Biomedical subjects

S Muralidhara

Publications and source records attributed to S Muralidhara.

At least 19 recordsLinked to original sources

PubMed2005

Analysis of dichloroacetic acid in rat blood and tissues by hydrophilic interaction liquid chromatography with tandem mass spectrometry.

Dichloroacetic acid (DCA) is a compound found in chlorinated drinking water. In addition, the compound is a metabolite of several halogenated solvents, including trichloroethylene (TCE) and perchloroethylene (PCE). Exposure to DCA is of concern because high doses of the compound have been shown to cause cancer in laboratory animals. Dosages of TCE administered to animals in cancer studies are designed to elicit maximal DCA formation in vivo, whereas levels of DCA to which individuals are exposed in drinking water are very low. Analysis of DCA in biological samples has been quite challenging. Derivatizing reagents commonly used to convert DCA into a more volatile form for analysis by gas chromatography (GC) have been found to convert trichloroacetic acid (TCA), a major metabolite of TCE and PCE, into DCA. High-performance liquid chromatography (HPLC) analysis does not require derivatization of DCA and can thus avoid this problem. However, the most popular stationary phases in HPLC columns do not retain small, polar compounds such as DCA well. The liquid chromatography/tandem mass spectrometry (LC/MS/MS) method described in this paper uses hydrophilic interaction liquid chromatography (HILIC), a type of chromatography that is able to retain these small, polar compounds. Method validation was performed using the United States Food and Drug Administration (USFDA) and International Conference on Harmonziation (ICH) Guidance for Industry: Bioanalytical Method Validation as a guide. Levels of DCA found in rats dosed with 2 g/kg TCE were 17.2 ng/mL (liver), 262.4 ng/mL (kidney), 175.1 ng/mL (lung), and 39.5 ng/mL (blood).

Animals↗

PubMed2004

Determination of deltamethrin and its metabolite 3-phenoxybenzoic acid in male rat plasma by high-performance liquid chromatography.

The pyrethroid insecticide-deltamethrin [(S)-alpha-cyano-3-phenoxybenzyl-(1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylate] is widely used throughout the world in agricultural applications. It is also used to treat humans, thereby creating a possible public health concern. The toxic effects of deltamethrin in mammals include choreoathetosis, hyperexcitability and salivation. The principal mechanisms of metabolism for deltamethrin are ester hydrolysis and oxidation at the 4' position of the terminal aromatic ring. Few studies have been conducted on the toxicokinetics of deltamethrin or its metabolites, mainly due to the lack of quick, sensitive, and validated analytical methods. In this study, we describe the first method to simultaneously determine deltamethrin and its major metabolite 3-phenoxybenzoic acid (3-PBAcid). This method utilizes protein precipitation and high-performance liquid chromatography to support a toxicokinetic study in the rat. The limit of quantitation for both deltamethrin and 3-PBAcid was 0.1 microg/ml. The recoveries for deltamethrin and 3-PBAcid were approximately 91 and 94%, respectively. Intra-day (n = 5) precision (relative standard deviation, %R.S.D.) and accuracy (%Error) for deltamethrin ranged from 1.5 to 12.3% and from 4.0 to 10.6%, respectively. The inter-day (n = 15) precision (%R.S.D.) and accuracy (%Error) for deltamethrin ranged from 7.1 to 11.6% and from 6.3 to 8.2%, respectively. Intra-day (n = 5) precision (%R.S.D.) and accuracy (%Error) for 3-PBAcid ranged from 1.7 to 13.1% and from 1.3 to 14.5%, respectively. The inter-day (n = 15) precision (%R.S.D.) and accuracy (%Error) for 3-PBAcid ranged from 5.4 to 14.5% and from 5.1 to 12.8%, respectively. Finally, this method was applied to a toxicokinetic study of deltamethrin in the rat.

Animals↗

PubMed2003

Trace level determination of trichloroethylene from liver, lung and kidney tissues by gas chromatography-magnetic sector mass spectrometry.

