2,3,7,8-Tetrachlorodibenzo-p-dioxin: Acute oral toxicity in hamsters

The acute oral toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was evaluated in hamsters. Male golden Syrian hamsters received 0 (corn oil only), 300, 600, 1000, 3000, or 6000 μg TCDD/kg body wt by single-dose gavage. To facilitate dosage, TCDD was fed as a suspension in acetone/corn oil (1:9). The 55-day single-dose oral LD50 was 5051 μg/kg (3876–18,487 μg/kg, 95% confidence interval). Deaths occurred from Day 9 through Day 43 following single-dose administration. Initially, no hamsters exhibited adverse effects related to dosage with TCDD, but 4–5 weeks following dosage, hamsters of the 1000, 3000, and 6000 μg/kg dose groups began to develop unkempt hair coats. A dose-related depression of mean body weight when compared to control weights was apparent in hamsters of the 1000, 3000, and 6000 μg/kg dose groups by 3 weeks posttreatment. Gross necropsy revealed the primary target organs affected in the hamster to be the same as in other laboratory species, namely, liver and thymus; this was accompanied by a slight decrease in adipose tissue reserves. No other significant effects were noted upon necropsy. Based on these results, the hamster appears to be much less sensitive than other laboratory species to the acute oral toxicity of TCDD.     

Effect of monooxygenase inducers and inhibitors on the hepatic metabolism of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the rat and hamster

The rat and hamster exhibit about a 100-fold difference in sensitivity to the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), with the hamster representing the most resistant species examined to date. The present study compared the induction and inhibition of hepatic TCDD metabolism in these species using suspensions of isolated hepatocytes. Purified 14C-TCDD or 3H-TCDD (2.2 microM) was incubated for 2-6 hr with hepatocytes isolated from untreated, TCDD-pretreated (5 micrograms/kg, ip), 3-methylcholanthrene-pretreated (3-MC, 50 mg/kg, ip, x 3 days), isosafrole-pretreated (ISO, 150 mg/kg, ip, x 3 days), or phenobarbital-pretreated (PB, 80 mg/kg, ip, x 3 days) rats and hamsters. Untreated rat and hamster hepatocytes metabolized TCDD at a similar rate (0.20 and 0.18 pmol/hr/mg, respectively). In both species, TCDD and 3-MC pretreatments elevated the rate of TCDD metabolism by 5-6-fold, while PB pretreatment had no effect. isosafrole modestly increased (1.8-2.5-fold) TCDD metabolism in each species. Analysis by high performance liquid chromatography indicated similarities in the TCDD-metabolite profiles formed by hepatocytes from both species, with two major metabolite peaks detected following induction by TCDD and 3-MC. The in vitro metabolism of TCDD in hepatocytes from TCDD-pretreated rats and hamsters was inhibited by 7,8-benzoflavone (100 microM), but not by metyrapone (100 microM). The effect of these cytochrome P-450 inducers and inhibitors on the metabolism of 3H-benzo(a)pyrene (BaP) in rat hepatocytes was similar to their effect on TCDD metabolism. However, marked differences were observed in their effects on the metabolism of BaP and TCDD in hamster hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tissue distribution,excretion, and metabolism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the Golden Syrian hamster

The hamster has been reported to be the least sensitive mammalian species to the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The fate of a single dose of [³H]- or [¹⁴C]TCDD (650 μg/kg, ip or po) was assessed in male hamsters for up to 35 days following treatment. The greatest content (percentage dose/g tissue) of radioactivity was found in the liver, adipose tissue, and adrenals. The radioactivity in liver and adipose tissue was identified as unmetabolized TCDD. The rate of ³H or ¹⁴C elimination in urine and feces suggested a first-order process. Similar half-life of elimination ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) values of 12.0 ± 2.0 and 10.8 ± 2.4 days (mean ± SD) were obtianed with ip administered [³H]- and [¹⁴C]TCDD, respectively. With both [³H]- and [¹⁴C]TCDD, approximately 35 and 50% of the radioactivity was eliminated in urine and feces, respectively. The $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for po administered [³H]TCDD was 15.0 ± 2.5 days. High-pressure liquid chromatography of the urine and bile of animals receiving [¹⁴C]TCDD revealed one major and several minor radioactive peaks, none of which corresponded to [¹⁴C]TCDD. The apparent absence of TCDD metabolites in extracts of liver or adipose tissue indicates that the biotransformed products of TCDD are readily excreted in urine and bile. The enhanced rate of metabolism and excretion of TCDD in hamsters relative to other species may in part contribute to, but not totally explain its unusual resistance to TCDD toxicity.     

