Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on liver phosphoenolpyruvate carboxykinase (PEPCK) activity, glucose homeostasis and plasma amino acid concentrations in the most TCDD-susceptible and the most TCDD-resistant rat strains

Reduced gluconeogenesis due to decreased activity of key gluconeogenic enzymes in liver, together with feed refusal, has been suggested to play an important role in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced lethality in rats. This study was carried out to further analyse the toxicological significance of reduced gluconeogenesis by comparing dose-responses and time-courses of effects of TCDD on the activity of phosphoenolpyruvate carboxykinase (PEPCK) in liver, liver glycogen concentration as well as plasma concentrations of glucose and amino acids in both genders of TCDD-sensitive Long-Evans (L-E) rats and TCDD-resistant Han/Wistar (H/W) rats. A dose-dependent decrease in PEPCK activity was observed in H/W rats, but in L-E rats the activity was not decreased. However, TCDD impaired the strong increase in liver PEPCK activity observed in pair-fed controls of the L-E strain. Liver glycogen concentrations were severely decreased in L-E rats and moderately in H/W rats. This effect seems to be secondary to reduced feed intake, since a similar decrease was seen in pair-fed controls. Decreases in plasma glucose concentrations were also more profound in L-E rats than in H/W rats, but pair-fed controls were generally less affected. Circulating concentrations of amino acids were markedly increased in TCDD-treated L-E rats, which is likely to reflect increased mobilization of amino acids and their decreased metabolism in liver. Reduction of liver PEPCK activity cannot account for the sensitivity difference of these two strains of rats in terms of mortality. Nevertheless, the response of both strains of TCDD-treated rats regarding gluconeogenesis is different from that seen in pair-fed controls and suggesting that impairment of this pathway contributes to the development of the wasting syndrome. Received: 29 March 1999 / Accepted: 17 May 1999     

Body weight loss and changes in tryptophan homeostasis by chlorinated dibenzo-p-dioxin congeners in the most TCDD-susceptible and the most TCDD-resistant rat strain

We compared the effects of 2,3,7,8-tetra (TCDD), 1,2,3,7,8-penta (PeCDD), 1,2,3,4,7,8-hexa (HxCDD) and 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) on brain serotonin metabolism, plasma tryptophan and liver tryptophan pyrrolase activity in two rat strains, TCDD-sensitive Long-Evans (Turku AB; L-E) and TCDD-resistant Han/Wistar (Kuopio; H/W). Previously it was shown that L-E rats exhibit the expected rank order of potency for CDDs in terms of acute toxicity with TCDD being the most potent, followed by PeCDD, HxCDD and HpCDD. In contrast, to H/W rats HxCDD was the most toxic and TCDD the least toxic of these congeners. In the present study, the CDDs decreased body weight in L-E rats in the following order of potency: TCDD>PeCDD>HxCDD>HpCDD. The same rank order was recorded for elevations in brain tryptophan and plasma free tryptophan concentrations as well as for inhibition of the main hepatic tryptophan metabolizing enzyme, tryptophan pyrrolase. By contrast, in H/W rats HxCDD was the most effective congener in producing loss of body weight, followed by HpCDD, PeCDD and TCDD. This was also true of changes in tryptophan homeostasis. These findings imply that in TCDD-susceptible L-E and TCDD-resistant H/W rats the potency of dioxin congeners in inducing acute toxicity highly correlates with their ability to disrupt tryptophan homeostasis. However, there may not be a direct causal relationship between body weight loss and altered tryptophan homeostasis, because the magnitudes of these two phenomena were not consistently parallel across the dioxin congeners tested. Received: 23 June 1998 / Accepted: 22 September 1998     

The hr locus and the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in newborn mice

