Halothane In Rats Research Articles

Sleep deprivation reduces the minimum alveolar concentration of halothane in rats

Sleep deprivation reduces the minimum alveolar concentration of halothane in rats

Determining Minimum Alveolar Anesthetic Concentration of Halothane in Rats: The Effect of Incremental Change in Halothane Concentration and Number of Crossovers

Computer simulations for the technique of estimating minimum alveolar anesthetic concentration (MAC) in patients (quantal design) suggest that incremental concentration changes and the number of crossovers affect MAC. We hypothesized that these variables may also apply to estimating MAC in rats (bracketing design). This study tested that hypothesis and also examined whether these variables might mask differences in MAC between groups in which MAC might be expected to differ (pregnant [P] versus nonpregnant [NP]). There were 2 cohorts (n = 27 and n = 30 rats). Each cohort included NP females, females in early P, and females in late P. MAC was tested by using an incremental concentration change of 0.20% and one within-subject crossover in the first cohort and by using an increment size of 0.10% and four crossovers in the second cohort. MAC was statistically significantly increased in the three groups in the second cohort (NP, 1.16 +/- 0.12; early P, 1.14 +/- 0.10; late P, 1.07 +/- 0.10; mean +/- sd) compared with values in the three comparable groups in the first cohort (NP, 0.95 +/- 0.06; early P, 1.01 +/- 0.09; late P, 0.93 +/- 0.13). Values did not differ among groups within each cohort. Post hoc simulations indicated that up to 36% of the difference between cohorts was due to increment size, with the balance due to experimental factors. Our findings confirmed the hypothesis that increment size affects estimates of MAC when a bracketing design is used.

Measurement of aversion to determine humane methods of anaesthesia and euthanasia

AbstractThe distress experienced by animals during the induction of unconsciousness remains one of the most important and yet overlooked aspects of effective methods of anaesthesia and euthanasia. Here we show that considerable differences exist in the aversive responses elicited by 12 common methods of inhalational anaesthesia and euthanasia in laboratory rats and mice. Carbon dioxide, either alone or in combination with oxygen or argon, was found to be highly aversive to both species. The least aversive agents were halothane in rats and enflurane in mice. Exposing these animals to carbon dioxide in any form, either for anaesthesia or for euthanasia, is likely to cause considerable pain and distress and is therefore unacceptable when efficient and more humane alternatives are readily available.

Prolonged exposure to halothane and associated changes in carbohydrate metabolism in rat muscles in vivo

Halothane, an anesthetic presently used in animal experimentation, is reported to stimulate glycogen breakdown in isolated preparations of rat skeletal muscles, suggesting that it may not be a suitable anesthetic for the study of glycogen metabolism in rats in vivo. The purpose of this study was to establish whether prolonged exposure to halothane in rats in vivo is associated with accelerated glycogenolysis. Exposure of rats to halothane for up to 1 h was not accompanied by either any change in the levels of glycogen or increase in activity ratios of glycogen phosphorylase in muscles, irrespective of their fiber compositions. In marked contrast, the levels of lactate, inorganic phosphate, glucose 1-phosphate, glucose 6-phosphate, fructose 1,6-bisphosphate, and fructose 2, 6-bisphosphate changed progressively during anesthesia. Accordingly, the interpretation of muscle metabolite levels must be performed with caution in experiments involving prolonged exposure to halothane. Overall, our findings indicate that the reported halothane-mediated stimulation of glycogen breakdown in vitro is likely to be an artifact and that halothane is a suitable anesthetic for experiments concerned with glycogen metabolism in rats.

