Mode of action of trichloroethylene on squid axon membranes

The mode of action of trichloroethylene on electrical properties of squid giant axons has been studied by means of voltage clamp techniques. Trichloroethylene decreased the resting membrane potential in a manner dependent upon the concentration, the depolarization by 50% saturated trichloroethylene attaining 28.4 and 32.7% of the initial value at 20 and 10 degrees C, respectively. Leakage conductance was decreased to 34.6% of the control by 30% saturated trichloroethylene at 10-12 degrees C. It appears that the trichloroethylene-induced depolarization is at least in part due to a decrease in resting potassium permeability. Both peak transient and steady-state conductance increases were suppressec by trichloroethylene, and the curve relating the steady-state conductance to the membrane potential was shifted in the depolarizing direction while the peak transient conductance curve was not appreciably shifted. The reversal potential for the peak transient current was greatly shifted by trichloroethylene in the direction of hyperpolarization in a manner dependent on the concentration, the maximum shift amounting to 25 mV at 10 degrees C. This effect was less pronounced at 20 degrees C. The shift in the reversal potential is mostly due to a decrease in selectivity of the peak transient channel and partly due to an accumulation of sodium ions inside. Analyes of dose-response relation in suppressing peak transient and steady-state conductances show that trichloroethylene interacts with receptor on a one-to-one stoichiometric basis. Steady-state sodium inactivation curve was shifted by trichloroethylene in the direction of hyperpolarization. All of these effects were partially reversed after washing the axon with anesthetic-free media. The accumulation of sodium ions inside would be much more pronounced in small nerve fibers in the brain than in giant axon and, together with the observed decrease in the selectivity of peak transient channels, would play a significant role in general anesthesia.

Effects of 1,1,1-trichloroethane administered by different routes and in different solvents on barbiturate hypnosis and metabolism in mice

A 24-hr inhalation of 1,1,1-tricholoroethane (methylchloroform), 3,000 ppm, reduced pentobarbital hypnosis and increased hexobarbitaloxidation by the 9,000 x g liver supernatant fraction in male mice. On the other hand, an ip injection of methylchloroform, l ml/kg, increased the duration of pentobarbital hypnosis and reduced hexobarbital metabolism by the liver microsomal enzymes. The potentioating effect of methylchloroform on pentobarbital hypnosis as diminished when it was diluted with olive oil, but was markedly enhanced when diluted with dimethysusoxide (DMSO) before injection. Three local applications of methylchloroform )1:1 dilution with DMSO) had an effect similar to that of inhalation on pentobarbital hypnosis.

Behaviour of rats exposed to trichloroethylene vapour

Rats were exposed to trichloroethylene (TCE) vapour for about five five-day weeks at concentrations from 100 to 1 000 ppm, and at 100 ppm for 12 1/2 weeks. The social behaviour of paired male rats was observed periodically in the home cage for five minutes after they had been exposed to TCE. The principal finding was a consistent reduction of up to 24% in the total acitivity. A single day's exposure to TCE was sufficient at the highest concentration. At 100 ppm, a similar decline in activity was significant after 1 1/2 weeks' exposure in one experiment and 8 1/2 weeks' in another. The decline in activity was fairly uniform and not usually because of specific reductions in particular kinds of behaviour. However, exploration of the cage and submission to, or escape from, the other rat were sometimes specifically reduced. In an 'exploration-thirst' test, rats were deprived of water overnight and placed on two or three occasions in a previously unfamiliar cage. Rats exposed to 100, 200, or 1 000 ppm TCE found water and began drinking sooner than their controls without altering the rate of movement about the cage. These results suggest lowered performance in a familiar situation where rats are usually very active and some loss of inhibitory control in an unfamiliar one. At the present threshold limit value, repeated exposure to TCE eventually had effects similar to those of one day's exposure to a higher concentration, but only after a widely variable delay.

