Potential estrogenic and antiestrogenic activity of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and the linear siloxane hexamethyldisiloxane (HMDS) in immature rats using the uterotrophic assay.

The cyclic siloxane octamethylcyclotetrasiloxane (D4) and the linear siloxane hexamethyldisiloxane (HMDS) have numerous industrial and consumer applications and thus have the potential for human exposure. The present study was undertaken to examine potential estrogenic and antiestrogenic activities of D4 and HMDS. To address potential differences in sensitivity between rat strains the study used both Sprague-Dawley (SD) and Fischer 344 (F-344) rats. Estrogenicity of the test compounds was determined by measuring absolute and relative uterine weights in immature rats and by monitoring uterine epithelial cell height. In order to place the data obtained for D4 into perspective relative to strong and weak estrogenic compounds, the response produced by D4 at 0, 10, 50, 100, 250, 500, and 1000 mg/kg/day was compared to responses produced by ethinyl estradiol (EE) (1, 3, 10, or 30 microg/kg/day), diethylstilbestrol dipropionate (DES-DP) (0.5, 1.5, 5, 15 microg/kg/day), and coumestrol (CE) (10, 35, 75, 150 mg/kg/day). Antiestrogenic effects were evaluated by co-administering D4 (500 mg/kg/day) with EE at 1, 3, 10, and 30 microg /kg/day. All compounds were administered in sesame oil at a volume of 5 mL/kg by oral gavage. Beginning on postnatal day 18 (SD) or 21 (F-344) each pup (12 per group) received a single dose of test compound once a day for 4 consecutive days. The pups were euthanized the morning after the last treatment and their uteri removed, weighed, and processed for histological examination. EE and DES-DP produced a significant dose-dependent increase in absolute and relative uterine weights and uterine cell height. The maximum increase in uterine weight following EE exposure was approximately 350% relative to controls in both strains. The weak phytoestrogen CE also produced a dose-related increase in absolute and relative uterine weight and epithelial cell height, but the response occurred over a much higher range of doses. At the highest dose of CE, uterine weight was increased approximately 230% relative to controls. Following exposure to D4, absolute and relative uterine weights and uterine epithelial cell height were statistically significantly increased in both strains of rats at doses above 100 mg/kg/day. In terms of uterine weight, D4 was approximately 0.6 million times less potent than EE or DES-DP in SD pups and 3.8 million times less potent than EE or DES-DP in F-344 pups. The maximal increase in uterine weight, relative to controls, produced by D4 at 1000 mg/kg/day was approximately 160% in SD rats, while the maximum increase produced by D4 in F-344 rats was 86%. D4 co-administered over a wide range of EE doses, resulted in a significant reduction in uterine weight compared to EE alone. HMDS was evaluated in SD rats only. The response produced by HMDS (600 and 1200 mg/kg/day) was compared to EE (3 microg/kg/day). Antiestrogenic effects were evaluated by co-administering HMDS (1200 mg/kg/day) with EE at 3 microg/kg/day. HMDS had no measurable effect on uterine weight under the experimental conditions described here. However, HMDS coadministered with EE did produce a small, but statistically significant reduction in uterine weight compared to EE alone. In conclusion, D4 showed weak estrogenic and antiestrogenic activity that was several orders of magnitude less potent than EE, and many times less potent than the weak phytoestrogen CE.     

Effect of inhaled dimethylselenide in the Fischer 344 male rat.

