Relative sensitivity of 32P-postlabelling of DNA and the autoradiographic UDS assay in the liver of rats exposed to 2-acetylaminofluorene (2AAF)

Groups of male Alderley Park rats were dosed concomitantly with 2-acetylaminofluorene (2AAF) by gavage at doses between 0.01 mg/kg and 40 mg/kg, and livers sampled 2-72 h later. The liver of one group of animals was perfused to yield hepatocytes which were assayed in vitro for unscheduled DNA synthesis (UDS) via incorporation of tritiated thymidine and autoradiography. DNA was extracted from the livers of the other group and DNA adduct levels determined using the 32P-postlabelling technique. The major C-8 2-aminofluorene/guanosine adduct and 3 minor adducts were quantitated, enabling the relative sensitivity of the 2 techniques to be compared. A dose- and time-related UDS response was observed, which, at the most sensitive time-point (12 h) enabled DNA repair to be discerned at a dose level of 0.1-1 mg/kg of 2AAF, a response classified as formally positive at 5 mg/kg 2AAF. Only the C-8 adduct, as determined by 32P-postlabelling, was discernible at 0.01 mg/kg of 2AAF, although other adducts were visible on autoradiograms at higher dose levels. It is concluded that as part of a well-defined dose response, UDS can be discerned with confidence for doses of 2AAF between approximately 0.1 and 5 mg/kg, and DNA adducts for doses of 2AAF between approximately 0.01 and 1 mg/kg. Discernible UDS for 2AAF in the rat liver is apparent at approximately 13 DNA (total) adducts/10(8) nucleotides, or approximately 8 DNA (C-8) adducts/10(8) nucleotides. The presumed C-8 2-acetylaminofluorene/guanosine adduct, prepared by reaction of 2-acetoxy-2-acetylaminofluorene (2AAAF) with DNA, was a significant but unreliable marker of 2AAF/DNA adducts in the rat liver in vivo. DNA repair did not appear to remove DNA adducts selectively, and adducts remained in DNA when discernible DNA repair had ceased.     

Relative sensitivity of 32P-postlabelling of DNA and the autoradiographic UDS assay in the liver of mice exposed to 2-acetylaminofluorene (2AAF)

In contrast to earlier studies conducted at lower dose levels, 2AAF is shown to induce a positive UDS response in the liver of mice dosed orally at dose levels between 500 and 1000 mg/kg. Similarly exposed mice had low levels of 2AAF-related hepatic DNA adducts at dose levels in the range 10-1000 mg/kg 2AAF, as determined by 32P-postlabelling analysis. It is concluded that the attenuated UDS response observed in the mouse liver, as compared to the rat liver, is due primarily to metabolic differences between these two species, coupled to a reduced capacity for UDS in the mouse liver for a given level of total 2AAF-related adducts per unit of DNA. These observations are compared and contrasted with identical studies conducted in the rat and reported in the preceding paper (Gallagher et al., 1991).     

The rat-liver carcinogen N-nitrosomorpholine initiates unscheduled DNA synthesis and induces micronuclei in the rat liver in vivo

Alkylation of DNA is generally accepted as the primary event in the carcinogenicity of nitrosamines. However, the cyclic nitrosamine N-nitrosomorpholine (NMOR), a potent rat hepatocarcinogen, has been reported as binding at very low levels to the liver DNA of treated rats. This led us to investigate the activity of NMOR in two in vivo rat-liver genotoxicity assays--for the induction of unscheduled DNA synthesis (UDS) and the production of micronucleated hepatocytes in the liver micronucleus assay (LMN). Rats treated with oral doses of NMOR (10-200 mg/kg) gave a positive liver UDS response either 2.5 h or 12 h after dosing. Similarly, treatment with oral doses of NMOR (10 or 100 mg/kg) followed by mitogenic stimulation with 4-acetylaminofluorene (4AAF) resulted in high incidences of micronucleated hepatocytes in the LMN assay. These data confirm that the genotoxicity reported for NMOR in vitro can be reproduced in vivo and that NMOR interacts with liver DNA of treated rats. Earlier reports of only very weak binding of radiolabelled NMOR to rat liver DNA in vivo are discussed within the context of these data.     

