A markedly diminished pleiotropic response to phenobarbital and structurally-related xenobiotics in Zucker rats in comparison with F344/NCr or DA rats.

Phenobarbital (PB) and certain structurally-related compounds induce a variety of hepatic drug-metabolizing enzymes in many strains of rats. Thus, following administration of PB (300, 500 ppm), barbital (BB, 1500 ppm) or 5-ethyl-5-phenylhydantoin (EPH, 500 ppm), CYP2B1-mediated benzyloxyresorufin O-dealkylase activity and epoxide hydrolase activity were profoundly induced in female DA and F344/NCr rats. In contrast, outbred female lean and obese Zucker rats showed markedly reduced CYP2B1 responses (less than 15% and less than 5% of those observed in the female DA or F344/NCr rat) to PB (doses less than or equal to 300 ppm), BB (1500 ppm) or EPH (500 ppm). In parallel studies, profound increases in RNA levels coding for CYP2B1, glutathione S-transferases Ya/Yc (alpha subclass), or epoxide hydrolase were detected in the female F344/NCr rat following treatment with PB (300 ppm), BB (1500 ppm) or EPH (500 ppm). In contrast, lean Zucker rats showed a strong response only to the highest dose of PB (500 ppm), implying that the diminished response in the Zucker rats may occur at some pretranslational level. Similar studies with lower doses of PB, EPH or BB in male lean Zucker rats showed a decreased response, relative to that in male F344/NCr rats. However, this insensitivity was not as profound as that observed in the female Zucker rats. In fact, the response to PB-type inducers in male or female Zucker rats is probably most clearly explained as a shift of the dose-response curve sharply to the right (decreased responsiveness, compared to F344/NCr or DA rats of the same sex). This decreased responsiveness of female lean Zucker rats to induction of CYP2B1, relative to that of F344/NCr rats, was also observed with the structurally-diverse PB-type inducers clonazepam, clotrimazole and 2-hexanone. In contrast, the female Zucker rat (obese or lean) displayed a pronounced response to induction of CYP1A-mediated ethoxyresorufin O-deethylase activity by beta-naphthoflavone, a prototype inducer of CYP1A1 and CYP1A2. The Zucker rat would thus appear to represent a potentially exploitable genetic model for examining the mechanism of enzyme induction by the myriad xenobiotics which induce a PB-type response.     

Effects of drug-metabolizing enzyme inducers on cephaloridine toxicity in Fischer 344 rats

High doses of cephaloridine produce necrosis of renal proximal tubular cells and this nephrotoxicity has been shown to be reduced by piperonyl butoxide (a mixed-function oxidase inhibitor) in rats and rabbits, and potentiated by phenobarbital (a mixed-function oxidase inducer) in rabbits but not rats. Phenobarbital is known to increase rabbit but not rat renal mixed-function oxidase activities; however, several other compounds such as polybrominated biphenyls (PBB), trans-stilbene oxide (TSO) and beta-naphthoflavone (BNF) have been shown to induce renal enzyme activities in rats. Thus, it was of interest to determine the effects of PBB, TSO and BNF on cephaloridine toxicity in Fischer 344 rats. Nephrotoxicity was estimated by measuring alterations in the kidney-to-body weight ratio, blood urea nitrogen and accumulation of p-aminohippurate (PAH) and tetraethylammonium by renal cortical slices. Hepatotoxicity was quantified as changes in serum glutamic pyruvic transaminase (SGPT) activity. Cephaloridine produced only minor changes in SGPT activity. Animals fed diet supplemented with 100 ppm of PBB for 10 days became less susceptible to cephaloridine nephrotoxicity. Similarly, pretreatment of animals with TSO (300 mg/kg) or BNF (100 mg/kg) for 4 days decreased cephaloridine toxicity. Thus, these results suggest that induction of renal drug-metabolizing enzyme activities by these 3 inducers may enhance some detoxification pathway(s) which convert cephaloridine to a non-toxic metabolite(s). Alternatively, treatments with these inducers may alter cephaloridine pharmacokinetics and decrease renal cortical accumulation of cephaloridine.     

