Effect of organochlorine pesticides on maturation of starfish and mouse oocytes.

Methoxychlor, lindane, and dieldrin are organochlorine pesticides that have been described as altering different reproductive functions in mammals and in invertebrates. However, few data have been published concerning the effects these pesticides have on oocyte maturation and fertilization. The aim of this study was to determine whether these compounds could affect maturation of mouse and starfish oocytes. We observed that germinal vesicle breakdown (GVBD) in starfish oocytes was significantly inhibited by the pesticides. Furthermore, formation of the first meiotic spindle and extrusion of the first polar body were also altered in mouse as well as in starfish. Our results suggest that the three pesticides act on common intracellular targets in invertebrates as well as in vertebrates.     

Aroclor 1254 causes atrophy of exocrine pancreas in mice and the mechanism involved

Polychlorinated biphenyls (PCBs) are a class of organic pollutants that have been linked to pancreatic disease. However, their role in affecting the exocrine function of pancreas and the underlying mechanism remains elusive. In the present study, male C57 mice were treated with Aroclor 1254, a commercially available PCBs mixture, at a dosage of 0.5, 5, 50, or 500 μg kg^?1 every 3 days by oral gavage. Decrease in pancreas/soma index and acinar atrophy were observed in the mice after exposure for 50 days. Aroclor 1254 exposure significantly decreased the PCNA‐positive cells in the pancreatic acini in a dose‐dependent manner. In addition, western blot analysis showed that PCNA expression was decreased in pancreas in the presence of Aroclor 1254, which suggests that Aroclor 1254 suppresses cell proliferation. TUNEL‐positive apoptotic cells as well as the expression of Bcl2, BclXL, BAX, and Bad of exocrine pancreas did not show significant changes in the treated mice, indicating that Aroclor 1254 has no effect on apoptosis. We also found that phosphorylation of ERK1/2, P90RSK1 and Bad was increased in the treated groups; this compensatory activation of phosphorylation in ERK1/2‐P90RSK1‐Bad signaling cascade could protect cell from apoptosis to maintain the cell numbers and function of exocrine pancreas. Moreover, we found that the expression of Kras and TNFα was increased in the pancreas, indicating that Aroclor 1254 exposure could result in increased risk of inflammation and carcinoma. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 671–678, 2016.     

Estrogen receptors are involved in polychlorinated biphenyl-induced apoptosis on mouse spermatocyte GC-2 cell line

Polychlorinated biphenyls (PCBs) are widespread persistent environmental contaminants which have been shown to have reproductive toxicity and to disturb spermatogenesis. But the precise mechanism is not clear. A mouse pachytene spermatocyte-derived cell line, GC-2 cells were used in the present study to investigate the toxic effect of PCBs (Aroclor 1254) and explore the underlying molecular mechanism. Results showed that Aroclor 1254 inhibited cell proliferation, caused the arrest of cells in G0/G1 phase and induced apoptosis which might be partly explained by the decreased expression of Bcl-2 and cell cycle regulator cyclin D1 together with the activation of caspase-3. Besides, the treatment of Aroclor 1254 decreased the protein expression of estrogen receptor (ER)-α while increasing that of ERβ. Then the administration of selective ERα agonist PPT partly reversed Aroclor 1254-induced alteration in Bcl-2, caspase-3 and cyclin D1 protein expression while selective ERβ agonist DPN accelerated it. These results suggest that Aroclor 1254, working through ERα and ERβ, interferes with the expression of proteins involved in the balance between cellular apoptosis and proliferation.     

Protective role of Lycopene against Aroclor 1254-induced changes on GLUT4 in the skeletal muscles of adult male rat