The induction of DNA-strand breaks and unscheduled DNA synthesis in F-344 rat hepatocytes following in vivo administration of caprolactam or benzoin

Benzoin (ZOIN) and caprolactam (CAP) were administered by gavage to Fischer 344 rats at a dose of 750 mg/kg and the hepatocytes isolated 12, 24 or 48 h after treatment. The isolated hepatocytes were subsequently examined for the induction of DNA-strand breaks (SB) and unscheduled DNA synthesis (UDS). Neither ZOIN nor CAP induced SB or UDS in hepatocytes, however ZOIN did induce an increase in the fraction of cells in S-phase 24 h after treatment. These results correlate well with the observed lack of carcinogenicity of these compounds.     

Concomitant observations of UDS in the liver and micronuclei in the bone marrow of rats exposed to cyclophosphamide or 2-acetylaminofluorene

Oral dosing of between 5–30 mg/kg of cyclophosphamide (CP) to Alderley Park rats induced micronuclei in the bone marrow between 12 and 36 h after dosing, but failed to induce unscheduled DNA synthesis (UDS) in the liver at similar dose levels and treatment periods. Dose levels of > 30 mg/kg were toxic to the liver. In contrast, 2-acetylaminofluorene (2AAF) induced UDS in the rat liver between 4–36 h after dosing, but gave only a weak response in the bone marrow assay at dose levels between 0.5 and 2 g/kg. Selected observations were made for each chemical using both tissues of the same test animal.

It is concluded that an assessment of the genotoxicity in vivo of chemicals defined as genotoxic in vitro will contribute to an assessment of their possible mammalian carcinogenicity, and that these should involve assays conducted using both the bone marrow and the liver of rodents. Due to its relative ease of commission, the bone marrow micronucleus assay will usually be conducted first; in the case of negative results it is recommended that a liver genotoxicity assay should also be conducted. The case for employing in vivo short-term genotoxicity tests to predict the possible organotropic carcinogenicity or germ cell mutagenicity of a new in vitro genotoxin is discussed.     

Evaluation of the potential in vivo genotoxicity of quercetin

Quercetin, a naturally occurring flavonol commonly detected in apples, cranberries, blueberries, and onions, has been reported to possess antioxidant, anti-carcinogenic, anti-inflammatory, and cardioprotective properties. While positive results have been consistently reported in numerous in vitro mutagenicity and genotoxicity assays of quercetin, tested in vivo, quercetin has generally produced negative results in such studies. Furthermore, no evidence of carcinogenicity related to the oral administration of quercetin was observed in chronic rodent assays. In order to further define the in vivo genotoxic potential of quercetin, a bone marrow micronucleus assay and an unscheduled DNA synthesis (UDS) assay were conducted in Wistar rats. Administered orally to male rats at dose levels of up to 2000 mg/kg body weight, quercetin did not increase the number of micronucleated polychromatic erythrocytes (MN-PCE) 24 or 48 h following dosing in the micronucleus assay. Likewise, orally administered quercetin (up to 2000 mg/kg body weight) did not induce UDS in hepatocytes of male or female rats. While measurable levels of metabolized quercetin were observed in rat plasma samples for up to 48 h after dosing, peaking at 1h following treatment administration, the unmetabolized aglycone was not identified in either plasma or bone marrow. With the exception of only a few rats, the aglycone was also not detected in liver tissue. These results demonstrate that quercetin is not genotoxic under the conditions of these assays and further support the negative results of previously conducted in vivo assays.     

Evaluation of the potential in vivo genotoxicity of quercetin

Quercetin, a naturally occurring flavonol commonly detected in apples, cranberries, blueberries, and onions, has been reported to possess antioxidant, anti-carcinogenic, anti-inflammatory, and cardioprotective properties. While positive results have been consistently reported in numerous in vitro mutagenicity and genotoxicity assays of quercetin, tested in vivo, quercetin has generally produced negative results in such studies. Furthermore, no evidence of carcinogenicity related to the oral administration of quercetin was observed in chronic rodent assays. In order to further define the in vivo genotoxic potential of quercetin, a bone marrow micronucleus assay and an unscheduled DNA synthesis (UDS) assay were conducted in Wistar rats. Administered orally to male rats at dose levels of up to 2000 mg/kg body weight, quercetin did not increase the number of micronucleated polychromatic erythrocytes (MN-PCE) 24 or 48 h following dosing in the micronucleus assay. Likewise, orally administered quercetin (up to 2000 mg/kg body weight) did not induce UDS in hepatocytes of male or female rats. While measurable levels of metabolized quercetin were observed in rat plasma samples for up to 48 h after dosing, peaking at 1 h following treatment administration, the unmetabolized aglycone was not identified in either plasma or bone marrow. With the exception of only a few rats, the aglycone was also not detected in liver tissue. These results demonstrate that quercetin is not genotoxic under the conditions of these assays and further support the negative results of previously conducted in vivo assays.     

