Strain difference of cadmium-induced testicular toxicity in inbred Wistar–Imamichi and Fischer 344 rats

Previously, we reported that Wistar–Imamichi (WI) rats are highly resistant to cadmium (Cd)-induced lethality and hepatotoxicity compared to Fischer 344 (F344) rats. Since the testes are one of the most sensitive organs to acute Cd toxicity, we examined possible strain-related differences in Cd-induced testicular toxicity between inbred WI and F344 rats. Rats were treated with a single dose of 0.5, 1.0 or 2.0 mg Cd/kg, as CdCl₂, sc and killed 24 h later. Cd at doses of 1.0 and 2.0 mg/kg induced severe testicular hemorrhage, as assessed by pathological and testis hemoglobin content, in F344 rats, but not WI rats. After Cd treatment (2.0 mg/kg), the testicular Cd content was significantly lower in WI rats than in the F344 rats, indicating a toxiokinetic mechanism for the observed strain difference. Thus, the remarkable resistance to Cd-induced testicular toxicity in WI rats is associated, at least in part, with lower testicular accumulation of Cd. When zinc (Zn; 10 mg/kg, sc) was administered in combination with Cd (2.0 mg/kg) to F344 rats, the Cd-induced increase in testicular hemoglobin content, indicative of hemorrhage, was significantly reduced. Similarly, the testicular Cd content was significantly decreased with Zn co-treatment compared to Cd treatment alone. Thus, it can be concluded that the testicular Cd accumulation partly competes with Zn transport systems and that these systems may play an important role in the strain-related differences in Cd-induced testicular toxicity between WI and F344 rats.     

Changes in hepatic glutathione concentration modify cadmium-induced hepatotoxicity

Cd has a strong affinity for sulfhydryl groups and is hepatotoxic. Thus, to further understand the mechanism of Cd-induced liver injury, the effect of increased and decreased hepatic glutathione (GSH) concentration on Cd-induced liver injury was examined. Liver GSH was lowered by pretreating rats with phorone (250 mg/kg, ip) or diethyl maleate (0.85 mg/kg, ip) 2 hr prior to challenge with various doses of Cd. Ten hours after Cd (1) 40–80% of the rats pretreated with phorone or diethyl maleate and challenged with 1.0–2.0 mgCd/kg died whereas no mortality was observed in the control group; (2) plasma enzyme activities of alanine (ALT) and aspartate (AST) aminotransferase and sorbitol dehydrogenase (SDH) were markedly increased in phorone and diethyl maleate-pretreated rats challenged with Cd (0.7–2.0 mg/kg) versus control rats; and (3) moderate changes in liver histology were observed in corn oil pretreated and Cd challenged rats, while prior depletion of GSH potentiated histopathologic changes in liver produced by Cd alone. Another group of rats received cysteine (1.9 g/kg, po) 3 hr prior to injection of a lethal dose of Cd. Cysteine pretreatment increased liver GSH levels by 22% 3 hr after administration and attenuated Cd-induced liver injury as evidenced by marked decreases in plasma ALT, AST, and SDH activities. Pathological changes in liver were also reduced. These data indicate that liver reduced GSH concentration is important in modulating Cd-induced hepatotoxicity.     

