Skin water uptake and renal function in the toad

Polychlorinated biphenyls (PCBs): environmental impact, biochemical and toxic responses, and implications for risk assessment

Commercial polychlorinated biphenyls (PCBs) and environmental extracts contain complex mixtures of congeners that can be unequivocally identified and quantitated. Some PCB mixtures elicit a spectrum of biochemical and toxic responses in humans and laboratory animals and many of these effects resemble those caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related halogenated aromatic hydrocarbons, which act through the aryl hydrocarbon (Ah)-receptor signal transduction pathway. Structure-activity relationships developed for PCB congeners and metabolites have demonstrated that several structural classes of compounds exhibit diverse biochemical and toxic responses. Structure-toxicity studies suggest that the coplanar PCBs, namely, 3,3',4,4'-tetrachlorobiphenyl (tetraCB), 3,3',4,4',5-pentaCB, 3,3',4,4',5,5'-hexaCB, and their monoortho analogs are Ah-receptor agonists and contribute significantly to the toxicity of the PCB mixtures. Previous studies with TCDD and structurally related compounds have utilized a toxic equivalency factor (TEF) approach for the hazard and risk assessment of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) congeners in which the TCDD or toxic TEQ = sigma([PCDFi x TEFi]n)+sigma([PCDDi x TEFi]n) equivalent (TEQ) of a mixture is related to the TEFs and concentrations of the individual (i) congeners as indicated in the equation (note: n = the number of congeners). Based on the results of quantitative structure-activity studies, the following TEF values have been estimated by making use of the data available for the coplanar and monoortho coplanar PCBs: 3,3',4,4',5-pentaCB, 0.1; 3,3',4,4',5,5'-hexaCB, 0.05; 3,3',4,4'-tetraCB, 0.01; 2,3,3',4,4'-pentaCB, 0.001; 2,3',4,4',5-pentaCB, 0.0001; 2,3,3',4,4',5-hexaCB, 0.0003; 2,3,3',4,4',5'-hexaCB, 0.0003; 2',3,4,4',5-pentaCB, 0.00005; and 2,3,4,4',5-pentaCB, 0.0002. Application of the TEF approach for the risk assessment of PCBs must be used with considerable caution. Analysis of the results of laboratory animal and wildlife studies suggests that the predictive value of TEQs for PCBs may be both species- and response-dependent because both additive and nonadditive (antagonistic) interactions have been observed with PCB mixtures. In the latter case, the TEF approach would significantly overestimate the toxicity of a PCB mixture. Analysis of the rodent carcinogenicity data for Aroclor 1260 using the TEF approach suggests that this response is primarily Ah-receptor-independent. Thus, risk assessment of PCB mixtures that uses cancer as the endpoint cannot solely utilize a TEF approach and requires more quantitative information on the individual congeners contributing to the tumor-promoter activity of PCB mixtures.

Effects of the fungicide prochloraz on xenobiotic metabolism in rainbow trout: inhibition in vitro and time course of induction in vivo

1. Interactions between the fungicide prochloraz and the hepatic cytochrome P-450 of rainbow trout were studied by determination of enzymic activities in vitro using the microsomal fraction, and by kinetic studies. 2. Prochloraz inhibited 7-ethoxyresorufin-O-deethylase (EROD) in vitro. This inhibition was partially non-competitive: the enzyme-substrate-inhibitor (ESI) complex was catalytically active (68% of the activity of the enzyme-substrate complex). 3. Prochloraz in vitro inhibited aldrin epoxidase (AE) by a linear mixed-type mechanism. This inhibition might be high because of high affinity for prochloraz and lack of catalytic activity of the ESI complex. 4. Effects of prochloraz in vivo were studied as a function of time after intraperitoneal injection. Total cytochrome P-450 increased for more than 21 days. 5. EROD increased slightly at day 4 and then returned to control level. Kinetics showed an increase in apparent Km and Vmax. AE was strongly inhibited at day 4 (large increase in apparent Km) and then returned to control level in 21 days. 6. Spectral interactions with aniline showed strong inhibition and recovery to an activated level at day 21.

Effects of the fungicide prochloraz on xenobiotic metabolism in rainbow trout: in vivo induction

1. Rainbow trout were dosed with prochloraz by i.p. injection of sprayed food pellets. Cytochrome P-450, two P-450-dependent activities, and two conjugase activities were measured in vitro in microsomal or cytosolic fractions. 2. Prochloraz increased cytochrome P-450 in liver, intestine, and pyloric caeca: maximum response occurred at 30-100 mg/kg i.p. In cold conditions, this increase persisted for more than 8 days after injection. 3. Hepatic 7-ethoxycoumarin-O-dealkylase (ECOD) and 7-ethoxyresorufin-O-dealkylase (EROD) were inhibited by prochloraz except in one assay in warm water where they increased. In intestine and pyloric caeca, ECOD and EROD were not detected, even when cytochrome P-450 was increased. 4. UDP-glucuronosyltransferase (1-naphthol as substrate) was unchanged or inhibited after prochloraz dosing. 5. Glutathione-S-transferase (o-dinitrobenzene as substrate), was unchanged or inhibited by prochloraz. 6. The measured level of enzymic activities was the result of induction and inhibition by prochloraz residues. Variations in basal activities and perhaps in prochloraz interactions were due to temperature acclimatization.