福定碱对大鼠学习和记忆的作用

用大鼠逃避反射及家免EEG等方法测试了从石杉科植物分离到的福定碱(fordine)对学习和记忆的作用,10～40μg/kg ip或20μg/kg po明显加快大鼠主动迥避反应形成速度,提高反应率;10～40μg/kg ip减少QNB破坏主动迴避反应的作用;20～40μg/kg iv对抗QNB和樟柳碱引起家兔EEG的变化。福定碱每天40μg/kg ip连续8天,大鼠脑与浆胆碱酯酶活力为正常的88.8±8.8%。福定碱有有效剂量小,安全系数大和口服有效的优点。以色林也加快大鼠主动迴避反应形成,但未能对抗QNB的破坏作用。     

Species differences in estrogen receptors and in the response to 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure

The acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibits marked interspecies variability, with the guinea-pig, rat and hamster representing the species most sensitive, intermediate and most resistant to acute toxicity. Prepubertal guinea-pigs, rats and hamsters were treated with a single intraperitoneal injection of TCDD in olive oil at doses of 4, 50 and 1500 micrograms/kg, respectively. These exposures were chosen to produce acute toxicity and all 3 species exhibited a decrease in the rate of body weight gain during the 7 days following TCDD exposure when compared with control (olive oil-treated) animals. On the 7th day after exposure, the density and affinity of 17 beta-estradiol receptors were determined in the uterus and liver of TCDD-treated and control animals. The treatment with TCDD did not alter the affinity of the receptors in these 3 species. The density of hepatic 17 beta-estradiol receptors was decreased 65% in the guinea pig and 92% in the rat following exposure to TCDD. In contrast, TCDD-treated hamsters exhibited no change in the density of hepatic 17 beta-estradiol receptors. The uterine 17 beta-estradiol receptors were increased in density by TCDD treatment in the hamster and in the rat when expressed per mg protein. Uterine wet weights in the guinea-pig and rat were also significantly decreased by TCDD treatment but were not changed in the hamster. When the Bmax for uterine 17 beta-estradiol receptors was expressed as pmol/g tissue wet weight. TCDD exposure was found to produce an 11% decrease in density in the rat, while producing a 44% increase in the hamster. In control animals, the density of uterine 17 beta-estradiol receptors correlated inversely with the lethal dose of TCDD in these 3 species (i.e., the guinea-pig has the lowest LD50 and highest density of uterine 17 beta-estradiol receptors). The different responses to TCDD in the 3 species suggest that the changes in 17 beta-estradiol receptors may be related to species-specific toxic responses associated with TCDD exposure.     

抗癌新药-乙双吗啉(AT-1727)的药理研究

乙双吗啉(AT-1727)是我国合成的一种抗癌新药。它是一种双内酰亚胺化合物,实验证明,乙双吗啉对小鼠肉瘤S₃₇、S₁₈₀有显著抗肿瘤作用,对ECS,HCS,脑瘤B₂₂及L₆₁₅等移植性肿瘤亦有明显抗肿瘤作用。它对S₃₇的50%抑制剂量(ID₅₀)为1.88 mg/kg(ip)及6.61 mg/kg(po)。其抗肿瘤作用与给药方案有一定关系。乙双吗啉对小白鼠毒性LD₅₀为372.8±27.mg/kg(ip)及243.8±26.1 mg/kg(po)。因此,乙双吗啉腹腔注射及口服时,对S₃₇的化疗指数分别为47.5及36.9。给健康犬肌肉注射乙双吗啉25及50 mg/kg/天,连用10天,除出现食量减少,白细胞轻度下降外,对红细胞,血小板、肝、肾功能均无明显影响。乙双吗啉对以溶血素反应为指标的体液免疫有抑制作用;对以移植物抗宿主反应为指标的细胞免疫则无抑制作用。     

Biological activity of WIN 63759, an orally bioavailable inhibitor of human neutrophil elastase