 In mice, the recessive mutation hairless (hr) controls the cutaneous response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) but its influence on TCDD’s systemic toxicity is unclear. To clarify this, we compared the effects of lactational TCDD exposure on standardized litters of newborn HRS/J mice homozygous for either hr or + that were fostered by haired dams exposed to 0, 6, 8 or 12 μg TCDD/kg body weight on postnatal day 0. At 12 μg/kg, TCDD was lethal to both haired and hairless pups. At the lower doses (6 and 8 μg/kg) the survival of hr/hr pups was significantly lower than +/+ pups. Affected pups succumbed following a 1 to 2-day period of cachexia and wasting. As has been reported for other mouse strains, TCDD exposure impacted on their neonatal development and lessened the time to eye opening for both haired and hairless pups. However, the hairless animals were affected at lower doses than were the haired. The results of this study document that the hr/hr genotype does influence the systemic toxicity of TCDD in mice. Received: 26 April 1994 / Accepted: 23 June 1994     

Adult 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure and effects on male reproductive organs in three differentially TCDD-susceptible rat lines.

The contribution of genetic factors to adult male reproductive system toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was analyzed in three rat lines differentially resistant to TCDD acute lethality: line A, B, and C rats (selectively bred from TCDD-resistant Han/Wistar [Kuopio; H/W] and TCDD-sensitive Long-Evans [Turku/AB; L-E] rats). The resistance is linked to a mutated H/W-type aryl hydrocarbon receptor allele in line A and to an H/W-type unknown "B" allele in line B. Line C rats do not have resistance alleles. Mature male line A, B and C rats were given single oral doses up to 1000, 300, and 30 micrograms/kg TCDD, respectively. The dose-responses of TCDD effects on male reproductive organ weights, sperm numbers, and serum testosterone concentrations were analyzed 17 days after exposure. Serum testosterone concentrations were decreased by the highest doses of TCDD, and there were no major sensitivity differences among the rat lines. Correspondingly, the decrease in relative weight of ventral prostate and seminal vesicles was seen only after a dose of >/=100 micrograms/kg TCDD. Thus the effect was observed only in resistant lines A and B. The relative weights of testes and epididymides were not affected. Significant decrease in spermatogenesis was observed in each rat line, but the amount of decrease was reduced by resistance alleles. The highest TCDD dose decreased the daily sperm production by 37, 38, and 60% in line A, B, and C rats, respectively. Therefore, the resistance alleles appear to selectively modify the TCDD effects on the adult male reproductive system. The fact that the influence of resistance alleles on spermatogenesis is different from that on androgenic status indicates that the effect of TCDD on sperm numbers is not fully related to decreased serum testosterone.     

Four generation reproductive toxicity study with 2,3,7,8-tetrachlorodibenzo-P-dioxin (TCDD) in rats

 A multigeneration study on the reproductive toxicity of TCDD in rats was conducted. In this paper, the results of extensive pharmacokinetic evaluations are presented. The time course of tissue concentrations within the framework of a multigeneration study was investigated, using radioactive labeled 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), a substance with a long elimination half-life. So far, long term exposure to TCDD has generally been conducted by administering the same daily doses via the feed. Since the half-life of TCDD in rats is several weeks, the concentration of the test substance can be predicted to change continuously during such a study. Therefore we intended to expose the animals to a constant tissue concentration by using a loading dose/maintenance dose approach. To achieve this, the animals were treated with initial loading doses of 50, 120 or 250 ng TCDD/kg body wt. Based on the elimination half-life of 3 weeks and a planned dosing interval of 7 days, the weekly maintenance doses were calculated to be 20% of the loading dose. During the postnatal phase of rapid growth, this dosing schedule was insufficient to keep the tissue concentration of TCDD constant. It was necessary to administer a second loading dose and to increase the weekly mainte nance dose to 40% of the loading dose. While it was possible to control the tissue concentrations in the F₀ generation, a considerably larger variation was observed during the different developmental stages of the F₁ generation. The fluctuations could be reduced by using a complex dosing schedule, but even with that it was impossible to achieve completely steady levels in liver and adipose tissue. This was mainly due to the fact that levels in liver and adipose tissue did not change together. In the case of a lipophilic substance with a long elimination half-life, attempts at a risk assessment on the basis of a multigeneration test cannot rest on the assumption of defined tissue levels during the study while pharmacokinetic variables are difficult to control in such a study. Received: 13 May 1993/Accepted: 10 August 1994     