Trichloroethylene (TCE) is a common industrial chemical that has been heavily used as a metal degreaser and a solvent for the past 100 years. As a result of the extensive use and production of this compound, it has become prevalent in the environment, appearing at over 50% of the hazardous waste sites on the US EPA's National Priorities List (NPL). TCE exposure has been linked to neurological dysfunction as well as to several types of cancer in animals. This paper describes the development and validation of a gas chromatography-mass spectrometry (GC-MS) method for the quantitation of trace levels of TCE in its target tissues (i.e. liver, kidney and lungs). The limit of quantitation (5 ng/ml) is substantially lower than currently published methods for the analysis of TCE in tissues. The % RSD and % Error for the assay falls within the acceptable range (<15% for middle and high QC points and <20% for low QC points), and the recovery is high from all tissues (>79%).

Animals↗

PubMed2001

Acute, short-term, and subchronic oral toxicity of 1,1,1-trichloroethane in rats.

1,1,1-Trichloroethane (TRI) is a widely used solvent that has become a frequent contaminant of drinking water supplies in the U.S. There is very little information available on the potential for oral TRI to damage the liver or to alter its P450 metabolic capacity. Thus, a major objective of this investigation was to assess the acute, short-term, and subchronic hepatotoxicity of oral TRI. In the acute study, male Sprague-Dawley (S-D) rats were gavaged with 0, 0.5, 1, 2, or 4 g TRI/kg bw and killed 24 h later. No acute effects were apparent other than CNS depression. Other male S-D rats received 0, 0.5, 5, or 10 g TRI/kg po once daily for 5 consecutive days, rested for 2 days, and were dosed for 4 additional days. Groups of the animals were sacrificed for evaluation of hepatotoxicity 1, 5, and 12 days after initiation of the short-term experiment. This dosage regimen caused numerous fatalities at 5 and 10 g/kg, but no increases in serum enzymes or histopathological changes in the liver. For the subchronic study, male S-D rats were gavaged 5 times weekly with 0, 0.5, 2.5, or 5.0 g TRI/kg for 50 days. The 0 and 0.5 g/kg groups were dosed for 13 weeks. A substantial number of rats receiving 2.5 and 5.0 g/kg died, apparently due to effects of repeated, protracted CNS depression. There was evidence of slight hepatocytotoxicity at 10 g/kg, but no progression of injury nor appearance of adverse effects were seen during acute or short-term exposure. Ingestion of 0.5 g/kg over 13 weeks did not cause apparent CNS depression, body or organ weight changes, clinical chemistry abnormalities, histopathological changes in the liver, or fatalities. Additional experiments did reveal that 0.5 g/kg and higher doses induced hepatic microsomal cytochrome P450IIE1 (CYP2E1) in a dose- and time-dependent manner. Induction of CYP2E1 activity occurred sooner, but was of shorter duration than CYP2B1/2 induction. CYP1A1 activity was not enhanced. In summary, 0.5 g/kg po was the acute, short-term, and subchronic NOAEL for TRI, for effects other than transient CYP2E1 induction, under the conditions of this investigation. Oral TRI appears to have very limited capacity to induce P450s or to cause liver injury in male S-D rats, even when administered repeatedly by gavage in near-lethal or lethal dosages under conditions intended to maximize hepatic effects.

Administration, Oral↗

PubMed2001

Acute, subacute, and subchronic oral toxicity studies of 1,1-dichloroethane in rats: application to risk evaluation.