The proteolytic activity of human neutrophil elastase (HNE) has been implicated in a number of pulmonary diseases. We report on the activity of an orally bioavailable, selective HNE inhibitor, WIN 63759 [6-methoxy-4-(1-methylethy)-3-oxo-1,2-benzisothiazol-2(3H)-yl]methyl 2,6-dichloro-3-[2-(4-morpholinyl)ethoxy] benzoate S, S dioxide. WIN 63759 is a potent inhibitor of HNE (K_i = 14 pM) and is at least 70,000-fold selective for HNE relative to other serine proteases or receptors. In vivo, WIN 63759 produces dose-related inhibition of HNE-induced pulmonary hemorrhage following either intravenous (ED₅₀ = 3 mg/kg; 4.5 μmol/kg) or subcutaneous (ED₅₀ = 19 mg/kg; 28.5 μmol/kg) administration in hamsters. WIN 63759 selectivity inhibits HNE in vivo (relative to chymotrypsin or trypsin), and is equally efficacious following acute or chronic administration in the hamster. WIN 63759 is not orally bioavailable in hamsters, rats, or monkeys, and this lack of bioavailability is related to rapid in vitro metabolism in liver, jejunum, or blood. In contrast, WIN 63759 is stable in canine tissues in vitro and is orally bioavailable in dogs. Bioavailability is enhanced in fed relative to fasted dogs. Bronchoalveolar lavage studies indicate that WIN 63759 is present in the target organ (lung) at concentrations 3–5 X higher than those found in plasma following oral administration of 3–100 mg/kg (4.5–150 μmol) in dogs. These data show that WIN 63759 is a potent, selective, and orally bioavailable inhibitor of HNE. Since oral bioavailability was predictable based on in vitro metabolism, and since in vitro metabolism in humans is similar to that observed with dogs, WIN 63759 and other members of this chemical series may be orally bioavailable inhibitors of neutrophil elastase in man. © 1995 Wiley-Liss, Inc.     

Patulin mycotoxicosis in the rat: Toxicology,pathology and clinical pathology

Patulin, a secondary metabolite produced by species of the genera Penicillium and Aspergillus, was administered to male Sprague-Dawley rats, weighing 50–60 g, by the oral, sc and ip routes. The 72-hr LD₅₀ values (in mg/kg weight) were: oral, 55·0; sc, 11·0; ip, 10·0. Mortality was greatest 0–24 hr after administration by the oral and sc routes and 49–72 hr after ip dosing. Gross alterations consisted of gastric and intestinal hyperaemia and distention. Histopathological alterations consisted principally of ulceration and inflammation of the stomach. Patulin was administered orally to rats daily or every other day for 2 wk at doses of 50 or 75% of the oral LD₅₀. Mortality in the treated groups was greater than in controls but was similar for all treated groups. No evidence of cumulative toxicity was found and the gross and histopathological alterations were similar to those found in the LD₅₀ studies. Clinicopathological alterations included metabolic alkalosis with respiratory compensation, oliguria, decreased serum sodium, elevated blood glucose, reduced plasma protein and an elevated total leucocyte count which differential leucocyte counts indicated to be due to neutrophilia. The inflammatory alterations observed in the gastro-intestinal tract may be due to the irritant properties of patulin or to an alteration in the gastro-intestinal flora by the antibiotic activity of patulin.     

苯佐卡因凝胶剂药效学实验研究

将苯佐卡因制成以卡波姆为基质的外用凝胶剂,进行了药效学实验、口腔粘膜刺激性实验和急性毒性实验。结果表明苯佐卡因凝胶药效明显,与对照组有显差异;使用后口腔粘膜未见刺激性;口服及腹腔注射LD50分别为1327．9mg／kg及1222．6mg／kg。     

Gestational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) severely alters reproductive function of female hamster offspring.

