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J A Mitchell

Publications and source records attributed to J A Mitchell.

At least 145 records · Page 8Linked to original sources
PubMed1993

Nitric oxide-mediated hyporeactivity to noradrenaline precedes the induction of nitric oxide synthase in endotoxin shock.

1. The role of an enhanced formation of nitric oxide (NO) and the relative importance of the constitutive and inducible NO synthase (NOS) for the development of immediate (within 60 min) and delayed (at 180 min) vascular hyporeactivity to noradrenaline was investigated in a model of circulatory shock induced by endotoxin (lipopolysaccharide; LPS) in the rat. 2. Male Wistar rats were anaesthetized and instrumented for the measurement of mean arterial blood pressure (MAP) and heart rate. In addition, the calcium-dependent and calcium-independent NOS activity was measured ex vivo by the conversion of [3H]-arginine to [3H]-citrulline in homogenates from several organs obtained from vehicle- and LPS-treated rats. 3. E. coli LPS (10 mg kg-1, i.v. bolus) caused a rapid (within 5 min) and sustained fall in MAP. At 30 and 60 min after LPS, pressor responses to noradrenaline (0.3, 1 or 3 micrograms kg-1, i.v.) were significantly reduced. The pressor responses were restored by NG-nitro-L-arginine methyl ester (L-NAME, 1 mg kg-1, i.v. at 60 min), a potent inhibitor of NO synthesis. In contrast, L-NAME did not potentiate the noradrenaline-induced pressor responses in control animals. 4. Dexamethasone (3 mg kg-1, i.v., 60 min prior to LPS), a potent inhibitor of the induction of NOS, did not alter initial MAP or pressor responses to noradrenaline in control rats, but significantly attenuated the LPS-induced fall in MAP at 15 to 60 min after LPS. Dexamethasone did not influence the development of the LPS-induced immediate (within 60 min) hyporeactivity to noradrenaline. However,dexamethasone pretreatment prevented the hypotension and vascular hyporeactivity at 180 min.5. At 60 min after LPS a moderate increase in the activity of a calcium-independent (inducible) NOS activity was detected in the aorta, but not in any of the other tissues studied. However, at 180 min after LPS, a significant NOS induction was observed in the lung, liver, spleen, mesentery, heart and aorta.This NOS induction was substantially prevented by pretreatment with dexamethasone.6. These results suggest that the immediate hypotension and vascular hyporeactivity to noradrenaline in endotoxin shock is caused by an enhanced formation of NO due to activation of the constitutive enzyme. The delayed hypotension and vascular hyporeactivity, however, is due to enhanced NO formation by the LPS-induced enzyme.

Amino Acid Oxidoreductases↗
PubMed1993

Support of renal blood flow after ischaemic-reperfusion injury by endogenous formation of nitric oxide and of cyclo-oxygenase vasodilator metabolites.