Characterization of the role played by antigen challenge in the suppression of in vivo humoral immunity by 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD)

The goal of these studies was to characterize the role played by antigen challenge in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced immunosuppression. The effects of single exposure to TCDD (4.2, 14, and 42 μg/kg) in B6C3F1 mice on the reverse plaque assay (RPA; no sensitization) and the sheep red blood cell (SRBC) antibody response were compared. While the RPA was suppressed in a dose-dependent fashion with significance at the two highest doses, a much more dramatic effect was noted with the primary anti-SRBC response: a suppression was noted at the lowest dose, which was comparable to that observed with the highest dose in the RPA. Subsequent studies compared the RPA in B6C3F1 (Ah-high responder) and DBA/2 (Ah-low responder) mice after both single and repeated exposure to identical cumulative doses of TCDD (4.2, 14, and 42 μg/kg). The repeated exposures consisted of 14 consecutive daily treatments of 0.3, 1.0, and 3.0 μg/kg. The results indicated only a slight difference in the effects of TCDD in the two strains after single exposure, and even less difference after repeated exposure. Moreover, administering TCDD on different days relative to the SRBC challenge indicated a suppression in both strains when given 1, 2, or 3 days before antigen challenge, on the day of antigen challenge, or 1 or 2 days after antigen challenge. The only day of administration where the suppression was attenuated was 3 days after antigen challenge. These results confirm an important relationship between antigen challenge and TCDD exposure on immunosuppression. Received: 5 June 1997 / Accepted: 26 August 1997     

Peri- and postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin: effects on physiological development,reflexes, locomotor activity and learning behaviour in Wistar rats

 Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the development of rat offspring were studied after administration of a loading dose of 300 or 1000 ng TCDD/kg body wt on day 19 of pregnancy, followed by weekly maintenance doses of 120 or 400 ng TCDD/kg body wt. The dose regimens led to a fluctuation of average TCDD concentrations in the liver of the offspring of 4.9–14.9 ng/g (TCDD1000/400 group) or 1.4–6.3 ng/g (TCDD300/120 group) during the course of the experiment. In both TCDD-exposed groups the body weight of the offspring was significantly lower on postnatal day 7 (PND 7); in the high dose group from PND 7 to PND 31. Some landmarks of postnatal development were retarded in the exposed groups; in particular, the vaginal opening was delayed for several days in both TCDD-exposed groups. The TCDD-exposed animals revealed a reduced ability to remain on a rotating rod. During reflex testing, the rate of successfully responding animals was higher in the exposed groups. No statistically significant differences in the locomotor activity between controls and TCDD-exposed offspring were detectable under our experimental conditions. In a discrimination learning test no effects on the learning ability were found. However, TCDD-exposed offspring showed an increase in unanswered trials during critical phases of the task. They also exhibited increased locomotor activity in a novel environment; prior to an amphetamine challenge dose of 1 mg/kg body weight. Amphetamine-induced activity was decreased in a dose-dependent manner. Received: 2 May 1994 / Accepted: 13 July 1994     

Hepatic metabolism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the rat and guinea pig

