Sevoflurane is biotransformed by guinea pig liver slices but causes minimal cytotoxicity

Guinea pig liver slices were used to evaluate the biotransformation and hepatotoxic potential of sevoflurane. Precision-cut liver slices (250-300 microns thick) were incubated in sealed roller vials in buffer at 37 degrees C under 95% O2. Sevoflurane was added to produce 0.9 or 2.1 mM medium concentrations. After incubation (6-24 h), the intracellular K+ content and protein synthesis were determined, along with the defluorination of sevoflurane. Isoflurane was included for comparative purposes. Sevoflurane (2.1 mM) and isoflurane (2.3 mM) had no effect on slice K+ content, but both anesthetics depressed protein synthesis. The biotransformation of sevoflurane was maximal at 95% O2, with threefold more F- produced from sevoflurane than isoflurane. Sevoflurane appears to have a minimal effect on the guinea pig liver slices, which is consistent with in vivo studies in which minimal or no hepatotoxicity has been observed.

Corneal toxicity study of two perfluorocarbon liquids in rabbit eyes

Perfluorocarbon liquids are fully fluorinated, synthetic, transparent compounds with a high specific gravity. These compounds are being increasingly used as an intraoperative tool for repair of complicated retinal detachments. A potential complication of their use, however, is liquid entering the anterior chamber in aphakic patients. In the study described herein we evaluated the effects of two of these liquids when placed in the anterior chamber of the rabbit eye. Sixteen rabbit eyes underwent anterior chamber injection of 0.05 ml of either perfluoroctane, perfluoropolyether, or balanced salt solution (control eyes). Animals were monitored clinically by biomicroscopy and external photography for up to 14 days, after which they were sacrificed and the corneas processed for light and for scanning electron microscopy. The animals injected with perfluoropolyether showed more intense stromal inflammation and corneal vascularization (p less than 0.02) than did those that received perfluoroctane. However, the perfluoroctane group showed more of the "fish-egging" phenomenon (p less than 0.03). Loss of endothelial cells was similar in the two groups, as determined by light and scanning electron microscopy. These results suggest that the corneal toxicity of these two perfluorocarbon liquids is such that their use as vitreous substitutes should be limited to short-term replacement.

[Substantiation of maximum permissible water level of the flotation reagent EFK-1]

Threshold concentrations of the flotation reagent EFK-1 in the water of reservoirs at 0.8 mg/l and 10.0 mg/l for organoleptic and total sanitary indices, respectively, were reported. Dl50 was 7469 mg/kg. The MAC of 0.8 mg/l for EFK-1 in the water of reservoirs (the limiting sign is organoleptic) was proposed.

Laboratory and epidemiologic studies of fecapentaenes

Fecapentaenes are a class of conjugated ether lipids which have been identified as the major component of human fecal mutagenicity in the Ames Salmonella mutagenesis assay. Human epidemiologic data have indicated that most healthy North American populations eating a western diet do excrete detectable levels of fecapentaenes. Excreted fecapentaene levels seem to reflect levels throughout the colonic lumen, and levels vary characteristically between individuals. Those individuals found to excrete high levels of fecapentaene appear, based on limited data, to be at decreased risk of colorectal neoplasia. Carcinogenicity studies in rats and mice have been predominantly negative, however, increased tumor incidence in mice exposed to fecapentaenes as neonates has recently been reported. Fecapentaenes are direct-acting genotoxins, which may react with DNA through free radical mechanisms, and/or aldehyde formation. Mechanisms by which fecapentaene-induced DNA damage may mediate carcinogenesis are discussed.

Inhibition of protein synthesis and secretion by volatile anesthetics in guinea pig liver slices

The decrease in protein synthesis and secretion caused by volatile anesthetics was investigated using Hartley male guinea pig liver slices. Precision-cut liver slices (250-300 mM thick) were incubated in sealed roller vials (3 slices/vial) containing Krebs-Hensleit buffer at 37 degrees C under 95% O2 atmosphere. Volatile anesthetics were injected through a teflon septa cap on a filter paper wick and vaporized to produce constant concentration in the medium. A concentration (1-2.1 mM) and time related (0-24) decrease in protein synthesis (3H-leucine incorporation) and secretion by halothane and d-halothane was observed. d-Halothane was less inhibiting than halothane. Inhibition was not on the uptake of the 3H-leucine but with its incorporation in the nascent peptide. The effects of enflurane (2.2 mM), isoflurane (2.2 mM), and sevoflurane (1.3 mM) on protein synthesis and secretion were also studied. The rank order of decrease in protein synthesis caused by the volatile anesthetics studied was halothane greater than isoflurane greater than enflurane greater than sevofluane greater than d-halothane. Enflurane, isoflurane, and sevoflurane increased the protein secretion while halothane and d-halothane caused a pronounced decrease. Alterations in protein synthesis and secretion appears to be an early and sensitive indicator of cytotoxin injury.

