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M J Wells

Publications and source records attributed to M J Wells.

At least 19 recordsLinked to original sources
PubMed2000

Solid-phase extraction of acidic herbicides.

A discussion of solid-phase extraction method development for acidic herbicides is presented that reviews sample matrix modification, extraction sorbent selection, derivatization procedures for gas chromatographic analysis, and clean-up procedures for high-performance liquid chromatographic analysis. Acidic herbicides are families of compounds that include derivatives of phenol (dinoseb, dinoterb and pentachlorophenol), benzoic acid (acifluorfen, chloramben, dicamba, 3,5-dichlorobenzoic acid and dacthal--a dibenzoic acid derivative), acetic acid [2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)], propanoic acid [dichlorprop, fluazifop, haloxyfop, 2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and silvex], butanoic acid [4-(2,4-dichlorophenoxy)butanoic acid (2,4-DB) and 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB)], and other miscellaneous acids such as pyridinecarboxylic acid (picloram) and thiadiazine dioxide (bentazon).

Chromatography, Gas↗
PubMed2000

The protective effects of hypoxia-induced hypometabolism in the Nautilus.

Specimens of Nautilus pompilius were trapped at depths of 225-300 m off the sunken barrier reef southeast of Port Moresby, Papua New Guinea. Animals transported to the Motupore Island laboratory were acclimated to normal habitat temperatures of 18 degrees C and then cannulated for arterial and venous blood sampling. When animals were forced to undergo a period of progressive hypoxia eventually to encounter ambient partial pressure of oxygen (PO2) levels of approximately 10 mmHg (and corresponding arterial PO2's of approximately 5 mmHg), they responded by lowering their aerobic metabolic rates to 5-10% of those seen in resting normoxic animals. Coincident with this profound metabolic suppression was an overall decrease in activity, with brief periods of jet propulsion punctuating long periods of rest. Below ambient PO2 levels of 30-40 mmHg, ventilatory movements became highly periodic and at the lowest PO2 levels encountered, ventilation occasionally ceased altogether. Cardiac output estimated by the Fick equation decreased during progressive hypoxia by as much as 75 80%, and in the deepest hypometabolic states heart rates slowed to one to two cycles of very low amplitude per minute. By the end of 500 min exposure to ambient PO2 levels of 10 mmHg or less, the anaerobic end products octopine and succinate had increased significantly in adductor muscle and heart, respectively. Increased concentrations of octopine in adductor muscle apparently contributed to a small intracellular acidosis and to the development of a combined respiratory and metabolic acidosis in the extracellular compartment. On the other hand, increases in succinate in heart muscle occurred in the absence of any change in cardiac pHi. Taken together, we estimate that these anaerobic end products would make up less than 2% of the energy deficit arising from the decrease in aerobic metabolism. Thus, metabolic suppression is combined with a massive downregulation of systemic O2 delivery to match metabolic supply to demand.

Acid-Base Equilibrium↗
PubMed2000

Comparison among soil Series and extraction methods for the analysis of trifluralin.

Accurate analytical procedures are needed to improve understanding of the fate and transport of trifluralin, a chemical widely used as a herbicide. Analytical determination of trifluralin is challenging due to its hydrophobic, yet volatile, character and its tendency to degrade into numerous metabolites. In this research, efficient analytical methods for fortified and field-incurred soils were developed for simultaneous quantitation of trifluralin, I [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine, CAS Registry No. 1582-09-8; CAS Registry No. have been provided by the author], a trifluralin metabolite, II [2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine, CAS Registry No. 2077-99-8], and a related trifluoromethyldinitroaniline isomer of trifluralin, III [2,4-dinitro-N,N-dipropyl-6-(trifluoromethyl)benzenamine, CAS Registry No. 23106-20-9]. Extractions of trifluralin (0.5 and 2.5 microg/g) from silt loam, sandy loam, and silty clay soils were compared. A method was developed for the supercritical fluid extraction of trifluralin from soil using modified supercritical carbon dioxide, and the effects of cosolvent, pressure, and flow rate on recovery were evaluated. Supercritical fluid extraction was compared to liquid vortex extraction and automated Soxhlet (soxtec) extraction. Solid-phase extraction was examined for purifying soil extracts. Protocols were developed for analysis of extracts by gas and/or liquid chromatography. Immunoassay was investigated but proven to be impractical for this analysis. Soil properties and extraction methods were observed to affect the level of coextracted background interferences. Trifluralin exhibited concentration-dependent recovery regardless of soil series or extraction method.

Chromatography, Gas↗
PubMed1999

The use of an independent visual background to reduce simulator side-effects.

