Associations between congenital cryptorchidism in newborn boys and levels of dioxins and PCBs in placenta.

In animal studies, exposure to dioxins has been associated with disrupted development of the male reproductive system, including testicular maldescent. Some polychlorinated biphenyls (PCBs) have also dioxin-like effects. In addition, one previous case-control study has reported an association between congenital cryptorchidism and colostrum PCB levels. We performed a case-control study to evaluate whether congenital cryptorchidism in boys was associated with increased levels of dioxins or PCBs in placenta reflecting foetal exposure. In addition, associations between placenta levels of these chemicals and reproductive hormone levels in boys at 3 months were studied. Placentas were collected in a Danish-Finnish joint prospective cohort study on cryptorchidism (1997-2001). The boys were examined for cryptorchidism at birth and at 3 months. Altogether, 280 placentas [112 Finnish (56 cases, 56 controls) and 168 Danish (39 cases, 129 controls)] were analysed for 17 toxic polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and 37 PCBs (including 12 dioxin-like PCBs). Infant serum samples taken at 3 months were analysed for reproductive hormones. No significant differences between cases and controls were observed in either country in dioxin WHO-TEq levels (median 9.78 vs. 8.47 pg/g fat, respectively, in Finland, and 11.75 vs. 10.88 pg/g fat in Denmark) or PCB WHO-TEq levels (median 2.12 vs. 2.15 pg/g fat in Finland, 2.34 vs. 2.10 pg/g fat in Denmark) or total-TEq levels (median 11.66 vs. 10.58 pg/g fat in Finland, 13.94 vs. 13.00 pg/g fat in Denmark). Placenta WHO-TEq levels of dioxins were not associated with infant reproductive hormone levels at 3 months. In Finland, PCB WHO-TEq levels in placenta associated positively with infant LH levels. WHO-TEq levels of dioxins and PCBs and total-TEq levels were higher in Danish than Finnish samples. In conclusion, no association between placenta levels of dioxins or PCBs and congenital cryptorchidism was found. Significant country differences in chemical levels were observed.

Carcinogenicity of the drinking water mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone in the rat.

BACKGROUND: Several epidemiologic studies have suggested that the consumption of chlorinated drinking water may be associated with the development of certain cancers in humans. 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a byproduct of the chemical reactions that occur in chlorinated drinking water, has been found to be mutagenic in bacteria and mammalian cells; however, its potential to cause tumors in animals has not been tested previously. PURPOSE: The objective of this study was to evaluate the carcinogenicity of MX in rats given MX in their drinking water. METHODS: MX was administered to male and female Wistar rats (50 rats per dose group) in drinking water for 104 weeks at concentrations yielding the average daily doses of MX of 0.4 mg/kg of animal weight (low dose), 1.3 mg/kg (mid dose), and 5.0 mg/kg (high dose) for males and 0.6 mg/kg, 1.9 mg/kg, and 6.6 mg/kg for females, respectively. Control rats received water from the same source used for preparation of the MX dose formulations (after its adjustment to the same pH range). Body weight, clinical signs, and food and water consumption were recorded regularly. At the end of the treatment period, the animals were killed and full histopathologic analysis was performed on 47 tissues and all lesions. RESULTS: Dose-dependent increases in tumor incidence were observed in rats given MX-containing drinking water; the same MX doses had no obvious toxic effects on animals. MX consumption increased most drastically the prevalence of follicular adenoma (up to 43% and 72% in high-dose males and females, a test [one-sided] for positive trend in all dose groups P = .0045 and P = .0000, respectively) and carcinoma (55% [P = .0000] and 44% [P = .0000], respectively) in thyroid glands and cholangioma in the liver (8% [P = .0009] and 66% [P = .0000] in the high-dose males and females, respectively). Among rats given the higher doses of MX in their drinking water, cortical adenomas of the adrenal glands were increased in both sexes, alveolar and bronchiolar adenomas of the lungs and Langerhans' cell adenomas of the pancreas were increased in males, and lymphomas, leukemias, and adenocarcinomas and fibroadenomas of the mammary glands were increased in females. Even the lowest MX dose studied was carcinogenic. CONCLUSION: MX is a potent carcinogen in both male and female rats, and it causes tumors at doses that are not overtly toxic to rats. IMPLICATIONS: Although these findings cannot be extrapolated to humans, MX should be studied as a candidate risk factor in the possible association between consumption of chlorinated drinking water and cancer in humans.