Toxicity of halothane in guinea pig liver slices

Guinea pigs have proven to be a reliable model of halothane associated hepatotoxicity. An in vitro system with Hartley male guinea pig liver tissue was designed to assess the toxicity of halothane and other volatile anesthetics in the target organ. Precision-cut guinea pig liver slices (250-300 microns) were incubated in sealed roller vials containing Krebs-Henseleit buffer (plus vitamins, amino acids, glutamine, gentamycin) at 37 degrees C, under 95%, 21% and 5% O2/CO2 atmospheres. Halothane (10-15 microliters) was injected through a Teflon septa cap on a filter paper wick and vaporized. Viability of the slices was monitored by measuring intracellular K+ content which was maintained under 95% O2 up to 24 h. A dose- and time-related decrease in intracellular slice K+ by 1.9, 2.1, 2.7 mM halothane in the media was observed. At 2.7 mM halothane a direct physio-chemical effect may be occurring since incubating liver slices from allylisopropyl-acetamide-treated animals did not protect against the drop in intracellular K+. Concentration/time responses of halothane, d-halothane, enflurane, isoflurane and sevoflurane were compared. Sevoflurane had no effect on the liver slice K+ content up to 24 h while the other anesthetics caused the following rank-order decrease in intracellular K+ content: halothane greater than isoflurane and enflurane greater than d-halothane. Precision-cut cultured guinea pig liver slices offer a system where the target tissue for intoxication by anesthetics can be examined for its susceptibility and mechanism of intoxication.

Synthesis of perfluoroalkylated xylitol ethers and esters: new surfactants for biomedical uses

New, well-defined surfactants and cosurfactants were synthesized with the objective of enhancing the stability of fluorocarbon emulsions destined to serve as oxygen carriers for biomedical applications. Monoperfluoroalkylated ethers of xylitol were achieved by addition of perfluoroalkyl iodide on the double bond of a protected xylitol allyl ether in a one-step addition-elimination reaction. Monoesters were obtained specifically on position 5 by treating 1,2:3,4-di-O-isopropylidenexylitol with perfluoroalkylated acid chlorides of various chain lengths in pyridine at room temperature. The products display strong surface activity and produce a remarkable synergistic stabilization of a fluorocarbon/Pluronic F-68 type emulsion. Biocompatibility data are reported, which include in vitro toxicity tests on Namalva cell cultures and hemolysis tests on human blood cells; the latter was found to decrease as the length of the F-alkyl chain increased. IV injection in mice (n = 10) showed that these products were innocuous at 400-1000 mg/kg of body weight. Preliminary exchange-perfusion experiments on rats with an emulsion containing the F-octyl xylitol ether were encouraging.

Tissue response of the biliary and digestive system of rabbits after MTBE infusion into the gallbladder

We evaluated the tissue response of the biliary and digestive system after Methyl-tert-Butyl-Ether (MTBE) gallbladder infusion in 32 rabbits. After laparotomy, MTBE (5-11 ml) was infused into the gallbladder for eight hours. Animals were sacrificed after eight hours or after two months. Control animals received saline solution infusion into the gallbladder. Afterwards the gallbladder, the common bile duct, the liver, the pancreas and the duodenum were examined histologically. All animals receiving MTBE had different degrees of gallbladder necrosis, common bile duct necrosis and necrosis of intrahepatic bile ducts. After two months, scar formation and a hyperplastic cholecystitis were observed. Control animals did not have comparable tissue reactions; only small areas of necrosis in the gallbladder and the common bile duct occurred after eight hours. The gallbladder, common bile duct and liver remained unchanged in those animals which survived two months. Although the results of this animal study cannot be directly transferred to humans, the data suggest that MTBE should be used in gallstone therapy with caution, and that if it is used, a well-controlled follow-up of these patients is necessary.

Selection for increased desiccation resistance in Drosophila melanogaster: additive genetic control and correlated responses for other stresses

Previously we found that Drosophila melanogaster lines selected for increased desiccation resistance have lowered metabolic rate and behavioral activity levels, and show correlated responses for resistance to starvation and a toxic ethanol level. These results were consistent with a prediction that increased resistance to many environmental stresses may be genetically correlated because of a reduction in metabolic energy expenditure. Here we present experiments on the genetic basis of the selection response and extend the study of correlated responses to other stresses. The response to selection was not sex-specific and involved X-linked and autosomal genes acting additively. Activity differences contributed little to differences in desiccation resistance between selected and control lines. Selected lines had lower metabolic rates than controls in darkness when activity was inhibited. Adults from selected lines showed increased resistance to a heat shock, 60Co-gamma-radiation, and acute ethanol and acetic acid stress. The desiccation, ethanol and starvation resistance of isofemale lines set up from the F2s of a cross between one of the selected and one of the control lines were correlated. Selected and control lines did not differ in ether-extractable lipid content or in resistance to acetone, ether or a cold shock.