Effects of Blood Glucose Changes and Physostigmine on Anesthetic Requirements of Halothane in Rats

Although hyper- and hypoglycemia induce neurophysiologic changes, there have been no reports on the effects of blood glucose changes on anesthetic requirements. This study examined the effects of hyper- and hypoglycemia on the minimum alveolar concentration (MAC) of halothane in rats. In addition, based on a previous finding that the level of brain acetylcholine was reduced during mild hypoglycemia, the authors examined the influence of physostigmine on MAC during hypoglycemia. In Sprague-Dawley rats, anesthesia was induced and maintained with halothane in oxygen and air. The MAC was determined by observing the response to tail clamping and tested during mild hypoglycemia (blood glucose level, 60 mg/dl) and hyperglycemia (blood glucose level, 300 and 500 mg/dl) induced by insulin and glucose infusion, respectively (experiment 1). The effects of 0.3 and 1.0 mg/kg physostigmine given intraperitoneally on MAC were examined in rats with mild and severe hypoglycemia (blood glucose level, 60 and 30 mg/dl; experiment 2). In experiment 1, mild hypoglycemia significantly reduced the MAC of halothane (0.76 +/- 0.03%) compared with the control value (0.92 +/- 0.04%), but hyperglycemia did not change MAC. In experiment 2, mild and severe hypoglycemia reduced MAC of halothane in a degree-dependent manner. Physostigmine (1 mg/kg) had no effect on MAC regardless of blood glucose level, but 0.3 mg/kg reduced MAC. Hypoglycemia reduced anesthetic requirements in a degree-dependent manner, whereas hyperglycemia had no effects. Although the mechanism of hypoglycemic MAC reduction needs further investigations, physostigmine studies suggest that this may not be related to inhibition of cholinergic transmission.

Rat to Human Extrapolation of HCFC-123 Kinetics Deduced from Halothane Kinetics: A Corollary Approach to Physiologically Based Pharmacokinetic Modeling

The goal of this study was to develop a human physiologically based pharmacokinetic (PBPK) model for the chemical HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane) and its major metabolite, trifluoroacetic acid (TFA). No human kinetic data for HCFC-123 are available, thus a corollary approach was developed. HCFC-123 is a structural analog of the common anesthetic agent halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) and follows a common pathway of oxidative biotransformation, resulting in the formation of the same metabolite, TFA. In this study, halothane models for rats and humans were developed and validated. Then the corollary approach was used to develop a human HCFC-123 model from a rat HCFC-123 model. This strategy was implemented by using a previously validated PBPK model for HCFC-123/TFA in the Fischer 344 rat as a template model for halothane in rats. Model predictions were then compared to, and were in good agreement with, measured values for the concentration of halothane in rat blood and fat tissue. A human PBPK model for halothane was developed. The identical model structure (with the exception of the description for the fat compartment) that was used to describe halothane and TFA in the rat was used for describing halothane and TFA in the human. Human physiological parameters for tissue volumes and flows were taken from the literature, and human tissue partition coefficients for halothane were measured in the laboratory. Based on reported similarity in metabolism of halothane by humans and rats, metabolic constants for halothane in the rat were used in the human model, and specific parameters describing the kinetics of TFA were estimated by optimization. The model was validated against human exposure data for halothane from six published studies (expired breath concentrations of halothane and serum/urine data for TFA). A similar approach was then used to derive a human HCFC-123 model for humans from the HCFC-123 rat model. The corollary approach described here illustrates the innovative use of template model structures to aid in the development and validation of models for structural analogs with similar metabolism and activity in biologic systems. Furthermore, given that the PBPK model adequately describes the kinetics of halothane in rats and humans and of HCFC-123 in rats, use of the human PBPK model is proposed for deriving dose–response estimates of human health risks in the absence of human kinetic data.

Chronic treatment with nitric oxide synthase (NOS) inhibitor profoundly reduces cerebellar NOS activity and cyclic guanosine monophosphate but does not modify minimum alveolar anesthetic concentration.

We previously found that acute administration of a nitric oxide synthase (NOS) inhibitor (N omega-nitro-L-arginine methyl ester [L-NAME]) does not reduce the minimum alveolar anesthetic concentration (MAC) of halothane in rats. However, a recent study has suggested that brain NOS activity could not be inhibited by more than approximately 50% by acute administration of L-NAME. To investigate the effect of marked inhibition of NOS activity on the MAC of halothane, we measured cerebellar NOS activity, cerebellar cyclic guanosine monophosphate (cGMP) levels, and halothane MAC in rats chronically treated with L-NAME and compared the results to those of the saline-treated control group. Although the cerebellar NOS activity and cGMP levels were significantly decreased (14% and 2.7% of control, respectively) by L-NAME, the value of the halothane MAC was not significantly affected. These results suggest that the anesthetic action of halothane, as measured by its MAC in rats, is not related to NOS activity or cGMP levels in the brain.