1. Ischaemia-reperfusion injury in the kidney is associated with a loss of autoregulation, an increase in renal vascular resistance (RVR), a decrease of renal blood flow (RBF) and ultimately acute renal failure. The aim of this study was to investigate the role of the release of endogenous nitric oxide (NO) in the recovery of RBF after ischaemic injury of the renal vascular bed. 2. Anaesthetized rats (thiopentone sodium; 120 mg kg-1, i.p.) were submitted to acute renal ischaemia followed by 2 or 6 h of reperfusion (I/R). Reperfusion was associated with a significant reduction in RBF, an increase in RVR, and an impairment of the vasodilator effect of acetylcholine (ACh). 3. NG-nitro-L-arginine methyl ester (L-NAME, 30 micrograms kg-1 min-1, i.v., n = 5) significantly prevented the recovery of RBF after I/R injury. Similarly, inhibition of prostanoid formation with indomethacin (5 mg kg-1, i.v., n = 4) significantly enhanced the rise in RVR associated with I/R injury. 4. Infusion of L-arginine (L-Arg; 1 or 3 mg kg-1 min-1, i.v., n = 5 and 4, respectively) or D-Arg (1 mg kg-1 min-1, i.v., n = 6), starting 30 min after occlusion, did not improve the recovery of RBF. Furthermore, infusion of L-Arg (20 mg kg-1 min-1 for 15 min; n = 4) had no effect on the I/R-induced impairment of the vasodilator responses to ACh. 5. To elucidate the relative importance of the constitutive and inducible NO synthase isoforms for the formation of NO after I/R, calcium-dependent (constitutive) and calcium-independent (inducible) NO synthase activities were measured in kidney homogenates obtained from ischaemic or non-ischaemic kidneys. A calcium-independent NO synthase activity was not detectable in kidney homogenates obtained from either sham-operated control rats or from animals subjected to I/R. Moreover, dexamethasone(3 mg kg-1, i.v., 60 min prior to I/R, n = 6), an inhibitor of the induction of NO synthase,had no effect on either RBF or RVR in rats subjected to I/R. In contrast to I/R, lipopolysaccaride(LPS, endotoxin; 5 mg kg-1, i.p., n = 3) caused a significant induction of a calcium-independent NO synthase activity in the kidney.6. These results confirm the importance of the release of vasodilator cyclo-oxygenase metabolites in the compromised renal circulation and indicate that the formation of NO derived from the constitutive, but not the inducible NO synthase, is also important for the maintenance of RBF after I/R injury of the renal vascular bed.

Amino Acid Oxidoreductases↗
PubMed1993

Induction by endotoxin of nitric oxide synthase in the rat mesentery: lack of effect on action of vasoconstrictors.

1. Male Sprague-Dawley or Wistar rats were injected with bacterial lipopolysaccharide (LPS; 5 mg kg-1, i.p.) and killed after 1, 3, 6, 15, and 24 h. The brains, mesenteries, spleens, lungs, livers, kidneys, hearts, aortae and diaphragms were removed and frozen immediately. Control rats were injected with sterile saline and killed after 6 h. 2. The organs were homogenized in a semi-frozen state and NO synthase (NOS) activity measured in tissues from both LPS-treated and saline-treated groups by the ability of homogenates to convert [3H]-L-arginine to [3H]-L-citrulline in a NADPH-dependent manner. 3. The NOS activity in all organs taken from control animals was found to be calcium-dependent, with the highest activity being in the brain. After LPS-treatment an induced calcium-independent NOS was detected in all tissues tested, with the exception of the brain. The spleen, lung, mesentery and liver had the highest amounts of LPS-induced NOS activity. No induction of calcium-dependent NOS was detected. 4. Induction of NOS was maximum 6 h after administration of LPS and had returned to control levels in 24 h. 5. The constitutive NOS in brain and mesentery and the LPS-induced activities in the spleen, lung, liver and mesentery were inhibited by NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine methyl ester (L-NAME) according to concentration. The IC50 for L-NAME was 2.5 microM against the constitutive NOS from brain, and 20-25 microM against the inducible NOS. For L-NMMA the IC50 was 20-25 microM against either NOS isoform. 7. The vascular responses to endothelin-I (ET-1), the thromboxane A2-mimetic 11 alpha,9 alpha-epoxymethanoprostaglandin F2alpha (U46619), phenylephrine (PE) or 5-hydroxytryptamine (5-HT) were measured in the simultaneously perfused arterial and venous mesenteric vascular beds from both control and LPS-treated(6 h) rats. Vasoconstrictor responses to all agonists tested were unaffected by LPS treatment. In the presence of L-NAME (100 microM) vasoconstrictor responses were potentiated in both the arterial and venous portion of the mesenteric beds from both control and LPS-treated rats. The potentiation of responses to U46619 was significantly greater in beds from LPS-treated rats.8. Injection of LPS i.p. is associated with induction of NOS in all organs tested, except for the brain. In the mesentery this is not accompanied by a hyporesponsiveness to constrictor agents suggesting an increased sensitivity, particularly to U46619. This may explain the poor perfusion and tissue damage in the splanchnic circulation associated with sepsis.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1993

Platelet-activating factor contributes to the induction of nitric oxide synthase by bacterial lipopolysaccharide.