Low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), administered as a single dose to the dam during gestation, alter development of the fetal rodent reproductive system. In male rat and hamster offspring, dosing with TCDD during gestation reduces epididymal and ejaculated sperm counts and delays puberty. In female rats, in utero TCDD-exposure results in reduced ovarian weight and fecundity, and induces cleft phallus and a persistent thread of tissue across the vaginal orifice. Here, we demonstrate that 2-microgram TCDD/kg, administered as a single oral dose prior to sexual differentiation, alters reproductive function in female hamster offspring, a species relatively resistant to the lethal effects of TCDD. In the current study, pregnant hamsters (P0 generation) were dosed orally with vehicle (corn oil) or 2 micrograms TCDD/kg on gestational day (GD) 11.5. P0 maternal viability, body weight, fertility, and F1 litter size did not differ between control and treated groups. In the F1 generation, body weights were permanently reduced by about 30%, vaginal opening was delayed (p < 0.0001), and vaginal estrous cycles were altered by TCDD treatment. In contrast, most treated female offspring displayed regular 4-day behavioral estrous cycles, indicating that in utero TCDD treatment did not markedly disrupt hypothalamic-pituitary-gonadal hormonal cyclicity. Although both control and TCDD-treated F1 females mated successfully with a control male (estrous cyclicity was abolished by mating), 20% of the F1 treated females did not become not pregnant (no implants). In addition, 38% of pregnant F1 females from the TCDD group died near-term, and the numbers of implants in pregnant animals (treated 5.1 versus 11.3) and pups born live (2.7 treated vs. 8.7 control) were reduced by TCDD-treatment. In the F2, survival through weaning was drastically reduced (15% treated vs. 78% for control) by TCDD treatment of P0 dams. F1 female hamster offspring exposed in utero to TCDD displayed external urogenital malformations, with most females having complete clefting of the phallus, an effect previously reported in the rat. Unlike rats exposed to TCDD (0.2-1.0 microgram/kg) on GD 15 or GD 8, hamster offspring did not display vaginal threads. These results demonstrate that in utero administration of TCDD adversely affects growth, reproductive function, and anatomy in female hamster offspring given a dosage level nearly four orders of magnitude below the dosage level toxic to the adult animal. Adverse effects of TCDD persisted through two generations (F1 and F2), even though the F1 was only indirectly exposed during gestation and lactation.     

HI-6, an oxime which is an effective antidote of soman poisoning: A structure-activity study

In contrast to other organophosphates, soman poisoning is resistant to atropine (AT) + oxime therapy. However, new bispyridinium-type oximes + AT are effective antidotes of soman poisoning. In structure-activity studies, T 4925 (1,1′-[oxybis(methylene)]bispyridinium dichloride) had an LD₅₀ of 178 mg/kg and HS-14 (1-[[[pyridinio]methoxy]methyl]-2[(hydroxyiminio)methyl]pyridinium dichloride) had an LD₅₀ of 130 mg/kg. DL-10 (1-[[[3-(aminocarbonyl)pyridinio]methoxy]methyl]pyridinium dichloride) and DL-11 (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]pyridinium dichloride) had LD₅₀'s of 326 and 715 mg/kg, respectively, whereas HS-6 (Reg. No. 22625-23-6) and HI-6 (Reg. No. 34433-31-3) had LD₅₀s of 316 and 514 mg/kg (ip), respectively. T 4925, HS-14, DL-10, and DL-11 at an LD₁ dose + AT (17.4 mg/kg) were relatively ineffective against soman (540 μg/kg; sc) compared to HI-6 and HS-6. Prophylactic ED₅₀s for HI-6 and HS-6 vs soman were 17 and 110 mg/kg, producing safety ratios of 30 and 2.9, respectively. The therapeutic ED₅₀ for HI-6 was 20 mg/kg. Brain cholinesterase (ChE) in mice surviving soman (540 μg/kg; sc) + HI-6 (94 mg/kg) + AT was 0% of control activity at 1 and 2 hr, 5% at 24 hr, and 15% 48 hr later. Mice which died postsoman (540 μg/kg; sc) had 20% brain ChE activity. These results show that HI-6 was one of the least toxic and most efficacious compounds studied and suggest brain ChE inhibition was not the primary lesion in soman poisoning.     

