Acute cardiogenic shock secondary to blunt traumatic aortic valve injury

Background

Blunt cardiac injuries rarely result in aortic valve cusp rupture, leading to acute aortic insufficiency and cardiogenic shock. This rare clinical entity carries a high mortality rate if left undiagnosed and not managed surgically, with few patients surviving beyond 24 h. It presents a diagnostic challenge in the polytrauma patient in shock, with multiple possible and complementary etiologies.

Case presentation

We present a 56-year-old male with persistent hypotension, a wide pulse pressure, and elevated serum troponin levels suggesting blunt cardiac injury after a motor vehicle accident. Transthoracic and transesophageal echocardiography revealed normal biventricular function but severe aortic insufficiency due to prolapse of the left coronary cusp.He was taken emergently to surgery, where aortic valve exploration revealed complete left coronary cusp avulsion from the aortic annulus with a mid-cusp tear, requiring aortic valve replacement with a bioprosthetic valve. Postoperative echocardiography showed normal biventricular function with a well-seated bioprosthetic aortic valve with no insufficiency.

Conclusions

Traumatic aortic valve injury can lead to torn or prolapsed cusps causing acute aortic insufficiency leading to cardiogenic shock, but early recognition with appropriate and targeted diagnostic imaging is vital to prevent rapid patient deterioration and demise.

Multimodality Cardiac Imaging in COVID

Infection with SARS-CoV-2, the virus that causes COVID, is associated with numerous potential secondary complications. Global efforts have been dedicated to understanding the myriad potential cardiovascular sequelae which may occur during acute infection, convalescence, or recovery. Because patients often present with nonspecific symptoms and laboratory findings, cardiac imaging has emerged as an important tool for the discrimination of pulmonary and cardiovascular complications of this disease. The clinician investigating a potential COVID-related complication must account not only for the relative utility of various cardiac imaging modalities but also for the risk of infectious exposure to staff and other patients. Extraordinary clinical and scholarly efforts have brought the international medical community closer to a consensus on the appropriate indications for diagnostic cardiac imaging during this protracted pandemic. In this review, we summarize the existing literature and reference major societal guidelines to provide an overview of the indications and utility of echocardiography, nuclear imaging, cardiac computed tomography, and cardiac magnetic resonance imaging for the diagnosis of cardiovascular complications of COVID.

Multiancestry Genome-Wide Association Study of Aortic Stenosis Identifies Multiple Novel Loci in the Million Veteran Program

BACKGROUND

Calcific aortic stenosis (CAS) is the most common valvular heart disease in older adults and has no effective preventive therapies. Genome-wide association studies (GWAS) can identify genes influencing disease and may help prioritize therapeutic targets for CAS.

METHODS

We performed a GWAS and gene association study of 14 451 patients with CAS and 398 544 controls in the Million Veteran Program. Replication was performed in the Million Veteran Program, Penn Medicine Biobank, Mass General Brigham Biobank, BioVU, and BioMe, totaling 12 889 cases and 348 094 controls. Causal genes were prioritized from genome-wide significant variants using polygenic priority score gene localization, expression quantitative trait locus colocalization, and nearest gene methods. CAS genetic architecture was compared with that of atherosclerotic cardiovascular disease. Causal inference for cardiometabolic biomarkers in CAS was performed using Mendelian randomization and genome-wide significant loci were characterized further through phenome-wide association study.

RESULTS

We identified 23 genome-wide significant lead variants in our GWAS representing 17 unique genomic regions. Of the 23 lead variants, 14 were significant in replication, representing 11 unique genomic regions. Five replicated genomic regions were previously known risk loci for CAS (PALMD, TEX41, IL6, LPA, FADS) and 6 were novel (CEP85L, FTO, SLMAP, CELSR2, MECOM, CDAN1). Two novel lead variants were associated in non-White individuals (P<0.05): rs12740374 (CELSR2) in Black and Hispanic individuals and rs1522387 (SLMAP) in Black individuals. Of the 14 replicated lead variants, only 2 (rs10455872 [LPA], rs12740374 [CELSR2]) were also significant in atherosclerotic cardiovascular disease GWAS. In Mendelian randomization, lipoprotein(a) and low-density lipoprotein cholesterol were both associated with CAS, but the association between low-density lipoprotein cholesterol and CAS was attenuated when adjusting for lipoprotein(a). Phenome-wide association study highlighted varying degrees of pleiotropy, including between CAS and obesity at the FTO locus. However, the FTO locus remained associated with CAS after adjusting for body mass index and maintained a significant independent effect on CAS in mediation analysis.

CONCLUSIONS

We performed a multiancestry GWAS in CAS and identified 6 novel genomic regions in the disease. Secondary analyses highlighted the roles of lipid metabolism, inflammation, cellular senescence, and adiposity in the pathobiology of CAS and clarified the shared and differential genetic architectures of CAS with atherosclerotic cardiovascular diseases.

Reduced Circumferential Strain in Athletes with Prior COVID-19

Purpose

To characterize global and segmental circumferential systolic strain (CS) measured by cardiac MRI in athletes after SARS-CoV-2 infection.

Materials and Methods

This retrospective observational cohort study included 188 soldiers and collegiate athletes referred for cardiac MRI after SARS-CoV-2 infection (C19+) between July 2020 and February 2021 and a control group of 72 soldiers, collegiate, and high school athletes who underwent cardiac MRI from May 2019 to February 2020, prior to the first SARS-CoV-2 case detected in our region (C19-). Global and segmental CS were measured by feature tracking, then compared between each group using unadjusted and multivariable- adjusted models. Acute myocarditis was diagnosed according to the modified Lake Louise criteria and the location of pathologic late gadolinium enhancement (LGE) was ascertained.

Results

Among the 188 C19+ athletes (median age, 25 years [IQR, 23-30]; 131 men), the majority had mild illness. Global CS significantly differed between C19+ and C19- groups, with a median of -24.0 (IQR -25.8, -21.4) versus. -25.0 (-28.0, -22.4), respectively (p = .009). This difference in CS persisted following adjustment for age, sex, body mass index, heart rate, and systolic blood pressure β coefficient 1.29 [95% CI: 0.20, 2.38], p = .02). In segmental analysis, the basal- and mid- inferoseptal, septal and inferolateral segments were significantly different (p < .05), which had a higher frequency of post-COVID late gadolinium enhancement. The global and segmental differences were similar after exclusion of athletes with myocarditis.

Conclusion

Among athletes, SARS-CoV-2 infection was associated with a small but statistically significant reduced CS.

Genome-wide association study reveals novel genetic loci: a new polygenic risk score for mitral valve prolapse

AIMS

Mitral valve prolapse (MVP) is a common valvular heart disease with a prevalence of >2% in the general adult population. Despite this high incidence, there is a limited understanding of the molecular mechanism of this disease, and no medical therapy is available for this disease. We aimed to elucidate the genetic basis of MVP in order to better understand this complex disorder.

METHODS AND RESULTS

We performed a meta-analysis of six genome-wide association studies that included 4884 cases and 434 649 controls. We identified 14 loci associated with MVP in our primary analysis and 2 additional loci associated with a subset of the samples that additionally underwent mitral valve surgery. Integration of epigenetic, transcriptional, and proteomic data identified candidate MVP genes including LMCD1, SPTBN1, LTBP2, TGFB2, NMB, and ALPK3. We created a polygenic risk score (PRS) for MVP and showed an improved MVP risk prediction beyond age, sex, and clinical risk factors.

