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

Portocaval anastomosis and vagotomy operations were performed in Long-Evans (L-E) and Han/Wistar (H/W) rats to elucidate the mechanism of anorexia induced by TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). TCDD-sensitive L-E rats were given a sublethal (5 μg/kg) or a lethal dose (20 μg/kg) by gavage 5–8 weeks after portocaval anastomosis. TCDD-resistant H/W rats were given a nonlethal dose (500 or 7200 μg/kg). The shunt operation did not reduce lethality from TCDD. The effect on wasting of the marginally toxic dose of 5 μg/kg in L-E rats was potentiated by the portocaval operation, and the lethal dose was effective in both shunted and sham-operated L-E rats. TCDD failed to decrease food intake and body weight in shunted rats of H/W strain at either dose level though it did so in sham-oprated controls. The lack of effect may be due to the already reduced weight of shunted rats at the time of TCDD dosing. TCDD anorexia was not explained by changes in histamine or serotonin (5-HT) turnover in the brain. Vagotomy did not influence lethality after TCDD, although reduction in food intake was somewhat blunted in H/W rats. The results seem to indicate that the anorectic effect of TCDD is modified when portal blood bypasses the liver. The mechanisms remain to be elucidated in detail, but the results do not favor the role of liver as the only or the major initiator of TCDD anorexia. Little evidence was found to support a crucial role of vagal afferent input.

The enzymes of mitochondrial respiratory chain, NADH dehydrogenase (complex I) and cytochrome c oxidase (complex IV), were completely inhibited by 6-hydroxydopamine with IC₅₀ = 10.5 μM and IC₅₀ = 34 μM respectively. The enzyme inhibition was insensitive to the change of NADH or cytochrome c concentrations. The extent of complex I inhibition decreased as a consequence of both non-enzymatic and monoamine oxidase-catalyzed oxidation of 6-hydroxydopamine. Monoamine oxidase A and B inhibitors, tranylcypromine and clorgyline but not l-deprenyl increased the extent of 6-hydroxydopamine induced inhibition of complex I. Thus, 6-hydroxydopamine itself and not its oxidation products may be responsible for the neurotoxicity of this agent via inhibition of respiratory chain enzymes.

In mice pretreated intracerebroventricularly (i.c.v.) with either saline (1 μl/mouse), pertussis (1 μg/mouse) or cholera (2.5 μg/mouse) toxins, effect of κ-opioid receptor agonists on the colonic temperature and charcoal meal transit time were assessed. The κ-opioid receptor agonist, trans-(+)-3,4-dichloro-N-methyl-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide methane sulfonate hydrate (U-50488H, 50, 100 and 200 μg/mouse, i.c.v.) produced dose dependent hypothermia. Pertussis toxin pretreatment (72 and/or 144 h before) antagonized (P < 0.05) the hypothermic effect of U-50488H (100 μg/mouse) and (±)-trans-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl[benz[b]-thio-phene-4-acetamide (PD 117302, 30 μg/mouse). In contrast, cholera toxin pretreatment (48 and/or 96 h before) did not antagonize the hypothermic effect of the κ-opioid receptor agonists. Moreover, both i.c.v. and intrathecal (i.t.) administration of κ-opioid receptor agonists, U-50488H, {[5R-(5α,7α,8β)]-(±)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspirol[4,5]dec-8-yl]-benzeneacetamide} (U-65593) and PD 117302, produced dose dependent inhibition of the charcoal meal transit. Cholera toxin pretreatment (48 and 96 h before) augmented (P < 0.05) the antitransit effect of i.c.v. administered U-50488H (100 μg/mouse), U-69593 (100 μg/mouse) and PD 117302 (50 μg/mouse). However, pertussis toxin previous pretreatment did not affect the gastrointestinal inhibitory effect of the κ-opioid receptors agonists. The present results extend our previous results on the affect of κ-selective agonists on gastrointestinal motility and indicate, like the prototype opiate agonist morphine, κ-opioid receptor agonists are effective in inhibiting the gastrointestinal motility when administered either by intrathecal or intracerebroventricular routes. Thus, for the antitransit effect of κ-opioid receptor agonists, both spinal and supra spinal site could be implicated. Furthermore, these results also suggest that pertussis and cholera toxin-sensitive transducer G-proteins may be involved in the central κ-opioid receptor mediated hypothermia and gastrointestinal transit inhibition respectively.

Paraquat, a widely used herbicide, has been reported to be capable of producing superoxide. In the present paper, therefore, the possibility of paraquat inhibiting endothelium-dependent relaxation, mediated by the production of nitric oxide, was tested. The relaxing effects of acetylcholine and A23187, but not that of sodium nitroprusside, in the rat thoracic aorta were found to be inhibited by paraquat in a concentration-dependent manner. In contrast, paraquat was totally inactive with regard to the aortic contractions induced by either norepinephrine or prostaglandin F_2α. The inhibitory action of paraquat could be antagonized by superoxide dismutase but not by catalase and indomethacin. All of these findings indicate that superoxide anions produced by paraquat in the endothelium contribute to a decrease in the relaxation response to acetylcholine and A23187 by interfering with endothelium-derived nitric oxide.

Since it has been proposed that oxygen radical inactivation of key enzymes plays a critical role in cell aging, we have investigated the effects of a thiolic free radical scavenger on the oxidative phosphorylation enzymes of liver mitochondria from female OF-1 mice. At 48 weeks of age a control group was fed standard food pellets and another group received pellets containing 0.3% (w/w) of N-acetylcysteine. A 24-week treatment resulted in a significant increase in the specific activities of complex I, IV and V in the hepatic mitochondria of the N-acetylcysteine-treated animals as compared to aged controls.