1,1-Dichloroethane (DCE) is a solvent that is often found as a contaminant of drinking water and a pollutant at hazardous waste sites. Information on its short- and long-term toxicity is so limited that the U.S. EPA and ATSDR have not established oral reference doses or minimal risk levels for the volatile organic chemical (VOC). The acute oral LD(50) in male Sprague-Dawley (S-D) rats was estimated in the present study to be 8.2 g/kg of body weight (bw). Deaths appeared to be due to CNS depression and respiratory failure. In an acute/subacute experiment, male S-D rats were given 0, 1, 2, 4, or 8 g DCE/kg in corn oil by gavage for 1, 5, or 10 consecutive days. The animals were housed in metabolism cages for collection of urine and sacrificed for blood and tissue sampling 24 h after their last dose. There were decreases in body weight gain and relative liver weight at all dosage levels, as well as increased renal nonprotein sulfhydryl levels at 2 and 4 g/kg after 5 and 10 days. Elevated serum enzyme levels, histopathological changes, and abnormal urinalyses were not manifest. For the subchronic study, adult male S-D rats were gavaged with 0.5, 1, 2, or 4 g DCE/kg 5 times weekly for up to 13 weeks. Animals receiving 4 g/kg exhibited pronounced CNS depression, with more than one-half dying by week 11. The 2-g/kg rats exhibited moderate CNS depression. One 2-g/kg rat died during week 6. There were very few manifestations of organ damage in animals that succumbed or in survivors at any dosage level. Decreases in bw gain and transient increases in enzymuria were noted at 2 and 4 g/kg. Serum enzyme levels and blood urea nitrogen were not elevated, nor were glycosuria or proteinuria present. Chemically induced histological changes were not seen in the liver, kidney, lung, brain, adrenal, spleen, stomach, epididymis, or testis. Hepatic microsomal cytochrome P450 experiments revealed that single, high oral doses of DCE did not alter total P450 levels, but did induce CYP2E1 levels and activity and inhibit CYP1A1 activity. These effects were reversible and regressed with repeated DCE exposure. There was no apparent progression of organ damage during the 13-week subchronic study, nor appearance of adverse effects not seen in the short-term exposures. One g/kg orally (po) was found to be the acute, subacute, and subchronic LOAEL for DCE, under the conditions of this investigation. In each instance, 0.5 g/kg was the NOAEL.

Acetylglucosamine↗

PubMed2000

Contribution of direct solvent injury to the dose-dependent kinetics of trichloroethylene: portal vein administration to rats.

Presystemic elimination of trichloroethylene (TCE), a common contaminant of drinking water, has been shown by Lee et al. (Toxicol. Appl. Pharmacol. 139, 262-271, 1996) to be inversely related to dose. When relatively high doses were administered to rats via the portal vein (PV), first-pass hepatic extraction became negligible. This phenomenon could result not only from metabolic saturation, but from suicidal destruction of cytochromes P450 and hepatocellular injury as well. The objectives of the current investigation were to: (a) clarify the relative roles of P450 depletion and hepatocellular toxicity in the apparent cessation of hepatic elimination of TCE in animals given relatively high doses of TCE via the PV; and (b) investigate mechanism(s) of hepatocellular injury under such exposure conditions. TCE (16 and 64 mg/kg body weight (bw) was incorporated into a 5% aqueous Alkamuls emulsion and injected via an indwelling jugular vein (JV) or PV cannula into male Sprague-Dawley rats. Some animals received 73.5 micromol/kg of p-nitrophenol (PNP), a competitive metabolic inhibitor of TCE, through the PV cannula 3 min before TCE. Administration of TCE via the PV resulted in deposition of relatively high levels of TCE in the liver. PV dosing resulted in lower total hepatic P450 levels than did JV dosing. PV dosing produced marked elevations of cytoplasmic enzymes in serum, but JV dosing did not. Decreases in hepatic P450 were not selective for cytochrome P4502E1. Histological examination of the liver of PV-dosed rats revealed periportal rather than centrilobular necrosis. PNP pretreatment failed to prevent the increase in serum enzymes, decrease in hepatic P450 content, and hepatic necrosis following PV TCE. It is concluded that PV injection of bolus doses of TCE >/= 16 mg/kg causes liver injury within minutes in rats, primarily through direct solvent action on hepatocellular membranes rather than by P450-mediated effects. This liver damage likely plays a modest role in reducing the liver's capacity to metabolize high PV doses of TCE.

Animals↗

PubMed2000

Mechanisms of the dose-dependent kinetics of trichloroethylene: oral bolus dosing of rats.

