European Journal of Pharmacology: Environmental Toxicology and Pharmacology最新文献

The influence of dosing time on embryotoxicity of valproate was investigated in ICR (Institute of Cancer Research, USA) mice under light-dark (12:12) cycle. A significant circadian rhythm was shown for embryotoxicity, with the highest value at 17:00 and the lowest at 01:00. No significant difference between injection at 17:00 and 01:00 was demonstrated for valproate concentrations in the embryo. The rhythm in the embryotoxicity seems to be related to the rhythm in the sensitivity to the drug. Embryotoxicity and valproate concentrations were significantly higher on gestational day 13 than day 7. The timing of drug administration (i.e, gestational stage and circadian phase) appears to be essential in the study of embryotoxicity of valproate in mice.

The effect of methylmercury on mouse thymocytes was examined using fluorescent dyes for membrane potential and intracellular Ca²⁺. Methylmercury at concentrations of 1 ωM or higher (up to 30 ωM) produced hyperpolarization in a dose-dependent fashion. Charybdotoxin and quinine, but not 4-aminopyridine and tetraethylammonium, greatly suppressed methylmercury-induced hyperpolarization. Removal of external Ca²⁺ reduced the degree of hyperpolarization. Pretreatment of thymocytes with A23187 under Ca²⁺-free conditions abolished the hyperpolarization induced by methylmercury. Under both normal and Ca²⁺-free conditions methylmercury increased the intracellular concentration of Ca²⁺. The results suggest that the increase in intracellular Ca²⁺ is mediated through a Ca²⁺ release from intracellular stores as well as through influx of external Ca²⁺. Therefore, it is likely that methylmercury increases the intracellular concentration of Ca²⁺, resulting in activation of Ca²⁺-dependent K⁺ conductance of mouse thymocytes.

Influence of dosing time on pharmacological effects and toxicity of acetylsalicylic acid was investigated in ICR male mice under light-dark (12:12) cycle. Significant circadian rhythms (day-night rhythms) were demonstrated for hypothermal and analgesic effects at 1 h after an injection of acetylsalicylic acid (200 mg/kg, i.p.) (P < 0.01, respectively). The rhythmic patterns of acetylsalicylic acid induced analgesia and hypothermia resembled overall the rhythms occurring in the non-drugged state. Injection of acetylsalicylic acid resulted in a parallel increase in latency to hot plate and a parallel decrease in rectal temperature. The relationship between plasma salicylate concentrations and responses was not clear. There was also a significant circadian rhythm in acetylsalicylic acid (850 mg/kg, i.p) induced toxicity with the highest mortality at 17:00 and the lowest one at 05:00 (P < 0.05). Dosing time dependent kinetics of salicylate seems to be related to the rhythm of toxicity of the drug. The time in circadian stage at which acetylsalicylic acid is administered is essentially important in the actions of acetylsalicylic acid.

A V79 Chinese hamster cell line was constructed for stable expression of human cytochrome P450 2E1 (CYP2E1) by integration of a SV40 Early promoter recombinant CYP2E1 cDNA into the chromosomal DNA. The cDNA encoded CYP2E1 was effectively expressed and enzymatically active, as shown by hydroxylation of chlorzoxazone and of p-nitrophenol, at rates of about 70 pmol × mg⁻¹ total protein × min⁻¹. CYP2E1 content and activity was increased upon cultivation in the presence of ethanol indicating a substrate mediated stabilization effect. A similar stabilizing effect was also observed for inhibitors of CYP2E1, e.g. imidazole, 4-methylpyrazole, and isoniazid. The feasibility of the newly established cell line V79MZh2E1 for toxicological studies was shown by CYP2E1-mediated activation of N-nitrosodimethylamine and p-nitrophenol and a dose-dependent cytotoxic and mutagenic effect.

Administration of clenbuterol to rats in the drinking water over a 4 day period increased incorporation of [³H]leucine into muscle protein and caused a slight reduction in urinary 3-methylhistidine but did not result in an increase in body or muscle weight. However, both urinary and liver taurine were significantly reduced at the highest dose of clenbuterol (2 mg · kg⁻¹ · day⁻¹). Serum creatine kinase, muscle isoenzyme (CK-MM) was raised and single muscle fibre injury was observed in the soleus muscle in animals treated with the middle dose (0.2 mg · kg⁻¹ · day⁻¹) and highest dose (2 mg · kg⁻¹ · day⁻¹). The reduction in the body pool of taurine caused by clenbuterol is of concern as taurine has been shown to have protective properties.

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 (B_max) 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 B_max 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.

