Age-Related Changes in Dermal Absorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and 2,3,4,7,8-Pentachlorodibenzofuran

Age-Related Changes in Dermal Absorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxinand 2,3,4,7,8-Pentachlorodibenzofuran. BANKS, Y. B., BREWSTER,D. W., AND BIRNBAUM, L. S. (1990). Fundam. Appl. Toxicol. 15,163–173. Changes in the structure and function of agedskin may alter percutaneous absorption of environmental compoundssuch as the halogenated aromatic hydrocarbons. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)and 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) were previouslyfound to be poorly absorbed in 3 month male Fischer 344 ratswithin 3 days after dermal administration. In order to examineage-related changes in dermal absorption and changes in potentialfor systemic exposure, the absorption, distribution, and eliminationof TCDD and 4PeCDF were examined in male Fischer 344 rats ofvarious ages (TCDD: 10, 36, and 96 week; 4PeCDF: 10, 36, 64,96, and 120 week). Each compound was applied at a dose of 0.1µmol/kg and/or 0.04 µmol in 60 µ1 acetoneto a preclipped region of the back and covered with a stainless-steelperforated cap. Rats were housed in individual metabolism cagesfor 3 days. Dermal absorption of both compounds was decreasedin older age groups compared to 10 week rats. The major tissuedepots for both compounds were liver, adipose, skin, and muscleand in comparable age groups, the liver.fat ratio was greaterin 4PeCDF-treated animals. Age-related changes in the distributionof the administered dose and the absorbed dose varied with thecompound as well as the depot. Elimination of TCDD and 4PeCDFwas limited at all ages. Results indicate that percutaneousabsorption of these compounds is decreased in older animals,suggesting that systemic bioavailability may be decreased inolder organisms following dermal exposure to TCDD or 4PeCDF.     

Species Differences in 2,3,7,8-Tetrachlorodibenzo-p-dioxin Toxicity and Biotransformation in Fish

Species Differences in 2,3,7,8-Tetrachlorodibenzo-p-dioxin Toxicityand Biotransformation in Fish. KLEEMAN, J. M., OLSON, J. R.,AND PETERSON, R. E. (1988). Fundam. Appl. Toxicol 10, 206-213.Rainbow trout, yellow perch, carp, bluegill, largemouth bass,and bullhead were treated with graded doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD; 1, 5, 25, or 125 µg/ kg) or vehicle, ip. The lethalpotency of TCDD tended to be greater in yellow perch, carp,and bullhead than in the other three species (LD50 80 days post-treatment,3-5 versus 10-16 µg/kg, respectively). All species treatedwith the highest dose of TCDD (125 µg/kg) displayed alatency period of 1-4 weeks prior to death; longer latency periodswere produced by lower lethal doses. Effects of TCDD treatmenton body weight were both species-dependent and dose-dependent.Fin necrosis was observed in all fish species; however, cutaneoushemorrhage was observed only in TCDD-treated perch, carp, andbluegill, and cutaneous hyperpigmentation only in TCDD-treatedcarp and largemouth bass. Gallbladder bile was analyzed forTCDD and its metabolites 7 days after fish were injected with[¹⁴C]TCDD (60 µg/kg, ip). At least three TCDD metabolitesin addition to the parent compound were found in the gallbladderbile of all six species. In addition, the retention time ofthe major biliary TCDD metabolite (determined by HPLC) was similarin all species except yellow perch. ß-Glucuronidasetreatment of the bile from largemouth bass and bluegill suggestedthat at least two of the TCDD metabolites were glucuronide conjugates.Thus, species differences exist in the lethal potency, signsof overt toxicity, and biotransformation of TCDD among freshwaterfish.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin Pretreatment of Female Mice Altered Tissue Distribution but Not Hepatic Metabolism of a Subsequent Dose

2,3,7,8-Tetrachlorodibenzo-p-dioxin Pretreatment of Female MiceAltered Tissue Distribution but Not Hepatic Metabolism of aSubsequent Dose. CURTIS, L. R., JCERKVLIET, N. I., BAECHER-STEPPAN,L., AND CARPENTER, H. M. (1990). Fundam. Appl. Toxicol 14, 523–531.Lipid partitioning of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)inadequately explains its tissue distribution since higher concentrationsoccur in liver than fat except at high doses. This study providesIn vivo evidence that an inducible, saturable system plays apredominant role in disposition of [¹⁴C]TCDD in female miceat doses between 5 and 20 Mg/kg. Female C57BL/6J mice were gavagedwith 0, 5, or 15 µg, TCDD/kg, received a subsequent gavageof 5 or 20 11% [¹⁴C]TCDD after 6 days, and were killed 1 daylater. In mice pretreated with 5 and 15MgTCDD/ kg and subsequentlydosed with 20 µg [¹⁴C]TCDD/kg, liver weight and [¹⁴C]TCDDconcentration increased. Total liver [¹⁴C]TCDD burden increasedabout 50% in both pretreatment groups. Concentrations of [¹⁴C]TCDDin kidney, fat, heart, lung, gastrointestinal tract, but notplasma or splenic lymphocytes, decreased in a reciprocal manner.Alterations in absorption, concentrations of polar metabolitesof [¹⁴C]TCDD in liver, and hepatic lipid content failed to explainthese results. About 97% of hepatic ¹⁴C was hexane extractable.HPLC of this extract indicated [¹⁴C]TCDD was the only significantnonpolar form of radiolabel in liver. In mice pretreated with511% TCDD/kg and subsequently dosed with 5 µg [¹⁴C]TCDD/kg,a more marked pretreatment disposition response was observed.These results are consistent with a predominant role for aninducible, high affinity, low capacity system in whole animalpharmacokinetics of TCDD.     

