Effects of subacute toluene inhalation on its metabolism and disposition in rat

Chronic intermittent toluene inhalation in adolescent rats alters behavioural responses to amphetamine and MK801

Abuse of toluene-containing inhalants is common during adolescence, with ongoing chronic misuse associated with adverse outcomes and increased risk for addictive behaviours in adulthood. However, the mechanisms mediating the adaptive processes related to these outcomes are not well defined. To model human abuse patterns we exposed male adolescent Wistar rats (postnatal day 27) to chronic intermittent inhaled toluene (CIT, 10,000 ppm) or air (control) for 1h/day, three times/week for 3 weeks. The effects of CIT on behaviour and recovery were monitored. Locomotor activity was recorded following two consecutive injections of amphetamine (1mg/kg, i.p.) 72 and 96 h after the last exposure. This was followed with injection of the NMDA receptor antagonist MK801 (0.5mg/kg, i.p.) 20 days after the last exposure. CIT resulted in a significant and persistent retardation in weight gain during the exposure period and abstinence (p<0.05). Repeated exposure resulted in tolerance to the onset of toluene-induced behaviours and recovery latency. There was a reduction in the acute stimulant effects of amphetamine in CIT-exposed animals and an increase in the magnitude of locomotor activity (p<0.0125) following a subsequent exposure when compared to the responses observed in controls; this was associated with altered locomotor responses to MK801. Repeated exposure to CIT during adolescence alters parameters of growth, as measured by body weight, and leads to tolerance, indicating that increasing concentrations of the compound may be needed to reach the same behavioural state. Toluene during this period also alters responses to a psychostimulant which may be related to long-term glutamatergic dysfunction.

Repeated inhalation of toluene by rats performing a signal detection task leads to behavioral tolerance on some performance measures

Previous work showed that trichloroethylene (TCE) impairs sustained attention as evidenced by a reduction in accuracy and elevation of response latencies in rats trained to perform a visual signal detection task (SDT). This work also showed that these effects abate during repeated exposures if rats inhale TCE while performing the SDT. The present experiment sought to determine whether toluene, another commonly-used solvent, would induce tolerance similarly if inhaled repeatedly during SDT testing. Sixteen male, Long-Evans rats were trained to perform the SDT. Upon completion of training, rats were divided into 2 groups. In Phase I, concentration-effect functions were determined for toluene (0, 1200, 1600, 2000, 2400 ppm) in both groups. Toluene reduced the proportion of correct responses [P(correct)], and increased response time (RT) and response failures. In Phase II, Group-Tol inhaled 1600 ppm toluene while Group-Air inhaled clean air during 11 daily SDT sessions. In Group-Tol the effect of toluene on P(correct) abated after 3 days, while RT remained elevated for the duration of the repeated exposures. In Phase III, toluene concentration-effect functions were re-determined for both groups. Group-Air remained impaired on all test measures, whereas for Group-Tol, toluene did not reduce P(correct), but continued to increase RT. These data confirm our previous hypothesis that animals can develop tolerance to chemical exposures that impair appetitively-motivated behaviors if that impairment leads to loss of reinforcement.

Studies of nephrotoxicity due to mixed exposure to styrene and toluene

Adult male Sprague-Dawley rats were treated simultaneously with 4 mmol styrene per kg i.p., twice a day at an interval of 4 h, and 10 mmol toluene per kg once a day, 5 days a week for 4 consecutive weeks. After the last day of treatment, the rats were placed in metabolism cages for collection of urines for 24 h and then were sacrificed. Such mixed exposure produced significant increases in the urinary excretion of gamma-glutamyl transpeptidase, glucose and proteins as compared to those with either solvent alone. An increase, but not significant, in the urinary excretion of N-acetyl-beta-D-glucosaminidase was also noticed due to such exposure. Electron microscopic examination of renal cortex 24 h after the mixed exposure showed the appearance of many vacuoles of various sizes surrounded by a single membrane, which were not seen in rats treated with either styrene or toluene alone. Metabolism studies showed only a significant increase in the urinary excretion of hippuric acid due to mixed exposure. These data indicate that under certain conditions, mixed subchronic exposure to styrene and toluene may have the potential to increase further the nephrotoxic response as compared to that of either solvent alone.