Liver tumor-promoting activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in TCDD-sensitive and TCDD-resistant rat strains.

Risk assessment of dioxins is currently based on induction of liver tumors in rats. The toxicity of dioxins is characterized by large sensitivity differences among animal species and even strains of the same species, which complicates the risk assessment. The significance of these differences in dioxin-induced carcinogenicity is not known. We therefore studied the liver tumor-promoting activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the sensitive Long-Evans (L-E) and the resistant Han/Wistar (H/W) rats differing >1000-fold in their sensitivity to the acute lethaity of TCDD. Female rats were partially hepatectomized, initiated with nitrosodiethylamine, and treated with TCDD for 20 weeks. Altered hepatic foci (AHF) were stereologically quantitated using glutathione S-transferase P as a marker. AHF were significantly (P < 0.001) and dose dependently increased in L-E rats at 10 and 100 ng/kg/day, but in H/W rats only at 1000 ng/kg/day and above, indicating a remarkable (approximately 100-fold) sensitivity difference between L-E and H/W rats. The same sensitivity difference but 10-fold less foci were observed between nonhepatectomized/noninitiated L-E and H/W rats. Induction of AHF was related to hepatotoxicity but not to cytochrome P4501A1 activity in the liver. Liver TCDD concentrations were similar in both strains. H/W rats are exceptionally resistant to induction of AHF by TCDD, and the resistance is associated with an altered transactivation domain of the aryl hydrocarbon receptor. Genetic differences may account for significant interindividual/intraspecies sensitivity differences in dioxin-induced carcinogenesis. Understanding the role of transactivation domain of the aryl hydrocarbon receptor in carcinogenesis is therefore likely to improve dioxin risk assessment.

Transport-related measures to mitigate climate change in Basel, Switzerland: A health-effectiveness comparison study.

BACKGROUND: Local strategies to reduce green-house gases (GHG) imply changes of non-climatic exposure patterns. OBJECTIVE: To assess the health impacts of locally relevant transport-related climate change policies in Basel, Switzerland. METHODS: We modelled change in mortality and morbidity for the year 2020 based on several locally relevant transport scenarios including all decided transport policies up to 2020, additional realistic and hypothesized traffic reductions, as well as ambitious diffusion levels of electric cars. The scenarios were compared to the reference condition in 2010 assumed as status quo. The changes in non-climatic population exposure included ambient air pollution, physical activity, and noise. As secondary outcome, changes in Disability-Adjusted Life Years (DALYs) were put into perspective with predicted changes of CO2 emissions and fuel consumption. RESULTS: Under the scenario that assumed a strict particle emissions standard in diesel cars and all planned transport measures, 3% of premature deaths could be prevented from projected PM2.5 exposure reduction. A traffic reduction scenario assuming more active trips provided only minor added health benefits for any of the changes in exposure considered. A hypothetical strong support to electric vehicles diffusion would have the largest health effectiveness given that the energy production in Basel comes from renewable sources. CONCLUSION: The planned local transport related GHG emission reduction policies in Basel are sensible for mitigating climate change and improving public health. In this context, the most effective policy remains increasing zero-emission vehicles.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on bone in two rat strains with different aryl hydrocarbon receptor structures.