BACKGROUND: Simulator sickness (SS) is a major problem which potentially limits interface applications that feature simulated motion. While display imperfections play a role, a large part of SS is motion sickness (MS). Sensory rearrangement theory holds that MS is related to conflicting motion cues; in the case of simulators, mainly a conflict between inertial cues (usually indicating no self-motion) and visual stimuli from the display (indicating self-motion). It is suggested that MS does not arise from conflicting motion cues per se, but rather from conflicting rest frames selected from those motion cues. There is strong evidence that the visual rest frame is heavily influenced by the visual background. Providing an independent visual background (IVB) consistent with the inertial rest frame may reduce SS, even when the simulator's content-of-interest (CI) is not consistent with the inertial rest frame. METHODS: In two experiments, a circular vection stimulus was shown for 3-4.5 min in a head-mounted display, comparing see-through (i.e., IVB) to occluded (i.e., no IVB) modes. Measures included a standard SS questionnaire and a pre-exposure ataxia measure. Experiment 2 added a visual task which forced attention into the CI and a post-exposure ataxia measure. In both experiments, subjects rated the CI as significantly more visible than the IVB. RESULTS: A large effect was found for the reduction of SS and ataxia in the first experiment, and for pre-exposure ataxia in the second. CONCLUSIONS: Future research will further test the IVB idea and examine applications to high-end simulators.

Adolescent↗
PubMed1998

In vivo clearance of ternary complexes of vitronectin-thrombin-antithrombin is mediated by hepatic heparan sulfate proteoglycans.

Thrombin is inhibited by its cognate plasma inhibitor antithrombin, through the formation of covalent thrombin-antithrombin (TAT) complexes that are found as ternary complexes with vitronectin (VN-TAT). To determine whether the metabolism of VN-TAT ternary complexes is different from that previously reported for binary TAT complexes, plasma clearance studies were done in rabbits using human VN-TAT. 125I-VN-TAT was shown to be cleared rapidly from the circulation (t1/2alpha = 3.8 min) in a biphasic manner mainly by the liver. 125I-TAT had a similar initial clearance (t1/2alpha = 5.3 min) but had a significantly faster beta-phase clearance (t1/2beta = 42.8 min versus 85.4 min for VN-TAT; p = 0.005). Protamine sulfate and heparin abolished the rapid initial alpha-phase of 125I-VN-TAT clearance and reduced its liver-specific association and in vivo degradation. Heparin also reduced the alpha-phase clearance of 125I-TAT and was associated with the appearance of high molecular weight complexes, suggesting enhanced complex formation between VN and TAT. 125I-VN-TAT binding to HepG2 cells was reduced by competition with VN-TAT or heparin but to a much lesser extent in the presence of TAT. The binding of VN-TAT to HepG2 cells was not inhibited by competition with the low density lipoprotein receptor-related protein ligand, methylamine-alpha2-macroglobulin. 125I-VN-TAT binding was also inhibited by treating HepG2 cells with heparinase or by growing the cells in the presence of beta-D-xyloside. Finally, both heparin and chloroquine, but not methylamine-alpha2-macroglobulin, reduced the internalization and degradation of VN-TAT by HepG2 cells. Taken together, these data indicate the importance of VN in TAT metabolism and demonstrate that VN-TAT binds to liver-associated heparan sulfate proteoglycans, which mediate its internalization and subsequent intracellular degradation.

Animals↗
PubMed1997

Cytokeratin 18 is expressed on the hepatocyte plasma membrane surface and interacts with thrombin-antithrombin complexes.

During experiments to identify putative hepatic receptors for thrombin-antithrombin (TAT) complexes, a 45-kDa protein was identified by ligand blotting. Following gel purification, amino acid sequencing revealed the 45-kDa TAT-binding polypeptide to be cytokeratin 18 (CK18). The presence of CK18 on the surface of intact rat hepatoma cells was demonstrated by binding of 125I-anti-CK18 antibodies. Anti-CK18 antibodies reduced the binding and internalization of 125I-TAT by rat hepatoma cells. Immunocytochemical analysis, to determine the location of CK18 in vivo, revealed a periportal gradient of CK18 staining; with hepatocytes around the portal triads demonstrating striking pericellular staining. In addition, anti-CK18 IgG associated with perfused livers to a significantly greater extent than preimmune IgG. Taken together, these data provide evidence that CK18 is found on the extracellular surface of hepatocytes and could play a role in TAT removal. Finally, these data, in conjunction with recent reports of CK8 (Hembrough, T. A., Li, L., and Gonias, S. L. (1996) J. Biol. Chem. 271, 25684-25691) and CK1 cell membrane surface expression (Schmaier, A. H. (1997) Thromb. Hemostasis 78, 101-107), indicate a novel role for these proteins as putative cellular receptors or cofactors to cellular receptors.