Aroclor 1254 is the commercial mixture of highly toxic environmental pollutant, polychlorinated biphenyls (PCBs). Being immensely durable, it is extensively used and widely distributed. Studies show that Aroclor 1254 causes a variety of adverse health effects through free radical generation. The present investigation was designed to check the effect of Aroclor 1254 on the glucose transporter protein, GLUT4, which plays a key role in glucose homeostasis. The protective role of lycopene against the adverse effect of Aroclor 1254 was also tested. Group 1 rats received corn oil as vehicle and served as control. Groups 2, 3, and 4 were administered with Aroclor 1254 [2?mg kg^?1 body weight (b.w.) day^?1] intraperitoneally for 30 days. Groups 3 and 4 received lycopene (2 and 4?mg kg^?1 b.w. day^?1, respectively) orally in addition to Aroclor 1254. After 30 days, animals were euthanized and the skeletal muscles were dissected to determine the following parameters: GLUT4 messenger RNA (mRNA), GLUT4 protein (both plasma membrane and cytosolic fractions), and ¹⁴C-2-deoxyglucose uptake. Though there was no change in GLUT4 mRNA and fasting plasma glucose levels, Aroclor 1254 significantly decreased the GLUT4 protein level in both the subcellular fractions of the gracilis and triceps muscles. Most important, ¹⁴C-2-deoxyglucose uptake showed a significant decrease in Aroclor 1254 alone treated rats, and Aroclor 1254 plus 4?mg lycopene supplementation treatment maintained the same at par with control. Thus, Aroclor 1254 has adverse effects on GLUT4 translocation and ¹⁴C-2-deoxyglucose uptake, and lycopene administered along with Aroclor 1254 has a protective role over it.     

三氯化铬对小鼠卵母细胞成熟和体外受精的影响

采用小鼠卵母细胞体外培养 ,体外受精的方法研究了三氯化铬对小鼠卵母细胞成熟和受精能力的影响 .结果表明 ,三氯化铬可以抑制卵母细胞第一极体的释放 ,降低小鼠超排卵数和卵母细胞的存活率和体外受精率 .对小鼠体内生发泡破裂没有影响 ,但可以抑制体外培养卵母细胞的生发泡破裂 ;随着在正常培养液中培养时间的延长 ,卵母细胞的第一极体的释放率和体外受精率 (除了 6.0 mg· kg-1组外 )均有显著提高 ,且与对照组相比已经无显著性差异 .结果提示 ,三氯化铬可以破坏卵母细胞的成熟 ,降低卵母细胞的受精能力 ,具有明显的生殖毒性     

Augmented atherogenesis in ApoE-null mice co-exposed to polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) are persistent organic pollutants found as complex mixtures in the environment throughout the world. Therefore, humans are ubiquitously and simultaneously exposed to TCDD and PCBs. TCDD and PCBs alone have been linked to atherosclerosis. However, the effects of interactions or synergism between TCDD and PCBs on atherogenesis are unknown. We investigated the possible enhanced atherogenesis by co-exposure to TCDD and PCBs and the potential mechanism(s) involved in this enhancement. Male ApoE^−/− mice were exposed to TCDD (15 μg/kg) and Aroclor1254 (55 mg/kg, a representative mixture of PCBs) alone or in combination by intraperitoneal injection four times over six weeks of duration. Our results showed that mice exposed to TCDD alone, but not Aroclor1254 alone, developed atherosclerotic lesions. Moreover, we found that atherosclerotic disease was exacerbated to the greatest extent in mice co-exposed to TCDD and Aroclor1254. The enhanced lesions correlated with several pro-atherogenic changes, including a marked increase in the accumulation of the platelet-derived chemokine PF4, and the expression of the proinflammatory cytokine MCP-1 and the critical immunity gene-RIG-I. Our data demonstrated that co-exposure to TCDD and Aroclor1254 markedly enhanced atherogenesis in ApoE^−/− mice. Significantly, our observations suggest that combined exposure to TCDD and PCBs may be a greater cardiovascular health risk than previously anticipated from individual studies.     

Effect of Aroclor 1254 on Sertoli cellular antioxidant system, androgen binding protein and lactate in adult rat in vitro

Polychlorinated biphenyls (PCBs) are persistent and bioaccumulative environmental toxicants. Previous studies suggested that PCBs (Aroclor 1254) induce toxic effects including reproductive toxicity. The present study was designed to investigate the impact of Aroclor 1254 on Sertoli cellular function and antioxidant system of adult rat in vitro. Sertoli cells were isolated from adult rat testes and treated with various concentrations (10(-10) to 10(-7) M) of Aroclor 1254 for 6, 12 and 24 h. After the treatment period, cell viability was assessed and the Sertoli cellular antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), gamma-glutamyl transpeptidase (gamma-GT) and glutathione reductase (GR) and lipid peroxidation (LPO) were assayed. In addition, androgen binding protein (ABP) and lactate secretions were also quantified in Sertoli cell culture medium. Sertoli cellular viability and activity of antioxidant enzymes were significantly reduced in Aroclor 1254 (10(-10) to 10(-7) M) treatment for 6, 12 and 24 h whereas, the Sertoli cellular lipid peroxidation was significantly increased in a dose and duration dependent manner. In addition, ABP secretion diminished and lactate secretion was significantly elevated in the same manner. To conclude, the present study suggested that Aroclor 1254 disrupts Sertoli cellular metabolic functions such as ABP, lactate secretions and activity of antioxidant enzymes.     

