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Biomedical subjects

D Parker

Publications and source records attributed to D Parker.

At least 109 records · Page 6Linked to original sources
PubMed1997

On-line monitoring of nitrogenase activity in cyanobacteria by sensitive laser photoacoustic detection of ethylene.

A new and extremely sensitive method for measuring nitrogenase activity through acetylene reduction is presented. Ethylene produced by nitrogenase-mediated reduction of acetylene is detected by using laser photoacoustics (LPA). This method possesses a detection limit making it 3 orders of magnitude more sensitive than traditional gas chromatographic analysis. Photoacoustic detection is based on the strong and unique absorption pattern of ethylene in the CO(inf2) laser wavelength region (9 to 11 (mu)m). The high sensitivity allowed on-line monitoring of nitrogenase activity in a culture of the heterocystous cyanobacterium Nodularia spumigena, which was isolated from a water bloom in the Baltic Sea. This setup makes it unnecessary to take subsamples from the culture and avoids long incubations in sealed vials. The fast response of the LPA technique allows measurement of real-time dynamic changes of nitrogenase activity. The method was used to analyze in vivo saturation of nitrogenase by acetylene in N. spumigena. It is demonstrated that 20% acetylene does not saturate nitrogenase and that the degree of saturation depends on light intensity. With concentrations of acetylene as low as 2.5% it is possible to assess the degree of saturation and to extrapolate to total nitrogenase activity. In N. spumigena nitrogenase activity becomes independent of light intensity above 20 to 80 (mu)mol of photons m(sup-2) s(sup-1) at 20% O(inf2).

Journal Article↗
PubMed1997

Five years of work-related injuries and fatalities in Minnesota. Agriculture: a high-risk industry.

This report describes the Minnesota Fatality Assessment and Control Evaluation Study (MN FACE), a federally funded initiative to study fatal injuries in the workplace. The purpose of the program is to investigate various types of occupational fatalities and to identify risk factors that contribute to work-related fatalities. Initially, the MN FACE program only investigated fatalities related to falls, confined spaces, and electrocutions. In 1994, MN FACE also began investigating fatalities associated with agricultural work. Agriculture continues to be one of the nation's most hazardous industries, ranking fourth among industries in the United States at high risk for work-related fatalities. MN FACE investigated 46 agriculture-related fatalities during 1994-95. Forty-one percent of the fatalities involved tractors, and 66% of these accidents were tractor rollovers. Other leading causes of agricultural fatalities included grain bin and manure pit asphyxiations.

Accidents, Occupational↗
PubMed1996

No evidence of antibody to human foamy virus in widespread human populations.

The first human foamy virus (HFV) to be described was isolated from nasopharyngeal carcinoma tissue from a Kenyan patient. Early seroepidemiology concluded that there was a significant infection rate, particularly among Africans. Awareness of foamy viruses as potential vectors has stimulated interest in the natural seroprevalence of HFV infection. We, therefore, investigated the prevalence of HFV infection in more than 5000 human sera collected from diverse populations. To maximize the chances of including the major antigenic epitopes, recombinant proteins derived from the HFV gag and env genes divided into three (the 5' amino terminal, the 3' carboxy terminal, and an internal overlapping region) were used as antigens in an ELISA. In contrast to most other seroepidemiological investigations of HFV infection, highly reactive sera identified by ELISA were subjected to further analysis by additional serological assays and, where PBMCs were available, PCR. None of the serum samples were confirmed as positive. It is worth noting that with our ELISA, the highest level of serum reactivity to HFV was found in subjects from Pacific islands (17%), and in Central Africa (34% in Malawi), areas previously cited as having a high level of HFV infection. Taken together with sequence analysis endorsing the phylogenetic closeness of HFV to SFV-6/7, these data strongly suggest that HFV is not naturally found in the human population.

Blotting, Western↗
PubMed1996

Sensitive high-performance liquid chromatographic method for the determination of a benzonaphthazepine antipsychotic agent, SCH 39166, and its active metabolite, SCH 40853, in human plasma and its cross-validation with a gas chromatographic method.