This study investigates the role of endogenous platelet-activating factor (PAF) in the production of nitric oxide (NO) by constitutive and inducible isoforms of NO synthase (NOS) in endotoxin shock. In anesthetized rats, 3 hours of endotoxemia resulted in a fall in mean arterial blood pressure (MAP) from 127 +/- 5 (control) to 61 +/- 7 mm Hg and a reduction of the pressor responses to norepinephrine (NE, 1 microgram.kg-1) from 33 +/- 3 (control) to 17 +/- 2 mm Hg. Endotoxemia for 3 hours also resulted in a significant reduction in the contractile effects of NE (10(-8) to 10(-6) mol/L) in thoracic aortas ex vivo. This hyporeactivity to NE was due to an enhanced formation of NO, for it was restored by the NOS inhibitor NG-nitro-L-arginine methyl ester. Animals pretreated with the PAF receptor antagonist WEB 2086 maintained higher MAP (MAP at 180 minutes, 98 +/- 6 mm Hg) and exhibited more pronounced pressor responses to NE at 180 minutes after LPS injection. Moreover, WEB 2086 attenuated by 58% the lipopolysaccharide (LPS)-induced hyporeactivity of the rat aortic rings ex vivo. At 3 hours after LPS injection, calcium-independent NOS activity was induced in the lung. The activity of inducible NOS was significantly lower (by 31%) in lungs of rats pretreated with WEB 2086. The hypothesis that WEB 2086 attenuates the induction of NOS in vivo was substantiated in vitro by the finding that pretreatment with WEB 2086 for 30 minutes inhibited the LPS-stimulated NO production in cultured murine macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗
PubMed1993

Nifedipine inhibits the induction of nitric oxide synthase by bacterial lipopolysaccharide.

We investigated the effect of the calcium channel antagonist nifedipine on the induction of nitric oxide synthase (NOS) by bacterial endotoxin (lipopolysaccharide; LPS) in J774.2 macrophages, in cultured rat aortic smooth muscle cells and in a rat model of endotoxin shock. Stimulation by LPS for 24 hr increased nitrite accumulation in the supernatant of both cell types. NOS induction accounts for this nitrite accumulation, as both NG-methyl-L-arginine and cycloheximide reduced nitrite production in both cell types. Dexamethasone inhibited LPS-stimulated nitrite production in macrophages, but not in rat aortic smooth muscle cells. Nifedipine inhibited the production of nitrite in these LPS-treated cell types, with a more pronounced effect on macrophages. However, nifedipine did not inhibit the production of nitrite in J774.2 cells in which NOS had already been induced by prior exposure to LPS, and any possible further induction was inhibited by cycloheximide. In anesthetized rats subjected to LPS, pretreatment with nifedipine or dexamethasone ameliorated the fall in mean arterial blood pressure and the vascular hyporeactivity to norepinephrine at 180 min after LPS injection. At 180 min after LPS, an increase in a calcium-independent (induced) NOS activity was measured in lung homogenates. This induced NOS activity was reduced in lungs from rats treated with nifedipine or dexamethasone before LPS. Thus, nifedipine inhibits the induction of NOS in response to LPS in cultured cells in vitro and in the anesthetized rat.

Amino Acid Oxidoreductases↗
PubMed1993

Quality evaluation of controlled clinical information service trials.

Randomized controlled clinical trials are increasingly accepted as tools of computer technology assessment and, therefore, quality evaluation of trials has great theoretical and practical significance. The purpose of this study was to assist the design of evaluation studies and synthesis of published results by developing and validating an easy-to-use quality scoring method. The development of the new scoring system was based on the available quality evaluation methods and the analysis of 19 trial reports registered in the Columbia Registry of Controlled Clinical Information Service Trials. First critical aspects and afterwards the levels of quality were defined. In spite of the fact that all quality requirements were met by some trials, the average overall quality score was 52.6 (+/- 8.7) per cent. The minimum score was 37 and the maximum was 72 per cent. Data collection and site/sample definition were better in the good quality trials, but improvement in statistical analysis was erratic. The quality scoring method was validated by using another sample of 20 registered trials. While the number of published controlled clinical trials is increasing in medical informatics, the analysis was unable to demonstrate a significant positive correlation between the quality and year of publication.

