Jeffrey M. Baden

Halothane, isoflurane, and enflurane MAC in pregnant and nonpregnant female and male mice and rats.

The MAC of halothane, isoflurane, and enflurane was determined using the tail-clamp technique in pregnant female, nonpregnant female, and male Swiss Webster mice (n = 216) and Sprague-Dawley rats (n = 112). Mean MAC values (+/-SD) for halothane, isoflurane, and enflurane in mice were 0.95 +/- 0.07%, 1.34 +/- 0.10%, and 1.95 +/- 0.16%, respectively; values in rats were 1.03 +/- 0.04%, 1.46 +/- 0.06%, and 2.21 +/- 0.08%, respectively, all significantly higher than in mice. Neither the sex of the animals nor whether female animals were pregnant influenced the results.

Evidence for an adrenergic mechanism in the control of body asymmetry

The effect of phenylephrine, an alpha-1 adrenergic agonist, on development of body asymmetry was studied using a rat whole embryo culture system. Embryos were explanted at the presomite stage, cultured in 100% rat serum containing various concentrations of phenylephrine, and examined at the 20-25 somite stage for sidedness of asymmetric body structures, namely, bulboventricular loop, allantoic placenta, and tail. Phenylephrine treatment resulted in a dose-dependent increase of situs inversus with a maximum incidence of 52%. Coadministration of prazosin, an alpha-1 adrenergic antagonist, almost completely prevented this effect. Our results suggest that receptor-mediated stimulation of the alpha-1 adrenergic pathway is involved in the control of normal body asymmetry in developing rat embryos.

Methionine Prevents Nitrous Oxide-induced Teratogenicity in Rat Embryos Grown in Culture

BackgroundNitrous oxide (N2O)-induced teratogenicity in rats is commonly believed to be due to decreased tetrahydrofolate, which results in decreased DNA synthesis. The role of decreased methionine has been largely ignored as have the sympathomimetic effects of N2O. MethodsA rat whole-embryo culture system was used to determine whether N2O-induced teratogenicity can be prevented with supplemental methionine or folinic acid and whether N2O-induced situs inversus is mediated by α1-adrenergic stimulation. Embryos were explanted on day 9 of gestation, and those at stage 10b (late primitive streak stage) were cultured with or without N2O and the various chemicals, methionine (25 μg · ml-1), folinic acid (5 μg · ml-1), phenylephrine (range 0.5–50 μM) and prazosin (10 μM). Embryos in the N2O groups were exposed to a concentration of 75% for the first 24 h of culture. After 50 h of culture, embryos were examined for abnormalities including situs inversus. ResultsTreatment with N2O alone resulted in increased incidences of malformations and growth retardation. Methionine, but not folinic acid or prazosin, almost completely prevented N2O-induced malformations and growth retardation. N2O Itself did not cause situs inversus but increased the incidence of phenylephrine-induced situs inversus. This additive effect was blocked by prazosin. ConclusionsOur results indicate that decreased methionine rather than decreased tetrahydrofolate plays the major role in N2O-induced teratogenicity in rats. They also Indicate that N2O stimulates the α1-adrenergic pathway in the embryo and thereby increases the incidence of phenylephrine-induced situs inversus.

Mutagenicity of Halogenated Ether Anesthetics

An in vitro microbial assay system employing two histidinedependent strains of Salmonella typhimurium, TA1535 and TA100, was used to test the mutagenicities of enflurane, methoxyflurane, isoflurane and fluroxcne. Enflurane, isoflurane and fluroxene in concentrations ranging from 0.01 to 30 per cent and methoxyflurane in concentrations ranging from 0.01 to 7 per cent were incubated with bacteria in the presence or absence of homogenates of liver prepared from rats pretreated with the enzyme inducer, Aroclor 1254. Enflurane, methoxyflurane, isoflurane, and urines from patients anesthetized with these agents were not mutagenic. Fluroxene, however, was highly mutagenic, and therefore poses a possible hazard for operating room personnel and patients.