In this project, a total of 60 adult Fischer 344 male rats were exposed to dimethylselenide (DMSe) vapor at 1607, 4499, or 8034 ppm for 1 h (20 rats/group). In addition, 26 unexposed rats were used as controls. The exposed rats were observed frequently during the 7 d following exposure and appeared normal. The animals were sacrificed at either 1 or 7 d after inhalation and the major tissues were grossly examined and weighed. Selenium levels were found to be elevated only in the lung at d 1. At d 1, significant changes in organ weights were an increase in the lung weight at exposure levels of 1607 and 8034 ppm of DMSe and in liver weight at 4499 and 8034 ppm. At d 1, significant changes in the lung were an increase in protein at 1607 and 8034 ppm of DMSe, and an increase in RNA and a reduction in DNA at 4499 ppm DMSe. The only change in the liver was a reduction in DNA at 4499 ppm. At 7 d, the protein content and RNA content of spleen were increased. Lung, liver, kidney, spleen, thymus, lymph nodes, pancreas, and adrenal gland were examined microscopically and found to be normal. All of these observed responses were minor and did not severely impact the health of the rats. Overall, the data indicate that the inhalation of DMSe for 1 h has relatively low toxicity in rats even at high concentrations.     

Role of para-hydroxylation in phensuximide-induced urotoxicity in the Fischer 344 rat.

Phensuximide (PSX) is an antiepileptic agent which has been shown to induce hemorrhagic cystitis and mild nephrotoxicity following repeated administration in man or rats or when acutely administered to phenobarbital-pretreated rats. The purpose of this study was to explore the role of para-hydroxylation of the phenyl group of PSX in PSX-induced urotoxicity. Two PSX derivatives, 2-(4-fluorophenyl)-N-methylsuccinimide (FMPS) and N-methyl-2-(4-methylphenyl)succinimide (MMPS), were synthesized and evaluated for urotoxic potential. Male Fischer 344 rats (four rats/group) were administered intraperitoneally (i.p.) a succinimide (0.4 or 1.0 mmol/kg) or vehicle and renal function monitored for 48 h. In a separate experiment, rats were pretreated with phenobarbital (75 mg/kg/day; 3 days, i.p.) prior to succinimide or succinimide vehicle. In non-phenobarbital pretreated rats, acute FMPS or MMPS treatment had little effect on renal function or morphology at the doses tested. Hematuria (+) was noted in the FMPS (1.0 mmol/kg) group on post-treatment day 2. However, in the phenobarbital-pretreated rats, FMPS (0.4 or 1.0 mmol/kg) induced marked hematuria (++) and increased proteinuria while having little or no effect on other renal functional parameters or renal morphology. At killing, bladders of treated rats were distended with bloody urine and exhibited hemorrhagic areas within the bladder wall. In phenobarbital-pretreated rats, MMPS administration had little effect on any renal functional parameter measured or urological morphology. These results suggest that para-hydroxylation does not contribute to the hemorrhagic cystitis induced by PSX.     

Stereochemical inversion of haloxyfop in the Fischer 344 rat

The 2-aryloxypropionate haloxyfop is currently being evaluated for use as a herbicide. This compound is structurally similar to a group of 2-arylpropionates that have been shown previously to undergo stereochemical inversion in a variety of mammalian species. To support the data obtained from a number of toxicity/oncongenicity studies, in which racemic haloxyfop was employed, the stereochemical disposition of this compound was examined in the Fischer 344 rat. After administration of racemic haloxyfop (11 mg/kg, po) to male and female Fischer 344 rats, the day 1-10 urine samples were fortified with D4-haloxyfop (center ring label) and extracted, and the haloxyfop enantiomers were converted to diastereomeric derivatives [(S)-phenylethylamine] and analyzed by gas chromatography-mass spectrometry (GC/MS). Fecal samples for days 1-10 were fortified with D4-haloxyfop, extracted, and purified by reverse phase high-pressure liquid chromatography prior to derivation and GC/MS analysis. In the female rat, 77.3% of the administered dose was recovered in the day 1-10 urine and feces as parent compound. The stereochemistry of the haloxyfop present in these samples was found to be nearly all (R)-enantiomer (greater than 98%). In the male rat, 52.2% of the dose was recovered in the day 1-10 urine and feces as haloxyfop. The stereochemistry of the parent compound present in these samples was similar to the results seen in the female rat [greater than 98% (R)]. These results show that (S)-haloxyfop undergoes rapid and nearly complete inversion to the (R)-enantiomer in the female Fischer 344 rat. The data also suggest a similar stereochemical inversion of haloxyfop in the male Fischer 344 rat.     