The role of nitric oxide in cerebrocortical laser Doppler flow response to halothane in the rat.

Laser Doppler flowmetry was utilized to investigate whether nitric oxide (NO) plays a role in the cerebrocortical hyperemic effect of halothane in rats. A particular objective was to elucidate whether the increased vascular tone or the removal of basal NO secondary to NO synthase inhibition influenced the response to halothane. The animals were anesthetized with i.p. pentobarbital for surgery and 90 min later were ventilated with 1.0 minimum alveolar concentration (MAC) halothane for 1 h to achieve a steady-state baseline. The control group was infused with either 1 ml of saline or 20 mg/kg of D-NAME, and the treatment group received 20 mg/kg of L-NAME intravenously. In a subset of the treatment group, we restored baseline flow and vascular tone using i.v. sodium nitroprusside (SNP). Mean arterial pressure (MAP) was maintained constant with an infusion of phenylephrine (0.5-5 micrograms/kg/min). Then, 30 to 45 min later, inspired halothane was raised to 1.7 MAC in each group, and the increase in laser Doppler flow (LDF) was measured. On increasing halothane MAC in the control group, LDF increased by 28 +/- 4%. L-NAME increased MAP by 21 +/- 4% and reduced baseline LDF by 26 +/- 2%. In the L-NAME-only treated group, 1.7 MAC halothane increased LDF by 12 +/- 3%, significantly less than control. The decrease in cerebrovascular resistance induced by increasing inspired halothane MAC was similar in the control group and in the L-NAME treated group at 23 +/- 6% and 22% +/- 7, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide synthase inhibitor does not reduce minimum alveolar anesthetic concentration of halothane in rats.

Nitric oxide (NO) synthase inhibitor (N omega-nitro-L-arginine methyl ester [L-NAME]) has been reported to reduce minimum alveolar anesthetic concentration (MAC) of halothane when administered intravenously (i.v.) and to reduce thermal hyperalgesia, or produce antinociception in the formalin test, when administered intracerebroventricularly (ICV) or intrathecally (IT). This study attempts to identify the site(s) in the central nervous system (CNS) where L-NAME acts to reduce the halothane MAC. For this purpose, we examined the effects of i.v., ICV, and IT administration of L-NAME on the halothane MAC in rats. In contrast to an earlier study, we did not observe any decrease in the halothane MAC after i.v. (10-30 mg/kg) administration of L-NAME. ICV (100 micrograms) and IT (100 micrograms and 1 mg) administration of L-NAME also did not alter the halothane MAC. These findings indicate that the L-arginine-NO pathway is not involved in the mechanism of action of halothane to suppress mechanical nociceptive response or in the nociceptive neural mechanism of mechanical stimulation.

Effect of Chloride Transport Blockade on the MAC of Halothane in the Rat

There is a growing evidence that central nervous system chloride transport via gamma-aminobutyric acid (GABAA) related Cl- conductance or Cl-/HCO3- exchange affects anesthetic requirements. To delineate the effects of GABAA-related Cl- conductance blockade versus Cl-/HCO3- exchange inhibition, we determined the change in minimum alveolar anesthetic concentration (MAC) of halothane in rats after intracisternal infusion of 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). DIDS inhibits Cl-/HCO3- exchange transport in concentrations greater than 1 microM and in GABAA-related Cl- channels in concentrations greater than 0.1 mM. After control MAC determination, rats were given intracisternal mock cerebrospinal fluid (n = 6), 1.0 microM DIDS (n = 8), or 1 mM DIDS (n = 8) at a rate of 2 microL/min for 30 min. Mock cerebrospinal fluid did not change the MAC of halothane. The MAC of halothane increased significantly (P less than 0.001) from 0.96% +/- 0.02% to 1.11% +/- 0.03% (mean value +/- SEM) with 1 microM DIDS and from 0.94% +/- 0.02% to 1.16% +/- 0.04% with 1 mM DIDS. The increases in MAC with 1 microM and 1 mM DIDS were not statistically different. This suggests that Cl-/HCO3- exchange inhibition increases halothane requirements, whereas GABAA-related Cl- channel blockade does not.