Polychlorinated dibenzo-p-dioxins (PCDDs) are highly toxic environmental contaminants, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent dioxin. Here, we studied the effects of TCDD on bone. Two rat strains, Han/Wistar (H/W) and Long-Evans (L-E), were used because they exhibit a 1000-fold sensitivity difference in acute lethality of TCDD, which difference is related to the aryl hydrocarbon receptor (AHR). TCDD inhibited the tibial growth dose dependently, the effect being manifested at lower doses in the more sensitive L-E strain. In H/W rats the effect of TCDD was seen only at the high dose of 170 microg/kg (p < 0.05), whereas in the sensitive L-E rats a significant reduction of bone growth was already seen at 1.7 microg/kg (p < 0.01). This reduction was caused by the smaller tibial size because the diaphyseal bone mineral density (BMD) did not change. The three-point bending breaking force of the tibia was significantly reduced in H/W rats at 170 microg/kg (p < 0.05), but tibial stiffness was lower already at the dose of 17 microg/kg (p < 0.05). In the sensitive L-E strain, both breaking force and stiffness were reduced at the dose of 17 microg/kg (p < 0.001). These results indicate that TCDD dose-dependently interferes with bone growth, modeling, and mechanical strength. The altered transactivation domain of AHR is associated with a lower sensitivity of bone to TCDD in H/W rats, suggesting that AHR plays a role in modulating the effects of dioxins on bone.

Biochemical effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds on the central nervous system.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related compounds are an important class of environmental contaminants which induce several types of biochemical alterations. Their effects have been most thoroughly characterized in the liver, especially regarding the Ah receptor-mediated induction of xenobiotic metabolizing enzymes. The behavioral signs exhibited by animals exposed to TCDD (progressive anorexia and body weight loss) suggest a role for the central nervous system (CNS) in TCDD toxicity. At lethal doses, TCDD affects the metabolism of serotonin, a neurotransmitter able to modulate food intake in the brain. This effect is associated with an elevated concentration of free tryptophan in the plasma. There does not appear to be any major changes in catecholaminergic neurotransmitter systems in TCDD-treated rats. Cytochrome P-450 related enzyme activities are induced by TCDD in the brain. As is the case in the liver, this induction does not correlate with susceptibility to TCDD lethality in rats. The involvement of the CNS in TCDD toxicity is still obscure. Elucidation of this role as well as the mechanism of TCDD-induced wasting may well advance our understanding of the regulation of food intake and body weight.

Trimethoprim pharmacokinetics in children with renal insufficiency.

We studied the pharmacokinetics of trimethoprim in 14 children (two neonates) with renal insufficiency. They were 1 week to 16.4 years old and had glomerular filtration rates (GFR) between 10.8 to 72.3 ml/min/1.73 m2. The half-life (t1/2) of trimethoprim was inversely related to the GFR. The relation followed a power curve (correlation of t1/2 with GFR: r = -0.86; P less than 0.001). The slower elimination rate was mainly the result of lowered renal clearance of trimethoprim. The volume of distribution (Varea) was, in most patients, in the upper normal range for children. In some of the patients, chiefly infants with severe renal insufficiency, the Varea was larger than normal. In some individuals the pharmacokinetics of trimethoprim deviated from that to be expected from the GRF. We recommend reduced daily doses of trimethoprim if the GFR is less than 30 ml/min/1.73 m2. The reduction should be proportional to the reduction in GFR and primarily take the form of a prolonged dose interval.

Conformationally rigid amphetamine analogs as inhibitors of monoamine uptake by brain synaptosomes.

Four 3-phenyl-2-amino-trans-decalin isomers were synthesized in order to obtain derivatives of phenylethylamine with a rigid conformation between the phenyl ring and the amino function. The stereoisomers were tested as inhibitors of catecholamine uptake by rat brain synaptosomes, and their potency was compared with that of amphetamine. The most potent inhibitor of catecholamine uptake was the diaxial 2(a)-amino-3(a)-phenyl-trans-decalin, which was one-fourth to one-third as potent as (+/)-amphetamine. As a dopamine uptake inhibitor in the stiatum, this compound was competitive. The results differ from those obtained earlier with similar analogs with a norepinephrine moiety incorporated into the decalin structure, since a gauche derivative [2(a)-amino-3(e)-3,4-dihydroxyphenyl-3-trans-decalol] was then the most potent and over 20 times as potent as the diaxial anti derivative. It remains to be seen whether this indicates that the mode of binding of phenylethylamines is different from that of catecholamines.

Evidence for dopaminergic control of thyrotrophin secretion in the rat.