Disposition and metabolism of isoeugenol in the male Fischer 344 rat

The primary objective of these studies was to determine the absorption, distribution, metabolism and excretion of isoeugenol following oral and intravenous administration to male Fischer-344 rats. Following a single oral dose of [¹⁴C]isoeugenol (156 mg/kg, 50 μCi/kg), greater than 85% of the administered dose was excreted in the urine predominantly as sulfate or glucuronide metabolites by 72 h. Approximately 10% was recovered in the feces, and less than 0.1% was recovered as CO₂ or expired organics. No parent isoeugenol was detected in the blood at any of the time points analyzed. Following iv administration (15.6 mg/kg, 100 μCi/kg), isoeugenol disappeared rapidly from the blood. The t_1/2 was 12 min and the Cl_s was 1.9 l/min/kg. Excretion characteristics were similar to those of oral administration. The total amount of radioactivity remaining in selected tissues by 72 h was less than 0.25% of the dose following either oral or intravenous administration. Results of these studies show that isoeugenol is rapidly metabolized and is excreted predominantly in the urine as phase II conjugates of the parent compound.     

Disposition and pharmacokinetics of inhaled dimethylamine in the Fischer 344 rat

The disposition and pharmacokinetics of [14C]dimethylamine [( 14C] DMA) following 6-hr inhalation of either 10 or 175 ppm were determined in male Fischer 344 rats. Seventy-two hours after termination of exposure, the disposition of recovered radioactivity was similar for each airborne concentration, with more than 90% in the urine and feces, 7 to 8% in selected tissues and the carcass, and 1.5% exhaled as 14CO2. Over 98% of the radioactivity in the urine was unmetabolized DMA. Analysis of tissue radioactivity immediately after exposure to [14C]DMA showed that the respiratory nasal mucosa contained the highest concentration of 14C, followed by the olfactory nasal mucosa; concentrations of 14C in liver, lung, kidney, brain, and testes were approximately 2 orders of magnitude less than in the nasal mucosal tissues. Radioactivity in plasma of rats exposed by inhalation to 175 ppm of [14C]DMA decayed in a biphasic manner. The terminal half-life for plasma radioactivity was similar to the half-lives of some plasma proteins, suggesting incorporation of 14C into proteins subsequent to metabolism of [14C]DMA. The results indicate that, while most of the inhaled DMA is excreted unchanged, a small amount of oxidative metabolism of DMA occurs.     

Developmental toxicity of 2,3,4,7,8-pentachlorodibenzofuran in the Fischer 344 rat

Fischer 344 rats were exposed acutely to 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF) during the organogenic period to evaluate its potential as an inducer of teratogenic and embryolethal effects. All dams were treated by gavage with a single dose of 0, 30, 100, or 300 μg 4-PeCDF/kg body wt on gestation Day (gd) 8, 10, or 12. An additional treatment group was included on gd 12 and administered 10 μg 4-PeCDF/kg body wt po. All animals were killed on gd 20 and maternal and fetal toxicities were assessed. Determination of embryotoxicity involved both soft tissue and skeletal examinations. 4-PeCDF induced a dose-related decrease in corrected maternal weight gain following treatment on gd 8 and 10, as well as resulted in a concomitant increase in the liver/body weight ratios, first evident at 30 μg/kg for all 3 days of exposure. The maternal thymus weight decreased relative to body weight compared with those of controls. Embryo-fetal toxicity was evident from the high mortality (>80%) observed at 300 μg/kg for all 3 days of exposure. Mean fetal weight, a sensitive indicator of fetal toxicity, decreased compared to that of controls at 30, 100, and 300 μg/kg following treatment on either gd 8, 10, or 12. 4-PeCDF induced cleft palate in survivors at a dose of 300 μg/kg for all 3 days of exposure. In conclusion, 4-PeCDF is maternally and fetally toxic regardless of the gestation day of exposure, but induced terata only at doses where overt maternal and fetal toxicity were observed, in contrast to previously reported studies in the mice where teratogenic effects were observed at nonfetotoxic dose levels. Thus, the mouse may be a more sensitive model for evaluating specific toxic responses induced prenatally following exposure to the structurally related polyhalogenated aromatic hydrocarbons which include the dioxins, furans, biphenyls, and naphthalenes.     