The actions of volatile anaesthetics on synaptic transmission in the dentate gyrus

1. The action of four volatile anaesthetics on the evoked synaptic potentials of in vitro preparations of the hippocampus were examined. 2. All four anaesthetics (ether, halothane, methoxyflurane and trichloroethylene) depressed the synaptic transmission between the perforant path and the granule cells at concentrations lower than those required to maintain anaesthesia in intact animals. 3. The population excitatory post-synaptic potential (e.p.s.p.) and massed discharge of the cortical cells (population spike) were depressed at concentrations of the anaesthetics lower than those required to depress the compound action potential of the perforant path nerve fibres. None of the anaesthetics studied increased the threshold depolarization required for granule cell discharge. Furthermore, frequency potentiation of the evoked cortical e.p.s.p.s was not impaired by any of the anaesthetics studied. 4. It is concluded that all four anaesthetics depress synaptic transmission in the dentate gyrus either by reducing the amount of transmitter released from each nerve terminal in response to an afferent volley, or by decreasing the sensitivity of the post-synaptic membrane to released transmitted or by both effects together.

Effect of volatile anaesthetics on cell survival as measured by colony forming ability

Chinese hamster fibroblast cells in stirred suspension cultures were exposed to volatile anaesthetic agents for 3 hr or for 24 hr. Cell viability was measured as colony forming ability and was found to be reduced, in a dose related manner, by halothane, chloroform, methoxyflurane, trichloroetheylene and diethyl ether.

Mitosis in mammalian cells during exposure to anesthetics

The effects of methoxflurane, trichloroethylene, chloroform, halothane and diethyl ether on the division of Chinese hamster fibroblasts in spinner culture have been studied. All agents caused dose-dependent inhibition of cell multiplication. Halothane increased the cell cycle time roughly in accordance with its effect on multiplication rate. There was no evidence that mitosis was greatly prolonged, and only small numbers of "c-metaphases" were seen. However, exposure to halothane resulted in a marked and rapid reduction in the prophase count, suggesting prolongation of G2 (the post-synthetic phase). Cine-photo-micrography showed frequent delay in division of cytoplasm at mitosis, and many binucleate cells were seen.

Reduction of hypoxic pulmonary vasoconstriction during trichloroethylene anesthesia

A double-lumen tube was inserted into the trachea of dogs anesthetized with intravenous pentobarbital (30-40 mg/kg). Blood flow/unit lung volume in each lung was measured with 133Xe. Both lungs were initially ventilated with oxygen and measurements of pulmonary blood flow, CO2 output, cardiac output, and blood gases were made. When nitrogen was administered to one lung blood flow was diverted to the opposite lung. The diversion of flow was reduced by the inhalation of 1% trichloroethylene but returned after withdrawal of the anesthetic. There were no significant changes in cardiac output. Changes in CO2 output and arterial Po2 were compatible with the xenon results. It is concluded that trichloroethylene may increase arterial hypoxemia by reducing vasoconstriction in hypoxic areas of lung.

Comparative site of action of various anaestetic agents at the mammalian myoneural junction

Pre- and postjunctional effects of three ethers (enflurane, diethyle ether, and methoxyflurane) and three non-ethers (chloroform, halothane, and trichloroethylene) were studied in the rat phrenic nerve diaphragm preparation using standard microelectrode recording techniques. Depression of postjunctional function included depression of the amplitude of miniature endplate potentials, inhibition of suxamethonium induced depolarization of the muscle endplate, prolongation of duration of the endplate potential, and increase in threshold for generation of the muscle action potential. The last two effects were more marked for the ethers than for the non-ethers. Effects on pre-junctional function included a slight increase in fluctuation of the endplate potential (EPP) amplitude associated with the thers and chloroform, a faster rate of decline of EPP amplitude during a tetanus in presence of the ethers, and prolongation of the normal facilitatory period during paired stimulation in the presence of chloroform. Chloroform had no effect on the rate of decline of EPP amplitude during tetanic stimulation and the ethers had no effect on the facilitatory period during paired stimulation. These results indicate that volatile anaesthetic agents depress synaptic transmission by acting on multiple sites, and that the pattern of this depression is different for each drug or group of similar drugs.