[Comparison of the distribution and toxicity of alpha-, beta-, and gamma-hexachlorocyclohexane (HCH) following 30 days of administration to rats]

Administration of 1000 ppm alpha-HCH, 600 ppm beta-HCH and greater than or equal to 125 ppm gamma-HCH to rats caused a growth retardation. alpha-HCH and beta-HCH led to livermass enlargement. beta-HCH caused a decrease of absolute brain-mass. In case of alpha-HCH and gamma-HCH fat tissue, kidneys and adrenals had a high burden in residues. Fat tissue and adrenals had high residues of beta-HCH. The level of HCH-residues during the test period was gamma much less than beta less than alpha. The results are discussed taking into account the contradictory knowledge from literature.

Biochemical and morphological effects of long-term inhalation exposure of rats to ethylbenzene

Male Wistar rats were exposed (six hours/day, five days/week) to 0, 50, 300 or 600 p.p.m. of ethylbenzene vapour in the air, and killed after 2, 5, 9 or 16 weeks of exposure. After 600 p.p.m., liver-microsomal protein but not cytochrome P-450 concn. was slightly increased; NADPH-cytochrome c reductase was increased maximally by 30% (1.3-fold), 7-ethoxycoumarin O-deethylase (1.8-fold) and UDPG-transferase (2.3-fold). The increase in liver-cytosolic D-glucuronolactone dehydrogenase paralleled the glucuronidation activity (less than or equal to 2-fold). In the kidneys, only 7-ethoxycoumarin O-deethylase (less than or equal to 3.5-fold) and UDPG-transferase (less than or equal to 1.8-fold) showed dose-related increases. Ethylbenzene exposure did not deplete hepatic glutathione (GSH); kidney GSH was slightly increased (less than or equal to 1.3-fold) according to dose. Urine excretion of thioethers was increased with dose, and at 600 p.p.m. was eight times control levels. At 600 p.p.m. there was no increase in serum alanine aminotransferase activity, and liver cells showed slight proliferation of smooth endoplasmic reticulum, slight degranulation and splitting of rough endoplasmic reticulum and enlarged mitochondria, but no necrosis.

Tolerance and reverse tolerance to toluene inhalation: effects on open-field behavior

Rats were exposed by inhalation to extremely high concentrations of toluene vapors twice daily for six weeks, as an animal model of organic solvent abuse. At preset intervals during repeated exposure, the rats were exposed to test concentrations of toluene and effects on behavior in an open field were measured. Concentration-effect curves were determined during Weeks 4 to 6 of repeated exposure. Tolerance to toluene was measured as a decreased response to the test exposure and a shift of the concentration-effect curve to the right. Reverse tolerance was measured as an increased response to the test exposure and a shift shift of the concentration-effect curve to the left. Results demonstrated that the effects of repeated exposure to toluene showed behavioral selectivity: tolerance developed to ataxia, hindlimb myoclonus, and inhibition of rearing, whereas reverse tolerance developed to headshakes and increased locomotor activity.

Kinetics of white spirit in human fat and blood during short-term experimental exposure