Brevetoxin inhalation alters the pulmonary response to influenza A in the male F344 rat

Epidemiological studies demonstrated that the number of emergency-room visits for respiratory indications increases during periods of Florida Red Tides. The purpose of this study was to examine whether or not repeated brevetoxin inhalation, as may occur during a Florida Red Tide, affects pulmonary responses to influenza A. Male F344 rats were divided into four groups: (1) sham aerosol/no influenza; (2) sham aerosol/influenza; (3) brevetoxin/no influenza; and (4) brevetoxin/influenza. Animals were exposed by nose-only inhalation to vehicle or 50 μg brevetoxin-3/m3, 2 h/d for 12 d. On d 6 of aerosol exposure, groups 2 and 4 were administered 10,000 plaque-forming units of influenza A, strain HKX-31 (H3N2), by intratracheal instillation. Subgroups were euthanized at 2, 4, and 7 d post influenza treatment. Lungs were evaluated for viral load, cytokine content, and histopathologic changes. Influenza virus was cleared from the lungs over the 7-d period; however, there was significantly more virus remaining in the group 4 lungs compared to group 2. Influenza virus significantly increased interleukins-1α and -6 and monocyte chemotactic protein-1 in lung; brevetoxin exposure significantly enhanced the influenza-induced response. At 7 d, the severity of perivascular and peribronchiolar inflammatory cell infiltrates was greatest in group 4. Bronchiolitis persisted, with low incidence and severity, only in group 4 at d 7. These results suggest that repeated inhalation exposure to brevetoxin may delay virus particle clearance and recovery from influenza A infection in the rat lung.     

Effects of the oxazolidinedione anticonvulsants trimethadione and dimethadione and the barbiturate homolog 5,5-dimethylbarbituric acid onN-nitrosodiethylamine-initiated renal and hepatic carcinogenesis in the F344/NCr rat

The oxazolidinedione anticonvulsant trimethadione (3,5,5-trimethyl-2,4-oxazolidinedione, TMO) as well as its major metabolite, dimethadione (5,5-dimethyl-2,4-oxazolidinedione, DMO), and a structural analog from the barbiturate series, 5,5-dimethylbarbituric acid (DMB), were fed to F344/NCr male rats previously given a single initiating injection of N-nitrosodiethylamine (NDEA). The known promoter, phenobarbital (5-ethyl-5-phenylbarbituric acid, PB), was employed in this study as a positive control. At dosage levels equimolar to 500 ppm PB, none of the three compounds promoted development of hepatocellular adenomas or carcinomas, in contrast to PB. The two oxazolidinedione analogs and DMB caused minimal or no induction of cytochrome P450 isozyme 2B1 (CYP2B1)-mediated alkoxyresorufin O-dealkylase activities following short-term (2 weeks) feeding to separate groups of 6-week-old male F344/NCr rats, in contrast to the dramatic induction caused by PB. Promotion of neither thyroid nor renal neoplasia was observed following prolonged feeding of any of the tested compounds, although a significantly higher frequency of premalignant renal cortical tubular lesions (dysplasias) was seen in rats exposed to TMO following NDEA initiation than in those treated with NDEA alone. These studies provide important additional data on structure/liver tumor promoting activity relationships, and yield further evidence that within this group of structurally related anticonvulsants, it is possible to separate anticonvulsant activity from tumor promoting activity in the rat liver.     