CONCLUSION

We identified 14 genetic loci that are associated with MVP. Multiple analyses identified candidate genes including two transforming growth factor-β signalling molecules and spectrin β. We present the first PRS for MVP that could eventually aid risk stratification of patients for MVP screening in a clinical setting. These findings advance our understanding of this common valvular heart disease and may reveal novel therapeutic targets for intervention.

Left atrial appendage morphology predicts the formation of left atrial appendage thrombus

BACKGROUND

Nonchicken wing left atrial appendage (LAA) morphology is associated with higher risk for stroke in patients with atrial fibrillation (AF) than chicken wing (CW) morphology.

OBJECTIVE

Assess whether LAA morphology predicts the formation of LAA thrombus independent of age, sex, presenting rhythm, left ventricular ejection fraction (LVEF), or anticoagulant use.

METHODS

A cross-sectional analysis was performed on patients prospectively enrolled in the Vanderbilt LAA Registry or presenting for transesophageal echocardiogram (TEE) between January 1, 2015, and November 1, 2017 (n = 306). Two physicians independently reviewed TEEs interpreted as having LAA thrombus. Determination of LAA morphology, ejection velocity, and presence of thrombus (n = 102) were based on 0°, 45°, 90°, and 135° TEE views. The control cohort (n = 204) included consecutive AF patients undergoing TEE without LAA thrombus.

RESULTS

LAA morphology in patients with LAA thrombus was: 35% windsock, 47% broccoli, and 12% CW. Windsock (odds ratio [OR], 4.0; 95% confidence interval [CI]: 1.7-9.3, p = .001) and broccoli (OR, 6.6; 95% CI: 2.6-16.6; p < .001) morphology were higher risk for thrombus compared to CW. Female sex predicted higher-odds for LAA thrombus (OR, 2.6; 95% CI: 1.4-4.8; p = .002) as did LAA-EV < 20 cm/s (OR, 11.12; 95% CI: 5.6-22.1). Anticoagulation use (OR, 0.5; 95% CI: 0.3-0.9; p = .03) and higher LVEF (OR, 0.95; 95% CI: 0.93-0.98; p < .001) were associated with lower risk. In patients with a CW morphology who had LAA thrombus, 4 of the 7 had an LAA-EV < 20 cm/s and acute systolic heart failure with LVEF < 30% or active malignancy. In multivariable linear regression analysis controlling for presenting rhythm, anticoagulant use, age, sex, and LVEF, CW morphology appears relatively protective from LAA thrombus (p = .001).

CONCLUSION

CW LAA morphology appears relatively protective against the formation of LAA thrombus.

Standardization of doctoral study in agricultural and extension education: is the field of study mature enough for achievement of the optimum degree of order?

Agricultural and extension education--or some derivative name--is a field of study leading to the doctoral degree in universities around the world. Is there are body of knowledge or a taxonomy of the knowledge--e.g., a knowledge domain--that one should possess with a doctorate in agricultural and extension education? The purpose of this paper was to synthesize the work of researchers who attempted to define the field of study, with a taxonomy comprising the knowledge domains (standards) and knowledge objects--structured interrelated sets of data, knowledge, and wisdom--of the field of study. Doctoral study in agricultural and extension education needs a document that provides for rules and guidelines--rules and guidelines that in turn provide for common and repeated use--all leading to achievement of an optimum degree of order in the context of academic, scholarly, and professional practice in agricultural and extension education. Thus, one would know in broad categories the knowledge, skills, and abilities possessed by one who holds a doctoral degree in agricultural and extension education. That is, there would exist a standard for doctoral degrees in agricultural and extension education. A content analysis of three previous attempts to categorize knowledge in agricultural and extension education served as the primary technique to create a new taxonomy--or to confirm an existing taxonomy--for doctoral study in agricultural and extension education. The following coalesced as nine essential knowledge domains for a doctorate in agricultural and extension education: (1) history, philosophy, ethics, and policy; (2) agricultural/rural development; (3) organizational development and change management; (4) planning, needs assessment, and evaluation; (5) learning theory; (6) curriculum development and instructional design; (7) teaching methods and delivery strategies; (8) research methods and tools; and, (9) scholarship and communications.

Pharmacological effects of intravenous melatonin: comparative studies with thiopental and propofol

BACKGROUND

Possible utility of high-dose i.v. melatonin as an anaesthetic adjuvant has not been studied. This study compared its effects with thiopental and propofol.

METHODS

Sprague Dawley rats were assigned to receive bolus or cumulative i.v. doses of melatonin, thiopental or propofol. Righting reflex, hindpaw withdrawal to a noxious stimulus, response to tail clamping and haemodynamic effects were assessed.

RESULTS

Melatonin caused a dose-dependent increase in paw withdrawal threshold and the percent of rats displaying loss of the righting reflex. Melatonin was comparable to thiopental and propofol in terms of its rapid onset of hypnosis. The mean ED(50) values for loss of righting reflex were 5.4 (SEM 1.2), 12.5 (1.1) and 178 (1.1) mg kg(-1) for propofol, thiopental and melatonin, respectively. The percent of rats displaying loss of response to tail clamping was greater with propofol than with melatonin (P<0.05). Haemodynamic changes produced by melatonin or propofol were similar in onset and magnitude.

CONCLUSIONS

I.V. melatonin can exert hypnotic effects similar to those observed with thiopental and propofol. Melatonin exhibited significant antinociceptive effects but was less effective in abolishing the response to tail clamping.

Not to be and then to be: visual representation of ignored unfamiliar faces

Negative priming, the increase in response time and/or errors to targets previously encountered as distractors, is explained by inhibitory mechanisms that block the access of distractor representations to response systems. The processing of unfamiliar human faces was investigated using negative priming. Observers viewed a row of faces to decide whether 2 target faces were the same or different. Response latencies were longer when 1 or both targets had appeared as distractors on the immediately preceding trial--evidence that never-before seen faces are represented and require inhibition. Response latencies were shorter when face targets had appeared as distractors, either corrupted with high-frequency noise or contrast inverted--evidence that representations are facilitated. Finally, response latencies remained unaltered when face targets had appeared as upside-down distractors--evidence that not all distractor representations afford response priming. The visual system indeed represents ignored unfamiliar faces, but blocks these representations only if they vie with targets for the control of action.

Not to be and then to be: visual representation of ignored unfamiliar faces

Negative priming, the increase in response time and/or errors to targets previously encountered as distractors, is explained by inhibitory mechanisms that block the access of distractor representations to response systems. The processing of unfamiliar human faces was investigated using negative priming. Observers viewed a row of faces to decide whether 2 target faces were the same or different. Response latencies were longer when 1 or both targets had appeared as distractors on the immediately preceding trial--evidence that never-before seen faces are represented and require inhibition. Response latencies were shorter when face targets had appeared as distractors, either corrupted with high-frequency noise or contrast inverted--evidence that representations are facilitated. Finally, response latencies remained unaltered when face targets had appeared as upside-down distractors--evidence that not all distractor representations afford response priming. The visual system indeed represents ignored unfamiliar faces, but blocks these representations only if they vie with targets for the control of action.