Studies on the protective role of lycopene against polychlorinated biphenyls (Aroclor 1254)-induced changes in StAR protein and cytochrome P450 scc enzyme expression on Leydig cells of adult rats

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent environmental contaminants that disturb normal endocrine functions, including gonadal functions in humans and mammals. PCBs (Aroclor 1254) - induced toxic manifestations are associated with the production of free radicals. Lycopene belongs to the group of natural carotenoids, which are found in many fruits, vegetables and other green plants. Lycopene, the most potent antioxidant protects against oxidative damage. The present study was conducted to elucidate the protective role of lycopene against Aroclor 1254-induced changes in Leydig cellular steroidogenic acute regulatory (StAR) protein, cytochrome P450 side chain cleavage (P450 scc) enzyme expression and 3β-hydroxy steroid dehydrogenase (3β-HSD) activity. The rats were divided into four groups. Each group consists of six animals. Group I rats were administered with corn oil intraperitoneally (i.p.) for 30 days. Group II rats were treated with Aroclor 1254 (i.p.) 2 mg kg^?1 body weight (bwt) day^?1 for 30 days. Group III rats were treated with Aroclor 1254 (i.p.) 2 mg kg^?1 bwt day^?1 along with simultaneous supplementation of lycopene 4 mg kg^?1 bwt day^?1 (gavage) for 30 days. Group IV rats administered with lycopene alone at the dose of 4 mg kg^?1 bwt day^?1 (gavage) for 30 days. After 24 h of the last treatment, animals were decapitated, blood was collected and serum testosterone level was estimated by radioimmunoassay (RIA). Testes were removed and Leydig cells were isolated in aseptic condition. StAR protein, cytochrome P450 scc enzyme expression were studied by Western blot analysis and 3β-HSD activity was estimated spectrophotometrically. Aroclor 1254 treatment significantly reduced the serum testosterone level. Simultaneous supplementation of lycopene maintained the serum testosterone to near normal. Aroclor 1254 exposure decreased Leydig cellular StAR protein, cytochrome P450 scc enzyme expression and activity of 3β-HSD. However, simultaneous supplementation of lycopene improved Leydig cellular StAR protein, cytochrome P450 scc expression and activity of 3β-HSD. These results suggested that lycopene have ameliorative role against Aroclor 1254 induced Leydig cell dysfunction.     

POLYCHLORINATED BIPHENYLS ARE SELECTIVELY NEUROTOXIC IN THE DEVELOPING SPISULA SOLIDISSIMA EMBRYO

Polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants that accumulate to toxic levels in the food chain. Using Spisula solidissima (surf clam) embryos as a developmental model, it was shown that Aroclor 1254 specifically targets two neuronal structures during embryonic development. Embryos were exposed to 1, 10, or 100 ppm Aroclor 1254 or an acetone vehicle control posthatching for 24, 48, and 72 h. Embryos labeled with a serotonin antibody or a neural antigen antibody and a rhodamine-conjugated secondary antibody were viewed by confocal microscopy. The cerebropleural ganglion showed a decrease both in serotonin production and in the size of the serotonin-synthesizing region upon exposure to 10 and 100 ppm Aroclor 1254. These decreases were detectable as early as 48 h postfertilization. When exposed to 100 ppm Aroclor 1254, the primitive neural plexus, which coordinates the movements of the mouth and velum, showed a delay in onset and cessation of expression of a molluscan-specific neural antigen. Exposure to Aroclor 1254 did not affect the overall growth and morphology of the embryos. In addition, analyses of total protein profiles and heat-shock protein 70 levels showed that exposure to Aroclor 1254 did not trigger protein degradation or cause a stress or shock response. These results show that exposure of Spisula embryos to Aroclor 1254 specifically targets neurogenesis while having no effect on the overall growth of the embryo.     