Prevention of nickel subsulfide carcinogenesis by local administration of Mycobacterium bovis antigen in male F344/NCr rats

This study was designed to determine the effect of local inflammation on nickel subsulfide (Ni3S2) carcinogenesis. Male F344/NCr rats, 6-week-old, 20 rats/group, received a single i.m. injection of 2.5 mg of Ni3S2 alone or 2.5 mg of Ni3S2 mixed with either 0.5 mg of Mycobacterium bovis lyophilized cell walls (MB), 1 mg cortisol (CORT), or 1 mg indomethacin (IND). Two more groups of rats received i.m. Ni3S2 alone, as above, followed by a single s.c. dose of either 1 mg MB or 2 mg IND. The i.m. injections were made into the thigh muscles of both hind limbs; the s.c. injections were made at the neck area. The experiment was terminated at 71 weeks. The final yields of injection site sarcomas were 85% in the Ni3S2, 85% in the Ni3S2 + CORT, and 80% in the Ni3S2 + IND group. Only one injection site tumor (5%) was found in rats given i.m. Ni3S2 + MB. In contrast, the s.c. MB injection enhanced muscular carcinogenicity of Ni3S2 by shortening the latency and increasing the yield of tumors to 100% at week 39 (P less than 0.04 vs. Ni3S2 alone). The s.c. treatment with IND gave similar, though statistically nonsignificant results; 100% tumor yield was reached at week 42 (P less than 0.18 vs. Ni3S2 alone). Although local treatment with CORT or IND had no significant effect on the final tumor incidence by Ni3S2, it shortened the latency of tumors to 17 weeks compared with 23 weeks for Ni3S2 alone. MB, CORT, IND, or the injection vehicle (water) alone did not produce tumors. Local MB treatment had no significant effect on the retention of Ni3S2 at the injection site. The prevention of the Ni3S2 tumors by local MB might result from localization of numerous natural killer cells and macrophages and formation of giant cells observed at the injection site of Ni3S2, 1-14 days post injection. These cells could immobilize the carcinogen and destroy Ni3S2-transformed cells.     

Change of the sex-dependent response to clofibrate in F344 rat liver during postnatal development

Although it has been reported that male rats are more responsive than females to peroxisome proliferation induced by clofibrate, these sex differences have been confirmed in young adult rats. Using 4-, 8-, and 12-week-old F344 rats, postnatal change of the sex-dependent response to clofibrate was investigated. These animals were administered 200 mg/kg body wt./day clofibrate by gavage for 7 days. In 4-week-old rats clofibrate-dependent changes (hepatomegaly, induction of hepatic microsomal and peroxisomal enzymes, proliferation of smooth endoplasmic reticulum and peroxisomes of hepatocytes) were slight in both sexes. In 8- and 12-week-old rats clofibrate-induced changes of males were moderate, whereas those of females were slight. These results suggest that the responsiveness of immature rat to clofibrate is weak and in males the susceptibility is gradually strong during postnatal development.     

Lack of renal tumour-initiating activity of a single dose of potassium bromate, a genotoxic renal carcinogen in male F344/NCr rats.

The renal tumour-initiating activity of potassium bromate (KBrO3), a known genotoxic rat renal carcinogen, was investigated in male F344/NCr rats. 6-wk-old rats were given KBrO3 intragastrically as a single dose of 300 mg/kg body weight, which was confirmed by our preliminary toxicity study as a maximum tolerated single dose for this strain of rat. Starting 2 wk after KBrO3 treatment, groups of 39 rats received either a basal diet or a diet containing 4000 ppm barbital sodium (BBNa) as a promoting regimen and were killed at 30, 52, or 104 wk. Control rats received either dietary BBNa (4000 ppm) or the basal diet alone from wk 2 to 52 or 104 wk. Nephropathy was observed in all rats treated with KBrO3 followed by BBNa at 30 wk and in rats receiving BBNa alone, but not in rats exposed to KBrO3 alone. Dysplastic renal tubular cell foci (DTF), putative preneoplastic renal tubular cell lesions were found associated with nephropathy in rats exposed to KBrO3 followed by BBNa from 47 wk. The incidences and multiplicities of DTF and renal tubular cell tumours observed from 31 to 104 wk revealed no initiating effect of KBrO3 treatment. These results indicate that the KBrO3 dose of 300 mg/kg did not initiate renal carcinogenesis.     