Tissue distribution metabolism and excretion of 2,2',4,4',5-pentachlorodiphenyl ether in the rat

The tissue distribution, metabolism and excretion of 14C-2,2',4,4',5-pentachlorodiphenyl ether (PCDE) were studied in the rat. Radioactivity was distributed in all tissues examined, with the highest concentrations being found in the fat followed by the skin, liver, kidney and muscle. Most of the radioactivity found in the tissues was due to unchanged PCDE. Decay of PCDE in the blood was fitted to a four-compartment pharmacokinetic model, and the last compartment had a half-life of 5.8 days. A total of 55% and 1.3% of an orally administered dose was excreted in feces and urine, respectively, in 7 days. More than 64% of the fecal radioactivity was due to unchanged PCDE, while hydroxylated PCDE accounted for 23%.

The genetic toxicology of some hydrocarbon and oxygenated solvents

Two hydrocarbon solvents (heptane and Special Boiling Point Spirit 100/140) and eight oxygenated solvents [methyl ethyl ketone, methyl isobutyl ketone, diacetone alcohol, di-isobutyl ketone, isopropyl ether, hexylene glycol, secondary butyl alcohol and ME 6K (pentoxone)] have been tested for genotoxic activity. The solvents were tested in bacterial mutation assays, a yeast assay for mitotic gene conversion and in cultured mammalian cells (either rat liver or Chinese hamster ovary) for structural chromosome damage. All of the solvents gave a negative response in the bacterial mutation assays and the yeast mitotic gene conversion assay. In the rat liver chromosome assay, diacetone alcohol evoked a weak positive response, the remaining solvents gave a negative response.

Methyl tertiary butyl ether inhalation in rats: a single generation reproduction study

Male rats exposed to target concentrations of methyl tertiary butyl ether (MtBE) at 300, 1300 and 3400 ppm for 6 hours/day, 5 days/week for 12 weeks were mated to female rats exposed to the same concentrations for a 3-week period. Exposures continued through the mating period and the females continued exposures during gestation and from days 5-21 lactation of the litters (F1a) (no exposures days 0-4 lactation). A second litter (F1b) was produced under the same mating and post mating exposure regimen. No adverse effect of treatment was observed with the adult animals (Fo) throughout the in-life portion of the study. The only remarkable finding was an increased incidence of dilated renal pelves in the low- and high-dose females (Fo). All gonad weights, male accessory reproductive organ weights, organ-to-body weight ratios and reproductive organ histopathology were unremarkable upon comparison of treated animals with air sham controls. The mating indices and fertility indices in exposed animals for both mating intervals (F1a and F1b) were not significantly different from controls. Pregnancy rates were comparable between treated and control females for the first litter interval (F1a) but were slightly lower (not statistically significant) than control on the second litter interval (F1b). Treated animal mean gestation length and the mean number of pups at birth were not statistically different from controls. The pup viability indices at birth were comparable for control and treated groups for the F1a generation, but the mid- and high-dose groups displayed a slight statistically significant decrease in the F1b generation; the decrease was not considered to be biologically significant and perhaps not treatment-related. Litter survival indices were comparable between control and treated groups for both litter intervals. Pups of mid- and high-dose females had slightly lower (not statistically significant) mean weights at days 14 and 21 of lactation but this was not considered treatment-related. The most frequent post-mortem observation for pups sacrificed at day 21 of lactation was dilated renal pelves. This did not appear to be related to treatment. It is concluded that MtBE inhalation in rats results in little adverse reproductive toxicity as shown in a two litter, one generation reproduction assay in rats.

Toxicity of sevoflurane in rats

Sevoflurane, an experimental potent volatile anesthetic with a low blood/gas partition coefficient, degrades in the presence of soda lime to products the toxicity of which is unknown. We tested whether toxic products were produced by the passage of sevoflurane through soda lime, and a comparison was made of the toxicity of sevoflurane passed through soda lime with the toxicity of other potent volatile anesthetics in current clinical use. Halothane, isoflurane, sevoflurane (all in 1-MAC concentrations), or no anesthetic (control) were passed through soda lime for 4 hr with 12, 14, or 100% oxygen to groups of rats with hepatic microsomal enzyme induction. Separate groups of 12-13 rats were given 1 MAC of sevoflurane that had not passed through soda lime and either 14 or 100% oxygen. Sevoflurane was no more toxic than isoflurane and both of these anesthetics were less toxic than halothane. Soda lime was not a factor in any toxicity produced. Hepatic injury with all agents varied inversely with the oxygen concentration administered during anesthesia.