We recently reported changes in the density of muscarinic acetylcholine receptors cerebral cortex of mice treated neonatally with DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane) and receiving bioallethrin as adults. We also found behavioural aberrations in adult mice treated with bioallethrin, whether neonatally treated with DDT or the vehicle. To ascertain whether these changes were permanent, 10-day-old mice received an oral dose of DDT (0.5 mg/kg body weight) and at the age of 5 months they received bioallethrin orally (0.7 mg/kg body weight/day; 7 days). The animals were investigated at the age of 7 months. Here we report muscarinic acetylcholine receptor changes, additional behavioural disturbances and learning disabilities in mice receiving DDT as neonates and bioallethrin as adults, whereas the behavioural disturbances in mice receiving vehicle as neonates and bioallethrin as adults had diminished and changes in proportions of high- and low-affinity binding sites had developed. No changes in the density of nicotinic acetylcholine receptors were noted for any of the treated groups. In conclusion, exposure of neonates to DDT leads to increased susceptibility in adults to a short-acting pesticide with similar neurotoxic action. An adult exposure to this short-acting pesticide to mice neonatally exposed to DDT leads to irreversible muscarinic acetylcholine receptor changes and behavioural disturbances with additional changes 2 months after the exposure.

Effect of triethyllead on the specific [³H]flunitrazepam binding was studied in rat cortical and cerebellar P₂ fractions in vitro and in tissue homogenates of several rat brain regions ex vivo after 5 daily subcutaneous doses of 1.9 mg/kg triethyllead acetate to rats. Up to concentration of 100 μM, triethyllead did not significantly the specific [³H]flunitrazepam binding but attenuated marginally (14–18%) the GABA_A receptor agonist, muscimol-induced elevation of [³H]flunitrazepam binding in cerebellar tissue. After the subacute treatment of rats with triethyllead, the specific [³H]flunitrazepam binding was 27% lower in cerebellum compared to control animals. In other brain regions the receptor binding was not changed. The data suggest that triethyllead modified the cerebellar GABA_A receptor complex causing decreased binding in the benzodiazepine site. Such an inhibitory effect in the GABA_A receptor complex may decrease cerebellarinhibitory output and augment the triethyllead induced convulsions and tremor.

Endothelin-1 is a potent vasoconstrictor. This study was performed to determine whether arterial injury, induced by either hypercholesterolemia or mechanical disruption of the endothelium, is associated with increased localization of endothelin-1 in the artery. The blood clearance and tissue distribution of intravenously injected [¹²⁵I]endothelin-1 was evaluated in 33 rabbits - control animals (n = 7), balloon de-endothelialized animals (n = 12), cholesterol -fed animals (n = 6) and animals that had both balloon de-endothelialization and high cholesterol diet (n = 8). The blood clearance half time was less than 20 min, with slightly slower clearance in the ballooned/cholesterol-fed animals. [¹²⁵I]Endothelin-1 localized in the lung (∼ 12% injected dose (ID)/organ) and kidney (∼ 8%ID/organ). [¹²⁵I]Endothelin-1 localized in the lung (∼ 12% injected dose of 0.06%kgID/g to its highest level within 5 min of balloon de-endotheliazation (0.2%kgID/g) and decreased to 0.11%kgID/g within one week and remained essentially unchanged through 16 weeks. The area with increased binding of [¹²⁵I]endothelin-1 corresponded to the zone of arterial injury stained with Evans blue. On the other hand, the binding in the aorta did not increase with the atherogenic diet. These findings suggest that endothelin-1 accumulates in injured vessels, attaining the highest levels immediately after mechanical injury.

Human hydroxysteroid sulfotransferase, human phenol-sulfating form of phenol sulfotransferase, rat hydroxysteroid sulfotransferase a and rat phenol sulfotransferase IV were expressed in Escherichia coli. Cytosol preparations of transformed bacteria were used as activating systems in mutagenicity tests with Salmonella typhimurium TA 98. All test compounds, 1-hydroxymethylpyrene, 2-hydroxymethylpyrene, 1-(1-pyrenyl)ethanol, 9-hydroxymethylanthracene, 7-hydroxymethyl-12-methylbenz[a]anthracene and 4H-cyclopental[def]chrysen-4-ol, were activated by both hydroxysteroid sulfotransferases investigated. However, 1-(1-pyrenyl)ethanol was 67-fold more efficiently activated by the human enzyme, whereas 7-hydroxymethyl-12-methylbenz[a]anthracene was 27-fold more efficiently activated by the rat enzyme. The phenol sulfotransferases showed relatively low activities with the benzylic alcohols investigated. The only exception was 4H-cyclopental[def]chrysen-4-ol, which was activated efficiently by rat phenol sulfotransferase IV. We had previously tested the ability of rat and human hepatic cytosol preparations to activate the same compounds. The results of a statistical analysis suggest that the activities of human hydroxysteroid sulfotransferase, rat hydroxysteroid sulfotransferase a and phenol sulfotransferase IV can account for a substantial portion of the activation of benzylic alcohols in human, female rat and male rat liver, respectively.