Effects of hepatic microsomal enzyme inducers of the endogenous substrates vitamin D3 and folate in rat.

A procedure for the estimation of possible effects of potential inducers of hepatic microsomal enzymes on vitamin D₃ metabolism has been devised. Together with methods for the determination of plasma folate and urinary formimino glutamic acid levels, it has been applied to a 43 day study in rats. Two anticonvulsants, phenobarbitone and pheneturide. were employed as inducers. Although both compounds had variable yet positive effects on enzyme induction, only the former had a significant action on vitamin D₃ metabolism and plasma folate levels. These results are discussed in relationship to results from previous work carried out, predominantly in man.     

Enhancement of N-nitrosodiethylamine-initiated hepatocarcinogenesis by phentoin in male F344/NCr rats at a dose causing maximal induction of CYP2B

The effect of the clinically important anticonvulsant phenytoin (DPH) on hepatocarcinogenesis of male F344/NCr rats initiated with a single i.p. dose of N-nitrosodiethylamine (75 mg/kg b.w.) was studied. Beginning 2 weeks post-initiation, the rats received control diet or diet containing 500 or 1,500 ppm DPH or 500 ppm phenobarbital. At 52 weeks age, the incidences (and multiplicities, in units of tumors per tumor-bearing rat) of hepatocellular adenomas were 0%, 17% (1 +/- 0), 42% (1.8 +/- 0.8), or 67% (2.5 +/- 1.9) in rats exposed to N-nitrosodiethylamine alone, or the carcinogen followed by 500 ppm DPH, 1,500 ppm DPH, or 500 ppm phenobarbital, respectively. Between 53 and 79 weeks of age, 39% of rats receiving N-nitrosodiethylamine alone developed multiple (1.5 +/- 0.8) hepatocellular adenomas. A similar incidence (41%) occurred in the rats administered the carcinogen followed by 500 ppm DPH. The incidence of hepatocellular adenomas (88% and 89%) was significantly greater in rats exposed to N-nitrosodiethylamine followed by 1,500 ppm DPH or 500 ppm phenobarbital, respectively. Multiplicities of hepatocellular adenomas were significantly greater than the control value in rats fed 1,500 ppm DPH or 500 ppm phenobarbital (5.9 +/- 4.8 and 10.1 +/- 6.7, respectively), but not in the rats receiving 500 ppm DPH (2.3 +/- 1.6). No rats exposed to N-nitrosodiethylamine alone or the carcinogen followed by 500 ppm DPH developed hepatocellular carcinomas, while hepatocellular carcinomas occurred in 29% or 67% of the rats given 1,500 ppm DPH or 500 ppm phenobarbital, respectively, following initiation. Increases in hepatic CYP2B-mediated benzyloxyresorufin O-dealkylation activity in rats exposed to 500 and 1,500 ppm DPH for 2 or 23 weeks were approximately 50% and approximately 100%, respectively, of the maximal induction caused by 500 ppm phenobarbital. Thus, in the rat model, DPH enhanced N-nitrosodiethyl-amine-initiated hepatocarcinogenesis when administered at a dose causing maximal CYP2B induction.     

A predictive F344 rat immunotoxicology model: cellular parameters combined with humoral response to NP-CgammaG and KLH