Target Tissue Morphology and Serum Biochemistry following 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Exposure in a TCDD-Susceptible and a TCDD-Resistant Rat Strain

Target Tissue Morphology and Serum Biochemistry following 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) Exposure in a TCDD-Susceptible and a TCDD-Resistant RatStrain. POHJANVIRTA, R., KULJU, T., MORSELT, A. F. W., TUOMINEN,R., JUVONEN, R., ROZMAN, K.,MÄNNISTÖ, P., COLLAN,Y., SAINIO, E.-L., AND TUOMISTO, J. (1989). Fundam. Appl. Toxicol.12, 698–712. The mode of action of the highly toxic environmentalcontaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is unknown.It was recently discovered that two strains of rat, Long-Evans(L-E) and Han/Wistar (H/W), differ widely in susceptibilityto TCDD. Employing this strain divergence as a probe, the presentstudy set out to assess the role of various biochemical andmorphological effects in TCDD lethality. In the main experiment,the rats were treated once ip with 0, 5, 50, or (H/W) 500 µg/kgTCDD and killed 1 to 16 days postexposure. Several target organswere evaluated by light microscopy and a number of serum lipidand carbohydrate parameters as well as a few major regulatoryhormones were analyzed. The results demonstrated that most alterationscaused by TCDD were essentially similar in both strains. TCDDreduced circulating thyroxine to a slightly greater extent andmore permanently in the sensitive L-E strain. Moreover, a highlysignificant interaction on thyroid-stimulating hormone was foundamong strain, dose. and time. Serum concentrations of corticosteroneand free fatty acids were increased only in the L-E rats given50 µg/kg TCDD, i.e., at an apparent LDl00 dose level forthis strain. Yet, the most striking interstrain difference wasseen in the liver which was distinctly affected after Day 4in L-E rats given 50 µg/kg TCDD but only marginally affectedin rats from any H/W group. The lesion, while showing no necroticcell changes, was suggestive of plasma membrane damage, possiblyreflecting the production of free radicals. The relation ofthe findings to possible mechanisms of TCDD action is discussed.     

Differential Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in C57BL/6J Mice Congenic at the Ah Locus

Differential Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) in C57BL/6J Mice Congenic at the Ah Locus. BIRNBAUM,L. S., MCDONALD, M. M., BLAIR, P.C., CLARK, A. M., AND HARRIS,M. W. (1990). Fundam. Appl. Toxicol 15, 186–200. The acutetoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examinedin male C57BL/6J mice differing only at the Ah locus. Wild typemice (Ah^b/b; "b/b") were treated once with 0, 50, 100, 200,300, and 400 eg TCDD/kg po while congenic mice (Ah^d/d; "d/d")received a single dose of 0, 400, 800, 1600,2400, and 3200µgTCDD/kg. Mice were checked daily, weighed twice a week, andthose that survived, killed 35 days post-treatment. The LD5Ovalues were 159 and 3351 µg/kg for b/b and d/d mice, respectively.Mean time to death was 22 days and was independent of dose andgenotype. Decrease in body weight gain was noted in both strains5 days after treatment and occurred at doses 100 µ/kgin b/b mice and 1600 µg/kg in d/d mice. Dose-related increasesin liver weight (both absolute and relative to body weight)and decreases in thymus, spleen, testes, and epididymal fatpad weights were observed at 8–24–fold higher dosesin d/d than in b/b mice. A dose-related increase in segmentedneutrophils was observed in both strains. Serum chemistry valuesindicated that 8–24x greater doses of TCDD were neededto elevate sorbitol dehydrogenase, alanine aminotransferase,and 5'-nucleotidase and to decrease total and esterifled cholesterolin d/d than in b/b mice. Few effects were seen on total bileacids, serum triglycerides, glucose, or nonesterifled cholesterol.In the liver, hepatocellular cytomegaly, fatty change, and bileduct hyperplasia occurred in both strains in a dose-relatedmanner, as did thymic and splenic atrophy. Necrosis of germinalepithelium in the testes and edema in the stomach submu cosaoccurred at acutely toxic doses. These lesions also occurredat doses 8–24x greater in did than in b/b mice. Thus,the spectrum of toxicity is independent of the allele at theAh locus, but the relative dose needed to bring about variousacute responses is approximately 8–24x greater in congenicmice homozygous for the "d" allele than for the wild type animalscarrying two copies of the "b" gene.     