Mecamylamine-precipitated nicotine-withdrawal aversion in Lewis and Fischer 344 inbred rat strains

Many studies have indicated that Lewis and Fischer 344 inbred rat strains show marked differences in behavioral responses to abused drugs. In the present study, we sought to determine whether these two strains of rats show different responses in mecamylamine-precipitated nicotine-withdrawal aversion using the conditioned place preference paradigm. Rats were treated subcutaneously with 10 mg/kg/day nicotine for 7 days using an osmotic minipump. After chronic nicotine infusion, the nicotinic receptor antagonist mecamylamine produced a significant place aversion in Lewis, but not in Fischer 344 rats. These results suggest that mecamylamine-precipitated nicotine-withdrawal aversion is strongly regulated by genetic factors.     

Disposition of decamethylcyclopentasiloxane in Fischer 344 rats following single or repeated inhalation exposure to 14C-decamethylcyclopentasiloxane (14C-D5)

The disposition of decamethylcyclopentasiloxane (D5) in male and female Fischer 344 rats following single or repeated inhalation exposures was evaluated. Animals were administered a single 6-h nose-only exposure to 7 or 160 ppm 14C-D5 or fourteen 6-h nose-only exposures to unlabeled D5 followed on day 15 by a 6-h exposure to 14C-D5. Subgroups of exposed animals were used to evaluate body burden, distribution, elimination, and deposition on the fur. Retention of radioactivity following single and repeated exposures was relatively low (approximately 1-2% of inhaled D5). Radioactivity and parent D5 were widely distributed to tissues of both male and female rats, with the maximum concentration of radioactivity observed in most tissues by 3 h postexposure. Fat was a depot for D5, with elimination occurring much slower than observed for plasma and other tissues. In all groups, the primary route for elimination of radioactivity was through expired air. Analyses for parent D5 indicated that essentially all the radioactivity in the expired volatiles was unchanged D5. Repeated exposure gave rise to higher levels of parent D5 in the lung and fat of both sexes and in female liver relative to the single exposure. In fat, immediately after sacrifice approximately 50% of the radioactivity was attributed to parent. Five polar metabolites of D5 were identified in urine, with no parent D5 detected. Radiochromatograms demonstrated two peaks in feces. One corresponded to the retention time for D5. The second has been putatively identified as hydroxylated D5.     

Urinary tract effects of phensuximide in the Sprague-Dawley and Fischer 344 rat

Phensuximide is a succinimide antiepileptic drug useful in the treatment of petit mal epilepsy. Phensuximide has been reported to be nephrotoxic in man but not in animals. In the present study, the effects of single and subacute administration for seven days of phensuximide on renal function and urinary tract morphology were evaluated in Sprague-Dawley and Fischer 344 rats. Single administration of phensuximide (1.25 mmol/kg, ip) induced mild changes in renal function (trace hematuria, increased proteinuria and decreased p-aminohippurate uptake). No morphological changes were observed at 24 hr. Subacute administration of phensuximide (0.6 mmol/kg/day, ip) produced diuresis in the Sprague-Dawley rat, but little functional evidence of nephrotoxicity. Renal morphological changes in Sprague-Dawley rats were seen primarily in distal segments of the nephrons. These changes were characterized by distensions of the basal infoldings, apical protrusions, and occlusion of some lumen. In the Fischer 344 rat, subacute phensuximide administration (0.3 or 0.6 mmol/kg/day, ip) resulted in transient hematuria and proteinuria, but no change in the other renal function parameters studied. Renal morphological changes observed in Fischer 344 rats occurred primarily in proximal tubular cells. Damaged cells were characterized by large vacuoles at the basal infoldings, accumulations of opaque granules, migration of nuclei to the lumenal membranes, occlusion of the lumen and/or loss of the brush border. Morphological damage was more widespread in Fischer 344 rats than in Sprague-Dawley rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Teratologic and postnatal evaluation of aniline hydrochloride in the Fischer 344 rat