Mutagenicity of Volatile Anesthetics: Halothane

The mutagenicity of halothane was tested In an < in-vitro microbial assay system employing two histidine-dependent mutants of Salmonella typhimurium, TA9S and TA100. Halothane in concentrations ranging from 0.1 to 30 per cent was incubated with bacteria in the presence or absence of a metabolic activation system prepared from either nit liver treated with Aroclur 1254 or human liver. Trifluoroacelic acid, a major metabolite of halothane, and urine from patients anesthetized with halothane also were tested. Halothane, trifluoroacetic acid, and patients* urines were not mutagenic.

Carcinogenicity of halothane in Swiss/ICR mice.

: A simplified in-vivo bioassay system was used to test the carcinogenic potential of halothane in Swiss/ICR mice. Halothane was tested only at its maximum tolerated dose, and histologic examination was performed only on tumor masses and other grossly abnormal tissues found at necropsy. Two groups, each of 15 timed pregnant mice, were exposed to either halothane, 500 ppm (0.05 per cent), or compressed air for two hours on days 10--19 of pregnancy. Five days after birth the offspring were similarly exposed, three times weekly, for 78 weeks. After a ten-week, no-treatment, observation period, all remaining mice were examined by necropsy. Mice dying or killed in extremis before final sacrifice at 88 weeks of age also underwent complete gross necropsy unless extensive cannibalism or autolysis precluded examination. The incidences of malignant tumors, hepatomas or modular hyperplasias, and benign tumors in halothane-treated mice were 7, 6, and 20 per cent, respectively; there were similar incidences of these lesions in control animals. It is concluded that under the conditions of this experiment, lifetime administration of halothane at its maximum tolerated dose is not associated with an increased incidence of neoplasia in Swiss/ICR mice.

Lack of Mutagens in Urines of Operating Room Personnel

Mutagenic activity of urines obtained from operating room personnel was assayed in the Ames Salmonella/mammalian microsome system using three strains of histidine-dependent S. typhimurium, TA1535, TA1538, and TA100. Two procedures were employed. In the first, 100- and 200-microliter aliquots of urine obtained from 28 subjects working in either scavenged or unscavenged operating rooms were tested. In the second, urine samples obtained from 13 physicians before and after starting an anesthesia residency, as well as 250-fold concentrates of these samples, were assayed. There was no statistically significant difference in urinary mutagenic activities between individuals working in scavenged and those working in unscavenged operating rooms. Furthermore, urines of anesthesiologists collected before and after beginning training had similar mutagenic activities. Only heavy smokers had mutagenic urine. It was concluded that the majority of operating room workers do not excrete mutagens in the urine.

Mutagenic activity of vinyl compounds and derived epoxides

Many vinyl compounds, such as vinyl chloride and some inhalational anesthetics, are known to be mutagens. In the present study, 10 vinyl compounds or derived epoxides, widely used in industry, were assayed in the Salmonella typhimurium/mammalian microsome system. 3 strains of histidine-dependent S. typhimurium, TA1535, TA98 and TA100 were used. Of the 10 compounds, 4 were mutagens. They were 9-vinylanthracene, vinylcarbazole, 3-vinyl-7-oxabicyclo[4.1.0]heptane and 3-epoxyethyl-7-oxabicyclo[4.1.0]-heptane. The study confirmed the overall genotoxicity of vinyl compounds and epoxides and the need to carefully screen them for mutagenic/carcinogenic effects.

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.

Carcinogen bioassay of isoflurane in mice

A carcinogen bioassay of isoflurane was performed in groups of Swiss/Webster mice exposed to either air (n = 181), 0.1% isoflurane (n = 167), or 0.4% isoflurane (n = 165), for 4 h per day, 5 days per week. After 78 weeks of exposure, mice were left untreated for 3 weeks and were then killed. Mice killed at this time when they were 86 weeks of age, and those killed or dying at other times during the study were subjected to complete gross and microscopie examination. Throughout most of the study, mean body weights of mice exposed to 0.1% isoflurane and 0.4% isoflurane were less by 1–5% and 5–8%, respectively, than that of mice exposed to air alone. Otherwise, no gross toxic treatment effects were noted. The first neoplastic lesion was detected 23 weeks after starting treatment and, by the end of the study, 190 tumors had been detected in 179 mice. However, there were no statistical differences among the groups in the number of mice with a particular tumor at a specific site, the ratio of benign to malignant tumors, or the time to tumor appearance. It was concluded that isoflurane is unlikely to have carcinogenic potential and is a remarkably non-toxic anesthetic in mice.