iNOS-null mice are not resistant to cadmium chloride-induced hepatotoxicity

Acute administration of cadmium (Cd) to rats results in hepatotoxicity. Recent reports indicate that Kupffer cells, the resident macrophages of the liver, participate in the manifestation of Cd-induced hepatotoxicity. Nitric oxide (NO) is a reactive nitrogen radical produced by activated Kupffer cells via the induction of inducible nitric oxide synthase (iNOS). Nitric oxide can combine with superoxide to form peroxynitrite, a molecule that may participate in the toxic mechanisms of hepatotoxins, such as acetaminophen and bacterial endotoxin. It has been speculated that Cd also may exert its hepatotoxicity, in part, via the production of NO by iNOS. Therefore, this study was undertaken to determine whether iNOS contributes to Cd-induced hepatotoxicity. Wild-type (WT) mice were administered selective iNOS inhibitors (AMT and 1400W) concurrently and 3 h after administration of a hepatotoxic dose of Cd (4.0 mg Cd/mg). Additionally, WT and iNOS-null (iNOS-KO) mice were dosed iv with saline or 2.0, 2.5, 3.0, 3.5 or 4.0 mg Cd/kg. Serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) activities were quantified to assess liver injury. Administration of iNOS inhibitors failed to prevent Cd-induced hepatotoxicity. Also, Cd caused a dose-dependent increase in liver injury in both WT and iNOS-KO mice. The liver injury produced by Cd in the iNOS-KO mice was not different from that in WT at any dose. These data indicate that iNOS does not appear to mediate Cd-induced hepatotoxicity.     

Differential hepatotoxicity induced by cadmium in Fischer 344 and Sprague-Dawley rats.

A number of reports document that Fischer 344 (F344) rats are more susceptible to chemically induced liver injury than Sprague-Dawley (SD) rats. Cadmium (CdCl2), a hepatotoxicant that does not require bioactivation, was used to better define the biological events that are responsible for the differences in liver injury between F344 and SD rats. CdCl2 (3 mg/kg) produced hepatotoxicity in both rat strains, but the hepatic injury was 18-fold greater in F344 rats as assessed by plasma alanine aminotransferase (ALT) activity. This difference in toxicity was not observed when isolated hepatocytes were incubated with CdCl2 in vitro, indicating that other cell types contribute to Cd-induced hepatotoxicity in vivo. Indeed, the sieve plates of hepatic endothelial cells (EC) in F344 rats were damaged to a greater degree than EC in SD rats. Additionally, Kupffer cell (KC) inhibition reduced hepatotoxicity in both strains, suggesting that this cell type is involved in the progression of CdCl2-induced hepatotoxicity. Moreover, enhanced synthesis of heat shock protein 72 occurred earlier in the SD rat. Maximal levels of hepatic metallothionein (MT), a protein associated with cadmium tolerance, were greater in SD rats. These protective factors may limit CdCl2-induced hepatocellular injury in SD compared with F344 rats by reducing KC activation and the subsequent inflammatory response that allows for the progression of hepatic injury.     

Attenuation of cadmium-induced liver injury in senescent male fischer 344 rats: role of Kupffer cells and inflammatory cytokines

In the previous study we showed that senescent male Fischer 344 rats were resistant to Cd-induced hepatotoxicity compared with young-adult rats. In the present study we investigated the role of Kupffer cells and inflammatory cytokines in this effect of aging. The phagocytic activity of Kupffer cells, determined as the removal of carbon from blood, was stimulated by the administration of a hepatotoxic dose of Cd (3 mg/kg sc) in young-adult (5 months) rats but not in old (28 months) rats. Hepatic concentrations of interleukin (IL)-1beta and cytokine-induced neutrophil chemoattractant (CINC), but not of tumor necrosis factor-alpha or IL-6, were elevated in young rats treated with Cd. In old rats, however, the increase in IL-1beta produced by Cd was not statistically significant and the increase in CINC was much lower than in young-adult rats. Pretreatment with gadolinium chloride or cyclosporin A inhibited the elevations in hepatic cytokines and attenuated Cd-induced liver damage, assessed on the basis of serum alanine aminotransferase and sorbitol dehydrogenase activities. Cd-induced hepatotoxicity in the different treatment groups correlated well with hepatic levels of CINC (r = 0.98, p < 0.001) but not with those of IL-1beta. The results suggest that (1) Kupffer cell activation is essential for inflammatory liver damage from Cd, (2) IL-1beta and CINC are important mediators of the inflammatory response induced by Cd, and (3) the attenuation of Cd-induced liver injury in senescent rats is caused by an impairment in Kupffer cell activation, leading to a lower production of CINC and less inflammatory liver injury.     

