nephropathy in low dose animals than in controls or high dose animals. Carcinomas of the preputial gland occurred in high dose male rats. No isophorone-related lesions were observed in female rats. In male mice, isophorone exposure may have been associated with an increase in hepatocellular neoplasms and mesenchymal neoplasms of the integumentum in high dose animals, and with a marginally increased incidence of lymphoma in low dose male mice. In mice, no non-neoplastic lesions in males or females, or neoplastic lesions in females were considered associated with isophorone administration.

Synergistic toxicity of carbon tetrachloride and several aromatic organohalide compounds.

Subacute (20 days) oral administration of hexachlorobenzene (HCB) or the organohalide mixtures polybrominated biphenyls (PBB) or polychlorinated biphenyls (PCB) greatly increased th susceptibility of male rats to the toxic effects of carbon tetrachloride (CCl4). CCl4-induced acute growth retardation, renal tubular functional impairment and hepatocellular necrosis were quantitatively greater in rats pretreated with the aromatic organohalides than in naive rats. Pretreatment with HCB, PBB or PCB also reduced survival after i.p. administration of CCl4 and increased the severity of morphological liver injury. Despite functional impairment, only minor histological alterations attributable to CCl4 were detected in the kidney. CCl4 as well as HCB, PBB or PCB increased the lipid content of the liver, but not the kidney. CCl4 administration depressed energy-dependent accumulation of organic ions by renal cortical slices in vitro in a dose-dependent manner and increased the basal rate of respiration of renal cortical tissue in vitro. It is concluded from these results that exposure to certain commercial aromatic organohalides can greatly alter organ response to toxicants such as CCl4.

Adverse effects of butyl benzyl phthalate on the reproductive and hematopoietic systems of male rats.

A 14-day dietary study was conducted in adult, male, Fischer 344 rats at levels of 0.0, 0.625, 1.25, 2.5 and 5.0% butyl benzyl phthalate (BBP) to evaluate potential effects of this plasticizer on the male reproductive and hematopoietic systems. Total body, thymus, testis, epididymis, prostate and seminal vesicle weights were reduced in the 2.5% and 5% BBP dose groups, while pituitary weight was unaffected. Histological evaluations revealed dose-dependent atrophy of the testis, prostate and seminal vesicles at 2.5% and 5%, atrophy of the thymus and epididymis at 5%, and the presence of immature sperm cells in the tubular lumens and necrosis of the tubular epithelium in the epididymis at 2.5% and 5% BBP. Plasma testosterone concentration was decreased at 5%, while follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were increased at 2.5% and 5.0% BBP. The circulating components of blood, and clotting times (prothrombin time, activated partial thromboplastin time), were unaffected although bone marrow cellularity was reduced at 2.5% and 5%. Changes in non-reproductive organs included enlargement of liver and kidneys, thymic atrophy and associated morphological abnormalities in these organs. These data indicate a direct toxic effect of BBP on the testis with secondary effects on other reproductive organs. Pituitary and hypothalamic responses did not appear to be affected. The reduced bone marrow cellularities suggest that prolonged exposures to BBP could affect circulating blood components or compromise clotting ability.

Developed resistance to mercuric chloride nephrotoxicity: failure to protect against other nephrotoxicants.

Daily, oral treatment of rats for 14 days with 5 mg/kg of mercuric chloride (HgCl2) caused hypertrophy of the kidney, but no change in percent tissue water, or serum urea nitrogen (BUN) or creatinine concentrations. Upon histological examination, hypercellularity and increased basophilia of the outer medulla were observed. A single, subcutaneous injection of 20 mg/kg of potassium chromate (K2CrO4) increased kidney size and water content, as well as BUN and serum creatinine concentrations, and produced coagulative necrosis of the proximal convoluted tubules. Intraperitoneal injection of 125 mg/kg of hexachloro-1,3-butadiene (HCBD) increased kidney weight, percent water, BUN and serum creatinine, and produced necrosis of the proximal straight tubules in approximately half of the animals. 1 g/kg biphenyl, orally, produced only diffuse tubular swelling. Rats treated with 20 mg/kg K2CrO4, 125 mg/kg HCBD or 1 g/kg biphenyl following 14 days of treatment with 5 mg/kg HgCl2 generally displayed the symptoms of both types of treatment, and the severity of the K2CrO4, HCBD and biphenyl effects were substantially the same as in those without HgCl2 pretreatment. Developed resistance to HgCl2 nephrotoxicity, therefore, appears to have little effect on response of the kidney to other nephrotoxicants.