The Reasons for Living Inventory for Adolescents (RFL-A): development and psychometric properties

The role of adaptive beliefs and attitudes against suicide has not been given adequate attention in the clinical or assessment literature. This article reports on the development and initial psychometric properties of a 32-item self-report inventory, the Reasons for Living Inventory for Adolescents (RFL-A). In Phase 1, we used exploratory and confirmatory factor analyses to identify five correlated factors: Future Optimism, Suicide-Related Concerns, Family Alliance, Peer Acceptance and Support, and Self-Acceptance. In Phase 2, we cross-validated the 5-factor oblique model in a different group of adolescents recruited from two high schools. In addition, we examined evidence for convergent, discriminant, and construct validities. The coefficient alpha indices for the RFL-A total and scales were satisfactory. In Phase 3, we evaluated additional evidence of reliability and validity using samples of high school and psychiatric inpatient adolescents. The results suggest that the RFL-A is a short, reliable, and valid measure that is potentially useful in the assessment of adolescent suicidal behavior.

Alu-repeat Polymorphism in the Gene Coding for Tissue-Type Plasminogen Activator (t-PA) and Risks of Myocardial Infarction Among Middle-aged Men

An Alu -repeat polymorphism in the gene coding for tissue-type plasminogen activator has been described recently, and it has been hypothesized that this polymorphism may predict risk of coronary thrombosis. In a prospective cohort of nearly 15,000 apparently healthy men, presence of an Alu -repeat insertion/deletion ( I/D ) polymorphism in the gene coding for tissue-type plasminogen activator was determined among 369 study participants who subsequently suffered a first myocardial infarction (cases) and among a group of 369 ageand smoking-matched study participants who remained free of reported cardiovascular disease during follow-up (controls). The distributions of the II , DI , and DD genotypes of the tissue-type plasminogen activator polymorphism among men who subsequently suffered myocardial infarction (0.30, 0.50, 0.21) were virtually identical to those who remained free of disease (0.29, 0.50, 0.21; P =.9). There was no evidence of association between the Alu insertion polymorphism and risks of future myocardial infarction in models assuming either allelic recessive (relative risk, 1.05; 95% confidence interval, 0.8 to 1.4, P =.8) or allelic dominant (relative risk, 1.04; 95% confidence interval, 0.7 to 1.5, P =.8) modes of inheritance, nor were associations found in analyses stratified by age, family history, hypercholesterolemia, or the presence of other risk factors for premature coronary disease. Multivariate analysis had no important effects on these relationships. In this cohort of middle-aged US men, the presence of the insertion allele of the Alu -repeat polymorphism of the tissue-type plasminogen activator gene is not associated with future risks of myocardial infarction. ( Arterioscler Thromb Vase Biology. 1997;17:1687-1690.)

Alu-repeat polymorphism in the gene coding for tissue-type plasminogen activator (t-PA) and risks of myocardial infarction among middle-aged men

An Alu-repeat polymorphism in the gene coding for tissue-type plasminogen activator has been described recently, and it has been hypothesized that this polymorphism may predict risk of coronary thrombosis. In a prospective cohort of nearly 15,000 apparently healthy men, presence of an Alu-repeat insertion/deletion (I/D) polymorphism in the gene coding for tissue-type plasminogen activator was determined among 369 study participants who subsequently suffered a first myocardial infarction (cases) and among a group of 369 age- and smoking-matched study participants who remained free of reported cardiovascular disease during follow-up (controls). The distributions of the II, DI, and DD genotypes of the tissue-type plasminogen activator polymorphism among men who subsequently suffered myocardial infarction (0.30, 0.50, 0.21) were virtually identical to those who remained free of disease (0.29, 0.50, 0.21; P = .9). There was no evidence of association between the Alu insertion polymorphism and risks of future myocardial infarction in models assuming either allelic recessive (relative risk, 1.05; 95% confidence interval, 0.8 to 1.4, P = .8) or allelic dominant (relative risk, 1.04; 95% confidence interval, 0.7 to 1.5, P = .8) modes of inheritance, nor were associations found in analyses stratified by age, family history, hypercholesterolemia, or the presence of other risk factors for premature coronary disease. Multivariate analysis had no important effects on these relationships. In this cohort of middle-aged US men, the presence of the insertion allele of the Alu-repeat polymorphism of the tissue-type plasminogen activator gene is not associated with future risks of myocardial infarction.

The effects of plasma and brain magnesium concentrations on lidocaine-induced seizures in the rat

Lidocaine and MgSO4 are often coadministered to patients with pregnancy-induced hypertension. This study examined whether MgSO4 alters the lidocaine-seizure threshold in the rat and, if so, whether systemic MgSO4 administration is as effective as intracerebroventricular MgSO4 infusion. In Experiment 1, rats were administered 50% MgSO4 or 0.9% NaCl intravenously (IV) (20 microL/h) for 5 days. In Experiment 2, rats were administered 0.9% NaCl, 0.8% MgSO4, or 2.0% MgSO4 (10 microL/h) via intracerebroventricular infusion for 24 h. All rats then underwent continuous IV lidocaine infusion until onset of electroencephalographic seizures. In Experiment 1, plasma [Mg2+] was greater in the MgSO4 group (5.1 +/- 1.5 mg/dL vs 1.8 +/- 0.3 mg/dL) but neither the dose of lidocaine required to induce seizures (MgSO4 = 19 +/- 2 mg/kg; saline = 23 +/- 5 mg/kg) nor brain [Mg2+] (MgSO4 = 794 +/- 17 micrograms/g; saline = 788 +/- 33 micrograms/g) were changed. In Experiment 2, intracerebroventricular MgSO4 increased both brain [Mg2+] (2% MgSO4 = 923 +/- 79 micrograms/g; saline = 788 +/- 35 micrograms/g) and the lidocaine seizure dose (2% MgSO4 = 39 +/- 7 mg/kg; saline = 26 +/- 3 mg/kg). Although intracerebroventricular administration of MgSO4 produces an anticonvulsant effect, chronic hypermagnesemia does not alter whole brain [Mg2+] and therefore offers no protection from lidocaine-induced seizures in this model.

Isoflurane and cytochrome b5 stimulation of 2-chloro-1,1-difluoroethene metabolism by reconstituted rat CYP2B1 and CYP2C6

Isoflurane stimulates the metabolism of 2-chloro-1,1-difluoroethene (CDE) in liver microsomes from phenobarbital-treated rats or rabbits. The P450 isozymes involved and the mechanism by which such stimulation occurs have not been clarified. The present study examined the effects of isoflurane and cytochrome b5 on CDE metabolism in reconstituted systems containing purified rat CYP2B1 or CYP2C6. Under similar incubation conditions, CYP2B1 defluorinated CDE at approximately five times the rate of CYP2C6. Isoflurane was a potent stimulator of CDE metabolism, increasing it nearly 5-fold when catalyzed by CYP2B1, but only 2-fold when catalyzed by CYP2C6. Isoflurane had no stimulatory effect on benzphetamine metabolism by CYP2B1 or CYP2C6. Cytochrome b5 was not required for isoflurane-facilitated CDE metabolism; however, the addition of cytochrome b5 to CYP2B1 increased CDE metabolism 71 and 44%, in the absence and presence of isoflurane, respectively. In reconstituted CYP2B1, isoflurane generated a type I difference spectrum of approximately twice the magnitude of CDE and stimulated NADPH consumption more so than CDE. The same quantity of NADPH was consumed when CDE was present with isoflurane as compared with isoflurane alone. These data support the hypothesis that isoflurane stimulates CDE metabolism by a mechanism involving increased P450 reduction via direct isoflurane interaction with P450.