Role of Signal Transduction in Anesthetic Action

The molecular mechanism for general anesthetic action is not known. The alpha 2 adrenergic agonists represent a novel class of "anesthetic-like" agent because of their selectivity for receptor binding sites and because the transmembrane signaling systems mediating their biologic responses in non-CNS systems are known. We have begun to characterize the signal transduction pathway involved in the anesthetic-like action of the alpha 2 adrenergic agonists. The alpha 2 adrenergic agonists potently decrease both central noradrenergic neurotransmission and halothane anesthetic requirements (MAC). Since MAC is only reduced by 30-40% when noradrenergic neurotransmission is totally abolished and since the reduction in MAC with the highly selective alpha 2 adrenergic agonists exceeds 90%, factors in addition to noradrenergic neurotransmission must be contributing to the anesthetic action of the alpha 2 agonists. Studies with the superselective alpha 2 agonist dexmedetomidine confirmed this, as the alpha 2 agonist could still reduce the MAC for halothane in rats depleted of their central norepinephrine stores. The profound reduction in anesthetic requirements with dexmedetomidine raised the possibility that alpha 2 adrenergic agonists may be considered an anesthetic hypnotic agent by itself. This sole anesthetic hypnotic response was established together with the confirmation that a central alpha 2 adrenoceptor mediated this action. Subsequently, data using molecular biologic techniques suggested that the alpha 2 C4 isoreceptor was the probable receptor that mediated the anesthetic response. We further explored the postreceptor effector mechanism for the signal transduction pathway for alpha 2 anesthetic action and identified the participation of two other molecular components, namely, a pertussis-toxin-sensitive G protein and a 4-aminopyridine-sensitive ion channel. Whether the signal transduction pathway for alpha 2 anesthetic action mediates the further response to other non-alpha 2 anesthetic agents needs to be defined.

Influence of Hypertension on MAC of Halothane in Rats

This study was designed to assess the relationship between MAC and hypertension. To this purpose, MAC of halothane was determined in fully inbred spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Because MAC determination was performed in animals whose lungs were mechanically ventilated, the adequacy of the ventilation was initially established in 20 rats equally divided into SHR and WKY, and instrumented with catheters in the abdominal aorta. Subsequently, MAC of halothane was determined in 40 rats equally divided into SHR and WKY, including those instrumented. There were no differences in MAC of halothane between SHR (n = 20) and WKY (n = 20) (1.08 +/- 0.02% vs. 1.11 +/- 0.02%). Subgroup analysis indicated that MAC of halothane was not affected by the presence of an arterial catheter in the abdominal aorta (SHR 1.09 +/- 0.06% vs. 1.08 +/- 0.02%; WKY 1.15 +/- 0.04% vs. 1.08 +/- 0.02%). The authors' data provide experimental evidence that MAC is not affected by either chronic hypertension or limited instrumentation.

ハロセンによる肝腎グアニジノ化合物代謝の変動に関する実験的研究

ハロセンによる肝腎グアニジノ化合物代謝の変動に関する実験的研究

Halothane anesthetic requirements are not affected by aminophylline treatment in rats and dogs.