Trichloroethylene (TCE), a common contaminant of drinking water, is oxidized by high-affinity, low-capacity cytochrome P450 isozymes and subsequently converted to metabolites, some of which are carcinogenic in mice and rats. Although the initial oxidation step is known to be rate-limiting and saturable, the oral dosage-range over which saturation materializes is unclear. One objective of this study was to characterize the dose-dependency of gastrointestinal (GI) absorption of TCE and its kinetics over a wide range of oral bolus doses. A related objective was to investigate cause(s) of the apparent saturation kinetics observed. Cannulas were surgically implanted into a carotid artery and the stomach of male Sprague-Dawley rats. TCE was incorporated into a 5% aqueous Alkamuls emulsion and given in doses of 2 to 1200 mg/kg bw via the stomach tube. Serial blood samples were taken from the arterial cannula for up to 14 h postdosing and analyzed for TCE content by headspace gas chromatography. The rate of GI absorption of TCE diminished as the dosage increased. Pharmacokinetic analysis indicated that TCE was eliminated by capacity-limited hepatic metabolism, with incursion into nonlinear kinetics with bolus doses >/=8 to 16 mg/kg. Effects of p-nitrophenol, a competitive metabolic inhibitor, were manifest at a high, but not at a low TCE dose. Gavage bolus doses as high as 1200 mg/kg did not cause rapid elevation of serum enzyme levels, typical of the solvation of hepatocellular membranes observed after portal vein administration of TCE (Lee et al., Toxicol. Appl. Pharmacol. 163, 000-000, 2000). No evidence of cytochrome P4502E1 (CYP2E1) destruction was seen with oral doses up to 1000 mg/kg. Instead, CYP2E1 activity was induced as early as 1 h postdosing. Induction was maximal at 12 h, then returned toward controls during the next 12 h. Pretreatment with cycloheximide did not reduce CYP2E1 activity in rats given 432 or 1000 mg TCE/kg, suggesting that binding of TCE to CYP2E1 may stabilize the isozyme. Metabolic saturation, in concert with relatively slow GI absorption, are responsible for the prolonged elevation of blood TCE levels in rats given high TCE doses, while suicidal inactivation of CYP2E1 and hepatocellular injury apparently play little role.

Administration, Oral↗

PubMed1999

Simple method for rapid measurement of trichloroethylene and its major metabolites in biological samples.

A simple and rapid, yet sensitive technique was developed for concurrent measurement of trichloroethylene (TCE) and its major metabolites (i.e., trichloroacetic acid, trichloroethanol and dichloroacetic acid) in blood and in solid tissues. The method involves addition of an esterizer (water, sulfuric acid, methanol; 6:5:1; v/v/v) to blood or tissue homogenate in sealed vials, and subsequent gas chromatographic headspace analysis. The procedure should be useful in medical monitoring of TCE exposure as well as in experimental work, notably pharmacokinetic and pharmacodynamic studies pertaining to TCE carcinogenesis.

Animals↗

PubMed1998

Effects of acute inhalation exposure to isoamyl nitrite on the hypothalamo-pituitary-adrenal axis in male Sprague-Dawley rats.

Isoamyl nitrite (IAN) is a member of the family of volatile organic nitrites that exert vasodilatory effects and have recently exhibited a considerable potential for inhalation abuse. In an effort to provide mechanistic insight into the neurotoxic effects and abuse potential of these agents, the present study was designed to evaluate the acute effects of IAN on the hypothalamo-pituitary-adrenal (HPA) axis. Attempts were also made to correlate the neuroendocrine effects of IAN with its pharmacokinetic profile. Male Sprague-Dawley rats were exposed to 600 or 1200 ppm IAN by inhalation for 10 or 30 min. Following exposure, adrenocorticotropic hormone (ACTH) and corticosterone in plasma and corticotropin-releasing factor (CRF) in three brain regions (hypothalamus, hippocampus, and frontal cortex) were determined by radioimmunoassay. Levels of IAN in the three brain regions as well as in blood were measured by gas chromatography to determine the target tissue concentrations responsible for neuroendocrine changes. Uptake of IAN into blood and all brain regions was very rapid, as stable concentrations were achieved within 10 min of exposure and maintained for 30 min of continuous inhalation. Plasma corticosterone decreased significantly after 10 min inhalation of both IAN doses, and returned to control levels after 30 min. Moreover, plasma ACTH was significantly increased by 10 and 30 min of exposure to 600 and 1200 ppm IAN, while hypothalamic CRF increased significantly after 30 min of exposure to the 600 ppm dose. These latter findings suggest activation of the hypothalamus and pituitary due to a reduction in negative feedback resulting from the initial decrease in corticosterone. Although plasma ACTH was greatly increased after 30 min, plasma corticosterone levels were unchanged, indicating that IAN primarily acts to inhibit the synthesis or secretion of adrenal steroids and that activation of the HPA axis is not involved in the behavioral manifestations of IAN inhalation. These compensatory effects of HPA axis regulation, and possibly the vasodilatory properties of IAN, also likely precluded the establishment of definitive relationships between observed changes in hormone levels and blood or regional brain concentrations of the inhalant.