Ingestion of Soil Contaminated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Alters Hepatic Enzyme Activities in Rats

Ingestion of Soil Contaminated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) Alters Hepatic Enzyme Activities in Rats. LUCIER, G.W., RUMBAUGH, R. C., MCCOY, Z., HASS, R., HARVAN, D., AND ALBRO,P. (1986). Fundam. Appl. Toxicol. 6, 36.4–371. Femalerats were treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)in either corn oil or contaminated soil from the Minker sitein Missouri. Eight doses ranging from 0.015 to 5 µg TCDD/kgwere used in the corn oil group; the range was 0.015 to 5.5TCDD/kg in the TCDD-contaminated soil group. Rats in a thirdgroup were given equal amounts of soil uncontaminated with TCDD.No acute toxicity or effects on body weight gain were observedat these doses. In general, equivalent doses of TCDD in cornoil or TCDD in soil produced similar increases in hepatic arylhydrocarbon hydroxylase activity (AHH) and UDP glucuronyltransferaseactivity although effects were slightly greater in the TCDD–cornoil groups. In the corn oil groups, the induction of AHH rangedfrom about 30-fold at the highest dose to twofold at the lowestdose studied. TCDD also caused an increase in cytochrome P-450concentration and a shift in spectral peak from 450 to 448 nm.There was no effect of TCDD on ethylmorphine N-demethylase,consistent with previous reports. Liver concentrations of TCDD(mean ± SD) in the 5-µg/kg groups were 40.8 ±6.3 ppb in the TCDD- corn oil group and 20.3 ± 12.9 ppbin the TCDD-contaminated soil group. Our results suggest thatthe bioavailability of TCDD in soil in rats is approximately50%. Therefore, ingestional exposure to TCDD-contaminated soilmay constitute a significant health hazard in view of its extremelyhigh toxicity and relatively high bioavailability.     

Comparison of the T Cell-Independent Antibody Response of Mice and Rats Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmentalcontaminant that produces adverse effects on the immune systemof experimental animals. In this study, the effect that TCDDhas on the antibody plaque-forming cell (PFC) response to theT cell-independent (TI) antigen trinitrophenyl-lipopolysaccharide(TNP-LPS) was compared in adult female B6C3F1 mice and F344rats. Mice or rats were given a single intraperitoneal injectionof TCDD at doses ranging from 1 to 30 µg/kg, 7 days priorto immunization with TNP-LPS by intravenous injection. Threedays later body, spleen, thymus, and liver weights were measuredand the PFC response to TNP-LPS was determined. Thymus weightswere decreased at 10 and 30 µg TCDD/kg, whereas spleenweights were decreased and liver weights increased in mice dosedat 3,10, and 30 µg/kg. Mice dosed at 10 and 30 µgTCDD/kg had suppressed PFC responses and serum hemagglutinationliters. In rats, thymus weights were decreased and liver weightsincreased at 3, 10, and 30 µg TCDD/kg; however, the PFCresponse and serum hemagglutination titers to TNP-LPS were suppressedonly at 30 µg/kg TCDD. TCDD did not affect splenic lymphocytesubsets evaluated by flow cytometry. These results indicatethat TCDD suppresses the TI antibody response to TNP-LPS inboth B6C3F1 mice and F344 rats, with mice more sensitive tosuppression by TCDD than rats.     

Effect of Dose, Time, and Pretreatement on the Biliary Excretion and Tissue Distribution of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in the Rat