The effects of two dopamine agonists (apomorphine and bromocriptine) and a dopamine antagonist (pimozide) on cold- or thyrotrophin releasing hormone (TRH)-induced TSH secretion were studied in normal male rats. Apomorphine given in various doses (0-5-10 mg/kg body wt) 10 min before exposure to cold significantly depressed TSH secretion. Large doses of bromocriptine (5-10 mg/kg body wt) given 1 h before exposure to cold, also blocked this response whereas a smaller dose (2-5 mg/kg body wt) given 30 min, 1, 3 or 6 h before cold exposure or repeated doses (0-1-2-5 mg/kg body wt) for 3 days did not modify cold-induced TSH secretion. Pimozide given in various doses (-25-2-5 mg/kg body wt) 1 h before exposure to cold did not alter the cold response, but 2-5 mg/kg reversed the inhibition caused by apomorphine or bromocriptine. None of these drugs affected TRH-induced TSH secretion. These results suggest that there are no dopaminergic receptors on the pituitary thyrotrophs, but that dopamine might be an inhibitory transmitter in the brain involved in the regulation of TSH secretion in the rat.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induced ethoxyresorufin-O-deethylase (EROD) and aldehyde dehydrogenase (ALDH3) activities in the brain and liver. A comparison between the most TCDD-susceptible and the most TCDD-resistant rat strain.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent inducer of ethoxyresorufin O-deethylase (EROD) and aldehyde dehydrogenase (EC 1.2.1.3., ALDH3) enzyme activities in the liver. Little is known about their inducibility by TCDD in the brain, although it may be a target organ for TCDD toxicity. Two strains of rat, Long-Evans (L-E) and Han/Wistar (H/W) exhibit an over 1000-fold difference in their LD50-values for TCDD. The induction of EROD and ALDH3 in discrete brain regions and in the liver of L-E and H/W rats were now compared at 10 days after TCDD exposure to assess the role of these responses in the strain difference. Liver EROD and ALDH3 were maximally induced at 5 micrograms/kg and 50 micrograms/kg, respectively, in both strains. In the brain 50 micrograms/kg TCDD was mostly needed to enhance EROD activity in both strains. The induction occurred especially in olfactory bulbs, but was also seen in the midbrain plus thalamus of both rat strains. The induced EROD activity in the olfactory bulb was almost totally abolished by a monoclonal antibody (Mab) 1-7-1 raised against CYP1A1. ALDH3 activities were increased more dose dependently in olfactory bulbs of H/W than L-E rats. In other brain areas measured, ALDH3 activities were induced more in L-E rats. Kinetic factors did not explain the differential induction of EROD and ALDH3 among discrete brain regions. We conclude that both EROD and ALDH3 are induced in the brain by TCDD although the activities are much lower than in the liver. The induction in the brain is region specific with olfactory bulbs being the most responsive area. As in the liver, the TCDD-induced activity of EROD in the brain is primarily associated with CYP1A1. According to the present findings, enzyme induction in the brain does not seem to have a crucial role in determining the strain susceptibility to the acute lethality of TCDD.

In vivo up-regulation of aryl hydrocarbon receptor expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a dioxin-resistant rat model.

The aryl hydrocarbon receptor (AHR) mediates toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and regulates expression of several genes such as CYP1A1. Little is known about what regulates expression of the AHR itself. We tested the ability of TCDD to alter in vivo expression of its own receptor in rat strains that are susceptible to TCDD lethality [Long-Evans (Turku AB) (L-E) and Sprague Dawley (SD)] and in a rat strain that is remarkably resistant to TCDD lethality [Han/Wistar (Kuopio) (H/W)]. Rats were administered a single, intragastric dose of 5 or 50 microg/kg of TCDD. Hepatic cytosol, nuclear extract, and RNA were prepared at 1, 4, and 10 days after TCDD exposure. AHR expression was assessed at three levels: ligand binding function, immunoreactive protein and mRNA. TCDD at 5 microg/kg produced a 2- to 3-fold increase in cytosolic AHR in all strains; 50 microg/kg produced depletion at day 1 followed by recovery in SD and H/W but not L-E rats. Both the increase in AHR above basal levels and the recovery from initial depletion were accompanied by elevations in steady-state AHR mRNA, suggesting a pre-translational mechanism for AHR regulation by its own ligand. This up-regulation in vivo is in contrast to the sustained depletion of AHR caused by TCDD in cell culture. There was no clear relationship between AHR regulation and strain sensitivity; thus, the large inherent strain differences in susceptibility to TCDD lethality probably are not explained by differential regulation of AHR by TCDD.