Administration, Inhalation↗

PubMed1998

Effects of acute inhalation exposure to 1,1,1-trichloroethane on the hypothalamo-pituitary-adrenal axis in male Sprague-Dawley rats.

1,1,1-Trichloroethane (TRI) is a commonly used industrial solvent with a considerable potential for inhalation abuse. Previous studies in our laboratory and elsewhere have shown that this agent exerts a suppressant effect on operant responding, as well as a number of additional neurobehavioral effects that are similar to those of central nervous system (CNS) depressant drugs. In an effort to provide information relevant to potential mechanisms involved in the behavioral effects and abuse potential of TRI, the present study evaluated the acute effects of this agent on the activity of the hypothalamo-pituitary-adrenal (HPA) axis . Male Sprague-Dawley rats were exposed to 3500 or 5000 ppm TRI by inhalation for 10 or 30 min. Following exposure, plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone and levels of ACTH and corticotropin-releasing factor (CRF) in three brain regions--hypothalamus, hippocampus, and frontal cortex--were determined by selective radioimmunoassays. Levels of TRI in the three brain regions as well as blood were measured by headspace gas chromatography to determine the target tissue concentrations responsible for neuroendocrine changes. Uptake of TRI in blood and all brain regions was very rapid, with stable concentrations apparently achieved within 10 min and maintained for 30 min. During this time course, a significant decrease in plasma corticosterone was produced at 30 min but no significant change in plasma ACTH was observed with 3500 ppm TRI. However, after exposure to 5000 ppm, both plasma ACTH and plasma corticosterone were significantly reduced at 10 and 30 min. ACTH levels in the three brain regions were not significantly changed by TRI, while hypothalamic CRF was significantly increased during exposure to 3500 ppm. However, hypothalamic concentrations of CRF declined following 30 min at 3500 ppm and were not significantly changed by 5000 ppm. This complexity of effects on the regulation of HPA axis activity likely precluded the establishment of consistent relationships between changes in hormonal levels and blood or regional brain concentrations of the inhalant. However, these actions of TRI were strikingly similar to those previously reported for the benzodiazepines.

Administration, Inhalation↗

PubMed1997

Uptake, distribution, and elimination of carbon tetrachloride in rat tissues following inhalation and ingestion exposures.

Carbon tetrachloride (CCl4) has been studied extensively for its hepatotoxic effects. There is a paucity of information, however, about its tissue deposition following administration by different routes and patterns of exposure. The specific objective of this study was to delineate the uptake, distribution, and elimination of CCl4 in tissues of rats subjected to equivalent oral and inhalation exposures. Male Sprague-Dawley rats (325-375 g) were exposed to 1000 ppm CCl4 for 2 hr. The total absorbed dose (179 mg CCl4/kg bw) was administered to other groups of rats as a single oral bolus or by constant gastric infusion over a period of 2 hr. Animals were terminated at selected time intervals during and postexposure and tissues (liver, kidney, lung, brain, fat, skeletal muscle, spleen, heart, and GI tract) removed for measurement of their CCl4 content by headspace gas chromatography. CCl4 levels in all tissues were much lower in the gastric infusion group than in the oral bolus and inhalation groups. Inhalation resulted in relatively high tissue CCl4 concentrations, because inhaled chemicals enter the arterial circulation and are transported directly to organs throughout the body. It seems logical that the liver should accumulate more CCl4 following ingestion than following inhalation. This did not prove to be the case when comparing liver AUC values for the gastric infusion and inhalation groups. Substantially lower CCl4 concentrations in the liver of animals in the gastric infusion group appeared to be due to very rapid metabolic clearance of the relatively small amounts of CCl4 entering the liver over the 2-hr infusion period. It was hypothesized that the capacity of first-pass hepatic and pulmonary elimination could be exceeded, if CCl4 were given as a single, large oral bolus. Indeed, deposition of CCl4 in all tissues was greater in the oral bolus group than in the gastric infusion group. The time courses of uptake and elimination of CCl4 appeared to be governed largely by a tissue's rate of blood perfusion and lipid content. CCl4 was rapidly taken up, for example, by the brain and liver. These organs' CCl4 content then diminished, as CCl4 was metabolized and redistributed to adipose tissue. CCl4 accumulated slowly, but to very high concentrations, in fat and remained elevated for a prolonged period. Thus, concentrations of CCl4 in some tissues may not be reflective of blood levels. The most appropriate measure of internal dose for CCl4 acute hepatotoxicity appears to be the area under tissue concentrations versus time curve from 0 to 30 min. Tissue time-course data sets are essential for the refinement and validation of physiological models for CCl4 and other volatile organic chemicals.