Genetic background of resistance to cadmium-induced testicular toxicity in inbred Wistar-Imamichi rats

We have previously reported that inbred Wistar-Imamichi (WI) rats are highly resistant to cadmium (Cd)-induced testicular toxicity compared with inbred Fischer 344 (F344) rats. The present study was to elucidate the genetic background of resistance to Cd-induced testicular toxicity in WI rats. The genetic analysis of susceptibility to Cd-induced testicular toxicity was conducted by using Cd-resistant WI and Cd-sensitive F344 strains as the parental rats and by using the testicular hemoglobin level as the indicator. In the frequency distribution of testicular hemoglobin levels in parental, first filial (F₁) and second filial (F₂) rats treated with Cd at a dose of 2.0 mg/kg, F₁ rats had testicular hemoglobin levels intermediate to WI and F344 rats, and F₂ rats segregated into three groups of low, intermediate, and high phenotypes at the expected ratio. Furthermore, the backcross progeny between WI and F₁ or between F344 and F₁ segregated into two groups with the expected ratio. Based on a simple Mendelian genetic analysis, these segregation patterns lead us to conclude that two codominant alleles at a gene locus are responsible for the susceptibility to Cd-induced testicular toxicity in rats. This is the first report for the genetic analysis of susceptibility to Cd-induced testicular toxicity in inbred rat strains.     

Strain differences of cadmium-induced hepatotoxicity in Wistar-Imamichi and Fischer 344 rats: involvement of cadmium accumulation

We previously reported that Wistar-Imamichi (WI) rats have a strong resistance to cadmium (Cd)-induced lethality compared to other strains such as Fischer 344 (Fischer) rats. The present study was designed to establish biochemical and histological differences in Cd toxicity in WI and Fischer rats, and to clarify the mechanistic basis of these strain differences. A single Cd (4.5 mg/kg, s.c.) treatment caused a significant increase in serum alanine aminotransferase activity, indicative of hepatotoxicity, in Fischer rats, but did not in WI rats. This difference in hepatotoxic response to Cd was supported by pathological analysis. After treatment with Cd at doses of 3.0, 3.5 and 4.5 mg/kg, the hepatic and renal accumulation of Cd was significantly lower in the WI rats than in the Fischer rats, indicating a kinetic mechanism for the observed strain differences in Cd toxicity. Thus, the remarkable resistance to Cd-induced hepatotoxicity in WI rats is associated, at least in part, with a lower tissue accumulation of the metal. Hepatic and renal zinc (Zn) contents after administration were similarly lower in WI than in Fischer rats. When Zn was administered in combination with Cd to Fischer rats, it decreased Cd contents in the liver and kidney, and exhibited a significant protective effect against the toxicity of Cd. We propose the possibility that Zn transporter plays an important role in the strain difference of Cd toxicity in WI and Fischer rats.     

Tumor necrosis factor-alpha-null mice are not resistant to cadmium chloride-induced hepatotoxicity

Acute administration of cadmium results in hepatotoxicity. Recent reports indicate that Kupffer cells, the resident macrophages of the liver, participate in the manifestation of chemical-induced hepatotoxicity. Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that is a major product of Kupffer cells and mediates the hepatotoxic effects of lipopolysaccharide (LPS). It has been speculated that cadmium also may exert its hepatotoxicity via the production of TNF-alpha by the Kupffer cells. Therefore, this study was undertaken to determine whether mice deficient in TNF-alpha are resistant to Cd-induced hepatotoxicity. TNF-alpha-null (TNF-KO) and wild-type (WT) mice were dosed ip with saline, LPS (0.1 mg/kg)/Gln (d-galactosamine, 700 mg/kg), or CdCl2 (2.2, 2.8, 3.4, and 3.9 mg Cd/kg). Serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) activities were quantified to assess liver injury. Caspase-3 activity was quantified to assess hepatocellular apoptosis. LPS/Gln treatment increased ALT (17-fold) and SDH (21-fold) in WT mice. In contrast, LPS/Gln-treatment did not significantly increase ALT or SDH in TNF-KO mice. LPS/Gln-treatment caused a 7.8-fold increase in caspase-3 activity in WT mice but did not increase caspase-3 in TNF-KO mice. Cadmium caused a dose-dependent increase in liver injury in both WT and TNF-KO mice. However, the liver injury produced by Cd in the TNF-KO mice was not different from that in WT at any dose. No significant increase in caspase-3 activity was detected in any of the Cd-treated mice. These data indicate that, in contrast to LPS/Gln-induced hepatotoxicity, TNF-alpha does not appear to mediate Cd-induced hepatotoxicity.     