Induction of chromosmal aberrations in the syrian hamster by insecticides tested in vivo

The insecticides demeton, dimetoat, dichlorovos, endosulfan, trichlorofon, carbaryl, lindane, methoxychlor, propoxur and malathion were examined for their ability to induce chromosomal aberrations in the bone marrow cells of the Syrian hamster (Mesocricetus auratus) treated in vivo. Mutagenicity of commercial preparations was examined at four doses: LD₅₀; 1/2, 1/5 and 1/10 LD₅₀. The positive control was an IP injection of cyclophosphamide to hamsters at a dose of 40 mg/kg body wt. Demeton, dichlorovos and endosulfan gave positive results. Malathion, dimethoate and the mixture of methoxychlor and propoxur were weakly clastogenic; at some doses these compounds induced statistically significant increases in the number of aberrations. Trichlorfon and the mixture of carbaryl and lindane were negative in this test.This work was supported by the Polish Academy of Sciences within the projet 09.7.3.4.3     

Affinin and hexahydroaffinin: Chemistry and toxicological profile

The present work aimed to determine the safety parameters of two new alkamides, affinin and hexahydroaffinin, with antinociceptive activity. To predict the preliminary acute toxicity, we used the acute and subchronic toxicity (50 mg/kg, orally [po]) in Swiss Webster mice. Genotoxicity assayed via analysis of cell micronuclei of the femoral bone marrow in mice; at the same time, metabolic parameters determined from peripheral blood samples. Furthermore, to discard the neuropharmacological effects, we assessed the ambulatory activity in mice to determine the possible effects in the central nervous system. Finally, we used capsaicin as a positive control of alkamides. According to our results, hexahydroaffinin (LD₅₀ ≥ 5,000 mg/kg, po) is significantly less noxious than affinin (LD₅₀ = 1,442.2 mg/kg, po) or capsaicin (LD₅₀ = 489.9 mg/kg, po). In subchronic administration, we did not observe any changes in hematological or biochemical parameters in any compound analyzed from peripheral blood samples. Finally, the data from the genotoxicity assay showed micronuclei formation in 28%, 5%, and 3% of mice in the capsaicin, affinin, and hexahydroaffinin groups, respectively. With the results obtained in the present investigation, we suggest that affinin and hexahydroaffinin are not only useful candidates for possible new drugs but also safe compounds.     

二苯乙烯(芪)的一些药理作用

芪(二苯乙烯)通常用于化学工业,对其药理活性的研究很少。通过动物实验我们发现芪能明显保护CCl₄引起的小鼠肝损害,表现在使高的SGPT及SGOT降低、BSP潴留减少、肝组织病变减轻等。芪明显促进肝糖元生成,此作用强度与可的松相近,但芪没有可的松那样的抗炎作用。在去肾上腺小鼠,芪仍能明显促进肝糖元生成,故此作用似乎不通过体内的垂体-肾上腺系统。芪对小鼠戊巴比妥睡眠时间影响不明显。根据实验资料分析,芪对CCl₄肝损害的保护机制大概不是通过酶诱导,也不象某些抗氧化剂那样直接对抗CCl₄的作用,但有可能与其促进肝糖元生成有某种关系。芪有微弱的雌激素作用(约为己烯雌酚的数万分之一)。芪的毒性很低,小鼠一次腹腔注射LD₅₀为6.5 g/kg,灌胃LD₅₀大于8 g/kg,但油溶液毒性较大(灌胃LD₅₀为0.92g/kg)。长期大量给予芪,对雄小鼠的生长及睾丸发育有抑制作用,给狗服芪50 mg/kg/天连续一个月以上未见明显异常反应。     

Toxic effects of methylcyclopentadienyl manganese tricarbonyl (MMT) in rats: Role of metabolism

The toxicity of methylcyclopentadienyl manganese tricarbonyl (MMT) has been investigated in relation to its in vivo biotransformation in the rat. The LD₅₀ dose of MMT was found to be 50 mg/kg for oral administration and 23 mg/kg for ip administration. Death appeared to be caused by severe pulmonary hemorrhagic edema. Histological studies of MMT-treated animals revealed pathologic changes in lungs, liver, and kidney. Phenobarbital pretreatment protected rats from the lethal effects of 2.5 times the LD₅₀ dose of MMT, it shifted the site of tissue injury from the lungs to the liver, and it caused a doubling of the rate of biliary excretion of MMT metabolites. The possibility is discussed that MMT per se is toxic without bioactivation, and that the protective effect of phenobarbital pretreatment is due to a first-pass effect preventing toxic concentrations of orally administered MMT from reaching the systemic circulation.     