Adipose Tissue↗

PubMed1996

Characterization of presystemic elimination of trichloroethylene and its nonlinear kinetics in rats.

1,1,2-Trichloroethylene (TCE) is a volatile organic chemical which contaminates drinking water and food supplies and is primarily of concern because of the risk of cancer it may pose. The objectives of the present study were to evaluate the efficiency and dose dependency of presystemic elimination of TCE in rats. Cannulas were surgically implanted into male Sprague-Dawley rats (330-380 g) 24 hr before TCE dosing. TCE (0.17, 0.33, 0.71, 2, 8, 16, and 64 mg/kg) in a 5% aqueous Alkamuls emulsion was administered over 30 sec into the carotid artery, jugular vein (JV), hepatic portal vein, or the stomach. Serial arterial blood samples of 1-500 microliters were collected for up to 12 hr from the unanesthetized animals and analyzed for TCE content by headspace gas chromatography. Pharmacokinetic analyses indicated that TCE was eliminated through dose-dependent nonlinear processes. A three-compartment model with Michaelis-Menten and first-order elimination was derived to fit simultaneously the TCE blood data following JV administration. Total presystemic elimination of TCE was inversely related to dose, ranging from approximately 60 to < 1%. A dose-dependent decrease in hepatic extraction was primarily responsible for the reduction in total first-pass elimination at high doses, whereas pulmonary extraction (i.e., 5-8%) was relatively constant over the dosage range. When metabolic saturation was minimal or absent, hepatic presystemic elimination of TCE accounted for approximately 45-55% of the administered dose. These findings indicate that a substantial proportion of trace amounts of VOCs ingested in environmental media may not enter the systemic circulation nor reach extrahepatic target organs.

Administration, Oral↗

PubMed1996

Schedule-controlled operant behavior of rats following oral administration of perchloroethylene: time course and relationship to blood and brain solvent levels.

Previous studies have indicated that human exposure to perchloroethylene (PCE) produces subtle behavioral changes and other neurological effects at concentration at or below the current occupational exposure limit. Since comparable effects in animals may be reflected by changes in schedule-controlled operant behavior, the ability of orally administered PCE to alter fixed-ratio (FR) responding for a food reward was investigated in male Sprague-Dawley rats. Furthermore, since behavioral effects of solvents are likely to be more closely related to blood or target tissue (i.e, brain) concentrations than administered dose, the relationship between the pharmacokinetic distribution of PCE and its effects on operant responding was also evaluated. Rats trained to lever-press for evaporated milk on an FR-40 reinforcement schedule were gavaged with 160 or 480 mg/kg PCE and immediately placed in an operant test cage for 90 min. Separate animals gavaged with equivalent doses of PCE were used to determine profiles of blood and brain concentrations versus time. Perchloroethylene produced changes in responding that varied not only with dose but also among animals receiving the same dose. Changes in the response rates of rats receiving 160 mg/kg PCE were either not readily apparent, restricted to the first 5 min of the operant session, or attributable to gavage stress and the dosing vehicle. However, 480 mg/kg produced either an immediate suppression of responding for 15-30 min before a rapid recovery to control rates or a complete elimination of lever-pressing for the majority of the operant session. Although the two doses of PCE produced markedly different effects on operant behavior during the first 30 min of exposure, differences in brain concentrations of PCE were minimal. Furthermore, the majority of animals receiving 480 mg/kg PCE fully recovered from response suppression while blood and brain levels of the solvent continued to rise. Thus, relationships between blood and brain PCE levels and performance impairment were not discernible over the monitored time course. Since the rapid onset of response suppression suggests that the precipitating event occurs within the first few minutes of exposure, it is possible that altered responding is related to the rate of increase in blood or brain concentrations rather than the absolute solvent concentrations themselves. The relationship between the pharmacokinetic distribution of solvents and their effects on the central nervous system is obviously complex and may involve acute neuronal adaptation as well as the dynamics of solvent distribution among the various body compartments.