Timed-pregnant Fischer 344 rats were dosed by gavage with aniline hydrochloride (10, 30, or 100 mg/kg/day), a positive control agent (hydroxyurea, 200 mg/kg/day), or vehicle (distilled water) on gestational days (gd) 7 through 20 or gd 7 through parturition. At termination on gd 20 confirmed-pregnant dams exhibited characteristic signs of aniline HCl toxicity, i.e., methemoglobinemia, increased relative spleen weight, decreased red blood cell (RBC) count, and hematological changes indicative of increased hematopoietic activity. High-dose dams exhibited mild methemoglobinemia, increased relative spleen weight, and increased RBC size at termination on postnatal day (pnd) 30. At termination on gd 20, fetuses from aniline-treated dams exhibited increased relative liver weight and enhanced hematopoietic activity, but no evidence of an embryolethal or teratogenic effect was observed. Postnatal signs of toxicity in litters from aniline-treated dams (i.e., decreased body weight, elevated relative liver weight, and elevated relative spleen weight) were transient, and no evidence of toxicity was observed in pups surviving to pnd 60. Hydroxyurea (200 mg/kg/day) administered by gavage proved to be an excellent positive control for embryotoxicity, maternal toxicity, teratogenicity, and postnatal maturational deficits in the Fischer 344 rat. In conclusion, aniline hydrochloride was not teratogenic to Fischer 344 rats, even at maternally toxic doses; transient signs of toxicity were observed postnatally in the offspring in conjunction with mild, but persistent signs of maternal toxicity through pnd 30.     

Nephrotoxicity of p-aminophenol,a metabolite of acetaminophen,in the Fischer 344 rat

Acetaminophen (APAP) produces proximal tubular necrosis in the Fischer 344 rat. APAP is deacetylated to p-aminophenol (PAP) in the hamster, and PAP has been reported to be a potent specific cortical nephrotoxicant in the rat. However, the role of PAP in APAP nephrotoxicity has not been defined. Therefore, it was of interest to quantify PAP formation after APAP administration and to correlate PAP formation with renal injury produced by APAP in the Fischer 344 rat. Urinary PAP excretion, measured as an index of PAP formation, increased with increasing doses of APAP. In addition, APAP was metabolized to PAP in isolated perfused kidneys. PAP at doses as low as 100 mg/kg produced significant renal toxicity (elevation in blood urea nitrogen and reduction in accumulation of p-aminohippurate by thin renal cortical slices). Ortho- and meta-aminophenol were not nephrotoxic. Pretreatment with polybrominated biphenyls or β-naphthoflavone, inducers of mixed function oxidases, protected against nephrotoxicity of PAP, possibly as a result of enhanced hepatic biotransformation of the parent compound. These studies indicate that PAP is a potent, selective nephrotoxicant that can be generated from APAP by the kidney and may be responsible for the renal necrosis subsequent to APAP administration.     