N-acetyl-l-cysteine protects porcine oocytes undergoing meiotic resumption from heat stress

Heat stress (HS) is a notable risk factor for female reproductive performance. In particular, impaired oocyte maturation was thought to contribute largely to the HS-induced reproductive dysfunctions. In this study, we confirmed that oocytes undergoing GVBD were much susceptible to HS, and thus compromising subsequent embryonic development. Using N-acetyl-l-cysteine (NAC), we found supplementation of a relatively high dose NAC during in vitro maturation, can protect oocytes from HS-induced complications, and thus rescuing impaired embryonic development. Further analysis indicated that mechanisms responsible for protecting GVBD oocytes from HS by NAC may include: (1) reversing disorganized spindle assembly and inhibited extracellular signal–regulated kinase (ERK) signaling; (2) correcting erroneous H3K27me3 modification and dysregulated expression of imprinted genes; (3) alleviating increased intraoocyte reactive oxygen species accumulation and apoptosis initiation. Our study, focusing on the oocyte meiotic maturation, may provide a safe and promising strategy for protecting reproductive sows under environmental hyperthermal conditions.     

Effects of co‐exposure to 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin and polychlorinated biphenyls on nonalcoholic fatty liver disease in mice

2,3,7,8‐Tetrachlorodibenzo‐p‐dioxin (TCDD) and polychlorinated biphenyls (PCBs) are persistent organic pollutants which coexist in environment, and human are co‐exposed to these chemicals. Our present study was aimed to investigate the possible enhanced nonalcoholic fatty liver disease (NAFLD) in ApoE^?/? mice co‐exposed to TCDD and PCBs and to reveal the potential mechanisms involved in. Male ApoE^?/? mice were exposed to TCDD (15 μg/kg) and Aroclor1254 (55 mg/kg, a representative mixture of PCBs) alone or in combination by intraperitoneal injection four times over a 6‐week period. Those mice co‐exposed to PCBs and TCDD developed serious liver steatosis, necrosis, and inflammatory stimuli. Interestingly, all treatment induced hepatic cytochrome P450 1A1 (CYP1A1) expression, but the maximal level of CYP1A1 was not observed in the co‐exposure group. Furthermore, microarray analysis by ingenuity pathway analysis software showed that the nuclear factor‐erythroid 2‐related factor 2 (Nrf2)‐mediated oxidative stress response pathway was significantly activated following co‐exposure to TCDD and PCBs. Our data demonstrated that co‐exposure to TCDD and PCBs markedly worsen NAFLD in ApoE^?/? mice. © 2014 Wiley Periodicals, Inc. Environ Toxicol 30: 1364–1374, 2015.     

The degree of PCB chlorination determines whether the rise in urinary homovanillic acid production in rats is peripheral or central in origin

Commercial mixtures of polychlorinated biphenyls (PCBs, Aroclor 1016, 1254, and 1260) differing in their degree of chlorination and their accumulation in the brain were employed along with a peripheral monoamine oxidase inhibitor, debrisoquin sulfate (Declinax, DS) to determine whether the rise in urinary homovanillic acid (UHVA) following exposure to these PCBs is derived from the peripheral or central nervous system. Rats were gavaged with either corn oil or corn oil containing Aroclor 1016 or a mixture of Aroclors 1254 and 1260 and 24-hr UHVA production was determined by high-performance liquid chromatography with electrochemical detection. All animals also received ip injections of DS to inhibit peripheral production of HVA. Analysis of variance indicated that, following DS treatment, 24-hr UHVA production remained significantly elevated in the Aroclor 1254/1260-exposed animals; while no significant differences between Aroclor 1016-exposed animals and controls were noted. The rise in UHVA in the Aroclor 1254/1260 group involves HVA of central origin whereas the rise in the Aroclor 1016-treated animals is only peripheral. Thus, PCBs that differ in their degree of chlorination alter dopaminergic functions in anatomically different locations.     