Isoflurane-chlorodifluoroethene interaction in human liver microsomes. Role of cytochrome P4502B6 in potentiation of haloethene metabolism

Short-chain saturated halocarbons, including isoflurane and the chlorofluorocarbon substitute HCFC-123, can strongly potentiate the cytochrome P450-dependent oxidation of gaseous haloethenes, such as 2-chloro-1,1-difluoroethene (CDE) and vinyl chloride, in vivo and in vitro. P450 isozyme specificity in this effect is suggested by the fact that the interaction is pronounced in microsomes from rats treated with phenobarbital, but does not occur in microsomes of isoniazid- or beta-naphthoflavone-treated animals. We examined the effect of isoflurane on CDE defluorination in liver microsomes from 10 human organ donors to determine whether saturated halocarbon/haloethene interactions also occur in humans and, if so, to determine the cytochromes P450 involved. Three of the samples exhibited isoflurane-stimulated increases (24, 32, and 41%) in CDE defluorination; isoflurane either inhibited or had no effect on CDE metabolism in the other seven samples. Two samples in which isoflurane potentiated CDE metabolism to the greatest rates had higher coumarin 7-hydroxylase (indicative of CYP2A6), 7-ethoxycoumarin O-deethylase (CYP2B6), and nifedipine oxidase (CYP3A4) activities than the other eight samples. However, all 10 subjects had similar rates of phenacetin O-deethylation (CYP1A2) and chlorzoxazone 6-hydroxylation (CYP2E1). In microsomes from cells transfected with cDNAs coding for individual human P450s, CDE metabolism by CYP2B6 was stimulated (216%) by isoflurane, whereas isoflurane did not stimulate CDE metabolism by human CYP2A6, CYP3A4, CYP2D6, or CYP2E1. Isoflurane highly increased CDE defluorination in purified rat CYP2B1 (470%).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of volatile sevoflurane degradation product formation in an anesthesia circuit by a reduction in soda lime temperature

BACKGROUND

Sevoflurane reacts with carbon dioxide absorbents, such as soda lime, to release the volatile products compounds A and B. These two products, which have been detected in anesthesia circuits, are among five formed when sevoflurane is degraded by soda lime at increased temperature; the others, compounds C, D, and E, have been detected only in heated sealed systems. The current study attempted to determine the influence of soda lime temperature on compounds A and B generation in an anesthesia circuit and whether a decrease in soda lime temperature could eliminate product formation in the circulating gases.

METHODS

Sevoflurane (1.5% in oxygen) was circulated (6 l/min) in a partially closed, low-flow (215 ml/min fresh gas) anesthesia circuit that included a canister containing 1.2 kg fresh soda lime. Carbon dioxide was introduced into the circuit at 200 ml/min, and gas samples for analysis of sevoflurane, compounds A, B, C, and D, and carbon dioxide were taken at the opening of an attached artificial lung. The circuit was operated for 8 h under conditions whereby the soda lime temperature could increase freely or the soda lime was chilled with ice.

RESULTS

A maximum core soda lime temperature of about 46 degrees C was measured when the experiment was run under conditions whereby the soda lime temperature was allowed to increase. Compounds A and B increased with time to a maximum of 23 and 9 ppm, respectively. At 4.5 h of circuit operation, compound C/D was found. Chilling of the soda lime canister, which produced a maximum core soda lime temperature of 25 degrees C, resulted in neither compound B nor C/D being detected during the 8-h period. Compound A was present in the circuit at all times at approximately 10 ppm; however, its concentration did not increase as occurred when the experiment was conducted under nonchilled conditions. Carbon dioxide levels at the opening of the lung remained at a constant 5% for 8 h with or without soda lime chilling.

CONCLUSIONS

This study demonstrates that the release of volatile sevoflurane degradation products in an anesthesia circuit is highly dependent on soda lime temperatures. A reduction of the temperature of soda lime may be a feasible method of preventing the release of significant levels of sevoflurane degradation products without interfering with carbon dioxide absorption or altering the sevoflurane concentration.

Interaction of fluoroethane chlorofluorocarbon (CFC) substitutes with microsomal cytochrome P450. Stimulation of P450 activity and chlorodifluoroethene metabolism

The abilities of halothane and the fluoroethane chlorofluorocarbon (CFC) substitutes, FC-123, FC-133a, FC-124, FC-134a and FC-125, to stimulate cytochrome P450 activities and 2-chloro-1,1-difluoroethene (CDE) defluorination in hepatic microsomes from phenobarbital-treated rabbits were compared. At 1% (v/v) each, halothane and FC-123 similarly increased the consumption of NADPH and O2 by 300 and 100%, respectively, over that in microsomes without substrate. FC-133a and FC-124 were less effective, increasing NADPH and O2 consumption by 150-200 and 70%. FC-134a and FC-125 were the least effective, increasing NADPH and O2 consumption by only 70 and 50%, respectively. No metabolism of any fluoroethane could be detected under the incubation conditions used. Halothane and FC-123 were most effective in stimulating CDE metabolism with increases of CDE defluorination ranging from 1.5- to 2-fold. FC-133a and FC-124 enhanced CDE oxidation 89 and 74%, respectively, and FC-134a and FC-125 had no effect. While CDE metabolism was enhanced in the presence of the fluoroethanes, no additional NADPH or O2 was consumed when halothane or FC-124 was incubated with CDE compared with incubations containing only halothane or FC-124. Log-log plots of NADPH consumption and CDE metabolism with the olive oil/gas partition coefficients of each fluoroethane showed linear relationships. These data demonstrate that the activity of the fluoroethanes in stimulating P450 activity and CDE metabolism is a function of their lipid solubility, and fluoroethane-enhanced CDE metabolism is related to the ability of these compounds to increase uncoupled P450 activity.

Inhibitory effects of propofol on cytochrome P450 activities in rat hepatic microsomes

The effects of propofol on cytochrome P450 activity in rat hepatic microsomes were evaluated to determine the potential influence of this anesthetic on the metabolism of coadministered agents. In microsomes from untreated and isoniazid-treated rats, propofol was a weak inhibitor of enflurane metabolism, inhibiting activity only at 0.35 mM propofol. In contrast, toluene, a related compound, effectively impaired enflurane defluorination in microsomes from untreated, and isoniazid- and phenobarbital-treated rats at concentrations as low as 0.025 mM. Propofol, in contrast to toluene, was an effective inhibitor of benzphetamine demethylation where it inhibited this activity at propofol concentrations as low as 0.025 mM in microsomes from phenobarbital-treated rats. In microsomes from phenobarbital-treated rats, propofol potently inhibited the metabolism of aniline. Sixty-four percent inhibition was achieved at 0.03 mM propofol, whereas toluene had no effect at 1 mM. These data demonstrate that propofol does not effectively inhibit enflurane metabolism performed by the isoniazid-inducible cytochrome P450IIE1 but effectively impairs activities of the phenobarbital-inducible cytochrome P450 isozymes.