Evaluation Studies as Topic↗
PubMed1993

Mendelian inheritance in man: diagnoses in the UMLS.

Because they deal with many distinct but rare inheritance diseases, geneticists have difficulty translating from their codes to other biomedical coding schemes. The objective of this research was to investigate the potential uses and difficulties of using the UMLS Metathesaurus for genetic diagnoses and to make recommendations to UMLS developers for improvements in UMLS for common genetic disorders. The 110 most common Mendelian Inheritance in Man disorders from the Missouri Genetic Disease Program over the period of one year were translated into MeSH, ICD and SNOMED. The more common diseases are more likely to be mapped than the rarer ones. Diseases with a proven genetic inheritance pattern are more likely to be mapped than those with speculated inheritance patterns. Approximately one third of all diagnoses were not mapped across all three coding schemes in Meta-1.2. The ICD coding scheme was found to be too broad to be meaningful for genetic diagnosis or epidemiological purposes. MeSH and SNOMED need to be made more specific and complete, and all of the new version of SNOMED needs to be included in the Metathesaurus.

Abstracting and Indexing↗
PubMed1993

Students online: learning medical genetics.

It is possible to focus medical genetics education by using a model that integrates the skills of end-user searching of the medical literature into the traditional course content. Since 1988, 313 first-year medical students were studied as they accessed MEDLINE to retrieve information about biochemical genetic disorders. Their search behavior was studied by analyzing data from the National Library of Medicine's traffic files. The skills that they initially learned were reinforced as they searched clinical genetics problem cases in the second-year pathology course, and these skills were consolidated in the third year when the students addressed specific patient-care questions in pediatrics. The students' perception of the value of this model was studied by analyzing questionnaires completed during the exercise. It was demonstrated that when students were taught the skills of accessing MEDLINE by computer, they could formulate a question, retrieve current information, critically review relevant articles, communicate effectively, and use these skills to contribute to patient care.

Female↗
PubMed1992

AI/Learn/Rheumatology. A computer-assisted educational system for teaching about rheumatic diseases.

Education of health professionals about the rheumatic diseases is in need of improvement. The computer is an instrument that can be used efficiently to educate large numbers of users. With specific educational principles in mind, we developed AI/Learn/Rheumatology, a computer-assisted interactive videodisc system for teaching the rheumatic diseases. While interacting with the user, it conveys knowledge using visual and problem-solving techniques. The system is efficient, enjoyable to use, and useful for small groups and independent study. It is applicable for teaching medical and allied health professional students, postgraduate trainees, and primary care physicians.

Computer-Assisted Instruction↗
PubMed1992

Medical students using Grateful Med: analysis of failed searches and a six-month follow-up study.

Medical students at the University of Missouri were taught to search MEDLINE using the Grateful Med software. The traffic files of student searches were analyzed for search behavior. This paper reports on two specific aspects of these analyses: (1) failed searches where retrieval was either too large or too small (zero hits); and (2) a six month follow-up study which focused on error rates and retention of skills. The two major reasons for retrieving too many citations were entering a phrase on a single subject line and a search of only one concept. Of the zero hit searches, the most commonly occurring errors were MeSH (medical subject headings) not used, other MeSH errors, misspelling or keyboard errors, and faulty logic. During the six month follow-up study, the error rates of students declined in spite of the fact that they had not used the software in six months. Furthermore, a larger percentage of the searches showed a more sophisticated use of MeSH than previously employed.

Education, Medical↗
PubMed1992

GALE: a graphics assisted learning environment for computer-based interactive videodisc education.

GALE, a Graphics Assisted Learning Environment, is a computer-based interactive videodisc authoring tool. GALE was created as the authoring package for AI/LEARN/Rheumatology, an independent study system for teaching rheumatology to medical trainees. GALE has potential widespread application beyond rheumatology. Interactive videodisc technology is a prime feature of GALE. Other highlights are: WordPerfect macros which simplify programming, graphics-based large text characters, tracking of user responses, hypertext-like definition capabilities, color coded screens to distinguish between hypertext branches and the mainstream of the course content and ability to overlay text on the video image. GALE runs on a PC-compatible computer with selected Pioneer LaserDisc players. GALE uses WordPerfect 5.1 for text editing and has been designed for use by non-programmers.