Marked interspecies variability exists in the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), with the rat having an LD50 about 25-fold greater than the guinea pig. The metabolism of TCDD was examined by incubating hepatocytes isolated from these animals with purified [14C]TCDD (2.2 microM) for 8 hr. Over the 8-hr incubation, cytochrome P-450 content and ethoxyresorufin O-deethylase and benzphetamine N-demethylase activities were well maintained, indicating the functional viability of the hepatocytes. Quantitative differences were observed in the rate of [14C]TCDD metabolism, with hepatocytes from control rats metabolizing TCDD at a rate 2.8-fold greater than hepatocytes from control guinea pigs. The role of the hepatic cytochrome P-450-448-dependent monooxygenase system in the metabolism of TCDD was examined through the use of hepatocytes isolated from animals pretreated with either TCDD (5 micrograms/kg, ip; 72 hr prior to hepatocyte isolation) or phenobarbital (80 mg/kg, ip X 3 days; 24 hr prior to isolation). The rate of [14C]TCDD metabolite formation in hepatocytes from TCDD pretreated guinea pigs (0.26 +/- 0.14 pmol mg cell protein-1 hr-1) was unchanged from the control rate (0.25 +/- 0.07), while the rate in hepatocytes from TCDD pretreated rats (2.26 +/- 0.43 pmol mg-1 hr-1) was 3.2-fold greater than control (0.70 +/- 0.10) and nine times greater than in hepatocytes from TCDD-pretreated guinea pigs. In addition, significant differences were observed in the profiles of the metabolites formed by hepatocytes from TCDD-pretreated rats and guinea pigs. On the other hand, phenobarbital pretreatment produced little change in the rate of [14C]TCDD metabolism in rat hepatocytes (0.98 +/- 0.13 pmol mg-1 hr-1). These results suggest that TCDD may be metabolized by a TCDD inducible form of cytochrome P-448 which is expressed in the rat but not in the guinea pig. Furthermore, the differences in the hepatic metabolism of TCDD in the rat and guinea pig and in the ability of TCDD to induce its own rate of metabolism may play a major role in explaining the varying susceptibility of these species to the acute toxicity of TCDD.     

2,3,7,8-Tetrachlorodibenzo-p -dioxin (TCDD) and congeners in infants. A toxicokinetic model of human lifetime body burden by TCDD with special emphasis on its uptake by nutrition

Contents of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and of 16 further congeners – polychlorinated dibenzodioxins and dibenzofuranes (PCDD/PCDF) – were determined in lipids of adipose tissue and of livers of 3 stillborns and of 17 infants (0.43–44 weeks old) who died from sudden infant death syndrome. International toxic equivalents (I-TEq) calculated for the sum of TCDD together with all of the 16 congeners (1.55–29.63 ng/kg lipids of adipose tissue, n = 20; 2.05–57.73 ng/kg liver lipids, n = 19) were within the range of or lower than the values published for adults. TCDD concentrations in lipids of breast-fed infants were higher (0.38–4.1 ng/kg lipids of adipose tissue, n = 9; 0.49–3.9 ng/kg liver lipids, n = 8) compared to non breast-fed subjects (0.16–0.76 ng/kg lipids of adipose tissue, n = 8; 0.29–0.71 ng/kg liver lipids, n = 7). Neither I-TEq values nor TCDD concentrations exceeded values published for adults. Since even in stillborns PCDD/PCDF were found (I-TEq, 9.70–10.83 ng/kg lipids of adipose tissue, 6.17–8.83 ng/kg liver lipids; TCDD, 1.3–2.1 ng/kg lipids of adipose tissue, 0.76–1.5 ng/kg liver lipids; n = 3), transplacental exposure has to be deduced. All of the findings concerning TCDD concentrations in the organism become intelligible on the basis of a physiological toxicokinetic model which was developed to describe the body burden of TCDD for the entire human lifetime in dependence of TCDD uptake from contaminated nutrition. The model reflects sex and age dependent changes in the following parameters: body weight, volumes of liver, adipose and muscle tissue, food consumption, and excretion of faeces. TCDD is supposed to be taken up orally, to be distributed freely in lipids of the organism and to be eliminated unchanged by excretion in lipids of faeces as well as by metabolism in the liver. The model was used to predict the half-life of elimination of TCDD (4 months in newborns increasing to ∼5 years in adults) and concentrations of this compound in lipids of adipose tissue, blood, liver and faeces at different ages. Furthermore, the influence of breast-feeding on the TCDD burden of a mother, her milk and her child was simulated. The model was validated by means of own data gained in adipose tissue and livers of infants and also using a series of values measured by other authors in mother's milk and in tissues and faeces of infants and adults. Predictions as well as experimental findings demonstrate a distinct increase in the TCDD body burden of breast-fed infants. Generally, it can be concluded for the excretion of unchanged, non volatile, non protein bound highly lipophilic compounds that their half-life is short in infants (∼5 months) and increases to ∼10 years reached between 40 and 60 years of age. Received: 30 July 1996 / Accepted: 30 October 1996     