The authors determined the effects of aminophylline on the anesthetic requirements for halothane in rats and dogs. MAC for halothane was determined in rats (n = 24) before and after aminophylline, 100 mg X kg-1 ip, or an equal volume of saline. Because changes in central noradrenergic neurotransmission have been linked to drug-induced changes in the depth of the anesthetic state, we investigated the effect of aminophylline on the turnover of norepinephrine in discrete brain regions of halothane-anesthetized rats. To facilitate testing at steady-state aminophylline conditions and to permit frequent blood sampling, halothane MAC was determined in dogs (n = 7) before and after a therapeutic level of aminophylline (15 +/- 2 micrograms X ml-1) was obtained. Neither in the rats (1.0 vs. 1.0%) nor in the dogs (1.04 +/- 0.14 vs. 1.01 +/- 0.14%) was halothane MAC affected by aminophylline treatment. Commensurate with the lack of change of anesthetic depth, aminophylline treatment did not affect noradrenergic neurotransmission in the brain of halothane-anesthetized rats. Furthermore, the anticipated increase in circulating catecholamines following aminophylline treatment in dogs did not materialize. The authors conclude that halothane anesthetic requirements are not altered by aminophylline treatment, possibly because of the attenuation of the putative sympathomimetic effects of aminophylline by halothane.

Isoflurane Does Not Prevent Hepatic Injury Produced by Halothane in Rats

We speculated that the inhibitory effect of isoflurane on the metabolism of halothane might reduce hepatic injury produced by halothane. To test this hypothesis we pretreated male rats with phenobarbital and 24 hr later exposed them to one of three types of anesthesia. One group of rats was anesthetized with 0.6 MAC isoflurane in 21-25% oxygen for 20 min, followed by exposure to 0.3 MAC isoflurane and 0.3 MAC halothane either in 9% oxygen for 46 min (n = 5) or in 12% oxygen for 60 min (n = 11). A second group of rats received 0.3 MAC halothane in 9% oxygen for either 46 min (n = 12) or in 12% oxygen for 60 min (n = 10). The third group received 0.3 MAC isoflurane in 9% oxygen for either 46 min (n = 12) or for 120 min (n = 8). The rats were killed 24 hr after the exposures and liver slides prepared. Histologic examination revealed that rats treated with isoflurane plus halothane, or with halothane alone showed a significant hepatic injury (P less than 0.005) when compared with those treated with isoflurane. Thus isoflurane failed to protect the liver from halothane-induced injury.

In vivo 19F NMR imaging.

In vitro and in vivo 19F spectra and images were obtained using various clinically safe fluorinated compounds. Standard and chemical shift images were acquired in solutions of fluorinated anesthetics with the chemical shift images clearly separating signals arising from a mixture of halothane and methoxyflurane. The 19F images of halothane in rats were unsuccessful at anesthetic concentration. In vivo 19F nuclear magnetic resonance (NMR) images were acquired at 57.9 MHz in rats receiving chronic injections of 14% perfluorodecalin, 6% perfluorotripropylamine (Fluosol-DA). The liver accumulates Fluosol-DA in the reticuloendothelial cells to concentrations that allow images to be obtained in less than 30 min. Image intensity from the perfluorochemicals reflects reticuloendothelial cell activity and thus is a functional image. Conventional proton NMR images at corresponding levels confirmed that the 19F signal arose from the liver and not muscle or fat. The 19F NMR images of the large bowel and stomach in rats were obtained by filling the lumen with concentrated Fluosol-DA. High contrast anatomical images showing gross structure of the gastrointestinal tract were acquired in as little as 12 min. These data suggest that 19F NMR may have a potential role in clinical imaging.

Lack of tolerance to cyclopropane and cross-tolerance to halothane in rats.

Cyclopropane requirement (MAC) in rats was determined before, during, and after repeated exposure to anaesthetic concentrations of cyclopropane and halothane for one hour every day for 20 and 30 days, respectively. MAC values during and after exposure ranged from 93 to 103 per cent (mean = 99 per cent) of control values, which indicates a lack of significant tolerance to cyclopropane or a cross-tolerance between cyclopropane and halothane.