Polyene antibiotics increase the ionic permeability of synaptosomal plasma membranes.

The effects of antifungal heptaene antibiotics candicidin and amphotericin B were investigated in isolated cerebral cortical nerve terminals (synaptosomes). The synaptosomes were incubated with candicidin or amphotericin B in the presence or absence of external Ca2+. Candicidin (0.4-0.8 I.U./mL) increased intrasynaptosomal free Ca2+ significantly. This increase was not significantly suppressed by 30 microM verapamil or 2 microM nifedipine. In the absence of extrasynaptosomal Ca2+ intrasynaptosomal free Ca2+ was not changed by candicidin. Amphotericin B increased intrasynaptosomal free Ca2+ as well. Candicidin (0.05-0.6 I.U./mL) increased the respiration rate up to 3.5-fold above the basal rate. This response was not affected by the absence of extracellular Ca2+. Ouabain completely blocked the increase of respiration caused by candicidin, whereas tetrodotoxin was ineffective. The plasma membrane depolarized in a dose-dependent manner after candicidin (0.2-0.8 I.U./mL). The mitochondrial membrane potential was little affected and only at the highest concentrations. The results indicate that heptaene polyenes increase synaptosomal ionic permeability, which is reflected in increased Ca2(+)-influx and accelerated respiration. The increment in synaptosomal free calcium takes place probably as a nonspecific leak via typical polyene-cholesterol channels. The respiration is accelerated by increased Na(+)-permeability through the plasma membrane which stimulates the function of Na+, K(+)-ATPase and thus increases the energy demand.

Environmental chemicals and changes in sex ratio: analysis over 250 years in finland.

It has been proposed that environmental chemicalization is responsible for the recent decline in male ratio, but these speculations are based on statistics going back only a few decades. The objective of this study was to evaluate whether Finnish long-term data are compatible with the hypothesis that the decrease in the ratio of male to female births in industrial countries is caused by environmental factors. We analyzed the sex ratio of births from the files of Statistics Finland and all live births in Finland from 1751 to 1997. Running averages of 9 years (1751-1904) or 5 years (1905-1997) were analyzed for sex ratios. Additionally, to identify potential explanations for the findings, births from 1990 to 1997 were correlated with various family parameters. We found an increase in the proportion of males from 1751 to 1920; this was followed by a decrease and interrupted by peaks in births of males during and after World War I and World War II. None of the family parameters (paternal age, maternal age, age difference of parents, birth order) could explain the time trends. The turning point of male proportion precedes the period of industrialization or the introduction of pesticides or hormonal drugs, rendering a causal association unlikely. Moreover the trends are similar to those observed in other countries with worse pollution and much greater pesticide use.

Birth weight and sex of children and the correlation to the body burden of PCDDs/PCDFs and PCBs of the mother.

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) were analyzed in 167 random human milk samples from urban and rural areas in Finland. Dietary habits and background information on each mother and child were gathered by questionnaire. Body mass indexes (BMI) before pregnancy and delivery in the rural area were 5-10% higher than in the urban area, but fat content of mother's milk was about 10% higher in the urban area. The mean weights of children (+/- standard deviation) were similar in the rural and urban areas among primiparae, 3,500 +/- 597 g and 3,505 +/- 454 g, respectively, although dioxin international toxic equivalents (I-TEQs) were significantly higher in the urban area. The mother's level of education did not affect the weight of the child, but concentrations of PCDDs/PCDFs (I-TEQ, 2,3,4,7,8-Cl5 dibenzofuran,1,2, 3,7,8-Cl5 dibenzodioxin) and PCBs [sum of PCBs (sumPCB), PCB-TEQ, and most PCB congeners] increased with advanced education. This is considered to be due to differences in the mother's consumption of fish. The birth weight, especially of boys, slightly decreased with increasing concentrations of I-TEQ, 2,3,4,7,8-Cl5 dibenzofuran, 1,2,3, 7,8-Cl5 dibenzodioxin, and 2,3,7,8-Cl4 dibenzodioxin; however, when the analysis was restricted to primiparae, there was no statistically significant correlation between birth weight and the concentrations of PCDDs/PCDFs. No correlation was found between the weight of the child and PCBs, PCB-TEQs, or individual PCB congeners in the whole material or among primiparae, or among boys or girls. The concentrations of PCDDs/PCDFs and PCBs inhuman milk were modeled for primiparae by weighing fish consumption, age of mother, milk fat content, and BMI before pregnancy. The linear regression resulted in values of R = 0.67 and 0.30 for the modeled dioxin I-TEQs in the urban and rural areas, respectively, and the corresponding values for sumPCBs of R = 0.60 and 0.11. The increase of PCDD/PCDF body burden was calculated to be on average 0.58 pg I-TEQ/g milk fat/year in the urban area and 0.39 pg I-TEQ/g milk fat/year in the rural area.