Effect of Dose, Time, and Pretreatment on the Biliary Excretionand Tissue Distribution of 2,3,7,8-Tetrachlorodibenzo-p-dioxinin the Rat. KEDDERIS, L. B., ANDERSEN, M. E., AND BIRNBAUM,L. S. (1993). Fundam. Appl. Toxicol. 21, 405–411. Previous studies of the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) pretreatment on the biliary excretion and hepatic dispositionindicated that TCDD did not induce its own metabolic elimination.Pretreatment with TCDD did enhance its hepatic uptake. The presentwork was designed to further examine the effects of dose, time,and pretreatment on the tissue distribution and biliary eliminationof [³H]TCDD. Adult male F-344 rats were administered 0 or 100nmol [¹⁴C]TCDD or [³H]-TCDD/kg body weight po 3 days prior tobile duct cannulation and iv injection of 0 or 1 nmol [³H]TCDDor 1, 10, or 100 nmol [¹⁴C]TCDD/kg. Bile was collected for upto 8 hr while rats were maintained under pentobarbital anesthesia.Biliary TCDD and TCDD metabolites were quantified by liquidscintillation spectrometry. In naive animals which receivedno pretreatment, similar rates of excretion (% dose) were observedfollowing iv administration of 1 nmol [³H]TCDD/kg or 10 or 100nmol [¹⁴C-TCDD/kg. Metabolic elimination of highly purified[³H]TCDD (<99%) appeared to be linear with respect to timewith 0.8% of the dose being excreted in the bile over a 5- to8-hr collection period 0 or 24 hr after iv dosing (1, 10, or100 nmol/kg) and 72 hr after oral dosing (100 nmol/kg). In allgroups, higher concentrations of TCDD were found in liver versusfat, and perirenal fat concentrations were elevated relativeto epididymal fat concentrations, probably reflective of theenhanced blood perfusion of the former tissue. Pretreatmentenhanced hepatic concentrations and decreased fat concentrationsof the challenge dose. The time dependence of factors involvedin the dose-related hepatic accumulation of TCDD dispositionwas illustrated by the elevated liver:fat concentration ratiosobserved at the 100 versus 10 or 1 nmol/kg dose at 30 hr, butnot by 5–6 hr after dosing. In studies designed to evaluatethe role of CYP1A2 in the hepatic disposition of TCDD, pretreatmentwith isosafrole, a selective inhibitor of CYP1A2, diminishedhepatic concentrations of [³H]TCDD. In conclusion, TCDD wasmetabolically cleared at a fairly constant rate over an 80-hrperiod, and the rate of elimination was proportional with regardto dose. Studies with isosafrole suggest that TCDD is boundto CYP1A2 in the liver.     

Interactive Effects between 2,3,7,8-Tetrachlorodibenzo-p-dioxin and 2,2',4,4',5,5'-Hexachlorobiphenyl in Female B6C3F1 Mice: Tissue Distribution and Tissue-Specific Enzyme Induction

The distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) was studiedin female B6C3F1 mice. Single doses of TCDD alone (0, 0.1, 1,or 10 µg [³H]TCDD/kg), PCB 153 alone (0, 3.58, 35.8, or358 mg [¹⁴C]PCB 153/kg), and all possible combinations of thesedoses were administered in corn oil, po. At 7 days after dosing,11 different tissues were analyzed for radioactivity. When TCDDwas administered alone, TCDD-derived radioactivity distributedto all tissues in a dose-dependent manner, increasing with dosein the liver, while decreasing (as a percentage of the administereddose) in all other tissues. When PCB 153 was administered alone,the PCB 153 concentration was dose-dependently (percentage ofdose) decreased in liver, skin, lung, adrenals, kidney, andblood; no dosimetric effects were observed in the other organs.Coadminis-tration of low doses of both TCDD and PCB 153 resultedin little or no effect on the distribution of either compound.Interactive effects occurred in the pharmacokinetic behaviorof both compounds only at higher doses. For example, the amountof TCDD in the liver was increased by 358 mg PCB 153/kg. Inmost other organs administration of PCB 153 resulted in a dose-dependentdecrease in the TCDD content Coadministration of PCB 153 with10 µg TCDD/kg increased PCB 153 in the liver, but notin other tissues. These results clearly demonstrate that interactiveeffects on pharmacokinetic behavior occur only at high doses.     

Characterization of the Peak Period of Sensitivity for the Induction of Hydronephrosis in C57BL/6N Mice following Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Characterization of the Peak Period of Sensitivity for the Inductionof Hydronephrosis in C57BL/6N Mice following Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin.COUTURE, L. A., HARRIS, M. W., AND BIRNBAUM, L. S. (1990). Fundam.Appl. Toxicol. 15, 142–150. 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) is an extremely potent teratogen in mice. Hydronephrosisand cleft palate are the most sensitive measures of teratogenicityin mice following exposure to TCDD and other structurally relatedpolyhalogenated aromatic hydrocarbons. Despite a relativelylong half-life, investigators have identified a critical windowfor the induction of cleft palate in C57BL/6N mice. To characterizethe critical period for renal teratogenesis, pregnant C57BL/6Nmice were treated once by gavage with 0–24 µg TCDD/kgbody wt on Gestation Day (GD) 6, 8, 10, 12, or 14. All damswere killed on GD 18, and the fetuses were examined for thepresence of hydronephrosis and cleft palate. Maternal liver-to-bodyweight ratios were significantly elevated above controls onall days, while maternal weight gain was unaffected. Fetal mortalitywas increased relative to controls only at 24 µg TCDD/kgon GD 6. There was no significant difference in fetal body weightsbetween control and TCDD-treated fetuses. The incidence of cleftpalate increased in a dose-related fashion from GD 6 to GD 12,and identification of GD 12 as the critical window for inductionof clefting of the hard palate was confirmed. Hydronephrosiswas observed at all dose levels, regardless of exposure day,and the incidence was close to 100% at 3 µg TCDD/kg andhigher doses on GD 12 and earlier. At all doses on GD 14, boththe incidence and severity of hydronephrosis were decreasedrelative to all other days. There was a dose-related increasein the severity of the renal lesion on each day, but betweenGD 6 and 12 severity was constant Thus, while palatal sensitivityto TCDD increased with gestational age between GD 6 and 12,there was no difference among these days in development of hydronephrosis.The data suggest, however, that on GD 14 the urinary tract maybe less sensitive to TCDD.     

