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Biomedical subjects

J R Mitchell

Publications and source records attributed to J R Mitchell.

At least 91 records · Page 5Linked to original sources
PubMed1988

Reactive oxygen species during ischemia-reflow injury in isolated perfused rat liver.

The hypothesis that intracellular generation of reactive oxygen species in hepatocytes or reticuloendothelial cells may cause ischemia-reperfusion injury was tested in isolated perfused livers of male Fischer rats. GSSG was measured in perfusate, bile, and tissue as a sensitive index of oxidative stress. After a preperfusion phase of 30 min, the perfusion was stopped (global ischemia) for various times (30, 120 min) and the liver was reperfused for another 60 min. The bile flow (1.48 +/- 0.17 microliters/min X gram liver weight), the biliary efflux of total glutathione (6.54 +/- 0.94 nmol GSH eq/min X g), and GSSG (1.59 +/- 0.23 nmol GSH eq/min X g) recovered to 69-86% after short-term ischemia and to 36-72% after 2 h of ischemia when compared with values obtained from control livers perfused for the same period of time. During reperfusion, the sinusoidal efflux of total glutathione (16.4 +/- 2.1 nmol GSH eq/min X g) and GSSG (0.13 +/- 0.05 nmol GSH eq/min X g) did not change except for an initial 10-30-s increase during reperfusion washout. No increased GSSG secretion into bile was detectable at any time during reperfusion. The liver content of total glutathione (32.5 +/- 3.5 nmol GSH eq/mg protein) and GSSG (0.27 +/- 0.09 nmol GSH eq/mg protein) did not change significantly during any period of ischemia or reperfusion. We conclude, therefore, that at most only a minor amount of reactive oxygen species were generated during reperfusion. Thus, reactive oxygen species are unlikely to cause ischemia/reperfusion injury in rat liver by lipid peroxidation or tissue thiol oxidation.

Adenosine Triphosphate↗
PubMed1988

Liver membrane calcium transport in diquat-induced oxidative stress in vivo.

Hepatic necrosis is produced rapidly by 0.1 mmol/kg diquat in male Fischer-344 rats but not Sprague-Dawley rats, yet massive oxidant stress is caused by diquat in both strains of rat. Liver plasma membrane calcium uptake was unaltered by diquat treatment in either strain. However, diquat inhibited ATP-dependent calcium sequestration by hepatic microsomes from Fischer rats by 33% (33 +/- 2 versus 50 +/- 2 nmol/mg/20 min), whereas liver microsomal calcium uptake in Sprague-Dawley rats was not decreased by diquat treatment. Microsomes of diquat-treated Fischer rats showed marked increases in calcium efflux versus controls (k efflux = 0.115 +/- 0.027 versus 0.051 +/- 0.005 min-1; p less than 0.025), but microsomes of diquat-treated Sprague-Dawley rats exhibited no significant change in efflux rate. Calcium uptake by the endoplasmic reticulum of saponin-permeabilized isolated hepatocytes was diminished in parallel with diquat cytotoxicity. Significant increases in 11-, 12-, and 15-hydroxy 20:4 fatty acids were found in liver microsomes isolated after diquat treatment in vivo and administration of desferrioxamine (0.24 mmol/kg, intraperitoneally) administered before diquat significantly protected against the inhibition of microsomal calcium uptake. These data suggest a possible role for Fenton chemistry and lipid peroxidation in this feature of diquat-generated hepatic damage in vivo.

Animals↗
PubMed1987

Interim discharge summaries: how are they best delivered to general practitioners?

All patients discharged from a medical ward during four months were randomly assigned to one of two groups. In one group the patients were given their interim discharge summary for delivery to their general practitioner by hand; in the other group the summary was posted by the hospital. Of the 289 summaries sent by either method, 279 (97%) arrived at the general practitioner's surgery. A mean (median) time of two (one) days elapsed before arrival when summaries were delivered by hand and a mean (median) of four and a half (four) days when they were posted; at least 55% of summaries delivered by hand arrived within one day of the day of discharge compared with 8% of those posted. If all interim discharge summaries were given to patients to deliver communication between hospitals and general practitioners would be accelerated and considerable savings might be made.

Communication↗
PubMed1987

Therapeutic doses of acetaminophen stimulate the turnover of cysteine and glutathione in man.

In spite of the importance of glutathione (GSH) in the detoxification of toxic metabolites of drugs, virtually nothing is known about the regulation of hepatic GSH homeostasis in man. In order to estimate the turnover of hepatic GSH and to assess the effect of different doses of acetaminophen (paracetamol) on the synthesis of GSH in man, [3H]cystine and varying doses of acetaminophen were administered to healthy volunteers, and the time course of the specific activity of the cysteine moiety of N-acetylcysteinyl-acetaminophen excreted in urine was followed. The fractional rate of turnover of the tracer in N-acetylcysteinyl-acetaminophen increased significantly from 0.031 +/- 0.007 h-1 after doses of acetaminophen ranging from 50 to 300 mg to 0.045 +/- 0.011 and 0.121 +/- 0.027 h-1 following 600 and 1200 mg of acetaminophen, respectively. The data indicate that therapeutic doses of acetaminophen markedly stimulate the rate of turnover of the pool of cysteine available for the synthesis of GSH, most likely due to an increased rate of synthesis of GSH which is required to detoxify the toxic metabolite of acetaminophen. Patients who are not able to respond to a similar demand on their stores of GSH by increasing the synthesis of GSH may be at higher risk of developing hepatic injury from drugs that require GSH for their detoxification.