Isoflurane Does Not Prevent Hepatic Injury Produced by Halothane in Rats

We speculated that the inhibitory effect of isoflurane on the metabolism of halothane might reduce hepatic injury produced by halothane. To test tliis hypothesis we pretreated male rats with phenobarbital and 24 hr later exposed them to one of three types of anesthesia. One group of rats was anesthetized with 0.6 MAC isofliirane in 21–25% oxygen for 20 min, followed by exposure to 0.3 MAC isofliirane and 0.3 MAC halothane either in 9% oxygen for 46 min (n = 5) or in 12% oxygen for 60 min (n = 11). A second group of rats received 0.3 MAC halothane in 9% oxygen for either 46 min (n = 12) or in 12% oxygen for 60 min (n = 10). The third group received 0.3 MAC isoflurane in 9% oxygen for either 46 min (n = 12) or for 120 min (n = 8). The rats were killed 24 hr after the exposures and liver slides prepared. Histologic examination revealed that rats treated with isoflurane plus halothane, or with halothane alone showed a significant hepatic injury (P < 0.005) when compared with those treated with isoflurane. Thus isoflurane failed to protect the liver from halothane-induced injury.

A physiologically based toxicokinetic description of the metabolism of inhaled gases and vapors: Analysis at steady state

In studying the kinetics of metabolism of inhaled gases and vapors the rate of metabolism is estimated as a function of inhaled concentration. In the past, pharmacokinetic modeling has been routinely conducted by fitting these data to linearized forms of the Michaelis-Menten (M-M) equation to estimate V max and an apparent inhalation K m . We have determined rate curves for benzene and halothane in rats. These curves were not smooth M-M hyperbolas. They had extended first-order portions, up to greater than 80% V max, and abruptly converted to zero-order dependencies. In addition, achieved steady-state blood:gas concentration ratios have been shown to be variable with respect to inhaled concentration, and maximum rates of metabolism for a wide variety of chemicals were found to cluster toward a common value. These phenomena are difficult to reconcile with the M-M description above. To describe this observed steady-state and kinetic behavior, one must consider enzymatic (biochemical) constants, blood flow to metabolizing organs, and limitations to pulmonary equilibration caused by extensive systemic metabolism. A physiologically based kinetic model for metabolism of inhaled gases and vapors has been developed incorporating these factors and relying on clearance terminology to analyze steady-state behavior. One parameter important in the steady-state formulation is C max-the maximum transhepatic concentration gradient sustainable at a given hepatic blood flow, Q̇ L. C max is equal to V max/Q̇ L. The model shows that M-M hyperbolas are only expected when the affinity of the metabolizing enzyme is low ( K m large) with respect to C max. When affinity is high ( K m small) with respect to C max, abrupt first-order to zero-order transitions are expected. This is the concentration range where organ perfusion, not biochemical constants, is rate limiting. When perfusion is rate-limiting, observed steady-state blood:gas concentration ratios will be lower than predicted by the thermodynamic partition coefficient, and increasing the number of enzymatic centers by induction will not increase the rate of metabolism of inhaled chemical. To properly interpret results of inhalation experimentation one must understand both the role of various physiological factors in controlling the rate of metabolism of inhaled gases and vapors in vivo and the conditions under which perfusion and other physiological factors become rate-limiting.

Renal function in Fischer 344 rats with chronic renal impairment after administration of enflurane and gentamicin.

To assess the potential for producing nephrotoxicity in rats with abnormal renal function, the renal effects of enflurane or halothane anesthesia, 1 MAC for two hours, were examined in six groups of six Fischer 344 rats each with surgically induced chronic renal impairment. As an additional predisposing factor, gentamicin, 5 mg/kg/day, was administered for one week before and for one week after anesthesia to three of the groups, one anesthetized with enflurane, one anesthetized with halothane, and one unanesthetized. No significant change in renal function could be attributed to either anesthetic agent. Serum inorganic fluoride levels four hours and 24 hours after enflurane anesthesia were similar in the gentamicin-treated and the non-gentamicin-treated groups. Clinically small but statistically significant increases in serum creatinine concentration and urinary flow occurred in all three gentamicin-treated groups during the period of treatment. Anesthesia with either enflurane or halothane in rats with chronic renal impairment treated with gentamicin did not result in additional renal damage.