Effect of thyroidectomy and thyroxine on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced toxicity

Chemical thyroidectomy effectively protected athyroid rats from mortality during 45 days after dosing with 100 micrograms 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg, whereas 70 to 80% of nonthyroidectomized-euthyroid and thyroidectomized-T4 (thyroxine)-maintained-euthyroid rats died within the same period of time. There was a significant decrease in body weight of all TCDD-treated groups compared to vehicle controls. However, body weight loss was much slower in thyroidectomized-athyroid (congruent to 1 g/day) than in nonthyroidectomized-euthyroid or in thyroidectomized-T4-euthyroid (congruent to 8 g/day) rats. TCDD significantly reduced feed intake in nonthyroidectomized-euthyroid and thyroidectomized-T4-euthyroid rats, but no altered feed consumption was observable in thyroidectomized-athyroid animals. These data indicate that thyroid hormone(s) play(s) an important role in mediating the toxicity of TCDD.     

Transfer of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via placenta and milk,and postnatal toxicity in the mouse

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was found to be efficiently transferred to mouse neonates and offspring by lactating mothers. During the first 2 postnatal weeks the pups received doses of TCDD via the milk which were, on a body weight basis, similar to those which had been administered prenatally to their mothers.The distribution of TCDD in the offspring (high in liver, low in other tissues) was similar to that found in the maternal organism.Maternal TCDD levels rapidly decreased during the lactation period while tissue levels in the nursing pups increased, resulting in offspring tissue levels which greatly exceeded those of their mothers at the respective 3-week periods after birth.The postnatal development of pups from mothers treated on days 14–17 of gestation and nursed by untreated foster mothers was studied. Postnatal mortality was increased. Surviving animals did not exhibit visible signs of abnormal development, although the reduced number of pups per litter may have contributed to this apparently normal development.In small rodents excretion into milk constituted a major pathway for the elimination of maternal TCDD. Whether the same holds true for man is still unknown, but the measurement of TCDD levels in breast milk may be an appropriate and practical method for the assessment of human exposure to this substance.     

Hepatic Ah-receptor levels and the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on hepatic microsomal monooxygenase activities in a TCDD-susceptible and -resistant rat strain

Previous studies have shown that in two inbred strains of mice, straightforward correlations exist among the number of hepatic Ah-receptors, enzyme inducibility by TCDD, and lethality of TCDD. Here, studies were conducted in two strains of rats (Han/Wistar and Long-Evans) which differ widely in susceptibility to the lethal effects of TCDD, to determine if these are general phenomenona in TCDD toxicity. The total number of specific binding sites (Ah-receptors) for [3H]TCDD proved to be approximately equal in the livers of both rat strains. Likewise, no notable difference was detected in the effect of TCDD on the activities of 7-ethoxyresorufin O-deethylase, 7-ethoxycoumarin O-deethylase, and ethylmorphine N-demethylase or on the amount of cytochrome P-450 in hepatic microsomal fractions. Immunoblot analysis was carried out with monoclonal antibodies (Mabs). Mab 1-7-1 directed against rat liver 3-methylcholanthrene (MC)-inducible P-450 recognized forms P-450c and P-450d in TCDD-treated rats in a dose-dependent fashion and to a similar extent in both strains. In contrast, Mab 2-66-3 (against phenobarbital-inducible P-450) did not recognize any proteins in either strain, confirming the conclusion that TCDD elicits a MC-type induction of hepatic cytochrome P-450 in both strains of rats. Thus, it seems that the correlations observed in mice do not hold in rats and therefore should not be generalized. The parameters measured in the present study are causally unrelated to the mechanism of lethal action of TCDD in these rat strains.     