The purpose of this study was to examine the predictive value of humoral and cellular immune parameters in determining the immunotoxic effects of the oral administration of azathioprine (AZA), cyclophosphamide (CY), or cyclosporin A (CsA) at doses of 25/17, 10, or 25 mg/kg per day, respectively, for 30 days in F344 female rats. The effect of these known immunosuppressive compounds on the immune response was assessed in a humoral model that consisted of the administration of nitrophenyl-chicken gamma globulin (NP-CgammaG) and keyhole limpet hemocyanin (KLH) antigens during immunosuppressive treatment and the measurement of resulting rat antigen-specific IgG and IgM, as well as total IgG, levels. Cellular assessment parameters were collected from the same groups of animals as the humoral parameters and included organ weights and cellularity, hematology, lymphocyte phenotype characteristics, spleen cell mitogen stimulation (T and B cell-dependent), splenic natural killer (NK) cell cytotoxicity, and bone marrow cellularity and lymphocyte phenotype differential. Although decreases in several of the cellular assay parameters were observed, the only functional assays to demonstrate a statistically significant immunosuppressive effect by all three immunosuppressive agents were the antigen-specific serum IgG levels. The primary (day 10; 15 days post-immunization) and secondary (day 25; 5 days post-rechallenge) nitrophenyl (NP) responses were significantly suppressed by > or =60%. The use of NP hapten provided consistent responses when analyzed with a sensitive, well developed, ELISA methodology. Absolute lymphocyte phenotyping and lymphocyte hematology were also predictive of T cell immunosuppression for all three compounds. The data presented herein suggests that these two parameters, NP-IgG humoral response and lymphocyte phenotyping, are sufficient for identifying immunosuppressive compounds.     

Effects of microsomal enzyme inducers upon UDP-glucuronic acid concentration and UDP-glucuronosyltransferase activity in the rat intestine and liver.

This study was conducted to evaluate UDP-glucuronosyl-transferase (UDP-GT) activity, UDP-glucuronic acid (UDP-GA) concentration, and UDP-glucose (UDPG) concentration in the rat intestine and liver following oral administration of butylated hydroxyanisole (BHA), benzo[a]pyrene (BaP), 3-methylcholanthrene (3MC), phenobarbital (PB), pregnenolone-16 alpha-carbonitrile (PCN), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), or trans-stilbene oxide (TSO). Microsomal UDP-GT activity was assayed in vitro with acetaminophen (AA), harmol (HA), and 1-naphthol (NA) as the aglycones. Intestinal HA and AA glucuronidation were enhanced by BHA, BaP, and TSO, whereas 3MC, PB, PCN, and TCDD augmented hepatic HA-glucuronide formation and BHA, PB, PCN, TCDD, and TSO significantly increased hepatic AA glucuronidation. All inducing agents except PB and PCN markedly increased both intestinal and hepatic NA glucuronidation. PB, PCN, and TCDD paradoxically decreased intestinal glucuronidation of AA and HA. A similar effect upon hepatic glucuronidation was not observed with any of the agents studied. Hepatic UDP-GA concentration was increased significantly by all inducers studied except PCN and TCDD, whereas hepatic UDPG concentration was increased only by BHA. In the intestine, significant increases in UDP-GA concentration were produced only by BHA and BaP, which also elevated intestinal UDPG. These results demonstrate that microsomal enzyme inducers evoke different effects upon intestinal and hepatic glucuronidation. These differences are manifested with regard to induced changes in UDP-GT activity as well as treatment-induced alterations in UDP-GA content. Thus, the present study further underscores the marked variance of intestinal and hepatic xenobiotic glucuronidation.     

Toxicokinetics of 4-methylimidazole in the male F344 rat

1. The toxicokinetics and metabolism of 4-methylimidazole (4-MZ) have been studied in the male F344 rat using ¹⁴C radiolabelled compound. Radioactivity in plasma and urine was profiled by hplc.

2. After gavage administration of 50?mg/kg, about 85% of the administered radioactivity was recovered in urine within 48?h. The majority of the radioactivity in urine or plasma was associated with the parent compound and only one minor hydrophilic metabolite was present in urine and in plasma. Elimination of radioactivity via fecal, biliary or respiration was negligible.

3. Elimination of 4-MZ after an i.v. dose of 5mg/kg can be described by a two-compartment process with an estimated half-life of 1.8?h and an estimated apparent volume of distribution of 2.3 litre/kg.