A-80426, a potent and selective α2-adrenoceptor antagonist with serotonin uptake-blocking activity and putative antidepressant-like effects: II. Pharmacology profile

A-80426 N-[2-(benzofuran-6-yl)ethyl]-N-[(R)?( + (-5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl methyl]-N-methylamine) is a compound that combines in vitro selective inhibition of serotonin synaptosomal uptake and α₂-adrenoceptor antagonism. In the present studies, A-80426 was evaluated in vivo for its ability to block serotonin uptake and α₂-adrenoceptors. The antidepressant potential of the compound was also assessed. In rats, A-80426 significantly reduced p-chloroamphetamine (PCA)-induced hyperactivity, a measure of the in vivo blockade of serotonin uptake, after acute (ED₅₀ = 13 μmoles/kg, po) and chronic (14 day) (ED₅₀ = 4.1 μmoles/kg, po) dosing. At doses of 6.7 and 22 μmoles/kg, po, A-80426 was effective in this test procedure for at least 12 h following administration. Doses of 6.7 to 224 μmoles/kg, ip, of A-80426, however, failed to block hypothermia and hypoactivity produced by the α₂-adrenoceptor agonist clonidine, and doses of 100 and 300 μmoles/kg, po, were required to blocked clonidine-induced mydriasis. Thus, the in vitro α₂ receptor binding and blocking effects observed with A-80426 did not translate into the in vivo situation. A-80426 was able to reverse the step-down passive avoidance deficit seen in olfactory bulbectomized rats (ED₇₀ = 7.1 μmoles/kg, po), a finding suggesting that the compound has antidepressant potential. The compound was, however, inactive in the tail suspension and forced swim tests of antidepressant activity in mice at doses up to 72 μmoles/kg, ip. In contrast, fluoxetine was active in all three paradigms. Despite its favorable in vitro profile, A-80426 is not an effective α₂ blocker in vivo and is inactive in the behavioral dispair models of depression. It is unlikely that A-80426 would have antidepressant activity equivalent to existing selective serotonin reuptake inhibitors. α₂ blockade as a potential approach to eliciting antidepressant activity is discussed. © 1995 Wiley-Liss, Inc.     

Changes in thyroid hormones and thyroxine glucuronidation in hamsters compared with rats following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin

In rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, serum thyroxine (T4) is depressed. Since hamsters are relatively insensitive to TCDD-induced lethality, the effects of TCDD on several parameters of thyroid status were measured in hamsters as a comparison with the more sensitive rat. At 7 days after ip injection of TCDD, there was a dose-dependent increase in serum 3,5,3'-triiodothyronine (T3) and T4 in hamsters to a maximum level 200% of control; the ED50 was approximately 10 micrograms/kg. Hamsters receiving 100 micrograms/kg lost up to 4% of their body weight but began to recover after about 3 weeks. Serum T4 in these animals was elevated compared to pair-fed and ad libitum controls throughout the 53-day experiment, although it also began to recover after Day 21. This was in direct contrast to the marked reduction of T4 in rats exposed to lower doses of TCDD. T3 was significantly higher in TCDD-treated hamsters than in pair-fed controls on Days 2-7, and TSH was also elevated on Days 2-21. Reverse T3, like T4, was increased by TCDD in hamsters whereas it was decreased in rats. Hepatic microsomal UDP-glucuronosyltransferase (GT) activity was measured using T4 as substrate (T4-GT). On a whole liver basis, T4-GT was induced by TCDD by the same proportion in both rats and hamsters (170-180% of controls) although absolute activities in rats were 3- to 4-fold higher than in hamsters. This similarity in T4-GT inducibility by TCDD suggests that there are likely mechanisms in addition to T4-GT induction which account for the species-specific alterations in T4. Thus, while the response of thyroid hormones to TCDD differed qualitatively, effective doses in hamsters were higher than in rats, suggesting that these changes, although secondary, may correlate more directly with toxicity than does enzyme induction (whose ED50s are similar in both species). An understanding of the mechanism of this species difference may be helpful in unravelling the primary mechanisms of TCDD toxicity.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced decrease in the fluidity of rat liver membranes

1. 2,3,7,8-Tetrachlorodibenzo-ρ-dioxin (TCCD)-induced lipid peroxidation has previously been demonstrated by assessing the hepatic content of thiobarbituric acid reactive substances (TBARS) as well as the NADPH-dependent microsomal formation of TBARS as well as the NADPH-dependent microsomal formation of TBARS using malondialde-hyde as the standard.