Acute nephrotoxicities and hepatotoxicities of 1,2-dibromo-3-chloropropane and 1,2-dibromoethane in male and female F344 rats.

Four consecutive intraperitoneal (i.p.) injections with 40 mg/kg of 1,2-dibromo-3-chloropropane (DBCP) reduced the in vitro accumulation of p-aminohippurate (PAH) and tetraethylammonium (TEA) by slices of renal cortex and increased blood urea nitrogen (BUN) concentration in both male and female rats, but elevated serum glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) activities in females only. Four consecutive treatments with 1,2-dibromoethane (EDB) reduced the accumulation of PAH in male rats, but failed to alter TEA accumulation, BUN concentration or GPT and GOT activities in rats of either sex. Single i.p. injections of EDB or DBCP (40 mg/kg, approximately one-half of the acute, i.p. LD50 values) were without effect on serum GPT and GOT activities, BUN concentration or the accumulations of PAH and TEA in male rats when measured 24, 48 or 96 h after treatment, except that PAH accumulation was reduced at 96 h. These results indicate that BUN and the accumulations in vitro of PAH and TEA by renal cortical slices are appropriate endpoints for studying DBCP nephrotoxicity. Measurements of serum GOT and GPT activities detected DBCP hepatotoxicity in female rats only. The nephrotoxicity of EDB was indicated by measurement of TEA accumulation only.

Encephalopathy in rats and nephropathy in rats and mice after subchronic oral exposure to benzaldehyde.

Male and female Fischer 344 rats and B6C3F1 mice were treated daily (5 days/wk) with benzaldehyde by gavage either in 12 doses of 0 (vehicle control), 100 (rats only), 200, 400, 800, 1600 or (for mice only) 3200 mg/kg body weight/day (followed by 2 days' observation without treatment), or for 90 days in doses of 0, 50, 100, 200, 400 or 800 mg/kg/day (rats) or 0, 75, 150, 300, 600 or 1200 mg/kg/day (mice). In the acute studies, benzaldehyde induced deaths and decreased body-weight gain in both sexes of rats given 800 or 1600 mg/kg/day and caused deaths in both sexes of mice given 1600 or 3200 mg/kg/day. In the 90-day studies, deaths occurred in both sexes of rats on 800 mg/kg/day and in male mice on 1200 mg/kg/day. Body-weight gain was depressed in male rats on 800 mg/kg/day, in male mice on 600 mg/kg/day and in female mice on 1200 mg/kg/day. Necrotic and degenerative lesions were seen in the cerebellar and hippocampal regions of the brain in both sexes of rats given 800 mg/kg/day, but not in mice. Renal tubular necrosis occurred in male and female rats on 800 mg/kg/day and in male mice on 1200 mg/kg/day. Mild epithelial hyperplasia or hyperkeratosis of the forestomach was seen in male and female rats on 800 mg/kg/day. In this limited study, the no-observed-toxic-effect doses of benzaldehyde administered by gavage were 400 mg/kg/day in male and female rats, 300 mg/kg/day in male mice and 600-1200 mg/kg/day in female mice.

The relevance of hepatic peroxisome proliferation in rats to assessment of human carcinogenic risk for pharmaceuticals.

There exists a strong association between the ability of drugs and other chemicals to induce hepatic peroxisomes in rodents and to increase the frequency of liver tumors in these same species. Despite several years of intensive investigation, a plausible mechanism causally relating peroxisome induction to tumor formation has not been found. Two major theories of how such compounds produce tumors--prolonged oxidative stress and cellular growth dysregulation--have limited experimental support. The oxidative stress demonstrated in rodents as a consequence of peroxisomal activity may be irrelevant to man since primates appear to be much less susceptible to peroxisome proliferation than are rats or mice. Cellular growth dysregulation and other effects of test materials that often accompany--but are not directly attributable to--peroxisome proliferation in rodents can be assessed in other, more relevant species if a causal relationship between their presence and tumor development is ultimately shown in rodents. Currently, there is no reason to specifically avoid the clinical assessment and commercial development of new therapeutic drugs that induce peroxisomes in rodents if other measurements indicate the absence of DNA damage or growth dysregulation at reasonable exposures in relevant species.