The Effect to Pretreatment on the Biliary Excretion of 2,3,7,8-Tetrachlorodibenzo-p-dioxin, 2,3,7,8-Tetrachlorodibenzofuran, and 3,3',4,4'-Tetrachlorobiphenyl in the Rat

The Effect of Pretreatment on the Biliary Excretion of 2,3,7,8-Tetrachlorodibenzo-p-dioxin,2,3,7,8-Tetrachlorodibenzofuran, and 3,3',4,4'-Tetrachlorobiphenylin the rat. MCKINLEY, M. K., KEDDERIS, L. B., and BIRNBAUM,L. S. (1993). Fundam. Appl. Toxicol. 21, 425–432. The laterally halogenated chemicals 2,3,7,8-tetrachlorodibenzofuran(TCDF) and 3,3',4,4'-tetrachlorobiphenyl (TCB) exhibit the samespectrum of toxic effects as 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD), the prototype and most toxic member of the halogenatedaromatic hydrocarbon family. Metabolism of all three compoundsappears to be the rate-limiting step for excretion, which isprimarily via the bile into the feces. Therefore, the biliaryelimination of TCDF, TCDD, and TCB was examined as an indirectmeasure of metabolism. Male F344 rats were anesthetized withpentobarbital, the bile duct was cannulated, and 0.1 µmol[³H]TCDD, [¹⁴C]TCDF, or [¹⁴C]TCB/kg body wt was administerediv. Bile was collected for 0–8 hr while the animals werekept under anesthesia. To determine if TCDF was able to induceits own metabolism in vivo, a single dose of 1.0 µmolTCDF/kg was administered to rats by oral gavage 3 days priorto iv injection of 0.1 or 0.3 µmol [¹⁴C]TCDF/kg. Biliaryexcretion and hepatic concentrations of [¹⁴C]TCDF were significantlyincreased in the pretreated animals. These results suggest anautoinduction of TCDF metabolism. Essentially all biliary [¹⁴C]TCDFradioactivity was attributable to metabolites. High-pressureliquid chromatography profiles of biliary radioactivity from0 to 4 hr were qualitatively different between naive and pretreatedrats. To determine if pretreatment with TCDD altered the metabolismof TCDF and vice versa, a single dose of 1.0 µmol TCDF/kgor 0.1 µmol TCDD/kg was administered by oral gavage 3days prior to iv injection of 0.1 µmol [³H]TCDD or [¹⁴C]TCDF/kg,respectively. TCDD pretreatment increased the metabolism andhepatic concentrations of [¹⁴C]TCDF in pretreated rats, whilebiliary elimination and hepatic concentrations of [³H]TCDD wereunaffected by pretreatment with TCDF. In a fourth experiment,the ability of TCDD to alter the metabolism of TCB, a laterallysubstituted polychlorinated biphenyl (PCB), was examined. Pretreatmentwith TCDD increased the metabolism of [¹⁴C]TCB by approximatelytwofold, but no differences in hepatic concentrations were seendue to the rapid elimination of TCB. Rats pretreated with Aroclor1254, a commercial mixture of PCBs, demonstrated significantlyincreased metabolism of [¹⁴C]TCB compared to the naive group.Therefore, under these experimental conditions, induction ofTCDF metabolism occurred in the rat upon pretreatment with eitherTCDD or TCDF at doses which also elicited enhanced hepatic uptake.TCDD and Aroclor 1254 induced the metabolism of TCB. These findingssuggest that repeated exposure to a chemical or to a mixtureof these halogenated aromatic hydrocarbons can result in morerapid metabolism and elimination from the body than followinga single, acute exposure.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin tissue distribution, excretion, and effects on clinical chemical parameters in guinea pigs

The tissue distribution of ¹⁴C-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in adult male guines pigs was studied up to 15 days following its ip injection (2.0 μg/kg). On Day 1, the highest levels of radioactivity (% of original dose/g tissue) were located in the adipose tissue, adrenals, liver, spleen, intestine, and skin. All other tissues examined contained less than 0.3%/g tissue. By Day 15, the level of radioactivity in the liver increased to nearly three times its initial value. An increase in radioactivity was also noted in the adrenals, kidneys, and lungs. These increases appeared to be due to the mobilization of fat stores and the subsequent redistribution of radioactivity contained in these stores to other organs. Following a single intraperitoneal dose of 0.5 μg [³H]TCDD/kg the excretion of ³H in the urine and feces appeared to be linear up to 23 days. Assuming the excretion of radioactivity would continue in a linear manner, the time for excretion of half the administered dose by way of the urine and feces was calculated to be 30.2 ± 5.8 days. The effect of TCDD (1.0 μg/kg) upon various clinical chemical parameters was determined periodically up to 14 days and compared to pairfed controls. Statistically significant increases in plasma albumin, total protein, iron, urea nitrogen, cholesterol, and triglycerides were observed in TCDD-treated pigs.     