Administration, Oral↗

PubMed1995

Effect of route and pattern of exposure on the pharmacokinetics and acute hepatotoxicity of carbon tetrachloride.

The objectives of this study were to evaluate the influence of both route and pattern of exposure on the pharmacokinetics (PK) and target organ toxicity of a common volatile organic chemical, carbon tetrachloride (CCl4). Male Sprague-Dawley rats, 325-375 g, inhaled 100 or 1000 ppm CCl4 for 2 hr through a one-way breathing valve. The total amount of CCl4 retained by each rat (i.e., the systemically absorbed dose) during the 2-hr period was determined to be 17.5 and 179 mg CCl4/kg body wt, respectively. CCl4, in doses of 17.5 and 179 mg/kg body wt, was administered in an aqueous emulsion by bolus gavage or by constant gastric infusion over 2 hr. Serial micro blood samples from the animals were analyzed for CCl4, in order to delineate blood concentration-versus-time profiles. Serum enzyme activities and total liver microsomal cytochrome P450 level and glucose 6-phosphatase activity were measured 24 hr postdosing as indices of CCl4 hepatotoxicity. The pattern of oral exposure, or dosage regimen, had a significant effect on the PK and acute the hepatotoxicity of CCl4. Arterial blood levels in the gastric infusion group were much lower than in the oral bolus group with both doses. Since CCl4 is quickly and extensively absorbed from the GI tract, large amounts of CCl4 in the portal blood following the oral bolus apparently exceeded the capacity of the liver to metabolize the chemical. Thus, substantially higher Cmax and AUC0 integral of infinity values were manifest. Hepatotoxicity was also significantly greater in these animals. The route of exposure also had a significant effect on the PK of CCl4. Levels of CCl4 in the arterial blood were much higher during inhalation than during gastric infusion. However, AUC0 integral of infinity vales for the two groups were not significantly different, due to relatively slow elimination after gastric infusion. There was little difference between the two groups in hepatotoxicity indices 24 hr postdosing.

Administration, Inhalation↗

PubMed1995

Physiologically based pharmacokinetic model useful in prediction of the influence of species, dose, and exposure route on perchloroethylene pharmacokinetics.

The ability of a physiologically based pharmacokinetic (PBPK) model to predict the uptake and elimination of perchloroethylene (PCE) in venous blood was evaluated by comparison of model simulations with experimental data for two species, two routes of exposure, and three dosage levels. Unanesthetized male Sprague-Dawley rats and beagle dogs were administered 1, 3, or 10 mg PCE/kg body weight in polyethylene glycol 400 as a single bolus, either by gavage or by intraarterial (ia) injection. Serial blood samples were obtained from a jugular vein cannula for up to 96 h following dosing. The PCE concentrations were analyzed by headspace gas chromatography. For each dose and route of administration, terminal elimination half-lives in rats were shorter than in dogs, and areas under the blood concentration-time curve were smaller in rats than in dogs. Over a 10-fold range of doses, PCE blood levels in the rat were well predicted by the PBPK model following ia administration, and slightly underpredicted following oral administration. The PCE concentrations in dog blood were generally overpredicted, except for fairly precise predictions for the 3 mg/kg oral dose. These studies provide experimental evidence of the utility of the PBPK model for PCE in interspecies, route-to-route, and dose extrapolations.

Adipose Tissue↗

PubMed1994

Comparisons between operant response and 1,1,1-trichloroethane toxicokinetics in mouse blood and brain.