Induction of unscheduled DNA synthesis in liver and micronucleus in bone marrow of rats exposed in vivo to the benzidine-derived azo dye, Direct Black 38

The genotoxic activity of the benzidine-derived azo dye, Direct Black 38 (DB38), was studied in vivo, using two different genetic end-points: unscheduled DNA synthesis in liver (UDS) and bone marrow micronucleus (MN). Exposure times were 12, 24 or 36 h. Both assays were performed in the same rat, except for the 24-h exposure when only MN was investigated. For the liver UDS assay, the rat hepatocarcinogen, 6-dimethylaminophenylazobenzthiazole (6BT), was used as positive control and for the MN assay, cyclophosphamide (CP). In agreement with earlier results, 6BT gave rise to a dose-related increase in liver UDS after 12-h exposure to 25 or 50 mg/kg bw. After 36-h exposure, there was still an indication of a weak dose-response effect between 0 and 5 net nuclear grains (NG). DB38 induced liver UDS at the higher dose levels used (500 and 1000 mg/kg), and after both 12- and 36-h exposure. With the longer exposure time, a weak induction of UDS was also observed at 100 mg/kg. The strongest UDS induction (12.2 NG), was obtained in one rat after 36-h exposure to 500 mg/kg. DB38 also had a weak effect on the MN induction, which was statistically significant at the higher concentrations used. A dose-related response was observed at all exposure times used.     

Assessment of unscheduled DNA synthesis in Fischer 344 rat pachytene spermatocytes exposed to caprolactam or benzoin in vivo

Male Fischer 344 rats were treated with the non-carcinogenic chemicals CAP and ZOIN. The spermatogenic cells were isolated at selected times post-exposure for assessment of chemically-induced DNA damage by quantitative autoradiography of unscheduled DNA synthesis (UDS). Neither chemical (750 mg/kg administered by gavage) induced UDS in pachytene spermatocytes isolated 12, 24 or 48 h after treatment.     

Genotoxicity and cell proliferative activity of omeprazole in rat stomach mucosa.

Induction of unscheduled DNA synthesis (UDS) as a marker of genotoxicity and induction of ornithine decarboxylase (ODC) activity as a marker of cell proliferative activity by omeprazole were determined in the glandular stomach mucosa of male F344 rats after oral administration. Commercial enteric-coated omeprazole (Losec) at doses of 30 and 100 mg/kg body weight induced a dose-dependent increase in UDS but not replicative DNA synthesis in the pyloric mucosa of rat stomach 4 h after its administration. Dose-dependent significant induction of ODC activity was observed in fundic and pyloric mucosa with a maximum 8 h after administration of omeprazole at doses of 37.5-100 mg/kg body weight. These results show that omeprazole has genotoxicity and cell proliferative activity in the rat glandular stomach mucosa.     

N-Nitrosomorpholine induced alterations of unscheduled DNA synthesis, mitochondrial DNA synthesis and cell proliferation in different cell types of liver, kidney, and urogenital organs in the rat

In order to measure rates of unscheduled DNA synthesis (UDS), mitochondrial DNA synthesis, and cell proliferation, i.e. factors relevant in the early phase of carcinogenesis, young rats received by gavage 200 mg/kg N-nitrosomorpholine (NNM) or vehicle (distilled water), and were injected with 3H-thymidine 24 h later. Autoradiographs from liver, kidney, urethra, prostate, seminal vesicle, and ductus deferens were prepared from deparaffinized sections, using a 250-day exposure time. In the liver, UDS was at least doubled in 2n and 4n hepatocytes. Approximately 3% of these hepatocytes exhibited a fourfold increase in UDS. Such strongly labeled cells were only observed in the liver following NNM exposure. With the exception of renal epithelial cells of the proximal tubule, UDS in epithelial cells of bladder, urethra, ductus deferens, seminal vesicle and prostate was decreased in NNM-exposed rats. Mitochondrial DNA synthesis and cell proliferation were significantly increased only in hepatocytes, and were decreased in all other monitored organs in NNM-exposed rats. The strongly increased UDS and more moderately increased mitochondrial DNA synthesis in a subgroup of hepatocytes suggest that possibly some unrepaired damage persists in the DNA of these cells. The latter cells may be the precursors of so-called foci of hepatocellular alteration, which appear later during the process of carcinogenesis. The increased UDS but decreased rate of proliferation in the renal proximal tubule cells might be related to renal carcinogenesis which is observed in NNM-exposed rats after a long latency period.     