Seven volunteers were exposed to 100 p.p.m. white spirit (99% paraffins C8-C12) 6 hrs daily in 5 days. The mean concentration of white spirit after 5 days of exposure was 41.1 mg/kg fat (Friday afternoon). On the following Monday morning, the concentration was 31.7 mg/kg, i.e. only 23% had been eliminated during the exposure-free weekend. The estimated mean and median half-life was 7 and 8 days, respectively, elimination rate constant 0.0039 and 0.0036 hrs-1, time to reach steady state 5 to 8 weeks, maximal and minimal steady state concentration 85 and 66 mg/kg and 66 and 52 mg/kg, respectively. The concentration of white spirit in fat found each afternoon correlated significantly with the total dose. The concentration of white spirit/kg fat correlated positively with serum triglyceride and inversely with the percentage body fat (not significantly). The concentration of white spirit in the brain at steady state was estimated to maximum 11 mg/kg, while the half-life in the brain was estimated to maximum 18-19 hours. Minor differences occurred in the spectrometrical pattern produced by the in vivo biopsy evaporate as compared to in vitro specimens and white spirit vapours per se, thus indicating that the white spirit was slightly biotransformed or that the approximately 200 constituents of white spirit were absorbed differently. Thus, during exposure at the threshold limit value level, white spirit is accumulated in depot fat over weekends and in brain over working days. However, white spirit is almost eliminated from the brain during weekends.

Burden and biochemical effects of extended tetrahydrofuran vapour inhalation of three concentration levels

Adult male rats exposed to tetrahydrofuran vapour at 8.2 (200 p.p.m.), 41 (1,000 p.p.m.) or 82 mumol/l (2,000 p.p.m.) for 2 to 18 weeks, five days a week, 6 hrs daily, showed dose-dependent brain and perirenal fat solvent burden linearly correlated to each other. After two weeks of exposure, the body burden of tetrahydrofuran seems to decrease. This might have been caused by increased oxidative metabolism as enhanced 7-ethoxycoumarin O-deethylase activity was detected in liver and kidneys in the 2nd week and onwards. The exposure also caused inhibition of alcohol and formaldehyde dehydrogenase activities in liver at the highest dose. Biochemical effects in the cerebellum were not detected while gluteal muscle specimens showed increased succinate dehydrogenase activity in a dose-related manner. This points to effects on the energy metabolism. Muscle acetylcholine esterase activity was also increased showing possible effects on the myoneural junctions.

Antipyrine clearance during experimental and occupational exposure to toluene

Exposure to toluene vapour enhances hepatic microsomal enzyme function in animals as assessed by the metabolism of the test drug antipyrine. Thirty six printing trade workers with long term occupational exposure to a mixture of organic solvents and 39 matched controls were randomly allocated into four groups. Eighteen printers and 21 controls were exposed to 100 ppm of toluene during 6.5 hours in an exposure chamber. The remaining 18 printers and 18 controls were exposed to 0 ppm of toluene under similar conditions. The salivary clearance of antipyrine was measured immediately after the stay in the exposure chamber to investigate a possible acute change in liver function and was repeated two weeks later, shortly before the summer vacation. Antipyrine clearance was measured again at the end of the summer vacation-four weeks after exposure. To study a possible effect of chronic exposure on antipyrine clearance 12 printing trade workers with 17 years (median) of occupational exposure to toluene vapour at concentrations of about 100 ppm were investigated before and four weeks after cessation of exposure. No difference in antipyrine clearance was found either within the groups or between the groups at any of the measurements.

Neurochemical effects of short-term inhalation exposure to vinyltoluene vapor

Male rats were exposed to vinyltoluene vapor after pretreatment with polychlorinated biphenyl (PCB). Brain and body solvent burdens were in a linear relationship to the exposure level although it changed between the two weeks while the solvent accumulated in the perirenal fat. The pretreatment caused a significantly smaller burden in the fat samples. Lysosomal acid proteinase was above the control range in the brain homogenate in the highest exposure, while glutathione peroxidase and 2',3'-cyclic nucleotide 3'-phosphohydrolase showed a dose-dependent decrease in the homogenate during the first week. Acid proteinase activity in the glial cells increased above the control range only in the PCB-pretreated rats in the first week. Azoreductase increased in the glial cells above the control range only in the first week, and the pretreatment augmented the increase very significantly. All biochemical effects were largely abolished within two weeks of solvent-free period with the exception of an increase in the cerebral RNA at the highest dose level. Vinyltoluene can cause more pronounced neurochemical effects compared to styrene, xylene, or toluene at similar exposure levels.