Animals↗
PubMed1995

Concerns on little league elbow.

Little League elbow is a common overuse injury that will become more prevalent as more youths participate in baseball programs and other sports that involve overhead arm activities. The condition is highly treatable if diagnosed early in its development. Symptoms such as swelling and limited range of motion usually indicate an advanced overuse condition. Prevention and treatment should emphasize education of athletes, parents, and coaches about coaches about its etiology. Factors involved are proper pitching mechanics, stretching and strengthening programs, improving early recognition, and, most importantly, limiting the number of pitches thrown daily.

Journal Article↗
PubMed1994

Prevalence of antithrombin deficiency in healthy blood donors: a cross-sectional study.

The prevalence of antithrombin (AT) deficiency in the general population has been variously estimated to be between 0.05 and 5 per 1,000 in the population; 2,491 blood donors were screened in an attempt to clarify this issue using plasma samples taken from the blood donor units. From this initial population, 122 individuals were identified as having plasma AT levels lower than 2 standard deviations below the normal mean. Twenty-two samples had evidence that thrombin had been generated during blood collection and the remaining cohort of 100 blood donors were asked to return but only 59 complied. The data obtained from these 59 were compared with that from 51 age- and sex-matched control blood donors. Both groups of subjects were assessed for previous evidence, or family history, of thrombotic events, as well as exposure to risk factors associated with the development of deep vein thrombosis (DVT). All had venous blood samples taken from which the supernatant plasma was immediately removed and quick frozen for later assaying. Only 6 of the 59 subjects with initial low AT levels had repeat AT-Xa levels below 0.80 units/ml (normal range 0.94 +/- 0.14). Upon repeating the AT-Xa determinations on new samples from these six individuals, only three were found again to be low. One was found to have a type 3 AT deficiency (an Arg47Cys substitution). The other two with a low AT level had mean functional AT-Xa levels of 0.61 and 0.71 units/ml, respectively, with correspondingly low AT:Ag levels consistent with a type 1 AT deficiency. Two of these three subjects has been in high risk situations without evidence of having developed DVT and none had evidence of venous reflux on Doppler venography. In addition, none had personal or family histories of previous thrombotic events. These present data indicate that the prevalence of AT deficiency in our blood donor population is 2 per 1,000 (95% confidence intervals: 0.7-6/1,000).

Antithrombins↗
PubMed1993

An antithrombin III assay based on factor Xa inhibition provides a more reliable test to identify congenital antithrombin III deficiency than an assay based on thrombin inhibition.

OBJECTIVES: To determine whether functional antithrombin III (AT-III) levels measured by a factor Xa inhibition (AT-III-Xa) assay identifies AT-III deficient individuals more reliably than functional AT-III levels measured by a thrombin inhibition (AT-III-IIa) assay. STUDY DESIGN: Cross-sectional study. PATIENT POPULATION: Sixty-seven members of a large family with type 2 AT-III deficiency. INTERVENTION: DNA analysis was used as the reference diagnostic standard for AT-III status and subjects were classified as AT-III deficient or non deficient according to these results. Functional AT-III levels were measured in all subjects using: 1) a chromogenic substrate for thrombin and added human thrombin (AT-III-IIa), and 2) a chromogenic substrate for factor Xa and added bovine factor Xa (AT-III-Xa). Functional heparin cofactor II (HC-II) levels were measured using a commercially available kit. The proportions of 125I-alpha-thrombin complexed to AT-III and HC-II were measured by polyacrylamide gel electrophoresis and autoradiography. RESULTS: Thirty-one (46%) individuals were classified as AT-III deficient and 36 (54%) as AT-III non deficient. AT-III-Xa assay measured a significantly lower mean AT-III value and a narrower range for individuals classified as AT-III deficient than the AT-III-IIa assay. Using the AT-III-IIa assay, six subjects had borderline AT-III levels compared to none with the AT-III-Xa assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Molecular cloning and expression of rabbit antithrombin III.