A rat cytomegalovirus infection model for use in immunotoxicity testing has been developed. In resistance against viruses, natural killer cells and cytotoxic T-cells play an important role. Therefore, this model complements other rat host resistance models for immunotoxicity testing, i.e. existing bacterial and parasitic infection models in which cytotoxic T-cells and natural killer cells play a minor role. Host resistance against cytomegalovirus infections in the rat was determined by titrating infectious virus levels in organs after cytomegalovirus infection in an in vitro infectivity test denoted as the Plaque Forming Unit (PFU) Test. In this test, homogenates of different organs were investigated for infectious virus titers on rat embryonic cell monolayers. We demonstrated that in the salivary gland, the major target organ for rat cytomegalovirus, virus was detectable from 8 days onward after intraperitoneal infection. To show that this model is suitable for the detection of immunotoxicity four different methods for immunosuppression were investigated: 1. γ-irradiation, 2. congenitally athymic rats, 3. chemically induced immunosuppression, 4. ultraviolet-B (UVB) irradiation. Rat cytomegalovirus titers in the salivary glands of irradiated (500 rad 1 day prior to infection) or congenitally athymic rats were significantly increased as compared to non-irradiated rats and euthymic control rats respectively. In TOX-Wistar rats, given 20 or 80 mg bis(tri-n-butyltin)oxide (TBTO) per kg food beginning 6 weeks before cytomegalovirus infection, a regimen known to have immunotoxic effects, cytomegalovirus titers in the salivary glands were significantly increased as compared to non-TBTO-treated cytomegalovirus infected rats. Exposure to a suberythemal doses of UVB, which is known to induce immunotoxic effects, induced a significant increase in cytomegalovirus titers in the salivary gland as compared to non-UVB-exposed rats. Therefore it is concluded that this infection model is suitable for the assessment of immunotoxic effects induced by enviromental components.

To investigate cellular electrophysiologic alterations due to lipid peroxidation of the cell membrane by free radicals as a possible cause of coronary reperfusion arrhythmias, we studied the effects of t-butyl hydroperoxide on the spontaneous action potential and membrane currents of the rabbit sinoatrial and atrioventricular node preparations (0.2 × 0.2 × 0.1 mm). 1–5 min of superfusion with t-butyl hydroperoxide (100–500 μM) caused a transient increase in the spontaneous firing frequency by 9%, accompanied by a 4% increase in the action potential amplitude and a 33% increase in the maximal rate of depolarization (P<0.05, n = 6). t-Butyl hydroperoxide then gradually suppressed physiological automaticity, but induced abnormal repetitive firing due to early and delayed after-depolarizations. 15 min of superfusion with t-butyl hydroperoxide caused a complete standstill of nodal cells at a resting potential of −46 ± 3 mV (n = 12). Such effects of t-butyl hydroperoxide on the spontaneous action potential were attenuated by pretreating the cells with butylated hydroxytoluene, a lipid peroxidation inhibitor. Voltage clamp experiments using double microelectrode methods revealed that t-butyl hydroperoxide transiently increased the Ca²⁺ current by 22% after 5 min of superfusion but subsequently reduced it to 46% of the control value after 15 min (P<0.05, n = 6). Similar biphasic changes were observed in the delayed rectifying K⁺ current and hyperpolarization-activated inward current (n = 6). Background current was progressively increased without any change in its reversal potential (n = 6). These results suggest that membrane lipid peroxidation may accelerate or suppress physiological automaticity and induce abnormal automaticity by both impairing cellula metabolic function and damaging the lipid membrane structure as well as ionic channel protein.

Results demonstrate for the first time that ethanol exerts two different effects on the lipid order of chick-liver mitochondria and microsomes: a fluidizing effect both in the core and at the surface of the membrane, which depends on its physical presence, and a rigidization of the surface of these membranes which occurs after its removal. In addition, and directly related to the reduction in fluidity produced in the membrane surface after ethanol removal, we have detected a persistent alteration in different enzyme activities involved in the hepatic mitochondrial and microsomal electron-transport systems. The persistence of the alterations in the lipid order and enzyme activities may result from a structural rearrangement of the lipid and protein components produced in the lipid bilayer surface when ethanol is no longer present in the membrane.

Interleukin-2 (15 μg/mouse, i.p. twice daily for 4 days and once on the 5th day) significantly lowered cytochrome P-450 and heme content and increased heme oxygenase mRNA accumulation; the activities of 7-ethoxycoumarin O-deethylase, ethoxy- and pentoxyphenoxazone O-dealkylases were decreased. The activity of the type O form of hepatic xanthine oxidase increased, but there was no increase in lipid peroxide, expressed in terms of microsomal malondialdehyde. In vivo inactivation of xanthine oxidase activity by feeding mice with tungstate did not substantially change the degree of interleukin-2-induced cytochrome P-450 depression, suggesting that the two processes are not causally linked. Induction of tolerance to endotoxin by a 4-day pretreatment with lipopolysaccharide resulted in 50% protection against this depression despite inhibition of the interleukin-2 induced formation of tumor necrosis factor. This suggests that the release of tumor necrosis factor per se does not fully account for the depression of cytochrome P-450. Dexamethasone, already used in patients to reduce toxicity of interleukin-2 therapy, provided full protection against the cytochrome P-450 depression.