Relationship of Alterations in Energy Metabolism to Hypophagia in Rats Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Relationship of Alterations in Energy Metabolism to Hypophagiain Rats Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin. POTTER,C. L., MENAHAN, L. A., AND PETERSON, R. E. (1986). Fundam. Appl.Toxicol. 6, 89–97. Efficiency of energy utilization wasevaluated temporally in 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD, 50 µg/kg)-treated male Sprague—Dawley rats(275–300 g), their pair-fed counterparts, and a groupwith ad libitum access to ground feed. TCDD treated rats exhibiteda progressive reduction in feed intake and body weight. Theweight loss of vehicle-treated rats, pair-fed to the TCDD-treatedgroup, was comparable to that found in rats receiving TCDD.Following treatment, rats administered TCDD were as efficientin absorbing feed energy from the gut as control rats. Thiswas evidenced by similar relative digestible energy values inTCDD-treated rats, their pair-fed partners, and a group withad libitum access to feed. Equivalent decreases in oxygen consumptionand carbon dioxide production in TCDD-treated rats and theirpair-fed counterparts, relative to rats with ad libitum accessto feed, suggested that the decrease in both of these parametersin TCDD-treated rats was secondary to hypophagia and/or weightloss. Decline of respiratory quotient (RQ) to almost 0.7 inboth TCDD-treated rats and their pair-fed counterparts is indicativeof fat combustion. By Day 17 post-treatment, RQ increased significantlyin the TCDD-treated and pair-fed groups possibly due to a limitationin the availability of lipid stores. Also, TCDD-treated ratsand their pair-fed partners diminished their water intake toa similar extent without reducing urine output. Likewise, urinaryexcretion of both energy and urea was decreased to the sameextent in rats treated with TCDD as it was in their pair-fedcounterparts. However, TCDD-treated rats tended to excrete moreurinary ammonia than their pair-fed partners on Days 10 and16 post-treatment. Thus, TCDD treatment does result in a reductionof caloric intake in the rat, yet efficiency of energy utilizationis preserved.     

Modulation of TCDD-induced wasting syndrome by portocaval anastomosis and vagotomy in Long-Evans and Han/Wistar rats

Portocaval anastomosis and vagotomy operations were performed in Long-Evans (L-E) and Han/Wistar (H/W) rats to elucidate the mechanism of anorexia induced by TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). TCDD-sensitive L-E rats were given a sublethal (5 μg/kg) or a lethal dose (20 μg/kg) by gavage 5–8 weeks after portocaval anastomosis. TCDD-resistant H/W rats were given a nonlethal dose (500 or 7200 μg/kg). The shunt operation did not reduce lethality from TCDD. The effect on wasting of the marginally toxic dose of 5 μg/kg in L-E rats was potentiated by the portocaval operation, and the lethal dose was effective in both shunted and sham-operated L-E rats. TCDD failed to decrease food intake and body weight in shunted rats of H/W strain at either dose level though it did so in sham-oprated controls. The lack of effect may be due to the already reduced weight of shunted rats at the time of TCDD dosing. TCDD anorexia was not explained by changes in histamine or serotonin (5-HT) turnover in the brain. Vagotomy did not influence lethality after TCDD, although reduction in food intake was somewhat blunted in H/W rats. The results seem to indicate that the anorectic effect of TCDD is modified when portal blood bypasses the liver. The mechanisms remain to be elucidated in detail, but the results do not favor the role of liver as the only or the major initiator of TCDD anorexia. Little evidence was found to support a crucial role of vagal afferent input.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin in Pregnant Long Evans Rats: Disposition to Maternal and Embryo/Fetal Tissues

Prenatal exposue to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)interfereswith fetal development at doses lower than those causing overttoxicity in adult animals. In a multigeneration study (Murrayet al., 1979), female rats that were administered 0.01 µgTCDD/kg/day in their diet did not experience reduced fertility;however, reduced fertility was seen in the F₁ and F₂ generations.Exposure to TCDD during development produces alterations inthe reproductive system of the developing pups, such as delayedpuberty and reduced sperm counts in males (Mably et al., 1992a;Gray et al., 1995) and malformations in the external genitaliaof females (Gray and Ostby, 1995). Therefore, the objectivesof this study were to determine maternal and fetal tissue concentrationsof TCDD that are associated with the adverse reproductive effectsseen by Gray and co-workers. Pregnant Long Evans rats receiveda single oral dose of 1.15 µg [₃H]TCDD/kg on GestationDay (GD) 8 and maternal as well as fetal tissue concentrationsof TCDD were measured on GD9, GD16, and GD21. On GD9, the highestlevel of TCDD localized in the maternal liver (25.1% dose).In addition, the amount reaching all the embryos on GD9 was0.01% of the administered dose, which resulted in a concentrationof 0.02% dose/g . The amount of TCDD reaching the fetal compartment(fetuses + placentas) increased to 0.12% dose/tissue on GD16and 0.71% by GD21. The concentration of TCDD within the fetalcompartment (0.01% dose/g) on GD16 was comparable to that foundin the maternal blood and spleen. Concentrations of TCDD ina single embryo/fetus were 39.6, 18.1, and 22.1 pg/g on GD9,GD16, and GD21, respectively. Estimates of hepatic half-lifeof elimination in pregnant rats suggested that TCDD may be eliminatedfaster in pregnant LE rats. Therefore, measurements of biliaryelimination were made in pregnant and nonpregnant LE rats tocompare rates of metabolism; however, biliary elimination ofTCDD is not affected by pregnancy. In conclusion, this doseadministered during a critical period of organogenesis causesadverse effects on the developing reproductive system of rodents.This dose produced a body burden of 22.1 pg TCDD/g within asingle fetus on GD21. This indicates that low-level TCDD exposureduring the perinatal stage of life can produce adverse effectswithin the developing pups.     