Attenuation of cadmium-induced liver injury in senescent male fischer 344 rats: role of metallothionein and glutathione

The influence of aging on the sensitivity of the liver to the acute toxicity of cadmium has not been studied previously in adult rats. In this study hepatotoxicity caused by a single sc injection of CdCl(2) was compared in 5-, 18-, and 28-month-old male Fischer 344 rats. Doses of Cd were adjusted on the basis of the mean lean body mass for each age group of rats, and liver injury was evaluated 24 h after treatment. Cd treatment produced substantial increases in serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) activities in 5- and 18-month-old rats, whereas no significant increases were observed in 28-month-old rats. Histologic examination of representative livers from each age group confirmed the findings for serum enzyme activity; hepatocellular necrosis was observed only in livers from 5- and 18-month-old rats. The attenuation of Cd hepatotoxicity in senescent rats did not appear to be related to pretreatment levels of metallothionein or glutathione. Likewise, resistance to Cd could not be explained on the basis of metallothionein induction, which decreased as a function of aging. Thus, the mechanisms that account for the postmaturational decline in sensitivity to Cd do not appear to be associated with alterations in levels of the major factors that protect against Cd-induced hepatotoxicity.     

Tolerance to cadmium-induced hepatotoxicity following cadmium pretreatment

Tolerance to several toxic effects of Cd, including lethality, has been shown following pretreatment with Cd. This study was designed to determine if tolerance also develops to Cd-induced hepatotoxicity. Rats were challenged with Cd (2.0, 3.0, 4.0, or 5.0 mg/kg, iv) 24 hr after pretreatment with saline (2 ml/kg, sc) or Cd (2.0 mg/kg, sc). Ten hours following challenge, plasma enzyme activities were dramatically elevated in control rats (sorbitol dehydrogenase 30- to 300-fold and aspartate aminotransferase 3- to 40-fold). In addition, histologic examination revealed moderate to severe hepatic injury, evidenced by cell swelling, cytoplasmic eosinophilia, pyknosis, karyorrhexis, and necrosis. In Cd-pretreated rats, plasma enzyme levels were similar to control values and only slight morphologic changes were evident. This tolerance to Cd-induced hepatotoxicity is probably due to the increase in hepatic metallothionein induced by Cd pretreatment, which has been shown to alter the hepatic subcellular distribution of Cd such that less binds to subcellular organelles and more binds to metallothionein located in the cytosol.     

Gadolinium chloride pretreatment prevents cadmium chloride-induced liver damage in both wild-type and MT-null mice