4. After gavage at doses of 5, 50 and 150?mg/kg, 4-MZ was readily absorbed with a estimated bioavailability of 60–70%.

5. Urinary excretion data indicated that renal clearance of 4-MZ accounted for about 80% of total body plasma clearance. Based on the estimated AUC of metabolite and the estimated renal clearance of 4-MZ, the formation of metabolite and the renal clearance of 4-MZ appeared to be a saturable process.     

Effects of perinatal exposure to bisphenol A on the behavior of offspring in F344 rats

The objective of this investigation is to evaluate whether perinatal maternal exposure to bisphenol A (BPA) at 4, 40, and 400 mg/kg per day affects the behavior of offspring in F344 rats. Perinatal BPA exposure inhibited the body weight increases of male and female offspring in a dose-dependent manner, which continued after weaning. Spontaneous activity analyses revealed that BPA elongated immobile time during the dark phase in female offspring. At 4 weeks of age, male offspring exposed to BPA at 40 and 400 mg/kg per day performed avoidance responses significantly higher in the shuttlebox avoidance test. At 8 weeks of age, however, male offspring only at 4 mg/kg per day showed significantly lower responses. In the open-field behavior test at 8 weeks of age, male offspring exposed to BPA only at 4 mg/kg per day showed a higher percent of grooming than the control male offspring. In conclusion, perinatal exposure to BPA caused the behavioral alterations in the offspring.     

Morphine-induced conditioned taste aversions in the LEW/N and F344/N rat strains

Previous reports have shown that the LEW/N and F344/N inbred rat strains display a differential sensitivity to cocaine in a number of preparations, with the LEW/N rats displaying an increased sensitivity to both the reinforcing and aversive effects of cocaine (relative to the F344/N rats). Given that the LEW/N rats are also more sensitive to the reinforcing effects of morphine than the F344/N strain, the present experiment examined the ability of morphine to condition taste aversions in the LEW/N and F344/N strains to determine if the general sensitivity to cocaine generalizes to another drug of abuse. Specifically, on four conditioning trials, 35 LEW/N and 33 F344/N female rats were allowed access to a novel saccharin solution and then injected with varying doses of morphine (0, 10, 32 and 56 mg/kg). On intervening recovery days, subjects were allowed 20-min access to water. Following the fourth trial, a final aversion test was administered. The F344/N rats, but not the LEW/N rats, rapidly acquired morphine-induced taste aversions at all doses of morphine. Pharmacokinetic differences between the strains were also assessed. Specifically, 10 mg/kg morphine (or vehicle) was administered to subjects of both strains and plasma morphine levels were analyzed at 0.5, 2 and 4 h postinjection. No differences in plasma levels between the strains were observed. Unlike with cocaine, the LEW/N rats do not seem generally sensitive to morphine (relative to the F344/N rats). Rather, the differential sensitivity of the two strains to these compounds seems to be preparation dependent. Possible mechanisms underlying the differential sensitivity evident in the strains were discussed.     

Metabolism of [14C]benzyl selenocyanate in the F344 rat.