Induction of unscheduled DNA synthesis in primary rat hepatocytes by benzidine-congener-derived azo dyes in the in vitro and in vivo/in vitro assays

The genotoxicity of the benzidine-congener-derived azo dyes. Direct Blue 1 ( DB1 ), Direct Blue 14 ( DB14 ), Direct Brown 95 ( DB95 ), and Direct Red 46 ( DR46 ) was studied in the in vitro and in vivo/in vitro unscheduled DNA synthesis (UDS) assays in primary rat hepatocytes to determine if in vivo metabolism of these compounds was required for induction of UDS. Hepatocytes were isolated, cultured, and treated with the azo dyes and [3H]thymidine (in vitro assay); alternatively, in the in vivo/in vitro assay, rats were intubated with the azo dyes, the hepatocytes isolated at 17 h after dosing and incubated in a medium containing [3H]thymidine. UDS was quantified by an autoradiographic method. None of the azo dyes induced UDS in the in vitro assay. However, DR46 did induce marginal, but significant UDS in 1 experiment (1.2 net grains at 500 micrograms/ml media). No significant UDS was observed when DR46 was tested in a subsequent in vitro assay. In the in vivo/in vitro assay, DB95 (100 mg/kg), DB14 (125 mg/kg), and DR46 (100 mg/kg) induced significant UDS (12, 2.1, and 3.5 net grains, respectively). None of the azo dyes tested was mutagenic in the Salmonella/microsome assay in the presence and absence of rat liver enzymes. Therefore, in vivo reduction of azo dyes, presumably by the gut microflora, is a requirement for the genotoxicity of these azo dyes in the primary rat hepatocyte UDS assay.     

Contribution of serum protein association to discrepancy between the in vivo and in vitro UDS results for 6,7-dimethyl-2,4-di-1-pyrrolidinyl-7H-pyrrolo[2,3-d]pyrimidine (U-89843)

U-89843 has been shown to undergo biotransformation, both in vitro and in vivo, to form U-97924 as a major primary metabolite. U-89843 was found to be positive in an in vitro UDS mutagenesis screen conducted with primary rat hepatocytes in serum-free media. In contrast to in vitro results, no evidence of genetic toxicity of U-89843 was observed in rats in the in vivo/in vitro version of the UDS test with single oral doses up to 1400 mg/kg. The negative results may be related to more robust in vivo detoxification mechanisms or relatively lower exposure to reactive metabolites formed by bioactivation of U-89843 as compared to that observed in the serum-free in vitro hepatocyte test system. Further studies showed rat serum suppressed the in vitro metabolism of U-89843 as well as the formation of the corresponding hydroxylated metabolite, U-97924, the putative precursor of proposed reactive electrophilic metabolite. The measured in vivo systemic clearance of U-89843 (0.53 l/h/kg) in rats was about 1000-fold slower than the in vitro intrinsic clearance (606 l/h/kg) estimated by measuring the formation of U-97924 in rat liver microsomal incubations. Since U-89843 is extensively associated with serum proteins a poor extraction ratio into the liver may account for the slower biotransformation of U-89843 in vivo as compared to that exhibited in in vitro serum-free hepatocyte incubations. Addition of bovine serum albumin (1–40 mg/ml) to the in vitro UDS assay medium decreased the UDS mean net grains per nucleus response of U-89843. These results suggest that the effect of serum protein should be considered when comparing serum-free in vitro UDS and in vivo UDS results for highly serum protein bound compounds.     

Evaluation of the genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) in a battery of in vitro and in vivo genotoxicity assays

The genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) was evaluated in a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse-mutation assay (Ames test), an in vitro human lymphocyte chromosome-aberration assay, an in vivo mouse bone-marrow micronucleus assay and an in vivo rat-liver UDS assay. Maximum test concentrations in in vitro assays were determined by the TTX limit of solubility in the formulation vehicle (0.02% acetic acid solution). In the Ames test, TTX was tested at concentrations of up to 200 microg/plate. In the chromosome-aberration assay human lymphocytes were exposed to TTX at concentrations of up to 50 microg/ml for 3 and 20 h in the absence of S9, and for 3h in the presence of S9. For the in vivo assays, maximum tested dose levels were determined by the acute lethal toxicity of TTX after subcutaneous administration. In the mouse micronucleus assay TTX dose levels of 2, 4 and 8 microg/kg were administered to male and female animals, and bone-marrow samples taken 24 and 48 h (high-dose animals only) after administration. In the UDS assay, male rats were given TTX on two occasions with a 14-h interval at dose levels of 2.4 and 8 microg/kg, the last dose being administered 2h before liver perfusion and hepatocyte culturing. Relevant vehicle and positive control cultures and animals were included in all assays. TTX was clearly shown to lack in vitro or in vivo genotoxic activity in the assays conducted in this study. The results suggest that administration of TTX as a therapeutic analgesic agent would not pose a genotoxic risk to patients.     