Nrf2 protects against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced oxidative injury and steatohepatitis

Previous studies demonstrate that Nrf2, a master regulator of antioxidative responses, is essential in mediating induction of many antioxidative enzymes by acute activation of the AhR. However, the role of Nrf2 in protecting against oxidative stress and DNA damage induced by sustained activation of the AhR remains unknown and was investigated herein. Tissue and blood samples were collected from wild-type (WT) and Nrf2-null mice 21 days after administration of a low-toxic dose (10 μg/kg ip) of TCDD. Only Nrf2-null mice lost body weight after TCDD treatment; however, blood levels of ALT were not markedly changed in either genotype, indicating a lack of extensive necrosis. Compared to livers of TCDD-treated WT mice, livers of TCDD-treated Nrf2-null mice had: 1) degenerated hepatocytes, lobular inflammation, marked fat accumulation, and higher mRNA expression of inflammatory and fibrotic genes; 2) depletion of glutathione, elevation in lipid peroxidation and marker of DNA damage; 3) attenuated induction of phase-II enzymes Nqo1, Gsta1/2, and Ugt2b35 mRNAs, but higher induction of cytoprotective Ho-1, Prdx1, Trxr1, Gclc, and Epxh1 mRNAs; 4) higher mRNA expression of Fgf21 and triglyceride-synthesis genes, but down-regulation of bile-acid-synthesis genes and cholesterol-efflux transporters; and 5) trend of induction/activation of c-jun and NF-kB. Additionally, TCDD-treated Nrf2-null mice had impaired adipogenesis in white adipose tissue. In conclusion, Nrf2 protects livers of mice against oxidative stress, DNA damage, and steatohepatitis induced by TCDD-mediated sustained activation of the AhR. The aggravated hepatosteatosis in TCDD-treated Nrf2-null mice is due to increased lipogenesis in liver and impaired lipogenesis in white adipose tissue.     

四氯二苯二氧芑对人舌鳞癌细胞增生机制的研究

应用人舌鳞癌细胞株SCC-15G和SCC-25,通过单层细胞生长的细胞数和~3H-TdR掺入DNA的观察,进一步阐明了2,3,7,8-四氯二苯二氧(艹己)(TCDD)诱导刺激上皮细胞增生是由于降低了高密度生长抑制的敏感性引起的。SCC-15G细胞可作为研究TCDD对上皮细胞作用机制的理想模型。SCC-25细胞对TCDD反应较弱且不稳定,不宜用于研究上皮细胞增生机制。     

Antiteratogenic effects of alpha-naphthoflavone on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposed mice in utero

The effects of α-naphthoflavone, an aryl hydrocarbon receptor (AhR) antagonist, on the reproductive toxicity and teratogenicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were investigated. Pregnant C57BL/6J mice were orally administered α-naphthoflavone either once on gestational day 12 (GD12; 50 μg/kg) or for 6 days (GD8–GD13; 5 mg/kg/day) followed by an oral challenge with TCDD (14 μg/kg) on GD12. Cesarean section was performed on GD18 for the evaluation of maternal and fetal toxicities. TCDD caused severe fetal malformations including cleft palate (43.7%) and renal pelvic and ureteric dilatations (100%). The administration of α-naphthoflavone either in a single treatment or 6-days remarkably reduced the incidence of cleft palate to 27.6% and 26.5%, respectively. In addition, the degree of renal pelvic and ureteric dilatations caused by TCDD were significantly attenuated by repeated treatment of α-naphthoflavone. These results suggest that AhR antagonists such as α-naphthoflavone could be promising candidates for reducing the incidence and severity of fetal malformations caused by TCDD exposure in utero.     