Contrasting effects of 1,1,1-trichloroethane on [14C]vinyl chloride metabolism and activation in hepatic microsomes from phenobarbital- and isoniazid-treated rats

The interaction of 1,1,1-trichloroethane (TCE), a widely used chlorocarbon solvent, on the metabolism and activation of [14C]-vinyl chloride in rat hepatic microsomes was investigated to determine the effects of combined exposures to these compounds. In microsomes from phenobarbital (PB)-treated rats, TCE increased vinyl chloride-protein binding and vinyl chloride aqueous metabolite formation over twofold when vinyl chloride 0.32% (v/v) and TCE (0.65%) are incubated together. In contrast, under similar incubation conditions, TCE inhibited vinyl chloride metabolism and protein binding up to 45% in microsomes from isoniazid-treated animals. TCE also inhibited vinyl chloride metabolism and binding in microsomes from untreated rats, but to a lesser degree. Like the effect of TCE on vinyl chloride-protein binding, TCE increased vinyl chloride binding to DNA approximately 130% in microsomes from PB-treated rats, yet inhibited vinyl chloride-DNA binding in microsomes from isoniazid-treated and untreated animals. Consistent with TCE effects on vinyl chloride binding and aqueous metabolite production, TCE further increased cytochrome P450 loss due to vinyl chloride metabolism in microsomes from PB-treated rats, but was inhibitory to cytochrome P450 loss due to vinyl chloride metabolism in microsomes from isoniazid-treated and untreated rats. These data demonstrate that the relatively metabolically inert solvent, 1,1,1-trichloroethane, can directly increase vinyl chloride metabolism and activation catalyzed by the phenobarbital-inducible isozymes, but is inhibitory toward vinyl chloride metabolism catalyzed by the isoniazid-inducible CYP2E1.

NADPH and oxygen consumption in isoflurane-facilitated 2-chloro-1,1- difluoroethene metabolism in rabbit liver microsomes

2-Chloro-1,1-difluoroethene (CDE) metabolism can be facilitated by isoflurane in microsomes. In an effort to elucidate the mechanisms of increased CDE metabolism, NADPH and oxygen consumption during CDE metabolism were measured in the absence and presence of isoflurane in rabbit liver microsomes. In microsomes from phenobarbital-treated rabbits, isoflurane (1-4 mumol, 0.6-2.3%) enhanced CDE (2 mumol, 1.1%) metabolism, increasing fluoride release up to 2.5 times compared with CDE alone. Fluoride release increased with increasing amounts of CDE (1-4 mumol). Isoflurane alone strongly increased NADPH consumption (3.78 +/- 0.4 to 9.65 +/- 0.23 nmol/mg/min +/- SD) and oxygen consumption (3.27 +/- 0.03 to 6.62 +/- 0.75 nmol/mg/min) compared with control when incubated for 5 min at 30 degrees C. No isoflurane metabolism was detected by fluoride release. Incubation of CDE alone resulted in CDE metabolism (0.70 +/- 0.15 nmol/mg/min) and lesser, but significant increases in NADPH (4.79 +/- 0.14) and oxygen consumption (4.44 +/- 0.24) compared with control. Incubation of isoflurane with CDE at 30 degrees C for 5 min caused a 3-fold increase of CDE metabolism (2.18 +/- 0.25 nmol/mg/min); however, no more NADPH (8.59 +/- 0.95) or oxygen (7.22 +/- 0.16) was consumed compared with isoflurane incubation. No significant changes in H2O2 production were observed between all groups. These data indicate that isoflurane is an efficient uncoupler of cytochrome P-450, and suggests that increased CDE metabolism by isoflurane may result from a coupling of isoflurane-stimulated cytochrome P-450 activity to CDE oxidation.

Central nervous system toxicity of local anesthetic mixtures in the rat

Local anesthetics are often administered as mixtures during regional anesthesia. This study investigated whether a synergistic or antagonistic interaction between amide/amide or amide/ester local anesthetic combinations is present with respect to central nervous system toxicity. For surgical preparation, rats were anesthetized with 0.8% halothane in 30% O2/balance N2O and mechanically ventilated. Mean arterial blood pressure and the electroencephalogram were continuously monitored. After surgery, the halothane was discontinued for 15 min. An intravenous infusion of solutions containing lidocaine alone, bupivacaine alone, or any of three mixtures of the two drugs was then begun and continued at a fixed rate until seizure activity was observed on the electroencephalogram. Total administered doses of both drugs were compared by isobolographic analysis. After a similar protocol, a second experiment was performed evaluating lidocaine, tetracaine, or any of three mixtures of those two drugs. In both experiments, normocapnia, normoxia, and normothermia were maintained for all rats. For mixtures of lidocaine/bupivacaine (P = 0.40) and lidocaine/tetracaine (P = 0.24), there was no evidence that a significant degree of either synergism or antagonism was present. At the onset of seizures, mean arterial pressure was lowest in the lidocaine-alone groups in both experiments. Increasing doses of either bupivacaine or tetracaine (with correspondingly decreasing doses of lidocaine) were associated with greater mean arterial pressure values at onset of seizures. We conclude that central nervous system toxic effects of amide/amide or amide/ester anesthetic combinations, such as might occur during accidental intravascular injection, are no more than when the drugs are administered alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute stimulation of trifluoroethene defluorination and cytochrome P450 inactivation in the rat by exposure to isoflurane

The effect of isoflurane on trifluoroethene (TFE) defluorination and cytochrome P450 inactivation was examined in rats to determine the influence of this anesthetic on in vivo fluoroethene metabolism. Exposure of rats to TFE (0.5%, v/v) or a mixture of TFE and isoflurane (0.5% each) in oxygen for 60 min resulted in plasma fluoride increased over that in nonexposed or isoflurane (0.5%)-exposed animals. In untreated rats plasma fluoride levels following TFE and TFE-isoflurane exposures were approximately equal. In rats treated with phenobarbital, however, isoflurane increased plasma fluoride over two times that in rats exposed to TFE alone. Likewise cytochrome P450 levels declined 24% in TFE-exposed animals and 64% in rats exposed to TFE-isoflurane. The ability of microsomes from fluorocarbon-exposed animals to metabolize (R)- and (S)-warfarin indicates that TFE exposure inactivated the phenobarbital-inducible isozymes P450IIB1, P450IIC6, and P450IIIA to approximately equal degrees (21-35%). TFE-isoflurane exposure further inhibited P450IIB1 and PB450IIC6 to 50-70%, but had only a minor effect on P450IIIA activity. These data demonstrate that the defluorination of TFE in vivo by the phenobarbital-inducible cytochrome P450 isozymes is increased by isoflurane, and that isoflurane enhances the ability of TFE to inactivate cytochromes P450 in an isozyme-selective manner.