The heavy metal cadmium (Cd) causes hepatotoxicity upon acute administration. Kupffer cells, the resident macrophages of the liver, have been suggested to play a role in Cd-induced hepatotoxicity. Gadolinium chloride (GdCl3) may prevent Cd-induced hepatotoxicity by suppressing Kupffer cells. However, GdCl3 also induces the Cd-binding protein, metallothionein (MT). Therefore, this study was conducted to determine whether GdCl3 prevents Cd-induced hepatotoxicity via the induction of MT. Hepatic MT and Kupffer cell counts were analyzed 24 h after wild-type (WT) mice were administered saline or 10, 30, or 60 mg GdCl3/kg. GdCl3 induced MT in a dose-dependent manner without affecting nonprotein sulfhydryl content. All examined doses of GdCl3 were effective at eliminating Kupffer cells from the liver. To examine the hepatoprotective effects of GdCl3, WT and MT-null mice were pretreated with saline or 10, 30, or 60 mg GdCl3 24 h prior to a hepatotoxic dose of Cd (2.5 mg Cd/kg). Blood and livers were removed 16 h later and analyzed for hepatotoxicity as well as MT, Cd, and Kupffer cell content. Hepatotoxicity was alleviated in both WT and MT-null mice that were pretreated with 30 or 60 mg GdCl3/kg, indicating that MT induction is not required for the hepatoprotective effects of GdCl3. Hepatic Cd content was not decreased by GdCl3, demonstrating that GdCl3 does not negatively affect Cd distribution to the liver. Kupffer cells were depleted at all three doses of GdCl3, whereas hepatoprotection was only observed at doses of 30 and 60 mg GdCl3/kg. This does not rule out Kupffer cells in the mechanism of Cd-induced hepatotoxicity, but it does suggest that GdCl3 exerts hepatoprotective effects on the liver aside from depleting Kupffer cells. In summary, these data substantially rule out MT induction and decrease the importance of Kupffer cells as mechanisms of GdCl3-induced protection from Cd-induced hepatotoxicity.     

Strain differences in the responsiveness between Sprague-Dawley and Fischer rats to nephropathy induced by FYX-051, a xanthine oxidoreductase inhibitor

To determine a rat strain appropriate for carcinogenicity testing of FYX-051, a xanthine oxidoreductase inhibitor, we performed a 4-week oral toxicity study by administering 0.3, 1 and 3 mg/kg, and 1, 3 and 10 mg/kg of FYX-051 to male Sprague-Dawley (SD) and Fischer (F344) rats, respectively. Histopathology revealed that the degree of FYX-051-induced nephropathy was 3-fold stronger in SD rats than in F344 rats. Our previous study demonstrated that the key factor of species differences in FYX-051-induced nephropathy is purine metabolism. This observation led us to examine the involvement of purine metabolism in differences among two strains of rats. However, purine metabolism was proven not to be implicated as an important factor. Subsequently, other factors responsible for the strain differences were examined. FYX-051-induced increases in plasma xanthine concentrations were higher in SD rats than in F344 rats, suggesting more remarkable effects on pharmacodynamics in the former than the latter. Urinary volume was greater in F344 rats administered 10 mg/kg of FYX-051 (6.8 ml/h/kg) than in SD rats administered 3 mg/kg of FYX-051 (5.0 ml/h/kg), implying easier xanthine excretion in the former. Urinary xanthine solubility was 55 mg/dl in F344 rats aged 6 weeks, in contrast to 38 mg/dl in SD rats of the same age. Also, there were no significant differences in exposure levels at the same dose between SD and F344 rats. The outcomes of exposure levels and renal histopathology in both rats suggest the possibility that F344 rats could be exposed to a 3-fold higher amount of drug than SD rats in a carcinogenicity bioassay. The present study, therefore, suggested that strain differences of nephrotoxicity were caused by the combined effects of pharmacodynamics, xanthine excretion capacity, and urinary xanthine solubility. Furthermore, these results indicate that F344 rats would be a suitable strain for the carcinogenicity study of FYX-051.     