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on blood and spleen natural killer (NK) cell activity in the mouse.

The immunotoxic effects of 2,3,7,8-tetrachlorodibenzo-P-dioxin (TCDD) were studied in male A/J mice after a loading dose of 5 μg TCDD/kg body wt. followed by 3 weekly maintenance doses of 1.42 μg TCDD/kg b.w. administered intraperitoneally. Tissue samples and immune cells were prepared on two occasions, i.e. on days 28 and 120 after the first injection of TCDD. This dose of TCDD evoked classical histological signs of liver damage and lipid accumulation, as well as thymic atrophy. Red (RBC) blood cell counts were significantly lowered in the TCDD group on day 28, but were normal on day 120. White (WBC) blood cell counts were normal in the TCDD group. Natural killer (NK) cell activity increased 3.4-fold (P < 0.01) and 2.2-fold (P < 0.01) in the blood and spleen, respectively, after 28 days, and these effects persisted on day 120. The increased NK-cell activity occurred concomitantly with a decreased proliferativc response of spleen lymphocytes to the T-cell mitogen concanavalin A after both 28 (65%) and 120 days (58%). The proliferative response of spleen cells to the B-ccll mitogen lipopolysaccharide seemed, however, unaffected. We have thus shown for the first time that TCDD induces an increased activity of NK cells that occurs simultaneously in the blood and spleen. This effect may indicate a general compensatory activation of the body's defences brought about by disturbances in the function of other arms of the immune system.     

Relationships between tissue levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), mRNAs, and toxicity in the developing male Wistar(Han) rat.

We compared the effects of a single acute dose, or chronic fetal exposure, to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the male reproductive system of the Wistar(Han) rat. Tissue samples were taken from dams on gestation day (GD)16 and GD21, and from offspring on postnatal days (PND)70 and 120. Steady-state concentration of TCDD was demonstrated in the chronic study: body burdens were comparable in both studies. Fetal TCDD concentrations were comparable after acute and chronic exposure, and demonstrate more potent toxicity after chronic versus acute dosing. In maternal liver, cytochrome P450 (CYP)1A1 and CYP1A2 RNA were induced. In fetus, there was induction of both CYP1A1 and CYP1A2 RNA at medium and high doses, but inadequate evidence for induction at low dose in either study. The low level induction of CYP1A1 RNA at low dose in fetus argues against AhR activation in fetus as a mechanism of toxicity of TCDD in causing delay in balanopreputial separation (BPS), and the greater induction of CYP1A1 RNA in PND70 offspring liver from chronically-dosed dams suggests that lactational transfer of TCDD is crucial to this toxicity. These data characterize the maternal and fetal disposition of TCDD, induction of CYP1A1 RNA as a measure of AhR activation, and suggest that lactational transfer of TCDD determines the difference in delay in BPS between the two studies.     

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and fasting on body weight and lipid parameters in rats

This study compared the effect of fasting (feed deprivation) and the effect of exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on body weight and on key lipid parameters. The time-course study indicated a statistically significant (p less than 0.05) body weight loss in the TCDD-exposed rats 5 days after the oral administration of corn oil with TCDD (60 micrograms/kg body wt). Animals demonstrated a 10% body weight decrease either 1 week after this TCDD administration or after 72 hr of fasting. Marked increases in serum triglyceride and cholesterol were observed only in the TCDD-exposed rats, but not in the 0- or 72-hr fasted control rats. These results indicated that some body weight loss and decreased feed consumption occurred after TCDD exposure, but that the metabolic response, with respect to serum lipid metabolism, was not that of a control rat that had lost a similar amount of body weight due solely to fasting.