Subchronic peroral toxicity of triethylene glycol in the Fischer 344 rat

Ethylene and diethylene glycols produce systemic toxicity, including nephrotoxicity, by acute and repeated po dosing. To determine the potential for triethylene glycol (TEG; CAS Number 112-27-61) to produce nephrotoxicity, or other organ/tissue injury, a subchronic (90-d) study was conducted by continuous inclusion of TEG in the diet of Fischer 344 rats. This was preceded by a probe 14-d study. For both studies the dietary concentrations were 0 ppm (control), 10,000, 20,000 or 50,000 ppm TEG, resulting in daily TEG consumptions in the 14-d study of 1132, 2311 or 5916 mg/kg with males, and 1177, 2411 or 6209 mg/kg with females. The corresponding values for the 90-d study were 748, 1522 or 3849 mg/kg (males), and 848, 1699 or 4360 mg/kg (females). In the 14-d study there were no mortalities or clinical signs, and no effects on body weight, hematology, serum chemistry, organ weights, and gross or microscopic pathology. Food consumption was increased at the high dosage. Urinalysis showed increased urine volume and decreased pH with high dose males and females, and increased volume with mid-dose males. In the subchronic study there was neither mortality nor signs of toxicity, and no dosage-related effects with serum chemistry, gross and microscopic pathology. Body weights were reduced during the dosing period with both males and females of the high dosage. Body weight gains were reduced at all dosages with males and females. No hematological effects were seen with females, but males of the mid- and high-dosage groups had slightly reduced erythrocyte count and hematocrit, and high-dose males had decreased hemoglobin concentration with increased mean corpuscular volume. These were considered to reflect a mild hemodilution related to the absorption of large TEG doses. Urinalysis showed dosage-related decreased pH, and increased urine volume mainly at the high dose. These were probably related to the renal excretion of absorbed TEG and/or metabolites. Kidney weight was increased for high-dose females, and increased relative (to body) weight of kidneys for males and females from the mid- and high-dose groups were observed, probably related to the renal excretion of the absorbed TEG and/or its metabolites. These findings indicate that the subchronic continuous po dosing of TEG to rats does not result in local or systemic specific organ or tissue toxicity. These findings contrast with the known repeated po toxicity, notably nephrotoxicity, produced by ethylene and diethylene glycols. Thus, TEG has significantly lesser potential for systemic toxicity by the po route than its lower molecular weight homologues.     

Metabolism of nitrotoluenes by freshly isolated Fischer 344 rat hepatocytes

2-Nitrotoluene (2NT), but not 3-nitrotoluene (3NT) or 4-nitrotoluene (4NT), is genotoxic in the in vivo-in vitro hepatic DNA repair assay. These differences in genotoxicity may be due to hepatic metabolism. For this reason, the metabolism of the nitrotoluenes was compared in hepatocytes isolated from male Fischer 344 rats. Hepatocytes were incubated with [U-14C]2NT, 3NT, or 4NT at concentrations from 25 to 1000 microM for up to 60 min. Metabolites were separated by reverse phase HPLC and identified by coelution with standards on HPLC, specific enzyme hydrolysis, and GC-MS analysis. 2NT was converted to 2-nitrobenzyl alcohol (52%), 2-nitrobenzyl alcohol glucuronide (28%), an unidentified metabolite (20%), and 2-nitrobenzoic acid (3%). Metabolites from 3NT were 3-nitrobenzoic acid (56%), 3-nitrobenzyl alcohol (29%), and 3-nitrobenzyl alcohol glucuronide (13%). 4NT was metabolized to S-(4-nitrobenzyl)glutathione (68%), 4-nitrobenzyl alcohol (12%), sulfate and glucuronide conjugates of 4-nitrobenzyl alcohol (6%), and 4-nitrobenzoic acid (2%) (expressed as percentage of total metabolism). The formation of the respective nitrobenzyl alcohols by hepatocytes was linear with respect to time for 15-20 min. The formation of other metabolites was linear over a 45-min incubation period. Incubation of 2NT, 3NT, or 4NT (1 mM) with rat hepatic microsomes produced only the respective nitrobenzyl alcohols and the rate of formation was linear for 90 min. The data suggest that each nitrotoluene isomer is metabolized to the corresponding benzyl alcohol, but that substantial differences in the metabolism of the benzyl alcohols exist.     