Acetaminophen↗
PubMed1987

No evidence for reactive oxygen damage in ischemia-reflow injury.

The present studies show that ischemia and reperfusion cause severe injury without evidence of generation of large amounts of reactive oxygen. Calculations show that it is necessary that amounts of reactive oxygen several orders of magnitude greater than that measured during ischemia-reflow injury be generated intracellularly by redox-cycling compounds such as diquat or by direct oxidants such as t-butyl hydroperoxide before endogenous cellular antioxidant systems in ischemia-reperfused rat liver or canine heart are overwhelmed. Thus, our data are incompatible with the hypothesis that oxygen radicals cause ischemia-reflow injury by lipid peroxidation or tissue thiol oxidation as postulated in Figure 1. How might one reconcile these results with the important experiments documenting protection against ischemia-reflow injury by treatment with antioxidants, antioxidant enzymes, allopurinol, cyclooxygenase/lipoxygenase inhibitors, cobra venom factor, and antisera against leukocytes (Table 1)? It seems most likely that the small amounts of reactive oxygen that can be generated in a reduced, acidic environment, such as occurs in tissue ischemia, could only be playing a catalytic function and not producing a massive oxidative attack on tissue membranes. Thus, future studies might best be directed at the catalytic function of superoxide/hydrogen peroxide in modulating the availability of substances such as lipoxygenase and cyclooxygenase products and of endothelium-derived relaxing factor during ischemia-reflow injury.

Animals↗
PubMed1986

Physicians' attitudes to four common problems: hypertension, atrial fibrillation, transient ischaemic attacks, and angina pectoris.

A questionnaire was completed by 341 senior physicians on their attitudes to four common cardiovascular problems. Their replies showed that uncertainty about the end point for diastolic blood pressure still prevails and that their approach to the management of hypertension of differing severity in men and women of varying ages stems more from personal belief than from the results of clinical trials. Unless patients with atrial fibrillation also had mitral valve disease anticoagulation was not thought to be necessary, thereby making it ethically possible to carry out a trial of anticoagulants in stroke prevention on patients with atrial fibrillation but no valvular disease. The physicians' suggestions for very active management in transient ischaemic attacks extended beyond the evidence available to them, whereas their approach to the use of coronary arteriography closely reflected the results of clinical trials. These findings may indicate that recent cardiovascular trials that have provided definitive results have had more impact than earlier inadequate studies.

Adult↗
PubMed1986

Quantitation of lipid peroxidation products by gas chromatography-mass spectrometry.

A method for the quantitation of lipid peroxidation products in total hepatic lipid has been developed. Lipid extracts are reduced and subsequently transmethylated with sodium methoxide. The hydroxy fatty acid methyl esters are isolated by silicic acid chromatography and derivatized to their trimethylsilyl ethers prior to analysis by gas chromatography-mass spectrometry. Three isomers, 11-, 12-, and 15-hydroxyeicosatetraenoic acid (HETE), are quantitated using selected ion monitoring techniques relative to the internal standard, methyl 15-hydroxyarachidate. In mice treated with carbon tetrachloride (2 ml/kg), the HETE levels in total hepatic lipid were 20-fold greater than those found in control animals. HETE levels were also elevated (5- to 10-fold) in hepatic lipid from rats treated with the same dose of carbon tetrachloride. Studies on subcellular fractions with this methodology show that these lipid peroxidation products are 5- to 6-fold higher in hepatic plasma membrane vesicles isolated from rats treated with carbon tetrachloride when compared with those isolated from control animals.

Animals↗
PubMed1986

Enzyme-linked immunosorbent assay with major outer membrane proteins of Brucella melitensis to measure immune response to Brucella species.

We developed an enzyme-linked immunosorbent assay (ELISA) system to measure human immunoglobulin G (IgG) and IgM response to the major outer membrane proteins of Brucella melitensis. The ELISA was more sensitive in detecting antibody than a standard microagglutination (MA) test with B. abortus antigen. Of 101 sera from persons with suspected brucellosis, 79 (78.2%) gave ELISA IgM titers greater than or equal to the B. abortus MA titer without 2-mercaptoethanol (2ME), which measures both IgM and IgG. Of the 101 sera, 97% gave ELISA IgG titers greater than or equal to the MA with 2ME titer. A total of 58 sera, drawn from 11 human patients from 1 to 29 weeks after onset of brucellosis, gave higher geometric mean titers for the ELISA IgG test than for the MA with 2ME test. These 58 sera also gave ELISA IgM geometric mean titers that were greater than or within one doubling dilution of the geometric mean titers of MA without 2ME. In addition to detecting antibody response to B. abortus, B. melitensis, and B. suis, the ELISA was sensitive to antibody response to human and canine infections with B. canis. The B. canis antibody response is not detected by the MA test with B. abortus antigen. The ELISA, with a standard preparation of major outer membrane proteins of B. melitensis as antigen, appears to be useful in measuring antibody response in humans to infections by all species of Brucella known to infect humans.