Female Sprague--Dawley Rats Exposed to a Single Oral Dose of 2,3,7,8-Tetrachlorodibenzo-p-dioxin Exhibit Sustained Depletion of Aryl Hydrocarbon Receptor Protein in Liver, Spleen, Thymus, and Lung

There is currently little information concerning the time-dependentrelationship between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)exposure and aryl hydrocarbon receptor (AHR) and aryl hydrocarbonreceptor nuclear translocator (ARNT) protein concentration invivo. Therefore, female Sprague-Dawley rats were given a singleoral dose of TCDD (10 µg/kg), and the AHR and ARNT proteinconcentrations in liver, spleen, thymus, and lung determinedby Western blotting. In liver, the concentration of AHR proteinwas significantly reduced 8 and 24 h postdosing as comparedto time-matched controls. In spleen and lung, the concentrationof AHR protein was reduced 3, 8, 24, and 168 h posttreatmentcompared to time-matched controls but returned to control levelsby 336 h. In thymus, reductions in AHR protein concentrationwere observed 8, 24, 168, and 336 h postdosing as compared totime-matched controls. Significant reductions in the concentrationof ARNT protein were not observed in any of the TCDD-exposedtissues. Functional studies in cell culture showed that exposureof a mouse hepatoma cell line (Hepa-1c1c7) and a rat smoothmuscle cell line (A-7) to TCDD (1 nM) for 12 days resulted ina 50% reduction in TCDD-inducible reporter gene expression followingsubsequent challenge by an additional dose of TCDD (1 nM). Collectively,these results show that (i) TCDD-mediated depletion of AHR occursin vivo, (ii) AHR protein does not rapidly recover to pretreatmentlevels even though the tissue concentration of TCDD has fallen,and (iii) reduction in AHR protein concentration correlateswith reduction in TCDD-mediated reporter gene expression inmammalian culture cells.     

Opposite Effects of 2,2',4,4',5,5'-Hexachlorobiphenyl and 2,3,7,8-Tetrachlorodibenzo-p-dioxin on the Antibody Response to Sheep Erythrocytes in Mice

The effect that cotreatment with 2,2',4,4',5,5'-hexachlorobiphe-nyl(PCB153) and 2,3,7,8-terrachlorodibenzo-p-dioxin (TCDD) hason the antibody plaque-forming cell (PFC) response to sheepred blood cells (SRBCs) was determined in female B6C3F1 mice.Groups of eight mice per group were given a single oral doseof PCB153 alone (0, 3.58, 35.8, or 358 mg/kg), TCDD alone (0,0.1, 1, or 10 µg/kg), and all possible combinations ofthese doses in corn oil 7 days prior to immunization with SRBCs.Separate groups of mice were given phenobarbital (PB) parenterallyby intraperito-neal injection at a dosage of 160 mg/kg/day for3 days. Four days after intravenous immunization, body, spleen,thymus, and liver weights and the PFC response to SRBCs weredetermined. Exposure to TCDD alone resulted in a dose-relatedsuppression of the PFC response, with significant suppressionat 1 and 10 µg/kg. In contrast, exposure to PCB153 aloneresulted in the enhancement of the PFC response at 358 mg/kg.Combined exposure to 358 mg/ kg PCB153 and TCDD resulted inno change (PCB153 + 0.1 µg/ kg TCDD) or suppression (PCB153+ 1 or 10 µg/kg TCDD) of the PFC response relative toPCB153 alone; however, the PFC response was enhanced (PCB153+ 0.1 µ/kg TCDD), unaffected (PCB153 + 1 µ/kg TCDD),or suppressed (PCB153 + 10 µ/kg TCDD) relative to cornoil controls. PB did not affect the PFC response to SRBCs, despitea 13-fold induction of hepatic pentoxyresorufin O-dealkylase(PROD) activity. These results suggest that PCB153 enhancementof the PFC response is not related to PROD induction and thatit acts as a functional antagonist rather than an aryl hydrocarbonreceptor or dispositional antagonist. By enhancing the PFC responseto SRBCs, PCB153 raises the "setpoint" response level. Consequently,cotreatment with an immunosuppressive dose of TCDD fails tosuppress the PFC response relative to corn oil controls, whileclearly suppressing it relative to the appropriate control,PCB153 alone.     