Lithium-chloride-induced conditioned taste aversions in the Lewis and Fischer 344 rat strains

Conditioned taste aversions (CTAs) are differentially induced by cocaine and morphine in the Lewis and Fisher 344 (LEW and F344, respectively) rat strains. Although the acquisition of LiCl-induced aversions has recently been reported to be comparable between the two strains, these aversions were induced by the oral consumption of LiCl, and the possibility exists that, given their different weights, that differential doses were functionally administered. To address the issue of LiCl-induced aversions in LEW and F344 rats (and to control for this possible confound), the present study assessed the ability of intraperitoneally (ip) administered LiCl to induce aversions in the two strains. Specifically, rats from both strains were given 20-min access to saccharin and injected immediately, thereafter, with 0.3, 0.6, 0.9 or 1.2 mEq/kg, 0.15 M LiCl (or its distilled water vehicle). Under these conditions, both strains acquired dose-dependent aversions that increased over repeated trials. Although there was no overall strain difference in LiCl-induced aversions, LEW rats displayed a stronger aversion at the 0.3 mEq/kg dose (on Trial 3) and acquired the aversion at this dose more rapidly than the F344 rats did (by Trial 2 vs. Trial 3). Although evident, this strain difference with LiCl does not parallel that reported with morphine (in which F344 rats are more sensitive than LEW rats) or with cocaine (in which the differences between LEW and F344 rats are larger and occur at more doses and on more trials). These cross-drug comparisons suggest that strain differences in aversion learning are drug dependent. Because drug acceptability has been reported to be a function of the balance between the reinforcing and aversive effects of various compounds, the examination of possible strain differences in aversion learning with a range of such compounds may provide insight into drug acceptability (and use) in these strains.     

Metabolism and disposition of moxonidine in Fischer 344 rats.

The metabolism and disposition of moxonidine (4-chloro-5-(imidazolidin-2-ylidenimino)-6-methoxy-2-methylp yrimidine ), a potent central-acting antihypertensive agent, were investigated in F344 rats. After an i.v. or oral administration of 0.3 mg/kg of [(14)C]moxonidine, the maximum plasma concentrations of moxonidine were determined to be 146.0 and 4.0 ng/ml, respectively, and the elimination half-lives were 0.9 and 1.1 h, respectively. The oral bioavailability of moxonidine was determined to be 5.1%. The metabolic and elimination profiles of moxonidine were determined after an oral administration of 5 mg/kg of [(14)C]moxonidine. More than fifteen phase I and phase II metabolites of moxonidine were identified in the different biological matrices (urine, plasma, and bile). Oxidative metabolism of moxonidine leads to the formation of hydroxymethyl moxonidine and a carboxylic acid metabolite as the major metabolites. Several GSH conjugates, cysteinylglycine conjugates, cysteine conjugates, and a glucuronide conjugate were also identified in rat bile samples. The radiocarbon was eliminated primarily by urinary excretion in rats, with 59.5% of total radioactivity recovered in the urine and 38.4% recovered in the feces within 120 h. In bile duct-cannulated rats, about 39.7% of the radiolabeled dose was excreted in the urine, 32.6% excreted in the bile, and approximately 2% remained in the feces. The results from a quantitative whole body autoradiography study indicate that radiocarbon associated with [(14)C]moxonidine and/or its metabolites was widely distributed to tissues, with the highest levels of radioactivity observed in the kidney and liver. In summary, moxonidine is well absorbed, extensively metabolized, widely distributed into tissues, and rapidly eliminated in rats after oral administration.     