Strain comparisons of atrazine-induced pregnancy loss in the rat

Atrazine was administered by gavage, in 1% methylcellulose, to F344 Sprague-Dawley (SD), and Long Evans (LE) rats at 0, 25, 50, 100, or 200 mg/kg/day on gestation days 6 through 10. The dams were allowed to deliver and litters were examined postnatally. The F344 strain was the most sensitive to atrazine's effects on pregnancy, showing full-litter resorption (FLR) at >/=50 mg/kg. In surviving F344 litters, prenatal loss was increased at 200 mg/kg. In SD and LE rats, FLR occurred only at 200 mg/kg. Delayed parturition was seen at >/=100 mg/kg in F344 and SD rats. Regarding maternal toxicity, the SD dams were the most sensitive, with weight loss at >/=25 mg/kg. When 200 mg/kg was administered to F344 rats on days 11 through 15 (after the LH-dependent period of pregnancy), no FLR was seen. These findings suggest that atrazine-induced FLR is maternally mediated, and consistent with loss of LH support of the corpora lutea.     

Repeated cadmium exposures enhance the malignant progression of ensuing tumors in rats.

Prior studies show that a single subcutaneous (sc) exposure to cadmium (Cd) will induce injection site sarcomas (ISS) in rats. These tumors, thought clearly malignant, do not often metastasize or invade subdermal muscle layers because of their location. Recent evidence indicates that when tumorigenic cells chronically exposed to Cd in vitro are inoculated into mice, tumor progression and invasiveness in the mice are enhanced. Thus, we studied the effects of repeated Cd exposures on tumor incidence, progression, and metastatic potential in rats. Wistar (WF) and Fischer (F344) rats (30 per group) were injected sc in the dorsal thoracic midline with CdCl2 once weekly for 18 weeks with doses of 0, 10, 20, or 30 micromol Cd/kg. This resulted in total doses of 0, 180, 360, or 540 micromol/kg. One other group of each strain received a low, loading dose of Cd (3 micromol/kg) prior to 17 weekly injections of 30 micromol/kg (total dose 513 micromol/kg). Rats were observed for 2 years. Many F344 rats (57%) died within one week after the first injection of the highest dose, but WF rats were not affected. The low loading dose prevented acute lethality of the high dose in F344 rats. Surprisingly, latency (time to death by tumor) of ISS was the shortest in the groups given the low loading dose in both strains. ISS in these groups also showed the highest rate of metastasis and subdermal muscle layer invasion. Based on ISS incidence in the groups given the lowest total dose of Cd (180 micromoles/kg), F344 rats were more sensitive to tumor induction, showing an incidence of 37% compared to 3% in WF rats. On the other hand, Cd-induced ISS showed a higher overall metastatic rate in WF rats (18 metastatic ISS/68 total tumors in all treated groups; 27%) compared to F344 rats (6%). Immunohistochemically, the primary ISS showed high levels of metallothionein (MT), a cadmium-binding protein, while metastases were essentially devoid of MT. These results indicate that repeated Cd exposures more rapidly induce ISS. An initial low exposure to Cd further accelerates the appearance and enhances the metastatic potential and invasiveness of these tumors. The primary and metastatic ISS appear to have a differing phenotype, at least with regard to MT production. The association between multiple Cd exposures and enhanced metastatic potential of the ensuing tumors may have important implications in chronic exposures to Cd, or in cases of co-exposure of Cd with organic carcinogens, as in tobacco smoking.     

Strain sensitivity differences in the Hershberger assay

The Hershberger assay is a test method for detecting androgenic or antiandrogenic properties based on alterations in the weights of accessory sex organs in castrate male animals. We performed this study to examine strain sensitivity differences in the Hershberger assay. Flutamide (FLU) at a dose of 3.2 mg/kg was administered to castrated F344, SD, or Wistar rats, in addition to testosterone propionate (TP) administered at a dose of 0.4 mg/kg. Although FLU significantly attenuated the TP-induced increase in glans penis weight in SD and Wistar rats, this attenuation was not observed in F344 rats. Statistical analysis showed differences among the strains in all sex accessory organ weights. The interaction in the ventral prostate, seminal vesicle, and glans penis weights was significant between SD and F344 rats, and between Wistar and F344 rats, but not between SD and Wistar rats. F344 rats were less suitable than SD or Wistar rats for detecting FLU-induced changes.     