Measurements of the cytosolic Ah receptor among four strains of Drosophila melanogaster

Four strains of Drosophila melanogaster exhibit differences in aryl hydrocarbon hydroxylase (AHH) inducibility by phenobarbital or Aroclor 1254, yet do not show the typical AHH induction response when exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or benzo[a]anthracene. Adult flies were nevertheless examined for the presence of cytosolic TCDD-specific binding (Ah receptor). Berlin-K and Haag 79 exhibit AHH induction by Aroclor 1254 and possess detectable amounts of Ah receptor. Hikone-R has negligible AHH inducibility by Aroclor 1254, yet possesses measurable amounts of the receptor. Oregon-K displays AHH induction by Aroclor 1254 but has no detectable levels of the cytosolic receptor. Specific (high-affinity, low-capacity and saturable) binding of [³H-1,6]TCDD to the Ah receptor in D. melanogaster was shown to be similar to that observed in C57BL/6 mouse liver. Similar specific binding of generally labeled [³H]benzo[a]anthracene in D. melanogaster cytosol was not found. These data suggest that the presence of the Ah receptor per se, or quantity of receptor, does not guarantee AHH inducibility by TCDD or benzo[a]anthracene in adults of these four fruit fly strains.     

Ras-dependent maturation of Xenopus oocytes is blocked by modified peptides of GTPase activating protein (GAP)

Guanosine triphosphatase activating protein (GAP) is an important modulator of p21^ras (Ras)-dependent signal transduction in mammalian cells and in insulin-induced maturation of Xenopus oocytes. A synthetic octapeptide from the catalytic domain of GAP, residues 899-906 (F⁸⁹⁹VFLRLIC⁹⁰⁶), inhibited GAP-stimulated hydrolysis of GTP to GDP by Ras in an in vitro biochemical assay (IC₅₀= 12 μM). The peptide was assayed for its ability to block insulin- (Ras-dependent) and progesterone- (Ras-independent) induced maturation of stage VI Xenopus laevis oocytes, marked by germinal vesicle breakdown (GVBD). Microinjection of 50 pmol of the peptide inhibited insulin- but not progesterone-induced GVBD by 50%. A 7-residue peptide lacking F⁸⁹⁹, GAP(900-906)-NH₂, failed to inhibit GAP-stimulated GTPase activity and did not block GVBD. Replacement of the cysteine residue at position 906 with methionine resulted in a peptide with prolonged inhibitory activity in the oocyte. Moreover, sequential replacement of specific L-amino acid residues with the corresponding d -mino acids produced a peptide with a two-fold increased half-life after injection into oocytes. None of the peptides tested affected progesterone induced GVBD, suggesting that the modifications did not result in loss of specificity. These studies show that (a) peptides that were able to inhibit GAP-stimulated Ras GTPase activity in vitro were also able to block Ras-dependent GVBD in oocytes, and (b) specific substitutions in these peptides can result in improved stability in oocytes. © Munksgaard 1995.     

Polychlorinated biphenyls (PCBs) selectively disrupt serotonergic cell growth in the developing Spisula embryo.

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that exert neurotoxic effects during embryonic development. The present study demonstrates that early embryonic exposure to a mixture of PCBs (Aroclor 1254) results in a decrease in serotonergic cell growth. Using a novel, marine invertebrate embryo model, Spisula solidissima, immunocytochemistry, and confocal microscopy techniques, a dose-dependent decrease in serotonergic cell number was quantified within 24 h of exposure. This effect was seen with doses as low as 1 ppm Aroclor 1254. These findings demonstrate that environmentally relevant doses of Aroclor 1254 impair development of the serotonergic nervous system.     

Disruption of spermatogenesis and differential regulation of testicular estrogen receptor expression in mice after polychlorinated biphenyl exposure

The testicular toxicity of polychlorinated biphenyls (PCBs) has been extensively studied. However, the detailed mechanism is still obscure. In the present study, male C57 mice were treated with different doses of Aroclor 1254 (a commercial PCB mixture) once every 3 days by oral gavage. After exposure to Aroclor 1254 for 50 days, the sperm count decreased in a dose-dependent manner. Cell proliferation and apoptosis are key processes regulating development of the testis, and alterations in these processes may underlie testicular dysgenesis. Our results showed that the germ cell proliferation was inhibited and the apoptosis of the germ cell was induced in a dose-dependent manner after treatment with Aroclor 1254. Although there was no significant change in serum testosterone levels and androgen receptor expression levels after treatment with different dosages of Aroclor 1254, the estradiol levels decreased and the expression of estrogen receptor (ER) β increased in a dose-dependent manner, whereas an elevation of the expression of ERα was only observed in the 50μg/kg group. The data as a whole suggested that inhibited proliferation and induced apoptosis in germ cells, and a differential regulation of ER, may be involved in the testicular toxicity of PCBs.     