Agglutination Tests↗
PubMed1986

Steady state verapamil tissue distribution in the dog: differing tissue accumulation.

Plasma, heart, and extracardiac tissue verapamil concentrations were measured after sustained intravenous infusions in 11 dogs to determine the differential tissue accumulation of verapamil. A steady state verapamil concentration of 327 +/- 50 ng/ml decreased the mean arterial blood pressure from 104 +/- 9 to 90 +/- 6 mm Hg (p = 0.08) and the P-R interval increased from 118 +/- 4 to 176 +/- 13 ms (p less than 0.001) with second-degree atrioventricular block developing in 6 animals. Verapamil accumulated in organs in the following order: Lung much greater than kidney greater than spleen greater than ventricular myocardium = liver greater than atrial myocardium greater than cerebral cortex greater than fat = skeletal muscle. Levels in the ventricular free wall were consistently greater than atrial levels, but no difference was observed between left versus right-sided cardiac chambers. In summary, affinity of different organs for verapamil is highly variable and organ-specific; furthermore, differential intracardiac chamber accumulation occurs.

Animals↗
PubMed1986

Evidence for increased membrane permeability of plasmalemmal vesicles from livers of phenobarbital-induced CCl4-intoxicated rats.

We have observed a marked increase in Ca2+ permeability of plasma membranes isolated from rats treated in vivo with CCl4 (2 ml/kg), after phenobarbital induction and overnight fast. Regulation of intracellular free Ca2+ is vital to cell viability and function, and the increased plasma membrane permeability, if representative of a change occurring in vivo, may be a critical biochemical determinant of CCl4-induced hepatic necrosis. Permeability to small cations of liver plasma membrane vesicles of control and CCl4-dosed rats was tested by two independent methods: 1) Ca2+ efflux after passive loading in 1 mM Ca2+, and 2) 86Rb+ uptake driven by valinomycin-induced K+ diffusion potential after 100 mM KCl-equilibrated vesicles were stripped of external K+ by cation exchange. Both indicated markedly increased permeability in plasma membranes after CCl4 in vivo. First order rate constants of biphasic Ca2+ efflux were 0.272 and 0.0516 min-1 for controls and 1.78 and 0.171 min-1 for vesicles from CCl4-treated animals. 86Rb+ uptake by CCl4 vesicles was 47% of control. Total calcium contents of plasma membranes (prepared in the absence of EGTA) by atomic absorption were 17.4 +/- 2.0 (control) and 10.9 +/- 1.2 (CCl4) nmol/mg of protein (means +/- SE, p less than 0.025). In correlation with altered biochemical function, we found 4-fold increases in the content of 11-, 12-, and 15-hydroxyeicosatetraenoic acids in plasma membranes of CCl4-treated rats. Although these specific oxidized fatty acids are unlikely to be ionophores, the ionophoretic properties of certain other oxygenated polyunsaturated fatty acids suggest a mechanism whereby accumulation of lipid oxidation products may be responsible for the altered membrane permeability we have observed after CCl4, and perhaps ultimately for cell death in CCl4-induced hepatic necrosis.

Animals↗
PubMed1986

Traumatic avulsion of the proximal femoral articular cartilage as a cause of hip dislocation in broiler chickens.

Review of the normal anatomy of the coxofemoral joint in broiler chickens aged seven weeks and comparison with cases of so-called "hip-dislocation" revealed that the lesion is essentially an avulsion of the articular cartilage of the femoral head, traumatically caused by the manner of catching and handling of birds. No direct relationship to dyschondroplasia (osteochondrosis) was established.

Animals↗
PubMed1985

Acetaminophen hepatotoxicity in vivo is not accompanied by oxidant stress.

Hepatotoxic doses of acetaminophen in Fischer 344 rats did not increase biliary efflux of oxidized glutathione. Pretreatment of the animals with bis(2-chloroethyl)-N-nitrosourea inhibited hepatic glutathione reductase by 73 percent but did not potentiate the hepatotoxicity of acetaminophen and did not produce an increase in biliary efflux of oxidized glutathione in response to acetaminophen. Hepatic protein thiol content was not depleted by acetaminophen. A proposed role for oxidant stress mechanisms mediated either by reactive oxygen species or by the direct oxidant action of a reactive metabolite in acetaminophen-induced hepatotoxicity is unsubstantiated and unlikely.

Acetaminophen↗