Benzyl selenocyanate (BSC), a synthetic organoselenium compound, has been shown to inhibit chemically induced tumors in several animal model systems. However, it is not known whether BSC or one of its metabolites is responsible for the chemopreventive effect. An initial approach to this question requires the structural elucidation of BSC metabolites in vitro and in vivo. To determine the structures of BSC metabolites in vitro, we studied the metabolism of [14C]BSC using Aroclor-induced rat liver 9000g supernatant. Under these conditions, BSC was partially converted to dibenzyl diselenide (DDS) and phenylmethaneseleninic acid. The metabolism of [14C]BSC (12.5 mg/kg body weight, 8 mCi/mmol, oral administration) in male F344 rats was also studied. Excretion was monitored by measurement of radioactivity as well as by selenium content using atomic absorption spectrophotometry (AAS). The results indicate that urine was the major route of excretion. Approximately 22% of the dose was excreted in the urine over the course of 35 days; however, a large portion (approximately 70%) of the dose remained in the body. Benzoic acid, hippuric acid, and their sulfate and glucuronide conjugates, accounting for 16% of the dose, were identified in the urine. The formation of these metabolites indicates that BSC is metabolized in part via bond cleavage between the benzyl moiety and the selenocyanate function. Additional support for this cleavage was obtained from fecal analysis; over the course of 23 days 9% of the selenium (AAS) but only less than 1% of the radioactivity was recovered in feces. No radioactivity was detected in the exhaled air. We also studied the metabolism of [14C]DDS (17.3 mg/kg body weight, 2.5 mCi/mmol) in male F344 rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Toxicokinetics of pentachlorophenol in the F344 rat. Gavage and dosed feed studies

1. The toxicokinetics of pentachlorophenol (PCP) were studied in the Fischer 344 rat using i.v. and oral (gavage, dosed feed) routes of exposure.

2. Only minor sex differences were observed in the elimination kinetics of PCP after i.v. administration at 5?mg/kg.

3. Absorption of PCP from the gastrointestinal tract after gavage doses of 9.5 and 38?mg/kg in aqueous methylcellulose vehicles was first order with an absorption half-life of about 1.3?h.

4. The absorption rate constant of PCP from doses feed was comparable with that obtained from aqueous methylcellulose gavage formulations.

5. Bioavailability of PCP administered in dosed feed was significantly lower than the bioavailability of PCP administered by gavage.

6. Dose proportionality was established to a dosage of at least 38?mg/kg.

7. Daily fluctuation of PCP plasma concentrations was observed during the dosed feed study with peak and trough concentrations occurring in early morning and late afternoon, respectively.

8. The time course of PCP plasma concentrations during the dosed feed study were simulated using a computer model based on linear theory. The simulations were comparable with the experimentally determined concentrations.     

Biochemical characterisation of para-aminophenol-induced nephrotoxic lesions in the F344 rat

The acute biochemical effects of the nephrotoxin p-aminophenol (PAP) were studied in detail using a combination of conventional bioanalytical and ¹H-NMR spectroscopic methods. Dosing PAP (25–100 mg/kg) to male F344 rats resulted in a dose-related proximal nephropathy with consequent elevations in urinary enzymes, glucose, and urine total protein as shown by conventional methodology. ¹H-NMR spectroscopy at 400 MHz of urine from PAP-treated rats also revealed a characteristic glycosuria, with concomitant amino aciduria. The increased excretion of these compounds indicates functional defects in the proximal tubule and reduced solute reabsorption efficiency. In addition, ¹H-NMR urinalysis and conventional enzymatic analysis showed a dose-related lactic aciduria. Other changes detected by ¹H-NMR included a dose-related reduction in the excretion of citrate (confirmed by a conventional biochemical method) and an increase in the excretion of acetate. The degree of abnormalities shown by ¹H-NMR urinalysis agreed well with histopathological observations and conventional biochemical indices of nephrotoxicity. ¹H-NMR urinalysis therefore serves to highlight changes in the excretion of low MW urine components not routinely studied by conventional biochemical analysis.Abbreviations ALP alkaline phosphatase - APAP paracetamol - BUN blood urea nitrogen - GFR glomerular filtration rate - GOT glutamate oxaloacetate transaminase - LAP leucine aminopeptidase - LDH lactate dehydrogenase - MW molecular weight - NAG N-acetyl--D-glucosaminidase - PAP p-aminophenol - ppm parts per million - TMAO trimethylamine N-oxide - UFR urine flow rate     