Transfer of Polychiorinated Dibenzo-p-dioxins and Dibenzofurans to Fetal and Neonatal Rats

A fly ash extract from a municipal incinerator, containing polychlorinateddibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), was orallyadministered to rats on Days 10 to 17 of the pregnancy and duringthe first 10 days of the lactation period. PCDD and PCDF congenersretained in the fetuses and livers of the offspring had a 2,3,7,8-chlorinesubstitution pattern. The only non-2,3,7,8-substituted congenerretained in the liver of the offspring and females was 2,3,4,6,7-pentachlorodibenzofuran(PnCDF). In the fetuses 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) had the highest retention (0.13% of total dose) and adecrease in retention was found with increasing number of chlorineatoms. In the livers of the offspring, the highest retentionwas found for 2,3,7,8-TCDD and the three 2,3,7,8-substitutedhexachlorodibenzo-p-dioxins (HxCDDs) (5.26–8.12%). Inthe livers of the pregnant and lactating females penta- andhexachlorinated congeners had the highest retention (53.91–80.20%). For both groups the liver retention of the tetra- tooctachlorinated congeners was similar, but the lactating femalesstored less PCDDs and PCDFs in their adipose tissue. A linearrelationship was found between the retention of congeners inthe livers of the females and offspring.     

Use of Model-Based Compartmental Analysis to Study Effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Vitamin A Kinetics in Rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic,widespread environmental contaminant that has dramatic adverseeffects on the metabolism of vitamin A. We used model-basedcompartmental analysis to investigate sites and quantitativeimpacts of TCDD on vitamin A kinetics in rats given an oralloading dose of TCDD in oil (3.5 µg/kg) followed by weeklymaintenance doses (0.7 µg/kg) or oil only. [³H]retinylin its plasma transport complex (experiment 1) or lymph containingchylomicrons labeled mainly with [³H]retinyl esters (experiment2) were administered iv, and tracer kinetics in plasma, liver,carcass, urine, and feces were measured for up to 42 days. TCDDtreatment caused significant reductions in liver vitamin A levelsand significant changes in tracer kinetics and tracer excretion.A four-compartment model was used to fit tracer data for experiment1; for experiment 2, compartments were added to describe themetabolism of newly absorbed vitamin A. The compartmental modelspredict that TCDD caused a slight delay in plasma clearance(via an increased recycling to plasma), and in liver processing,of chylomicronderived vitamin A. Models for both experimentspredict that TCDD exposure did not affect the fractional uptakeof plasma retinol from the rapidly turning-over extravascularpool, but it doubled the fractional transfer of recycled retholfrom slowly turning-over pools of vitamin A to plasma The residencetime for vitamin A was reduced by 70% in TCDD-treated rats,transfer into urine and feces was tripled, and vitamin A utilizationrates were significantly increased. Since our results do notindicate that retino1 esterification is inhibited, we hypothesizethat some of the significant effects of TCDD on vitamin A metabolismresult from increased catabolism and mobilization of vitaminA from slowly turning-over pools (especially the liver).     

The fate of 2,3,7,8-tetrachlorodibenzo-p-dioxin following single and repeated oral doses to the rat.

Rats were given a single oral dose of 1.0 μg of [¹⁴C]-2,3,7,8-Tetrachlorodibenzo-p-dioxin ([¹⁴C]TCDD)/kg/day, or repeated oral doses of 0.01, 0.1, or 1.0 μg of [¹⁴C]TCDD/kg/day Monday through Friday for 7 weeks. Following a single oral dose of 1.0 μg of [¹⁴C]TCDD/kg, ¹⁴C activity could be detected only in feces, but not in urine. The half-life of ¹⁴C activity in the body was 31 ± 6 days. Twenty-two days after the single oral dose, concentrations of ¹⁴C activity were located principally in liver and fat. Following repeated oral doses the major route of excretion was via the feces; urine contained 3–18% of the cumulative dose of ¹⁴C activity by 7 weeks. The half-life of ¹⁴C activity in the body of these rats was 23.7 days. Assuming a one compartment open model, 76.2% of steady-state concentrations were achieved in the whole body after 7 weeks. ¹⁴C activity in liver and fat approached steady-state values at a rate similar to the whole body. Radioactivity in the liver was identified as TCDD by gas chromatography-mass spectrometry and could be extracted from liver tissue with organic solvents. The results of this study in rats indicate that TCDD approaches steady-state concentrations in the body within 13 weeks, and the rate constant defining the approach to steady-state concentrations is independent of the dosage of TCDD over the dose range of 0.01?1.0 μg of TCDD/kg/day.