The toxic effects of Aroclor 1254 exposure on the osteoblastic cell line MC3T3-E1 and its molecular mechanism

Polychlorinated biphenyls (PCBs) are still prevalent in the environment despite the fact that they have been banned in many countries for several decades. Recent epidemiologic studies have demonstrated a link between PCBs exposure and pathological alterations of bone tissues. The aim of this study was to investigate the toxic effects of the PCBs mixture Aroclor 1254 on MC3T3-E1 preosteoblasts and explore the underlying molecular mechanism. Different doses of Aroclor 1254 were used to treat MC3T3-E1 and the cell viability, apoptosis, ALP activity, intracellular calcium (Ca2+) level and oxidative stress response were measured. The expression level of related proteins TRPV6, Apaf-1 and Bax was evaluated with Western blot assay. The subcellular distribution of TRPV6 protein was detected with immunofluorescence assay. The results indicated that the higher dose of Aroclor 1254 (>10 mg/L) could inhibit the cell proliferation and induce apoptosis in MC3T3-E1. The ROS level following Aroclor 1254 exposure was elevated with the concentration, while the ALP activity and intracellular calcium (Ca2+) level decreased. After Aroclor 1254 exposure, the expression level of calcium transport related protein TRPV6 was down-regulated, while the expression level of apoptosis related proteins Apaf-1 and Bax up-regulated in a dose dependant manner. The immunofluorescence assay results showed that the expression of TRPV6 in the cytoplasm was greatly suppressed after Aroclor 1254 exposure. In conclusion, Aroclor 1254 exposure could induce toxic effects in MC3T3-E1 as evidenced by inhibition of proliferation, induction of apoptosis and suppression of ALP activity. The ROS production and alteration of intracellular Ca2+ level induced by down-regulation of TRPV6 might involve the toxic effects, and cell apoptosis induced by Aroclor 1254 exposure is associated with the pro-apoptotic Apaf-1 pathway as well as alteration of Bcl-2/Bax ratio.     

Comparison of the effects of acute and subchronic administration of Aroclor 1254, a commercial mixture of polychlorinated biphenyls, on pentobarbital-induced sleep time and [14C]pentobarbital disposition in mice

We have reported previously that polychlorinated biphenyls (PCBs) alter neurochemistry and suppress spontaneous locomotor activity in mice. The present study was initiated to determine whether orally administered (Aroclor 1254) would potentiate pentobarbital-induced sleep time. Sleep time was enhanced significantly by Aroclor 1254 (500 mg/kg) given 0 to 8 h prior to pentobarbital, with the peak effect occurring at 2 h. This effect was demonstrated to be dose-responsive in the range of 5 to 25 mg/kg given 2 h prior to pentobarbital, but only slightly larger increments in sleep time were observed with higher doses of PCBs (50, 100, 250, and 500 mg/kg). Administration of vehicle or Aroclor 1254 (30 or 100 mg/kg) for 14 successive days reduced sleep time when pentobarbital was given 45 min after the last dose of vehicle or Aroclor 1254, with a further reduction when pentobarbital was given 24 h after the last dose. As a correlate to the sleep-time studies, levels of pentobarbital and metabolites were measured in brain, liver, and plasma of mice that had received varying doses of Aroclor 1254 2 h prior to [14C]pentobarbital. Elevated levels of pentobarbital and decreased levels of metabolites were found after acute administration of Aroclor 1254 during a period of time when Aroclor 1254-treated mice were still asleep. These effects of Aroclor 1254 on pentobarbital disposition were found to be dose-dependent. Brain levels of pentobarbital in mice after 14 d of Aroclor 1254 treatment (30 mg/kg) were less than those in vehicle-treated animals, and these levels were consistent with the reduced sleep times. Thus, a correlation between pentobarbital brain levels and sleep time in both Aroclor 1254-treated and nontreated animals suggests that Aroclor 1254 does not alter pentobarbital narcosis by a direct action on the brain. Rather, acutely administered Aroclor 1254 may be augmenting sleep time by competing with pentobarbital for metabolic sites in the liver, while chronically administered Aroclor 1254 induces pentobarbital metabolism.