Chronic toxicity of sodium nitrite in the male F344 rat

A long-term feeding study was carried out in rats with sodium nitrite. The test substance was administered as part of a reduced-protein diet to groups of 50, 6-wk-old, male F344 rats at dose levels of 0.2 or 0.5% (w/w) sodium nitrite for up to 115 wk. A control group of 20 males received the reduced-protein diet alone. Throughout the study, there was a dose-related decrease in the rates of body-weight gains and a corresponding decrease in body weights among animals fed sodium nitrite in the diet. Food intakes of rats in the low-dose group were slightly raised over most of the study. In the high-dose group, food intakes were reduced during the first month, but thereafter were similar to those of the control group. This reduction in food intake together with the lower body weights in the nitrite-treated animals, may indicate a reduction in food utilization. In the first week of treatment the following haematological parameters were reduced: red blood cell count, haematocrit and haemoglobin concentration. The red blood cell count continued to fall for 8 wk, then slowly returned to normal by wk 52. A dose-related reduction was noted in both the incidence and time of onset of lymphomas, leukaemias and testicular interstitial cell tumours. Leukaemias were only found in animals with lymphoma, indicating an association between the two lesions. Under the conditions described in this study, sodium nitrite was found not to be carcinogenic when fed to rats in the diet for up to 115 wk, but rather that the incidence of tumours was reduced in a dose-related manner, which correlated with a similar trend in body weights.     

Effects of microsomal enzyme inducers on outer-ring deiodinase activity toward thyroid hormones in various rat tissues

Microsomal enzyme inducers, such as phenobarbital (PB), pregnenolone-16alpha-carbonitrile (PCN), 3-methylcholanthrene (3MC), and Aroclor 1254 (PCB) are more effective at reducing serum thyroxine (T(4)) than serum triiodothyronine (T(3)). It is possible that rats treated with PB and PCN maintain serum T(3) by increasing serum TSH, which stimulates the thyroid gland to synthesize more T(3). However, it is unclear how serum T(3) is maintained in rats treated with 3MC or PCB, because serum TSH is not increased in these rats. We hypothesized that increased conversion of T(4) to T(3), catalyzed by outer-ring deiodinases (ORD) type-I and -II, is the reason serum T(3) is maintained in rats treated with 3MC or PCB. Furthermore, 3MC and PCB do not increase serum TSH, whereas PB and PCN do, because type-II ORD activity in the pituitary of 3MC- and PCB-treated rats is increased greater than in rats treated with PB or PCN. To test these two hypotheses, male Sprague-Dawley rats were fed either a basal diet or a diet containing PB (300, 600, 1200, or 2400 ppm), PCN (200, 400, 800, or 1600 ppm), 3MC (50, 100, 200, or 400 ppm), or PCB (25, 50, 100, or 200 ppm) for 7 days. Type-I ORD activity was measured in thyroid, kidney, and liver, whereas type-II ORD activity was measured in brown adipose tissue, pituitary, and brain. Type-I ORD activity in thyroid was not affected by PB, 3MC, or PCB treatments, and was slightly increased by PCN. Type-I ORD activity in kidney was not affected by PB, PCN, or 3MC treatments, and was reduced by PCB treatment. Type-I ORD activity in liver was reduced by PB, PCN, 3MC, and PCB treatments. Type-II ORD activity in brown adipose tissue was unaffected by any of the four treatments. Type-II ORD activity in pituitary was unaffected by PB or 3MC treatments, and was increased by PCN or PCB treatments. Type-II ORD activity in brain was unaffected by PB treatment, and was increased by PCN, 3MC, and PCB treatments. Overall, total ORD activity, calculated by summation of ORD activities in thyroid, kidney, liver, brown adipose tissue, pituitary, and brain, was reduced rather than increased by the four microsomal enzyme inducers. In conclusion, increased conversion of T(4) to T(3) is not the reason serum T(3) concentration is maintained in 3MC- or PCB-treated rats. Furthermore, the reason serum TSH is not increased in 3MC- and PCB-treated rats is the result of mechanisms other than increased type-II ORD activity in pituitary.