Activity of 2-Acetylaminofluorene as a UDS inducting agent in B6C3F1 mouse hepatocytes in vitro

Summary 2-Acetylaminofluorene (2AAF) is shown to be reproducibly active in inducing UDS in cultured hepatocytes from a B₆C₃F₁ mouse liver.Abbreviations 2AAF 2-acetylaminofluorene - 6BT 6-dimethylaminophenylazobenzthiazole     

Influence of age,sex and strain on the in vitro induction of unscheduled dna synthesis in rat hepatocyte primary cultures

The activity of chemical-induced unscheduled DNA synthesis was evaluated in hepatocyte primary cultures from Fischer 344 and Sprague-Dawley rats over a period of two years. In this two-year study hepatocytes from both sexes and strains were prepared from animals 2, 8, 14, 20 and 25 months of age and UDS was measured by autoradiography following treatment with N-methyl-AP-vitro-N-nitrosoguanidine and 2-acetylaminofluorine. A dose-related positive response occurred for both compounds throughout the study in hepatocytes from male and female Fischer rats and male Sprague-Dawley rats. The magnitude of the response was greatest in hepatocytes from male Fischer rats and a markedly lower response in unscheduled DNA synthesis occurred in all cultures prepared from animals of both strains and sexes at 20 and 25 months of age. Hepatocytes from female Sprague-Dawley rats showed a low level of unscheduled DNA synthesis with N-methylN-vitro-N-nitrosoguanidine throughout the study. The most striking finding was the absence of a UDS response to 2-acetylaminofuorene by hepatocytes from Sprague-Dawley females at the 8, 14, 20 or 25 month periods. The results indicate an age-related decrease in chemical-induced unscheduled DNA synthesis activity among rats.Abbreviations 2AAF 2-acetylaminofluorine[deDMSO] - dimethylsulfoxide ³H-TdR, meth yl-3H-thymidine - MNNG N-methyl-N-vitro-N-nitrosoguanidine - UDS unscheduled DNA synthesis     

Age-related induction and disappearance of carcinogen-DNA-adducts in livers of rats exposed to low levels of 2-acetylaminofluorene

It was investigated whether in vivo aging of rat liver is associated with changes in the induction and rate of disappearance of DNA damage. For this purpose 6- and 36-month-old rats were intraperitoneally injected with a single, low dose (5 mg/kg body wt.) of the model liver carcinogen 2-acetylaminofluorene (AAF). Using the 32P-postlabeling assay we found that N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF) was the major DNA-adduct formed. The minor adduct N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-C8-AAF) could only be detected after doses of 20 mg/kg or more. Quantitation of adduct levels at various time points after treatment indicated a rapid induction of AF-adducts, which were already present at 6 h after treatment. The subsequent loss of AF-adducts was relatively slow, as was indicated by the presence of a substantial amount of AF-adducts as late as 21 days after treatment. Slight age-related differences in the pattern of induction and disappearance of AF-adducts and a somewhat higher level of persisting lesions in old than in young rats were observed.     

A comparative study of hepatic DNA repair, DNA replication and hepatotoxicity in the CD-1 mouse following multiple administrations of dimethylnitrosamine