Vesicular demyelination induced by raised intracellular calcium

Incubation of nerve with high concentrations of the divalent cation ionophore A23187 produces myelin vesiculation (Schlaepfer 1977). This observation has now been extended using segments of rat ventral or dorsal root incubated with high (19 microM, 10 micrograms/ml) or low (1-1.5 microM) concentrations of A23187, or another divalent ionophore, ionomycin. Low concentrations of A23187 induced no vesiculation within a 2-h period. However, subsequent incubation of these roots in fresh, ionophore-free medium for 20 h, resulted in a prominent vesicular demyelination at the Schmidt-Lanterman incisures and paranodes of many fibres. At this time (22 h) the Schwann cells associated with some demyelinating internodes appeared vital upon ultrastructural examination: the cells also excluded the nuclear dye nigrosin. High concentrations of A23187 induced a similar vesicular demyelination in affected fibres within only 15-20 min. While the Schwann cells continued to exclude nigrosin for a further 4 h, their ultrastructural appearance indicated that they were probably in the early stages of necrosis. Incubation of moribund root with the ionophore produced no myelin vesiculation. At all ionophore concentrations, the myelin vesiculation was dependent upon the presence of extracellular Ca2+, and could be modulated in severity by varying this concentration. Other divalent cations (Ba2+, Co2+, Mg2+, Mn2+, Ni2+, Sr2+) could not substitute for Ca2+. The vesiculation induced by A23187 could be entirely prevented by the addition of Zn2+ (greater than or equal to 1 microM), Ni2+ (greater than or equal to 1-10 microM), Co2+ (greater than or equal to 100 microM) or Mn2+ (greater than or equal to 100 microM) to the bathing medium. A23187 applied to only part of an isolated internode resulted in a localization of the myelin disruption to that region. Ionomycin (greater than or equal to 1 microM), an ionophore with a greater selectivity for Ca2+ than A23187, also induced a prompt Ca2+-dependent myelin vesiculation. We conclude that vesicular demyelination can be initiated in vital Schwann cells by a raised intracellular Ca2+ concentration. Such demyelination does not necessarily lead to Schwann cell death. The possible relevance of the findings to vesicular demyelinating neuropathies is discussed, and a hypothesis regarding the mechanism of demyelination is advanced.

Biochemical effects of methyl tertiary-butyl ether in extended vapour exposure of rats

Male Wistar rats exposed to 50, 100 or 300 ppm methyl tertiary-butyl ether vapour for 2-15 weeks, 6 h daily, 5 days a week, showed a dose-dependent blood ether concentration after 2 weeks' exposure. Blood concentrations of tertiary-butanol, were also dose dependent indicating metabolic breakdown of the ether in vivo. The blood ether concentrations decreased after 6 weeks of exposure at the 50 ppm dose level and remained unaffected at higher doses while tertiary-butanol concentrations increased after 6 weeks with all doses, and began to decrease thereafter. Exposure caused a transient increase in UDP-glucuronosyltransferase activities in liver and kidney microsomes, almost no effects on hepatic cytochrome P-450 concentrations and a minor induction of kidney microsomal cytochrome P-450 content. Exposure produced almost no effect on brain succinate dehydrogenase, creatine kinase or acetylcholinesterase activities, while early inhibition of muscle creatine kinase activity was noted, accompanied by increased activity at the end of exposure.

Mutagenicity of inhaled anesthetics in Drosophila melanogaster

The mutagenic effects of several inhaled anesthetic agents were investigated using the sex-linked recessive lethal assay in the fruit fly, Drosophila melanogaster. Male wild-type flies were exposed for 1 hr to either halothane, enflurane, isoflurane, or fluroxene at vapor concentrations of 1 or 2% or to nitrous oxide at concentrations of 40 or 80%. Control flies were exposed to air alone. Following treatment, male flies were mated with untreated virgin females of the Basc strain and the rate of sex-linked recessive lethals was determined in the F2 generation. Halothane and fluroxene produced a dose-dependent and statistically significant increase in the rate of sex-linked recessive lethals, whereas enflurane, isoflurane, and nitrous oxide were not mutagenic at the concentrations tested.