Computer Graphics↗
PubMed1992

Detection by bioassay and specific enzyme-linked immunosorbent assay of phosphoramidon-inhibitable endothelin-converting activity in brain and endothelium.

The endothelin-converting enzyme (ECE) activity present in endothelial cells and rat and human brains was characterized using a selective and rapid bioassay for endothelin-1 (ET-1) or endothelin-3 (ET-3) together with a sensitive enzyme-linked immunosorbent assay. We found that ECE activity was predominantly in the membrane fraction of endothelial cells from which it could be extracted by treatment with detergent. In rat brain tissue, the ECE activity was in the membrane fraction and was not solubilized by detergent treatment. Further dissection of the brain revealed that there was a strong localization of ECE activity in the hypothalamus, midbrain, and medulla oblongata in agreement with earlier observations of ET-like immunoreactivity and binding sites. Experiments with human brain tissue also showed the presence of ECE activity. In conclusion, our studies confirmed the presence of ECE activity within endothelial cells, and showed ECE to be localized in brain tissue in sites consistent with the selective distribution of the ET-1 synthetic pathway. In all tissues studied, the ECE activity was significantly inhibited by phosphoramidon or ethylenediaminetetra-acetate.

Animals↗
PubMed1992

Different patterns of release of endothelium-derived relaxing factor and prostacyclin.

1. Release of endothelium derived relaxing factor (EDRF) and prostacyclin (PGI2) from endothelial cells (EC) cultured from bovine aortae was measured by bioassay and radioimmunoassay, respectively, during infusions (10 min) of bradykinin (BK), adenosine diphosphate (ADP), arachidonic acid (AA), alkaline buffers and the free-bases (FB) of L-arginine or D-arginine. Release of EDRF from the luminally perfused rabbit aorta was also measured during infusions (10 min) of acetylcholine (ACh), substance P and ADP. 2. Bradykinin (10 or 30 nM) infused through the column of EC induced release of both EDRF and PGI2, neither of which was maintained for the duration of the infusion. 3. ADP (1.6 or 4 microM) infused through the column of EC induced release of a EDRF which was maintained for the duration of the infusion and a release of PGI2 which lasted for a much shorter period. 4. Arachidonic acid (30 or 90 microM) infused through the column of EC caused a sustained release of EDRF and PGI2, both of which outlasted the infusion of AA. 5. L-Arginine FB, D-arginine FB or alkaline buffer infused through the column of EC released EDRF, but only small amounts of PGI2. The release of EDRF outlasted the period of infusion and was due to an increase in the pH of the Krebs solution perfusing the EC. 6. Infusions of ACh (0.25-1 microM) or ADP (4-16 microM) caused a sustained release of EDRF from the luminally-perfused rabbit aorta, whereas infusion of substance P (3.3-10 microM) caused only a transient release of EDRF. 7. These results show that distinct patterns of EDRF release exist to different agonists in both cultured and in situ EC, and that EDRF and PGI2 do not necessarily follow the same time course of release. Furthermore, sustained release of EDRF does not require the constant infusion of the precursor, L-arginine, whereas sustained release of PGI2 only occurs when AA, the precursor of PGI2, is present in the extracellular medium.

Acetylcholine↗
PubMed1992

Human brain contains a metalloprotease that converts big endothelin-1 to endothelin-1 and is inhibited by phosphoramidon and EDTA.

Incubation of big endothelin-1 (bET-1) with protein derived from the detergent-extracted 100,000 g pellet prepared from human brain tissue resulted in the formation of endothelin-1 (ET-1) at a rate of 90 fmol mg-1 protein min-1. This formation was inhibited in a concentration-dependent manner by either phosphoramidon or EDTA, with half-maximal inhibitory concentrations of 2 and 20 microM, respectively. No conversion of big endothelin-3 (bET-3) to endothelin-3 (ET-3) was detected under the same conditions. These results show the presence in the human brain of a metalloprotease-like enzymatic activity which selectively converts bET-1 and ET-1. Together with earlier reports of mRNA for ET-1 this suggests the presence of the entire synthetic pathway for ET-1 in human brain.