The objective of this study was to quantify hepatic DNA repair and DNA replication following multiple administrations of dimethylnitrosamine (DMN) and to determine if these events were correlated with hepatotoxicity. Male CD-1 mice, 50-100 days old, were dosed daily, p.o., with DMN in water at dose levels of 2, 4, 7 and 10 mg/kg for 2 weeks. After 2, 7 and 14 days of dosing, hepatocytes were isolated by an in situ perfusion procedure, incubated in the presence of [3H] thymidine, and fixed. Unscheduled as well as scheduled DNA synthesis were assessed by quantitative autoradiography. Unscheduled DNA synthesis (UDS) represents DNA repair while scheduled DNA synthesis (S phase) represents DNA replication. In addition, the animals' serum was examined for enzymes which indicate hepatic toxicity. After 1, 7 and 14 days of dosing, animals were orbital-bled and the serum was analyzed for serum glutamic pyruvic transaminase (SGPT), serum glutamic oxalacetic transaminase (SGOT), alkaline phosphatase (AP) and gamma-glutamyl transpeptidase (GGT). No morbidity or mortality was observed at dose levels of 2 and 4 mg/kg, but all animals receiving 7 and 10 mg/kg died after 4-6 days of dosing. GGT or AP were not elevated at any dose level or at any time point examined. At 4 mg/kg only a slight increase (less than or equal to 2 X) in the concentration of SGOT and SGPT was observed but a sharp increase (greater than 20 X) in replicative DNA synthesis was seen. The 2 mg/kg dose level of DMN did not increase replicative DNA synthesis and SGOT and SGPT were not elevated above control values at any time point following dosing at 2 mg/kg. A weakly positive DNA repair response was observed for dose levels of 4, 7 and 10 mg/kg DMN after two consecutive days of dosing. No DNA repair was observed after either 7 or 14 days of dosing at the 2 and 4 mg/kg/day levels. These results indicate that hepatic toxicity is associated with the induction of replicative DNA synthesis (S phase) but not with the induction of DNA repair. The results also confirm and extend a previous study (Doolittle et al., 1987b) indicating that a significant elevation in hepatic DNA replication is induced by hepatocarcinogens after multiple administrations of dose levels which do not alter hepatic DNA replication after a single administration. This finding indicates that the utility of the in vivo-in vitro hepatocyte assay may be enhanced by using a multi-dose protocol.     

Induction of sister-chromatid exchange (SCE) and cell-cycle inhibition in mouse peripheral blood B lymphocytes exposed to mutagenic carcinogens in vivo

To determine the sensitivity of the mouse peripheral blood lymphocyte (PBL) culture system, male B6C3f1 mice were injected i.p. with either 2-acetylaminofluorene (AAF) (20, 40, 80, 160 mg/kg), benzo[a]pyrene (BP) 25, 75, 150, 300 mg/kg), dichlorvos (DCV) (5, 15, 25, 35 mg/kg), ethyl methanesulfonate (EMS) (10, 30, 90, 180, 270 mg/kg), or N-nitrosomorpholine (NM) (37.5, 75, 150, 300 mg/kg) dissolved in either RPMI 1640 (DCV, EMS, NM) or sunflower oil (AAF, BP). 24 h later blood was removed by cardiac puncture, and the lymphocytes were cultured in the presence of lipopolysaccharide for analysis of SCE in B lymphocytes. All 4 mutagenic carcinogens (AAF, BP, EMS, NM) induced significant dose-related increases in SCE frequency. DCV, a potent neurotoxicant, caused no change in the baseline SCE frequency. At the highest concentration of each chemical examined, AAF caused a 1.6-fold increase, EMS a 1.8-fold increase, NM a 3.0-fold increase, and BP a 3.1-fold increase in SCE frequency compared to concurrent controls. A comparison of these results for PBLs with those reported in the literature for bone marrow cells indicates that PBLs offer a good quantitative and qualitative estimate of the SCE-inducing potential for these 5 compounds in bone marrow cells.     

Effect of sex and time of sampling on selenium and glutathione peroxidase activity in tissues of mature rats

Sprague-Dawley rats were used to investigate variations in measures of glutathione peroxidase (GSH-Px) and selenium (Se) concentration resulting from diurnal cycles and sex. Mature rats (equal numbers of males and females) were killed at 4 h intervals over a 48 h period (0200, 0600, 1000, 1800 and 2200 h each day). Selenium and GSH-Px were measured in plasma, erythrocytes, and liver and kidney cytosols. Selenium concentrations did not vary diurnally, but plasma GSH-Px activities were higher during the light than dark periods. Males had greater plasma GSH-Px activities and Se concentrations (42 EU and .45 mg/kg, respectively) than females (35 EU and .41 mg/kg respectively). GSH-Px activities were also higher in male kidney cytosols than females (117 and 76 EU, respectively). Selenium and GSH-Px activities, however, were lower in male liver cytosols (.48 mg/kg and 272 EU) than females (1.19 mg/kg and 795 EU, respectively). These data suggest that Se is distributed differently in male and female rats and the difference in Se distribution is accomplished by differences in GSH-Px activities.