Propyl ether. I. Interaction with the sensory irritant receptor

The sensory irritating response of propyl ether, measured as a decrease in respiratory rate in mice, faded within one minute. The threshold was 620 p.p.m., calculated from the concentration-response curve, which had a low slope. The sensory irritating level depressing the respiratory rate to 50 per cent (RD-50 = 89,000 p.p.m.) could not be reached with saturated vapour at 20 degrees. The thermodynamic activity corresponding to the RD-50 was about 0.6, a rather high value. The low slope and high thermodynamic activity may be explained by steric hindrance of the oxygen atom and thereby decreasing the receptor-activating capacity and/or the stability of the active receptor conformation. A specific effect beyond the receptor offers another explanation.

Propyl ether. II. Pulmonary irritation and anaesthesia

After cessation of the sensory irritation response, described in part one (Nielsen et al. 1985), a mixed response due to pulmonary irritation and anaesthesia appeared, resulting a decrease in respiratory rate and tidal volume. The corresponding thresholds were 1490 p.p.m. and 1280 p.p.m., respectively, obtained from the last half hour of a four hours exposure period. As the decrease in respiratory rate and tidal volume was found to be correlated, the per cent decrease in respiratory minute volume could be approximated from the square of the respiratory frequency. A threshold limit value (TLV) about 100 p.p.m. based on pulmonary irritation and anaesthesia was proposed. No impurities in the technical grade ether influenced the responses.

Teratology evaluation of methyl tertiary butyl ether in rats and mice

Mated CD Sprague-Dawley rats and CD-1 mice were exposed during the period of organogenesis to target concentrations of 0, 250, 1000, and 2500 ppm methyl t-butyl ether (MTBE). None of the control or test-group animals died during the treatment or posttreatment periods. Females were sacrificed on d 20 (rats) or d 18 (mice). No adverse effects of treatment were reflected in maternal parameters of body weight, water consumption, or liver weight or in physical examination data for either species. Food consumption fell in the groups of treated rats during d 9-12; similar but nonsignificant effects were observed for mice during d 12-15. In rats, no treatment-related changes were recorded in the uterine implantation data, fetal size parameters, or fetal sex distribution data. Examination of fetuses for external abnormalities, skeletal malformations, or ossification variations did not reveal any changes caused by MTBE exposure. A slight increase in fetal resorptions was observed in the groups of mice exposed to low and high concentrations; this increase was attributed to two females in each group that had an unusually high number of resorptions, rather than to the treatment itself. No significant effects were observed in any groups of treated mice on external and soft-tissue examination or evaluation of skeletal abnormalities or ossification variations. The incidence of fused sternebrae in the high-concentration group increased slightly, which might be attributed to fetotoxicity.

Acute toxicity of fluorinated ether anesthetics: role of 2,2,2-trifluoroethanol and other metabolites

The fluorinated ethers 2,2,2-trifluoroethyl vinyl ether (TFVE), 2,2,2-trifluoroethyl ethyl ether (TFEE), and 2,2,2-trifluoroethyl allyl ether (TFAE) are lethal to rats pretreated with a variety of cytochrome P-450-inducing agents at doses not toxic to uninduced rats. The hepatic microsomal cytochrome P-450-catalyzed metabolic pathways have been elucidated: TFVE yields 2,2,2-trifluoroethanol (TFE) and glycolaldehyde; TFEE yields TFE and acetaldehyde; and TFAE yields TFE and acrolein. Time courses of metabolite concentrations in blood after administration of toxic doses of metabolites or anesthetics to variously induced rats were compared. For TFVE, phenobarbital (PB) or pregnenolone-16 alpha-carbonitrile (PCN) induction increased acute lethality 3.1- and 2.4-fold respectively, and blood TFE concentrations reached lethal levels. beta-Naphthoflavone (BNF) induction did not produce lethality and TFE concentrations did not reach lethal levels. Glycolaldehyde concentrations did not approximate lethal levels in any case. For TFEE, PB, BNF, or PCN induction increased lethality 3.4-, 2.6-, and 2.0-fold respectively, and TFE concentrations exceeded lethal levels in all cases. Acetaldehyde concentrations did not approximate lethal levels in any case. For TFAE, BNF, or PCN induction increased lethality 3.2- and 4.6-fold respectively, and TFE concentrations approached lethal levels. PB induction did not produce lethality nor did TFE concentrations reach lethal levels. Blood acrolein concentrations could not be determined. Thus the lethal effects of the three anesthetics arise from specific cytochrome P-450 isozyme-catalyzed metabolism to TFE. The relative rates of formation of TFE from the three anesthetics, catalyzed by microsomes from untreated and variously induced rats, supported this conclusion.