2. Changes in membrane fluidity as a result of lipid peroxidation may occur. Therefore the dose- and time-dependent effects of TCDD on lipid peroxidation in mitochondrial, microsomal, and plasma membranes, and changes in membrane fluidity in these subcellular fractions, were examined. Animals were treated with either 50 or 100 μg TCDD/kg orally, and killed 3, 6, or 9 days post-treatment.

3. Time-dependent increases occurred in TBARS content and formation following TCDD administration for all three membranes. Similar results were observed after 50 and 100 μg TCDD/kg.

4. Following TCDD administration, fluorescence polarization measurements as determined by the fluorescence polarization (r) and anisotropy parameter (a.p.) values demonstrated significant decreases in membrane fluidity in all membrane fractions, indicative of membrane structural alterations.

5. Excellent inverse correlations between lipid peroxidation and membrane fluidity were observed. Thus, decreased membrane fluidity and increased membrane damage may contribute to the toxic manifestations of TCDD as a consequence of an oxidative stress.     

Augmentation of sulfate ion absorption from the rat lung by heavy metals.

In rats injected ip with 500 mg of cyclotrimethylenetrinitramine (RDX)/kg, the respective mean times to first seizure and to death were 23.8 and 171.0 min, and the mean plasma concentrations of RDX at seizure and death were 5.2 and 13.8 μg/ml. Following 100 mg/kg po, the plasma concentration was 2.1 μg/ml at 4 hr and 3.0 μg/ml at 24 hr, while the urine concentration was 5.5 μg/ml at 4 hr and 6.9 μg/ml at 24 hr. In the 6 days following 50 mg/kg po, 0.7% was excreted as RDX in the feces and 2.4% in the urine. Irrespective of dosage or route of administration, the concentration of RDX was greatest in kidney, most variable in liver, and did not accumulate in the brain. Twenty-four hours after po dosing with 50 mg of [¹⁴C]RDX/kg, the liver and urine contained large amounts of RDX metabolites, and, after the first 4 days, 90% of the total radioactivity was recovered: 34% in the urine, 43% as ¹⁴CO₂, 3% in the feces, and 10% in the carcass. In miniature swine dosed with 100 mg/kg po, the plasma concentration was 1.6 μg/ml at 2 hr and 4.7 μg/ml at 24 hr, while the urinary concentration was 2.0 μg/ml at 2 hr and 3.6 μg/ml at 24 hr. At 24 hr, the concentrations of RDX in brain, heart, liver, kidney cortex, kidney medulla, and fat were between 4.4 and 9.1 μg/g. Convulsions in pigs occurred 12–24 hr after dosing with RDX.     

Immediate and highly sensitive aversion response to a novel food item linked to AH receptor stimulation

Aversion to novel food items was studied in male rats and mice after 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure using chocolate consumption as an indicator. The correlation of this phenomenon with susceptibility to acute toxicity and CYP1A1 induction was examined by determining the dose-response of chocolate aversion in differently dioxin-sensitive rat lines after TCDD (0.01-10 μg/kg). Furthermore, the dependence of this behavioral alteration on the AH receptor (AHR) was studied employing AHR-deficient and wild-type mice. We offered chocolate for both species as a novel food item immediately after the exposure, and it was available with standard rodent chow for 3 days. The ED₅₀ value for the extremely resistant rat line A (LD₅₀ value > 10,000 μg/kg) was 0.36 μg/kg, for the semi-resistant line B (LD₅₀ value 830 μg/kg) 1.07 μg/kg and for the TCDD-sensitive line C (LD₅₀ value 40 μg/kg) 0.34 μg/kg. Interestingly, the ED₅₀ values for chocolate aversion were very similar to those for CYP1A1 induction in these rat lines. Findings on AHR-deficient and wild-type mice implied the involvement of the AHR in this intriguing response, which may thus represent a mechanism to restrict exposure to potentially toxic dietary substances causing hepatic induction of drug-metabolizing enzymes.