Metabolism of dimethylamine in the nasal mucosa of the Fischer 344 rat

The metabolism of dimethylamine (DMA) in the nasal mucosa of the male Fischer 344 rat was investigated in vitro and in vivo. Microsomes were prepared from liver, and from respiratory and olfactory nasal mucosa. All microsomal preparations metabolized DMA to formaldehyde (CH2O), though DMA was a poor substrate for the N-demethylation reaction when compared to benzphetamine. Phenobarbital-induced microsomes metabolized DMA at a rate less than that of control. The results indicated that DMA was a substrate for both cytochrome P-450 and FAD-containing monooxygenase, and that both enzyme activities were present in all microsomal preparations. Finally, unextractable radioactivity was observed in DNA, RNA, and protein isolated from respiratory and olfactory mucosa of rats exposed to either 10 or 175 ppm of [14C]DMA, suggesting metabolism of [14C]DMA to 14CH20 with subsequent incorporation of 14C into macromolecules. The results demonstrate that the respiratory and olfactory nasal mucosa have the capability to metabolize DMA to CH2O, and indicate that such metabolism occurs in vivo.     

Renal effects of N-(3,5-disubstitutedphenyl)-succinimides in the Fischer 344 rat.

Previous studies have demonstrated the importance of substitution at the 3- and 5-positions of the phenyl ring in N-phenylsuccinimides for the production of nephrotoxicants in this series of compounds. The purpose of this study was to determine if the electronic nature of the 3,5-substituents is an important determinant for nephrotoxic potential. Male Fischer 344 rats (four rats per group) were administered a single intraperitoneal injection of a succinimide (0.4 or 1.0 mmol kg-1) or vehicle, and the renal function was monitored for 48 h. Only N-(3,5-dichlorophenyl)succinimide (0.4 or 1.0 mmol kg-1) induced marked changes in renal function. Urine volume, BUN concentration and proteinuria were increased following N-(3,5-dinitrophenyl)succinimide (1.0 mmol kg-1) treatment but other renal parameters and renal morphology were unchanged in this treatment group. These results indicate that the presence of halogen atoms at the 3- and 5-positions of the phenyl ring in N-phenylsuccinimides is more important for nephrotoxic potential than the presence of non-halogen substituents. The reason why halogen substitution is an important determinant for N-phenylsuccinimide nephrotoxicity is unknown.     

Chronic methylxanthine treatment in rats: A comparison of Wistar and Fischer 344 strains

Caffeine, theophylline or aminophylline were administered chronically to rats of both sexes, in the weight range 30–245 g. Self-injurious behaviour was noted only rarely in Wistar rats allowed free access to food, but developed over 3 to 4 weeks in half of the animals given a restricted diet of about one third of the intake of control rats. Fischer rats showed self-injurious behaviour more readily, 87% of animals showing signs within 9 days even on an ad lib diet. It is suggested that Fischer rats treated with methylxanthines may provide a model of the Lesch-Nyhan syndrome. Behavioural observations made during the period of methylxanthine treatment suggest than an activation of both the dopamine and 5-hydroxytryptamine neurone systems may be produced. Further work will seek a relationship between these systems and self-injurious behaviour.     

Elevation of metallothionein level in preneoplastic lesions during chemical hepatocarcinogenesis of the Fischer 344 rat.

Metallothionein (MT) is inducible by various stimuli such as metals and physiological stress. Although elevated MT expression in certain type of tumors has been reported, there are few data available on the roles of MT in tumor formation. In this study, we immunohistochemically examined MT expression in gluthathione S-transferase placental type p (GST-P)-positive preneoplastic liver lesions induced by a chemical carcinogen and further examined the relationship between MT expression and the proliferative activity of the preneoplastic cells, using bromodeoxyuridine (BrdU) labeling indices. Eleven male Fischer rats (F344/DuCrj, 9 weeks old) were subjected to the Solt-Farber protocol. Thereafter, the livers were removed, frozen and sectioned serially for immunohistochemical staining of MT and GST-P. Eight rats were given six injections of BrdU before sacrifice. In 92.8% of GST-P positive lesions, high MT staining intensity was demonstrated. On the other hand, there was no correlation between the intensity of MT staining and the BrdU labeling indices of the preneoplastic lesions. Our results indicate that MT is a useful positive marker for preneoplastic liver lesions, though the reason why MT is expressed in the preneoplastic and neoplastic lesions remains to be elucidated.