The complementary roles of in vitro and in vivo tests in genetic toxicology assessment.

Risk of genetic alteration (genetic toxicity) in humans as a consequence of exposure to exogenous agents is determined in large degree by the results of specific laboratory tests. Although the individual test procedures are uniform and standardized, there is often confusion when effects observed in vitro are not confirmed in vivo. This in vitro/in vivo difference is commonly misrepresented as demonstrating the insensitivity of in vivo genetic toxicology tests. Consideration of the mechanistic bases of the tests leads to a more rational interpretation: In vitro procedures, by avoiding pharmacokinetic limitations and many confounding interactions, are best able to detect the potential for an agent to affect genetic fidelity, while in vivo procedures, specifically because they are influenced by pharmacokinetics and competing reactions, are more suitable for determining the probability of genetic alterations occurring in an intact, dynamic organism. Expectations that in vivo test results should always confirm in vitro findings are unwarranted, as are comparisons of perceived sensitivities for detecting genetic toxicity. Human risk estimation should be based principally on the results of in vivo genetic toxicology tests, as is the case with other, nongenetic endpoints, and the in vivo tests must be sufficiently vigorous to detect genetic injury, including substantiation of the relevancy of the target cells monitored and documentation of their exposure. In contrast, the primary role of in vitro tests should be to guide in the design and selection of in vivo tests, as well as to assist in their interpretation and assessment of adequacy.

Effects of partial hepatectomy on organ-specific toxic response to 1,2-dibromo-3-chloropropane (DBCP).

The organ-specific toxic potency of subcutaneously administered 1,2-dibromo-3-chloropropane (DBCP) was compared in partially hepatectomized and sham-operated rats over a dose range of 20--80 mg kg-1 to assess the roles of hepatic and extrahepatic metabolism in protection against acute renal and gonadal injury. Relative kidney weight and the severity of DBCP-induced renal proximal tubular cell necrosis were increased in rats subjected to a partial (70%) surgical hepatectomy 48 h prior to treatment with DBCP at 80 mg kg-1. Relative liver weight was reduced by DBCP in the hepatectomized, but not in the sham-operated rats. The severity of DBCP-induced (80 mg kg-1) hepatocellular centrilobular necrosis was greater in hepatectomized than in sham rats. DBCP reduced the relative weights of the testis and epididymis in a progressive manner and produced dose-dependent seminiferous tubular atrophy within 12 days of treatment. The morphologically apparent lesions of the testis and epididymis were enhanced by hepatectomy. The concentration of non-protein sulfhydryl groups (NPS) in rat liver was increased by partial hepatectomy. Because of the resulting decrease in liver size, however, the total amount of hepatic NPS per kg body weight 48 h post-surgery was lower than in sham rats. The surgery had no effect on renal, testicular or epididymal NPS concentrations of organ weights. Partial hepatectomy greatly increased pentobarbital and ethanol sleeping times, while sleep induction time for pentobarbital was decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid, automated measurements of urinary protein and glucose concentrations.

Procedures are described for the quantitative determination of urinary protein and glucose concentrations using assay methodologies that are readily automated. Glucose was measured by the hexokinase method and protein by interaction with the dye Coomassie Brilliant Blue G-250. Both assays can be performed with a centrifugal analyzer. The linear range for the glucose assay was 10-500 mg/dl, encompassing the normal range of 10-30 mg/dl for glucose in rat urine. The linear range for the protein assay was 5-45 mg/dl, necessitating dilution of the urine (normal range for rats of 100-400 mg/dl) by a factor of 10. As with many other protein assay methodologies, response to gamma globulins was less than that to albumin. The procedures described herein require only minute quantities (5-10 microliters) of sample and are sufficiently simple and rapid to be used as screening procedures. Moreover, they provide quantitative results and are more sensitive than many of the more commonly used diagnostic tests for urine protein and glucose.