Zinc-induced tolerance to cadmium hepatotoxicity

Pretreatment with Zn is known to produce tolerance to several toxic effects of Cd. This study was designed to determine if zinc pretreatment decreased Cd-induced lethality and hepatotoxicity. Rats given 4.0 mg Cd/kg, iv, died within 10 to 20 hr while there was no mortality in rats pretreated with Zn (12 mg Zn/kg, sc, 48 and 24 hr prior to Cd challenge). Ten hr after Cd, plasma aspartate aminotransferase and sorbitol dehydrogenase activities were markedly elevated and extensive histopathologic lesions of the liver were evident in control rats while such injury was not evident in Zn-pretreated rats. To examine the mechanism of this tolerance, distribution of Cd to 14 organs and the subcellular distribution in 6 organs (liver, kidneys, intestines, heart, spleen, and testes) was determined in control and Zn-pretreated rats. Two hours after challenge (3.5 mg Cd/kg, iv, 7 μCi ¹⁰⁹Cd/mg Cd), the distribution of Cd to the liver markedly increased after Zn pretreatment without concomitant decreases in other tissues. Zn pretreatment resulted in distribution of more Cd to hepatic cytosol and less associated with endoplasmic reticulum. Gel filtration chromatography indicated that most cytosolic Cd was bound to metallothionein. These data suggest that Zn pretreatment reduces Cd-induced hepatotoxicity which prevents the lethal effects of Cd possibly by altering the hepatic subcellular distribution of Cd.     

Strain differences in tamoxifen sensitivity of Sprague-Dawley and Fischer 344 rats

Why some women are at increased risk for the development of endometrial carcinoma while taking the antiestrogen tamoxifen (Tam) for breast cancer treatment or prevention is unknown. Various strains of rodents display differences in sensitivity to compounds with estrogenic activity, but whether differences in Tam sensitivity exist in rodent strains has not been investigated. In the present study, we investigated whether rat strain differences in reproductive tract sensitivity to Tam and estrogen exist between Fischer 344 (F344) and Sprague Dawley (SD) rats. Immature (21-23 day; 6/group), ovariectomized F344 and SD rats were treated with vehicle (control), 17beta-estradiol (E2) [1 x 10 (-6) to 1.0 micro g/kg body weight (BW)] or 4-OH tamoxifen (4-OHT) (1 x 10 (-4) to 10 mg/kg BW) for 2 days and then sacrificed on day 3. Reproductive tracts were collected, weighed, and examined for changes in histomorphology and expression of ER and nuclear receptor co-regulators (SRC1, p300, CARM1, GRIP1, SPA, REA and Uba3). Treatment with E (1 x 10(-5) micro g/kg BW) increased ( <0.05) uterine epithelial cell height in F344 but not SD rats, demonstrating increased sensitivity of the F344 strain to E. Conversely, treatment with 1 x 10(-3) mg/kg BW 4-OHT increased ( <0.05) uterine weight and epithelial cell height in SD but not F344 rats, demonstrating that the SD strain is more sensitive to the antiestrogen. Northern and Western blot and immunohistochemical analysis revealed that ER expression levels in the SD and F344 uterus were not different. Expression of receptor co-regulators was higher in the uterus compared to the vagina regardless of strain and higher CARM1 expression was seen in SD uterus compared to F344 rats. Understanding differences in Tam sensitivity may help us to better understand why some women develop endometrial cancer while taking Tam and be beneficial in treatment decisions for breast cancer patients.     