The effect of 1,1,1-trichloroethane (TRI) inhalation on operant response was evaluated in relation to the concentration of TRI in blood and brain tissue in mice during exposure. Male CD-1 mice were trained to lever-press for an evaporated milk reinforcer on a variable interval (VI 60) schedule for 2 h. Trained mice were then exposed to either 3500 or 5000 ppm TRI for 100 min, and the changes in the schedule-controlled performance were measured. Additional groups of mice were exposed under the same conditions as those used in the behavioral study and sacrificed at various times during exposure, and the blood and brain samples were collected and subsequently analyzed for TRI content by headspace gas chromatography. Uptake of TRI into blood and brain was rapid, with near steady-state levels reached after approximately 40-60 min of exposure. Inhalation of 5000 ppm, but not 3500 ppm TRI was seen to cause inhibition of operant response, starting approximately 30 min following the initiation of inhalation exposure and beginning to recover after 80 min of exposure. The threshold concentrations for the maximal behavioral inhibition were approximately 110 micrograms/g and 130 micrograms/ml in mouse brain and blood, respectively. It appears that in addition to TRI concentrations in blood and brain tissue, the time it takes to reach the apparent threshold TRI concentration was also a determinant for the onset of TRI neurobehavioral depression.

Administration, Inhalation↗

PubMed1994

Use of tissue disposition data from rats and dogs to determine species differences in input parameters for a physiological model for perchloroethylene.

Tissue disposition of perchloroethylene (PCE) was determined experimentally in two mammalian species of markedly different size in order to derive input parameters for the development of a physiologically based pharmacokinetic (PBPK) model, which could forecast the disposition of PCE in each species. Male Sprague-Dawley rats and male beagle dogs received a single bolus of 10 mg PCE/kg body wt in polyethylene glycol 400 by gavage. Serial samples of brain, liver, kidney, lung, heart, skeletal muscle, perirenal fat, and blood were taken for up to 72 hr following PCE administration. Blood and tissue PCE concentrations were analyzed using a gas chromatography headspace technique. Dogs exhibited considerably longer tissue and blood half-lives than did rats. The dogs also exhibited larger area under tissue concentration versus time curves for all tissues except the liver. Whole body clearance of PCE in the rat was greater than that in the dog. Model simulations indicated this could be attributed to more rapid and extensive PCE exhalation and metabolism by the rat. The in vivo blood:air partition coefficient determined for rats was similar to an in vitro value previously reported. In vivo tissue: blood partition coefficients, however, were 1.4 to 2.8 times greater than published in vitro values. The PCE in vivo blood:air partition coefficient for the dog was twice that of the rat, but tissue:blood partition coefficients were 1.5 to 3.0 times greater in the rat than in the dog. These results demonstrated the existence of significant differences in partition coefficients in two species commonly used in toxicity testing. The PBPK model was shown to have utility in predicting the impact of metabolism and exhalation on pharmacokinetics of PCE in different species of widely differing size.

Adipose Tissue↗

PubMed1994

Development of a physiologically based pharmacokinetic model for perchloroethylene using tissue concentration-time data.

The tissue disposition of perchloroethylene (PCE) was characterized experimentally in rats in order to (1) obtain input parameters from in vivo data for the development of a physiologically based pharmacokinetic (PBPK) model, and (2) use the PBPK model to predict the deposition of PCE in a variety of tissues following inhalation exposure. For the derivation of model input parameters, male Sprague-Dawley rats received a single bolus of 10 mg PCE/kg body wt in polyethylene glycol 400 by ia injection through an indwelling carotid arterial cannula. Other male Sprague-Dawley rats inhaled 500 ppm PCE for 2 hr in dynamic exposure inhalation chambers. Serial samples of brain, liver, kidney, lung, heart, skeletal muscle, perirenal fat, and blood were taken for up to 72 hr following ia injection, during the 2-hr inhalation exposure, and for up to 72 hr postexposure. Blood and tissue PCE concentrations were analyzed using a gas chromatography headspace technique. Following ia administration, the tissues exhibited similar terminal elimination half-lives (t1/2). As comparable tissue t1/2 are consistent with a blood-flow-limited model, tissue:blood partition coefficients were calculated for noneliminating compartments by division of the area under the tissue concentration-time curve (AUC) by the blood AUC. Liver PCE concentration versus time data were employed in the calculation of in vivo metabolic rate constants. A PBPK model was developed using these parameters derived from the ia data set and used to predict tissue PCE concentrations during and following PCE inhalation. Predicted tissue levels were in close agreement with the levels measured over time in the seven tissues and in blood. Tissue concentration-time data can thus provide valuable input for parameter estimation and for validation of PBPK model simulations, as long as independent in vivo data sets are used for each step.

Administration, Inhalation↗