Nitric oxide generation from nitroprusside by vascular tissue. Evidence that reduction of the nitroprusside anion and cyanide loss are required

Nitric oxide (NO) was produced from sodium nitroprusside in the presence of vascular tissue but was not released spontaneously from the nitroprusside anion. In the absence of tissue in the dark nitroprusside did not release NO. When solutions of nitroprusside alone were irradiated with visible light, nitric oxide was released at rates linearly proportional to nitroprusside concentration and light intensity. Nitric oxide was produced from solutions of nitroprusside in the dark after the addition of vascular tissue, including lengths of rabbit aorta, subcellular fractions of aorta, and human plasma. NO was also released from nitroprusside after reaction with various reducing agents including cysteine and other thiols, ascorbic acid, sodium dithionite, ferrous chloride, hemoglobin, myoglobin, and partially purified cytochrome P450 with an NADPH-regenerating system. HCN was simultaneously produced in these solutions, and addition of KCN blocked NO release. Iodine oxidized intermediate cyanoferrates and blocked nitric oxide release. KCN or iodine also blocked NO production by tissue, but had no effect upon photochemical NO release. These results show that, apart from photolysis which makes no physiological contribution, release of nitric oxide from nitroprusside, in simple solutions and in biological tissue, occurs after nitroprusside has undergone reduction and lost cyanide.

Effects of ketamine on outcome from temporary middle cerebral artery occlusion in the spontaneously hypertensive rat

This experiment evaluated the potential for ketamine HCl, a non-competitive glutamate antagonist, to minimize injury resulting from temporary focal cerebral ischemia. Male spontaneously hypertensive rats were randomly assigned to receive either ketamine (n = 13) or halothane anesthesia (n = 12) during 2 h of reversible middle cerebral artery occlusion (MCAO). Ketamine was administered as a 50 mg/kg i.v. loading dose followed by a continuous 1.25 mg/kg/min i.v. infusion beginning 25 min prior to ischemia and continued until 30 min after reperfusion. An additional group of rats (ketamine-shams, n = 8) underwent craniectomy and ketamine administration (as above) but the middle cerebral artery was not ligated. Physiologic values were similar between groups with the exception of plasma glucose which was elevated in the halothane-MCAO group. After 4 days recovery, rats in all groups were neurologically evaluated. There were no differences between the two groups undergoing MCAO for neurologic grading or open field behavior, although both groups performed worse than did ketamine-shams (P less than 0.05). In contrast, motor performance revealed more severe deficits in the ketamine-MCAO rats vs either the halothane-MCAO or ketamine-sham groups (P less than 0.05). Cerebral infarct volume was then planimetrically measured after triphenyl tetrazolium chloride (TTC) staining of fresh brain sections. Mean +/- S.D. infarct volume was not different between the halothane-MCAO (134 +/- 51 mm3) and ketamine-MCAO (131 +/- 64 mm3) groups. Seven of 8 sham rats were free of TTC demarcated injury and in the remaining rat injury was minimal.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the stability and cytochrome P450 specificity of the phenobarbital-induced reductive halothane-cytochrome P450 complex formed in rat hepatic microsomes

The hypothesis that the reduced spectral halothane-cytochrome P450 complex formed in rat hepatic microsomes is a stable cytochrome P450 specific species was examined. Comparisons of the cytochrome P450 inducers, phenobarbital (PB), pregnenolone-16 alpha-carbonitrile (PCN) and beta-naphthoflavone (beta-NF) showed that PB was the most effective inducer of the halothane-cytochrome P450 complex and the cytochrome P450 which liberates the halothane metabolites, 2-chloro-1,1-difluoroethene (CDE) and 2-chloro-1,1,1-trifluoroethane (CTE). However, the ratio of CDE produced to quantity of complex was found to be reduced 70-77% in these microsomes. A large portion of total microsomal cytochrome P450 was destroyed upon halothane reduction (up to 39%), yet the complexed cytochrome P450, particularly in microsomes from PB-treated animals, was resistant to the irreversible inactivation mechanisms of halothane reduction. The effects of reductive halothane metabolism on subsequent warfarin metabolism showed that 7-hydroxywarfarin formation from either (R)- or (S)-warfarin in microsomes from PCN-treated, PB-treated or untreated rats was highly susceptible to irreversible inhibition. In microsomes from PB-treated, but not PCN or untreated rats, the formation of one warfarin metabolite, 4'-hydroxywarfarin from (R)-warfarin, could be shown to be increased when complex was eliminated by photodissociation. These results suggest that PB-B is preferentially bound as complex and resistant to inactivation because of complex stability, and that halothane reduction readily destroys the cytochrome P450 form, PB-C.

Reliability and validity of the appraisal of diabetes scale

The present research evaluated the psychometric properties of a brief self-report instrument designed to assess appraisal of diabetes. Two hundred male subjects completed the Appraisal of Diabetes Scale (ADS) and provided blood samples that were subsequently assayed to provide an index of glycemic control (i.e., glycosylated hemoglobin). Subjects also completed either (a) additional measures of diabetes-related health beliefs, diabetic daily hassles, perceived stress, diabetic adherence, and psychiatric symptoms or (b) the ADS on two additional occasions. Results indicated that the ADS is an internally consistent and stable measure of diabetes-related appraisal. The validity of the measure was supported by correlational analyses which documented the relationship between the ADS and several related self-report measures.

The influence of inhalational anesthetics on in vivo and in vitro benzodiazepine receptor binding in the rat cerebral cortex

The effect of volatile anesthetics on benzodiazepine receptor binding was examined autoradiographically in the rat brain both in vivo and in vitro with the use of [3H]-Ro-15-1788, a benzodiazepine antagonist. For in vitro studies, slide-mounted brain sections were incubated at 37 degrees C in Tris buffer (50 mM, pH 7.4) with [3H]-Ro-15-1788 (flumazenil, 0.5-12.0 nM) in the presence of air (control) or 1 MAC concentrations of halothane or isoflurane. Brain sections were exposed to x-ray film and their images digitized, and specific cortical [3H]-Ro-15-1788 binding was determined. A Scatchard plot of specific cortical binding was constructed, and the dissociation constant (KD) and maximum bound ligand per milligram tissue (Bmax) were determined for each experimental group. In the in vivo trials, rats were anesthetized with 1 MAC halothane or isoflurane; 0.5 microCi/g [3H]-Ro-15-1788 was given intravenously, and the animals were killed 15 min later. Seven standardized sagittal brain sections were examined from autoradiographs. Mean specific cortical binding was determined for each group and was compared with binding in unanesthetized control rats. A third experimental trial analyzed the timed arterial blood history of [3H]-Ro-15-1788 in animals prepared exactly as in the in vivo study. The [3H]-Ro-15-1788 blood clearance over 20 min and plasma [3H]-Ro-15-1788 levels at 15 min after injection of isotope were evaluated. In vitro Scatchard analysis showed no difference in experimental groups in KD or Bmax at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

The development of the lamprey pattern generator for locomotion

The life cycle of the lamprey includes a larval stage that can last for several years. The motor behavior of the larval lamprey, the ammocoete, has been only minimally studied and little is known of the neural correlates of that behavior. Comparison of known larval behavior to that of adults leaves unclear whether there are large or small changes in the spinal nervous system during transformation. The motor output of isolated larval and transforming spinal cords when stimulated to "swim" with D-glutamate has some differences from that of comparable adult preparations, but shares many important features with adults. Primarily, the fictive swimming is less well regulated and less stable than adults of the same species. We propose that a major difference in the structure and organization of the central pattern generator for locomotion between adults and ammocoetes is a relative lack or immaturity of some cell types that participate in the coordination of the segments and the generation of the rhythm of the periodic bursting.