Subcellular localization and properties of cytochrome P-450 and UDP glucuronosyltransferase in the rainbow trout kidney

Rainbow trout kidney was subfractionated by differential centrifugation to obtain preparations suitable for the study of xenobiotic metabolizing enzymes and to ascertain the distribution of these activities in the cell. The cytochrome P-450-dependent monooxygenase, NADPH-cytochrome c reductase, and UDP glucuronosyltransferase, which are enzymes important in the biotransformation of xenobiotics, were enriched in the microsomal fraction. Another xenobiotic-metabolizing enzyme, epoxide hydrolase, was enriched in the mitochondrial and microsomal fractions almost to the same extent. Cytochrome P-450-dependent monooxygenase and UDP glucuronosyltransferase activities were characterized in the trout kidney microsomes. The cytochrome P-450 deethylation of 7-ethoxycoumarin and 7-ethoxyresorufin as well as the glucuronidation of p-nitrophenol in the kidney were found to proceed at rates comparable to those occurring in the liver. The difference spectrum of the complex between carbon monoxide and reduced trout kidney microsomes showed a peak at 448.5 nm. Addition of 7-ethoxycoumarin to kidney microsomes produced an absorbance change in difference spectrum similar to the substrate binding spectrum found in rainbow trout liver and rat liver microsomes.

Monitoring of cyclic organochlorines in the marine environment

Cyclic organochlorines are highly hydrophobic chemicals which usually possess a high persistence to microbial breakdown. These behavioural aspects determine the suitability of each environmental compartment for monitoring purposes, which is discussed.It is concluded, that monitoring of (cyclic) organochlorines should only be executed for compounds about which solid information is available on their environmental behaviour in abiotic and biotic environmental compartments. Under these conditions benthic invertebrates which use glycogen as their main energy-depot, appear to be the most suitable tool for environmental monitoring of lipophilic compounds. Concentrations should be expressed on the basis of (total) extractable lipids.The organisms to be compared should be sampled at a time when they have a similar physiological condition. This does not automatically mean synoptic sampling.Multi-component mixtures, such as PCB's, should be monitored on the basis of (selected) individual components in order to account for differences in behaviour of each component between different environmental compartments and animal species.Some representatives of the compounds discussed are strong inducers of mixed function oxygenase (MFO) enzyme systems. Therefore it should be investigated, if monitoring of MFO activity in addition to concentrations can be regarded as an early warning system of additive effects.

Polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs): biochemistry, toxicology, and mechanism of action

Polychlorinated and polybrominated biphenyls are industrial chemical mixtures which have been implicated in numerous human poisonings in Taiwan and Japan (PCBs) and Michigan (PBBs). Moreover, these polyhalogenated biphenyls have been widely detected in the environment including the air, water, fish, wildlife, human adipose tissue, and blood and breast milk. A major problem associated with the analysis and toxicology of this group of chemicals is their chemical complexity (e.g., there are 209 possible PCB isomers and congeners) and the remarkable effects of structure on activity. This article will discuss the effects of structure on the biologic and toxic effects of individual PCB and PBB congeners as well as reconstituted mixtures. The results clearly show that like "dioxin" (or 2,3,7,8-TCDD), the PCBs and PBBs elicit their effects through a cytosolic receptor protein which preferentially binds with the toxins which are approximate isostereomers of 2,3,7,8-TCDD. The evidence for this mechanism of action will be discussed in detail.

The in vivo electrical parameters of toad skin

Open-circuit voltage (PD) and short-circuit current (SCC) across toad skin were studied in in vivo conditions. An improved technique for fastening a lucite chamber on the abdominal region of the animal was developed. Saline bridges (230 mM NaCl in 4% agar solution) were placed subcutaneously to make the connections between the extracellular fluid and the half-cells. A clear relationship was observed between the electrical parameters and sodium transport by the skin, since PD and SCC were related to the sodium concentration of the bathing solution, and abolished by the presence of amiloride--a specific sodium transport inhibitor in epithelia. The initial control values of SCC in vivo were higher than those in vitro, which was attributed to hormonal stimulation. However, these high initial control values of SCC in vivo fell with time, reaching steady levels after a 2 hr period. Vasopressin failed to increase SCC in vivo when the external sodium concentration was 115 mM, being effective only when the sodium concentration was low (5 mM). On the other hand, in isolated preparations vasopressin significantly promoted an increase in both PD and SCC.