Acetaminophen nephrotoxicity in the rat. I. Strain differences in nephrotoxicity and metabolism

Acetaminophen (APAP) produced renal necrosis restricted to the straight segment of the proximal tubule in Fischer 344 (F344) rats but not in Sprague-Dawley (SD) rats. APAP-induced renal functional changes (elevation in blood urea nitrogen and reduction in the accumulation of p-aminohippurate by renal cortical slices) also correlated with strain-dependent histopathological changes. Such strain differences have been attributed to differences in renal P-450 activation of APAP or the deacetylation of APAP to the nephrotoxic metabolite, p-aminophenol (PAP). Kidneys from F344 rats displayed greater concentrations of P-450 and greater ethoxycoumarin-o-deethylase activity than kidneys from SD rats. However, covalent binding of [ring-14C]APAP to renal and hepatic microsomal protein in vitro was similar for both SD and F344 rats. Deacetylation of APAP to PAP was similar in renal and hepatic homogenates from SD and F344 rats. Furthermore, isolated kidneys from SD and F344 rats perfused with APAP excreted PAP at similar rates. PAP excretion, over a 24-hr period following APAP administration, was greater in F344 rats than in SD rats only at the highest dose (900 mg/kg) of APAP. Thus, strain differences in APAP-induced nephrotoxicity apparently cannot be attributed to differences in P-450 activation of APAP or in deacetylation to the nephrotoxic metabolite, PAP.     

Sexual dimorphism of cadmium-induced toxicity in rats: involvement of sex hormones

The toxic effect of cadmium varies with sex in experimental animals. Previous studies have demonstrated that pretreatment of male Fischer 344 (F344) rats with the female sex hormone progesterone markedly enhances the susceptibility to cadmium, suggesting a role for progesterone in the sexual dimorphism of cadmium toxicity. In the present study, we attempted to further elucidate the mechanism for sex differences in cadmium-induced toxicity in F344 rats. A single exposure to cadmium (5.0?mg Cd/kg, sc) was lethal in 10/10 (100?%) female compared with 6/10 (60?%) male rats. Using a lower dose of cadmium (3.0?mg Cd/kg), circulating alanine aminotransferase activity, indicative of hepatotoxicity, was highly elevated in the cadmium treated females but not in males. However, no gender-based differences occurred in the hepatic cadmium accumulation, metallothionein or glutathione levels. When cadmium (5.0?mg Cd/kg) was administered to young rats at 5?weeks of age, the sex-related difference in lethality was minimal. Furthermore, although ovariectomy blocked cadmium-induced lethality, the lethal effects of the metal were restored by pretreatment with progesterone (40?mg/kg, sc, 7 consecutive days) or β-estradiol (200?μg/kg, sc, 7 consecutive days) to ovariectomized rats. These results provide further evidence that female sex hormones such as progesterone and β-estradiol are involved in the sexual dimorphism of cadmium toxicity in rats.     

Acetaminophen nephrotoxicity in the rat. II. Strain differences in nephrotoxicity and metabolism of p-aminophenol, a metabolite of acetaminophen

Acetaminophen (APAP) produces renal necrosis restricted to the straight segment of the proximal tubule in Fischer 344 (F344) rats. On the other hand, Sprague-Dawley (SD) rats are extremely resistant to the nephrotoxic effects of APAP. Such strain differences may be due to different susceptibilities to the nephrotoxic metabolite, p-aminophenol (PAP). PAP administration in both strains of rats resulted in a renal lesion indistinguishable from the APAP-induced renal lesion in F344 rats. The PAP-induced renal lesions in F344 rats, however, were generally more severe than those in SD rats. PAP-induced renal functional changes (elevation in blood urea nitrogen and reduction in the accumulation of p-aminohippurate by renal cortical slices) correlated with strain-dependent histopathological changes. Analysis of urinary metabolites over a 24-hr period following PAP administration (200 and 400 mg/kg) indicated that more PAP was excreted as APAP in SD than in F344 rats. Covalent binding of PAP to renal microsomes in vitro was much greater in F344 rats than in SD rats at substrate concentrations less than 5 mM. These results suggest that strain differences in PAP-induced nephrotoxicity may be related to differences in the intrarenal activation of PAP. Furthermore, strain differences in APAP-induced nephrotoxicity may be related to strain differences in the activation of the nephrotoxic metabolite, PAP.