Metabolism of 2-chloro-1,1-difluoroethene to glyoxylic and glycolic acid in rat hepatic microsomes

The complete metabolic fate of the volatile anesthetic halothane is unclear since 2-chloro-1,1-diflurorethene (CDE), a reductive halothane metabolite, is known to readily release inorganic fluoride upon oxidation by cytochrome P-450. This study sought to clarify the metabolism of CDE by determining its metabolites and the roles of induce cytochrome P-450 forms in its metabolism. Upon incubation of [14C]CDE with rat hepatic microsomes, two major radioactive products were found which accounted for greater than 94% of the total metabolites. These compounds were determined to be the nonhalogenated compounds, glyoxylic and glycolic acids, which were formed in a ratio of approximately 1 to 2 of glyoxylic to glycolic acid. No other radioactive metabolites could be detected. Following incubation of CDE with hepatic microsomes isolated from rats treated with cytochrome P-450 inducers, measurement of fluoride release showed that phenobarbital induced CDE metabolism to the greatest degree at high CDE levels, isoniazid was the most effective inducer at low CDE concentrations, and beta-naphthoflavone was ineffective as an inducer. These results suggest that CDE biotransformation primarily involves the generation of an epoxide intermediate, which undergoes mechanisms of decay leading to total dehalogenation of the molecule, and that this metabolism is preferentially carried out by the phenobarbital- and ethanol-inducible forms of cytochrome P-450.

Evidence for functional regeneration in the adult lamprey spinal cord following transection

We report here that following partial spinal transections in adult lampreys, the fibers of the spinal cords can regenerate and restore some intersegmental coordination to the central pattern generator for locomotion, as tested in the isolated cord preparation. However, the regeneration by this test is not successful in all animals.

One-year psychosocial follow-up of patients with chest pain and angiographically normal coronary arteries

As many as 30% of patients with chest pain symptoms who are referred for arteriography are found to have normal coronary arteries. Research has shown that patients with anginal symptoms and normal coronary arteries score higher on neuroticism measurements (anxiety, depression and somatic concerns) at the time of catheterization than patients with anginal symptoms who have coronary artery disease. Research examining the cardiac course of chest pain patients with normal coronary arteries indicates that this is a nonprogressive disorder. Although follow-up studies of these patients report continued chest pain and diminished physical activity, these studies have ignored the psychologic status of the patients. Thus, it is not known whether their higher neuroticism scores at the time of catheterization persist following angiography or whether such elevated indexes of neuroticism are transient phenomena associated with precatheterization anticipatory stress. The present study examined 48 Veterans Administration Medical Center patients: 24 with anginal symptoms and normal coronary arteries and 24 with documented coronary artery disease. The patients completed a structured clinical interview and a set of psychologic inventories on the day before catheterization and 1 year later. The findings established continued high neuroticism scores among patients with anginal symptoms only and supported the findings of other investigators regarding continuing chest pain and restricted physical activity. The knowledge alone of benign coronary artery status resulted in virtually no change in the psychosocial status of these patients. Alternative treatment methods are discussed.

Reductive metabolism of halothane by purified cytochrome P-450

The reductive metabolism of halothane was determined using purified RLM2, PBRLM4 and PBRLM5 forms of rat liver microsomal cytochrome P-450. The metabolites, 2-chloro-1,1,1-trifluoroethane (CTE) and 2-chloro-1,1-difluoroethylene (CDE), were determined. All three forms of cytochrome P-450 produced CTE with relatively small differences in its production among the various forms. There were major differences, however, in the production of CDE, with PBRLM5 being the most active. PBRLM5 was also the only form to show the development of a complex between halothane and cytochrome P-450. This complex absorbed light maximally at 470 nm. The complex formation and the production of CDE by PBRLM5 were stimulated by the addition of cytochrome b5. Cytochrome b5 had no effect on CDE production by PBRLM4 and inhibited the production of both CTE and CDE by RLM2. These results show that the two-electron reduction of halothane by cytochrome P-450 was catalyzed by the PBRLM5 form and that cytochrome b5 stimulated the transfer of the second electron to halothane through PBRLM5, but not RLM2 or PBRLM4.

Metabolic activation of the halothane metabolite, [14C]2-chloro-1,1-difluoroethene, in hepatic microsomes

Halothane is reduced to 2-chloro-1,1,1-trifluoroethane (CTE) and 2-chloro-1,1-difluoroethene (CDE) by cytochrome P-450. These compounds may potentially undergo secondary metabolism in vivo, but their capacity to undergo metabolic activation and bind to macromolecules is unknown. This study, therefore, compared the abilities of CDE and CTE to bind to microsomal components in relation to that of halothane in hepatic microsomes. The results show that CDE, in addition to halothane, binds to microsomes under conditions of cytochrome P-450 activity. While halothane bound predominantly to lipids under nitrogen, CDE bound mainly to protein under oxygen. No CTE binding under any conditions could be detected. On an equimolar basis, CDE binding to protein was approximately one-third of that of halothane under oxidative conditions, however, CDE binding was enhanced in the presence of halothane. The results support the hypothesis that CDE metabolism may contribute to the metabolic binding due to halothane exposures.

Comprehension of informed consent information by young-old through old-old volunteers

Comprehension of typewritten informed consent information was evaluated for young-old (60-69 years) through old-old (80-89 years) volunteers as a function of years of education (less than 12, 12, and greater than 12), readability of information (low [college level] vs high [7th grade]), and typeface used in the preparation of the materials (Prestige Elite 72, Letter Gothic, and Orator). All volunteers (N = 235) read a typewritten information sheet and retained it for review while answering eight multiple choice questions. Immediate feedback was provided, and a second test was administered if any answers were incorrect. The findings indicated that comprehension varied directly with education and inversely with age. Typeface and age interacted due to age-related differences with the two smaller (Prestige Elite and Letter Gothic), but not with the largest of the typefaces (Orator). These findings suggest that the observed age-related differences may have been due to visual and not cognitive deficits. Readability did not affect performance either by itself or in combination with any other variable.

Stimulatory effects of halothane and isoflurane on fluoride release and cytochrome P-450 loss caused by metabolism of 2-chloro-1,1-difluoroethene, a halothane metabolite

The structural similarity of the halothane metabolite, 2-chloro-1,1-difluoroethene (CDE), to haloethenes that are metabolized by and inactivate cytochrome P-450, suggests that CDE may undergo secondary metabolism and degrade these isozymes. This possibility was examined in hepatic microsomes by determining fluoride release and cytochrome P-450 loss due to CDE metabolism in the presence of several anesthetics. CDE alone decreased cytochrome P-450 from phenobarbital-treated rats by as much as 37%, but the addition of isoflurane or halothane to incubations containing CDE increased the loss of cytochrome P-450 nearly twofold. Fluoride release was enhanced approximately 2.5 to 3 times by halothane or isoflurane; however, fluroxene inhibited fluoride release and did not enhance the loss of cytochrome P-450. Extrapolation of these results to the clinical situation suggests that the metabolism of CDE produced during halothane anesthesia and the accompanying cytochrome P-450 loss may contribute to the inhibition of drug metabolism produced by halothane.