Assessing the public health benefits of reduced ozone concentrations.

In this paper we examine scientific evidence and related uncertainties in two steps of benefit-cost analyses of ozone reduction: estimating the health improvements attributable to reductions in ozone and determining the appropriate monetary values of these improvements. Although substantial evidence exists on molecular and physiologic impacts, the evidence needed to establish concentration-response functions is somewhat limited. Furthermore, because exposure to ozone depends on factors such as air conditioning use, past epidemiologic studies may not be directly applicable in unstudied settings. To evaluate the evidence likely to contribute significantly to benefits, we focus on four health outcomes: premature mortality, chronic asthma, respiratory hospital admissions, and minor restricted activity days. We determine concentration-response functions for these health outcomes for a hypothetical case study in Houston, Texas, using probabilistic weighting reflecting our judgment of the strength of the evidence and the possibility of confounding. We make a similar presentation for valuation, where uncertainty is due primarily to the lack of willingness-to-pay data for the population affected by ozone. We estimate that the annual monetary value of health benefits from reducing ozone concentrations in Houston is approximately $10 per person per microgram per cubic meter (24-hr average) reduced (95% confidence interval, $0.70-$40). The central estimate exceeds past estimates by approximately a factor of five, driven by the inclusion of mortality. We discuss the implications of our findings for future analyses and determine areas of research that might help reduce the uncertainties in benefit estimation.

Decreased uptake of 5-hydroxytryptamine in blood platelets from patients with endogenous depression.

5-Hydroxytryptamine (5-HT) uptake was studied by using blood platelets from 13 patients with endogenous depression (Hamilton rating scale 33 +/- 7) and 13 healthy volunteers. An improved method with a short incubation time and low substrate concentration was used, and the incubation was performed in Krebs-Henseleit buffer (pH 7.4) at 37 degrees C. A clear difference in 5-HT uptake by blood platelets was noted: The Vmax of the reaction in patients was 39, and in controls 71 pmol per 2 x 10(7) platelets in 5 min. There was no significant difference in the Km. After a 4-week treatment with imipramine, a competitive inhibition of 5-HT uptake with an increased Km was seen; after a similar treatment with amoxapine there was little change in 5-HT uptake. Amoxapine was inferior to imipramine as an inhibitor of 5-HT uptake, also in vitro. There was no difference in clinical recovery in these treatment groups. These results may be of importance so as to understand the potential biological differences between depressed patients and normal persons.

Nomifensine and its derivatives as possible tools for studying amine uptake.

An experimental antidepressive drug, nomifensine, was tested in simultaneous experiments as an inhibitor of the uptake of noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) in rat brain synaptosomes. The drug was found to be a very potent inhibitor of NA (Ki 4.7 X 10(-9) M) and DA (Ki 2.6 X 10(-8) M) uptake, but relatively weak inhibitor of 5-HT uptake (Ki appr. 4 X 10(-6) M). According to kinetic studies on dopamine uptake, the inhibition was competitive. Time course studies indicated that the percentage inhibition did not increase with time. This finding suggests that inhibition of membrane uptake rather than inhibition of storage is the mechanism of action of this drug. 3 metabolites of nomifensine were also tested as inhibitors of NA and DA uptake. The addition of a 4-hydroxy group to the phenyl ring of nomifensine slightly decreased the potency, and addition of hydroxy and methoxy groups to the positions 3 and 4 in the phenyl ring, clearly decreased the potency. The structure of nomifensine is compared to that of chlorimipramine. It is suggested that the differences in selectivity as to dopamine and 5-HT uptake mechanisms might be due to 2 conformational differences: one of the phenyl rings is freely rotating in nomifensine but not in chlorimipramine, and the tertiary amine group is in a flexible side chain in chlorimipramine but rigidly tied in nomifensine.