[Swelling and loss of potassium in perfused livers following the influence of the vapours of carbon tetrachloride, chloroform and halothane on the perfusion medium (author's transl)]

Erythrocyte free perfused rat livers were treated with vaporous carbon tetrachloride, chloroform and halothane by equilibration in the oxygenator system. The potassium loss, the amount of swelling and the alteration of the perfusion rates were measured during the experiments as criteria of acute toxicity. In contrast to the well known behaviour of perfused livers during the intoxication with phalloidin the amount of liver swelling did not marekdly depend on the perfusion rates in acute CCl(4) poisoning. The mechanism of swelling must be different in both intoxications. Exposure of perfused livers to high concentrations of CCl(4) for several minutes only produced a marked K-+-loss within a short time. This injury could not be fully compensated after finishing the exposure. Dose response diagrams are presented for carbon tetrachloride, chloroform and halothane by use of the following criteria: potassium loss, swelling (increase of wet weight) and perfusion rates (ml.min-1.g-1). As total doses the amounts of solutes vaporized during the exposition were listed. In these diagrams chloroform appears to be more toxic than halothane. CCl4 occupies a middle position between chloroform and halothane. The course of dose response diagrams of halothane is different from those of CCl(4) and CHCl(3). The halothane diagrams increase critically at high doses, whereas the courves for CCl(4) and CHCl(3) rise continuously. With respect to effects on the hepatic microcirculation halothane seems to be less toxic than CCl(4). The results are discussed on the basis of the periods of exposition and the maximal concentrations of the solutes in the perfusion medium. With respect to these data CCl(4) is much more toxic than CHCl(3) and halothane. On the other hand there is no marked difference in acute hepatotoxicity between CHCl(3) and halothane.

[Psychomotor responses under standardized trichloroethylene load (author's transl)]

20 volunteers were exposed for 4 hrs to a concentration of trichloroethylene in room air of 95 ppm. Before and after exposure the Wiener Determinationsgerät, the Wiener Reaktionsgerät, and the motorische Leistungsserie (Schoppe) were used to perform 6 tests, each of which gave 15 measurements. A comparison with the results of a blank test which had been obtained 1 week before with the same volunteers under the same conditions, but without the use of trichloroethylene, yielded no statistically significant impairment of the psychomotorial function by trichloroethylene. Further investigations are being carried out.

Effects of general anaesthesia on the intraocular pressure in man. Trichloroethylene in nitrous oxide and oxygen

The effect of TCE on the intraocular pressure was investigated in eight patients under thiopentone nitrous oxide/oxygen anaesthesia, using a muscle relaxant (pancuronium bromide). Pulmonary ventilation was controlled and the end-tidal carbon dioxide was maintained at 5 per cent. In every patient the intraocular pressure was observed to rise as TCE was administered and then to return to the initial level when the administration of TCE ceased.

The Effect of Inhalational Anaesthetics on the Swimming Velocity of Tetrahymena Pyriformis

The effect of 6 inhalational anaesthetics on speed of swimming (produced by ciliary movement) has been studied in Tetrahymena pyriformis. There was no evidence of stimulation at low dose levels and higher levels caused rapid, reversible, dose-dependent reduction in swimming velocity. The concentrations of anaesthetics which depressed motility by 50% were of the same order as those required for anaesthesia in mammals, except in the case of cyclopropane, for which the required level was 4 times higher than the anaesthetic level. Correlation with lipid solubility was not as close as is the case for narcotic concentration. Oxygen consumption was reduced with increasing amounts of halothane in parallel with the reduction in swimming velocity. Halothane produced deciliation of Tetrahymena at about 10 times the anaesthetic dose for man; regrowth of cilia took place within 4 h of withdrawal of the drug. There were no changes in the ultrastructure of the cilia, basal bodies and associated microtubular systems at levels of halothane sufficient to stop cilial beat. At higher concentrations deciliation occurred immediately distal to the axosome and there was variable swelling of the mitochondria.