Comparative defluorination and cytochrome P-450 loss by the microsomal metabolism of fluoro- and fluorochloroethenes

Halogenated ethenes are oxidatively metabolized by cytochrome P-450 to intermediates which inactivate cytochrome P-450 by destroying heme and to epoxides which may react with cellular macromolecules or decompose to other products. To determine the relative capabilities of fluoroethenes to inactivate cytochrome P-450 and undergo metabolism, fluoride release, cytochrome P-450 loss, and heme loss due to the metabolism of trifluorochloroethene (TFCE), chlorodifluoroethene (CDE), difluoroethene (DFE), and trifluoroethene (TFE) were compared in rat hepatic microsomes. Fluoride release, in order of decreasing amounts of fluoride released, followed the order: CDE greater than TFCE much greater than TFE greater than DFE. In contrast, in order of each compound's decreasing effectiveness to destroy both cytochrome P-450 and heme, the following sequence was obtained: TFE greater than CDE greater than TFCE greater than DFE. In phenobarbital-induced hepatic microsomes, TFE inactivated up to 67% of the cytochrome P-450, whereas DFE inactivated only up to 17%. The results of this study indicate that chloro substituents enhance defluorination of the ethenes, and that cytochrome P-450 inactivation by the fluoroethenes is highly dependent on the degree and nature of the halogen substituents.

Stabilization of the reduced halocarbon-cytochrome P-450 complex of halothane by N-alkanes

Under anaerobic conditions, various halogenated compounds, when metabolized by cytochrome P-450, form complexes which are spectrally detectable. Previous studies have shown that halothane forms such a complex with cytochrome P-450, and the result is a strong absorption at 470 nm. Stabilization of this proposed intermediate carbanion complex has never been demonstrated in a biological system. Data are presented which show that several organic solvents (C5-C7N-alkanes) will stabilize the complex formed between halothane and cytochrome P-450. Stabilization allowed the decay of the complex to be studied, and it is demonstrated that the product of decay was chlorodifluoroethylene, which substantiates the hypothesis that the complex is a two electron-reduced carbanion. Carbon tetrachloride and benzyl bromide, which also produce spectrally visible intermediate complexes, were not stabilized by this treatment. Stabilization of the halothane complex in a biological system may facilitate studies to identify precisely the halothane-cytochrome P-450 complex and to clarify the mechanisms of halothane reduction by cytochrome P-450.

Informed consent for research. Effects of readability, patient age, and education

Comprehension of informed consent materials from a study of psychological variables associated with chest pain was evaluated as a function of age (27 to 69 years), education (5 to 20 years), and readability of information [low (college level) versus high (7th grade)]. The potentially confounding effect of memory was eliminated by allowing patients to use the written information sheets to find answers to the multiple choice test. Feedback and a repeat test were provided if any answers were incorrect. The findings indicated that comprehension varied inversely with age and directly with education. It is suggested that while ensuring informed consent may be difficult for all volunteers, it may be a critical problem for elderly patients with low education. The effects of readability were not consistent, suggesting that simplifying informed consent materials by shortening words and sentences may not, by itself, be sufficient to improve comprehension.

The formation of chlorobenzene and benzene by the reductive metabolism of lindane in rat liver microsomes

The major metabolite produced by incubating [14C]lindane with rat liver microsomes under anaerobic conditions was determined to be chlorobenzene, with lesser amounts of benzene also being formed. Using relatively high lindane concentrations (250 microM), four nonvolatile metabolites of lindane were also produced anaerobically, the predominant one being identified by mass spectrometry as tetrachlorocyclohexene (TCCH). TCCH, likewise, was reduced to chlorobenzene and benzene in microsomes under anaerobic conditions. Binding of [14C]lindane to microsomal protein occurred under aerobic as well as anaerobic incubation conditions; however, lindane protein binding was greatest in anaerobic incubations compared to those containing an atmosphere of air or 100% oxygen. Hemin reduced by dithionite also readily produced chlorobenzene and benzene from lindane. These results indicate that lindane interacts readily with heme and heme proteins, including cytochrome P-450, in the absence of oxygen to undergo multiple chloride eliminations forming chlorobenzene and benzene as end products.

Reductive halothane metabolite formation and halothane binding in rat hepatic microsomes

The production of the reductive [14C]halothane metabolites, 2-chloro-1, 1,1-trifluoroethane ( CTE ) and 2-chloro-1,1- difluoroethylene (CDE), was determined in anaerobic microsomal incubations by high pressure liquid chromatography (HPLC). The HPLC technique used allowed accurate measurements of low levels of [14C]halothane metabolites. Comparisons of metabolic profiles and halothane binding in microsomes reduced with NADPH and sodium dithionite show that dithionite stimulates CDE production and total halothane degradation, but inhibits CTE formation and [14C]halothane binding. Similarly, the addition of isoflurane, but not enflurane, to microsomes increases CDE production and decreases CTE formation and [14C]halothane-lipid binding. Measurement of fluoride in similar incubations show that fluoride release from halothane correlates with the formation of CDE and not CTE . The results demonstrate that the relative production of CTE and CDE may not remain constant in microsomal preparations, and that halothane binding correlates with CTE formation and not CDE and fluoride production.

Metabolism-dependent binding of the chlorinated insecticide DDT and its metabolite, DDD, to microsomal protein and lipids

Dichlorodi[U-14C]phenyltrichloroethane ( [14C]DDT), incubated with rat hepatic microsomes and NADPH, produced reactive intermediates which covalently bound to microsomal protein and lipids. In atmospheric oxygen, DDT bound to microsomal protein; however, binding was increased up to approximately 70% by oxygen depletion. Low levels of [14C]DDT binding to microsomal lipids occurred under atmospheric oxygen but, in contrast to protein binding, DDT-phospholipid binding was increased up to 20-fold by oxygen depletion. Dichlorodiphenyldichloroethane (DDD) was rapidly formed from DDT under anaerobic conditions, although when DDD was utilized as substrate, binding to microsomal protein occurred only in the presence of oxygen. Sodium dithionite, added to microsomes, produced [14C]DDT phospholipid and protein binding, and DDD formation, but failed to support DDD metabolism or binding. The data are consistent with the reductive formation of a DDT free-radical intermediate that led to the formation of DDD and that was bound preferentially to microsomal lipids.

Effect of thiamin deprivation on the in vitro metabolic activation of benzo(a)pyrene

Feeding a thiamin-deficient diet to male and female rats for 3 weeks alters the mixed function oxidases responsible for metabolizing benzo(a)pyrene and enhances the response of these enzymes to induction by phenobarbital or 3-methylcholanthrene. The caloric restriction observed in thiamin deprivation may be partially responsible for the enhanced metabolism in this condition but, as established in pair-feeding studies, was not responsible for the enhanced response to enzyme inducers seen in these animals. The degree of altered response was also seen to depend on the sex of the rat and on the substrate concentration of the incubation mixture.