Alterations in plasma tryptophan binding to albumin in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated Long-Evans rats.

We have previously shown that the wasting syndrome in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administration is associated with a specific increase in free tryptophan (unbound to albumin) in rats. The present series of experiments was undertaken to characterize how the binding of tryptophan to albumin is altered by TCDD and to find the underlying cause of the changes. TCDD administered to Long-Evans rats proved to diminish the maximal binding capacity (Bmax) of albumin for tryptophan by ca. 60% without any marked change in the binding affinity. Of candidate mediating factors, neither TCDD nor bilirubin affected the binding equilibrium of tryptophan with albumin in vitro. However, a mixture of free fatty acids greatly increased the proportion of free tryptophan at physiologically relevant concentrations. Similarly, the free fatty acid mixture added to plasma in vitro decreased only Bmax of albumin in a manner similar to the effect of TCDD administered in vivo. Extraction of lipid-soluble substances from the plasma with ether was effective in reversing the increase in free tryptophan in the plasma of TCDD-treated rats while dialysis of water-soluble substances was not. Ether extraction also resulted in a decrease in free fatty acids. We conclude that disturbances in lipid metabolism may be involved in the pathogenesis of TCDD-induced alterations in tryptophan binding to albumin in vivo.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced anorexia and wasting syndrome in rats: aggravation after ventromedial hypothalamic lesion.

Long-term regulation of body weight and food intake were studied after rats were subjected to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which causes hypophagia and body weight loss, and to ventromedial hypothalamic lesion, which causes hyperphagia, metabolic changes and obesity. These two factors appeared to have an interaction, as ventromedial hypothalamic lesion initially aggravated the effects of TCDD on body weight and food intake. This was seen in both TCDD-resistant and TCDD-susceptible rat strains. In contrast, if TCDD was given several weeks before the lesion and body weight had stabilized to a low level, no aggravation was seen, but TCDD completely blocked the effects of ventromedial hypothalamic lesion. Thus, TCDD seems to affect the same regulation chain that is involved in the lesioning of the ventromedial hypothalamus. TCDD might serve as a tool in studying different mechanisms of long-term food intake and body weight regulation.

Toxic equivalency factors do not predict the acute toxicities of dioxins in rats.

Risk evaluation of complex environmental mixtures of polychlorinated dibenzo-p-dioxins and related halogenated aromatic hydrocarbons (polychlorinated dibenzofurans, azo- and azoxybenzenes, naphthalenes and some of the biphenyls) is currently carried out by measuring the concentration of each congener in the mixture and then multiplying every figure by its specific constant, toxic equivalency factor (TEF). All congeners are thought to produce highly similar effects albeit at different doses, and the TEFs are believed to represent the potencies of the congeners relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), considered the most toxic derivative of this class of environmental contaminants. Here we compared the acute toxicities of TCDD, 1,2,3,7,8-penta-, 1,2,3,4,7,8-hexa- and 1,2,3,4,6,7,8-heptachloro-dibenzo-p-dioxin in the most TCDD-susceptible (Long-Evans Turku AB; L-E) and the most TCDD-resistant (Han/Wistar kuopio; H/W) rat strain. While L-E rats exhibited the expected rank order of sensitivities to the four dioxins, the higher chlorinated dioxins were more toxic than TCDD (in terms of acute lethality) to H/W rats, with the hexachlorodioxin showing the greatest potency. Even if the doses were adjusted according to the LD50 values, both biochemical and morphological effects elicited by the dioxins turned out to depend, often critically, on strain, congener or the interaction of these two determinants. These findings demonstrate that the dioxins have distinct profiles of acute toxicities and underscore the importance of response and test organism in defining the TEFs.