Brain↗
PubMed1992

Characterization and localization of nitric oxide synthase in non-adrenergic non-cholinergic nerves from bovine retractor penis muscles.

1. Partially purified soluble nitric oxide (NO) synthase was isolated from the bovine retractor penis muscle (BRP), a tissue in which the inhibitory response to non-adrenergic non-cholinergic nerve (NANC) stimulation appears to be mediated by NO or NO-like material. 2. NO synthase from BRP used L-arginine as a substrate, required NADPH, tetrahydrobiopterin, and FAD as co-factors and was Ca2+/calmodulin-dependent. The activity of NO synthase was inhibited by NG-methyl-L-arginine and NG-nitro-L-arginine, and haemoglobin blocked the effect of NO formed by the enzyme. 3. On reducing SDS polyacrylamide gel electrophoresis the apparent molecular mass of NO synthase from BRP was 160 +/- 2 kDa, which is similar to that of the cerebellar NO synthase. Protein immunoblot and immunoprecipitation showed that NO synthase from BRP cross-reacted with the selective antiserum to neuronal NO synthase from rat cerebellum. 4. Immunohistochemistry using the same antiserum demonstrated that NO synthase in BRP was located exclusively within nerve fibres. Thus, autonomic nerves synthesizing the NANC neurotransmitter seem to contain an isoform of NO synthase which is similar to that from rat cerebellum.

Amino Acid Oxidoreductases↗
PubMed1992

Regional differences in endothelin converting enzyme activity in rat brain: inhibition by phosphoramidon and EDTA.

1. It has been demonstrated previously that conversion of big endothelin-1 (bET-1) to endothelin-1 (ET-1) is inhibited in vitro and in vivo by phosphoramidon. In addition, ET-1 binding sites and mRNA have been shown within the brain. Here we expand upon our previous observation that rat brain contains phosphoramidon-inhibitable endothelin converting enzyme (ECE) and show that this activity is not uniformly distributed throughout the brain. 2. ECE activity was detected by a bioassay which depended upon the 10,000 fold difference in potency between bET-1 and ET-1 as stimulants of guanosine 3':5'-cyclic monophosphate (cyclic GMP) accumulation in kidney epithelial (PK1) cells of the pig. Data were confirmed by specific enzyme-linked immunosorbent assay (ELISA) employing antibody directed against ET-1/3(17-21). 3. Following homogenization of the whole brain and ultracentrifugation the 100,000 g pellet contained greater than 4 times more ECE activity than the cytosol. Washing of the pellet with KCl (1 M) and extraction with the detergent CHAPS (20 mM) revealed a phosphoramidon-inhibitable ECE within the residual particulate fraction (nominally classified as the cytoskeletal fraction). Phosphoramidon (IC50, approx. 5 microM) or EDTA inhibited the conversion of bET-1 to ET-1 by the cytoskeletal fraction of rat brain by more than 60%.2+ 4. Following dissection of rat brain into olfactory bulb, cerebral cortex, striatum, hippocampus, cerebellum, midbrain (including thalamus), hypothalamus and medulla oblongata (including pons) the greatest ECE was detected in the hypothalamus and medulla oblongata.After fractionation, the ECE-activities in the cytoskeletal fractions prepared from the hypothalamus or medulla oblongata were inhibited concentration-dependently by phosphoramidon or EDTA, with maximum inhibitions of>80% and >70%, respectively.5. These data show that rat brain contains a phosphoramidon- and EDTA-inhibitable ECE which maybe similar to that present in endothelial cells. The localization of this enzyme correlates with published reports of immunoreactive-ET-l, ET-1-binding sites, and messenger RNA for ET-1 in the rat brain, and suggests the presence of the entire synthetic pathway for ET-1.

Animals↗