A cDNA containing the complete open-reading frame encoding rabbit antithrombin III (AT-III) was isolated from a rabbit liver cDNA expression library, using a specific antibody as a probe. Sequence analysis showed 84% identity between the deduced amino acid sequences of the rabbit and human proteins. A previously described cell-free expression system was used to verify the identity of the clone. The full-length cDNA was inserted into an expression vector, and messenger RNA (mRNA) transcripts generated. In vitro translation of these transcripts, in the presence of [35S]methionine, in an mRNA-dependent rabbit reticulocyte lysate system resulted in the synthesis of a 51-Kd polypeptide, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This nonglycosylated protein was capable of forming SDS-stable complexes with human alpha-thrombin. Complex formation was significantly enhanced following the deletion of nucleotides encoding the signal peptide, and the resultant generation of a 47-Kd nonglycosylated mature protein product. When the template DNA giving rise to this product was internally truncated, two rabbit AT-III deletion mutants were generated that lacked the ability to interact with thrombin, but retained the ability to bind heparin. Cell-free expression plasmids encoding the human and rabbit AT-III mature molecules were manipulated to produce two interspecies fusion proteins. For the first, human codons were used to replace rabbit codons from residue 369-433, while in the second human codons replaced rabbit codons from residue 217-433. Both fusion proteins exhibited less efficient thrombin-complexing ability than the original cell-free-derived mature rabbit AT-III. Thus, portions of AT-III molecules from the two species, despite their high degree of homology, are not interchangeable. Knowledge of the structure of rabbit AT-III, combined with the availability of the rabbit cDNA, will permit defined experimentation aimed at understanding antithrombin III structure relative to its function in vivo.

Amino Acid Sequence↗
PubMed1990

Disaster planning.

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Disaster Planning↗
PubMed1987

Smodingium dermatitis.

Smodingium argutum is the plant most commonly responsible for causing acute allergic contact dermatitis in South Africa. When an outbreak of Smodingium dermatitis occurred in a local school the allergenic principle present in this plant was chemically isolated and identified, and its allergenic property proved in the clinic by patch testing. The value of using an extract of fresh Smodingium leaves in lieu of fresh leaves themselves was confirmed, but freeze-dried material was found to be unsuitable for patch-test purposes.

Acute Disease↗
PubMed1987

Flight trial of a helmet-mounted display image stabilisation system.

An image stabilisation system for improving reading performance with a helmet-mounted display (HMD) during whole-body vibration was tested at night in a helicopter. Six subjects read arrays of 50 numerals as quickly and as accurately as possible while flying in three different flight conditions. The mean reading time for each array while stationary on the ground was approximately 21 s, and the mean reading error was 0.4% without stabilisation. In-flight mean reading time increased to approximately 40 s, and reading error was 18% without the stabilisation system. Stabilising the image significantly reduced the mean in-flight reading time to approximately 25 s with a 4% reading error. Data from the flight trial support the results of previous experiments, which suggest that HMD reading performance with vibration and night viewing conditions may be inferior to performance with daylight conditions.

Adult↗
PubMed1984

Anticonvulsant activity of some 4-aminobenzamides.

A series of 4- aminobenzamides of some simple primary and secondary amines were prepared and evaluated for anticonvulsant effects. The compounds were tested in mice against seizures induced by electroshock and pentylenetetrazole ( metrazole ) and in the rotorod assay for neurologic deficit. For those N-alkyl amides tested, 4-amino-N- amylbenzamide (6) was the most potent against maximal electroshock seizures (MES): ED50 = 42.98 mg/kg; however, the N- cyclohexylbenzamide (8) showed the greatest protective index (PI = TD50/ED50), 2.8. The introduction of a second aromatic ring produced more potent compounds, with d,l-4-amino-N-(alpha-methylbenzyl)-benzamide (12) showing the highest level of activity. This compound has an anti-MES ED50 of 18.02 mg/kg in mice when administered intraperitoneally (ip) and a TD50 of 170.78 mg/kg (PI = 9.5) in the same species. These data compare quite favorably with those for phenobarbital and phenytoin in the same assays.

Animals↗
PubMed1984

Benefits of helmet-mounted display image stabilisation under whole-body vibration.

The effects of whole-body vertical vibration in the range 2.5-25 Hz on visual performance with two types of raster scan helmet-mounted display have been determined. The benefit of an image stabilisation system on numeral reading performance during vibration was also assessed with both display systems. Increases in mean reading time of over 130%/m . s-2 R.M.S. and increases in percentage reading error of more than 30%/m . s-2 R.M.S. were recorded with unstabilised displays. With vertical and horizontal image stabilisation, these decrements in performance were reduced to less than 40%/m . s-2 R.M.S. increase in reading time and less than 10%/m . s-2 R.M.S. increase in reading error. Data on the transmission of vibration from the seat to the head and from the head to the helmet were also obtained. These indicate a relation between biodynamic behaviour and visual performance during vibration.

Biomedical Engineering↗