A sensitive high-performance liquid chromatographic (HPLC) method was developed for the determination of a benzonaphthazepine antipsychotic agent, SCH 39166, and its active metabolite, SCH 40853. The HPLC method required a single-step organic extraction at alkali pH followed by HPLC analysis utilizing a CN column with UV detection at 205 nm. The limit of quantitation was 1 ng/ml for SCH 39166 and 0.5 ng/ml for SCH 40853. The HPLC method was cross-validated with a previously reported GC method by the analysis of 73 plasma samples spiked with various concentrations of SCH 39166 and SCH 40853. The correlation coefficient was 0.9969 for SCH 39166 and 0.9984 for SCH 40853. Both GC and HPLC methods were used for the determination of plasma concentrations and yielded similar pharmacokinetic parameters for SCH 39166 and SCH 40853 in man following oral administration of SCH 39166 (100 mg).

Adult↗
PubMed1996

Earth-Based Observations of the Galileo Probe Entry Site

Earth-based observations of Jupiter indicate that the Galileo probe probably entered Jupiter's atmosphere just inside a region that has less cloud cover and drier conditions than more than 99 percent of the rest of the planet. The visual appearance of the clouds at the site was generally dark at longer wavelengths. The tropospheric and stratospheric temperature fields have a strong longitudinal wave structure that is expected to manifest itself in the vertical temperature profile.

Journal Article↗
PubMed1996

Attenuation of morphine-induced delirium in palliative care by substitution with infusion of oxycodone.

We have observed among patients of the Southern Community Hospice Programme that up to 25% experience acute delirium when treated with morphine and improve when the opioid is changed to oxycodone or fentanyl. This study aimed to confirm by a prospective trial that oxycodone produces less delirium than morphine in such patients. Oxycodone was administered by a continuous subcutaneous infusion, as this allowed more flexible and reliable dosing, and patients were monitored for any adverse reactions to the drug. Thirteen patients completed the study. Statistically significant improvements in mental state and nausea and vomiting occurred following a change from morphine to oxycodone. Pain scores improved but did not reach a level of statistical significance. The phenotype status of the patients was tested to establish their capacity to metabolize oxycodone. One patient who did not achieve adequate pain control proved to be a poor metabolizer. These results show that oxycodone administered by the subcutaneous route can provide effective analgesia without significant side effects in patients with morphine-induced delirium. This treatment allows patients to remain more comfortable and lucid in their final days. A small proportion of patients who do not metabolize oxycodone effectively may not receive this benefit.

Aged↗
PubMed1996

Association of intravenous phenytoin toxicity with demographic, clinical, and dosing parameters.

Previous studies investigating intravenous phenytoin toxicity have been largely anecdotal, and have inferred an association with older patients, cardiovascular disease, and higher doses, concentrations, and infusion rates of phenytoin. This investigation sought to elucidate both the incidence and nature of acute intravenous phenytoin toxicity in emergency department patients, and to identify any demographic, clinical, or dosing associations with toxicity, by analyzing a retrospective case series over 3 years in a municipal teaching hospital. A consecutive series of 164 patients who received intravenous phenytoin loading in the emergency department following acute seizure presentation was identified. Demographic, clinical, and dosing data were collected, and the nature of toxicity was noted. Data were then analyzed statistically for potential associations with toxicity. Eight cases of hypotension and no apnea or arrhythmias were noted in the 164 patients (4.9% incidence). Analysis of demographic, clinical, and dosing data found statistically significant associations between hypotension and both a lower phenytoin dose administered (537 mg in hypotensive patients v 787 mg in normotensive patients, P = .00046) and the presence of abnormal neurological signs at initial presentation (20% incidence when abnormal signs present v 3.5% incidence when absent, P = .026). No other associations were found between toxicity and other variables. This sample size could detect differences ranging from 4% to 11% in complication rate (hypotension) for the various demographic, clinical, and dosing parameters with a statistical power of 80%. It was concluded that the incidence of hypotension from intravenous phenytoin administration in this study population was approximately 5%, and the incidence of apnea and cardiac arrhythmia in this series was 0%. No associations with age, comorbidities, or infusion rates were found, in contrast to other studies. Association of intravenous phenytoin toxicity with lower phenytoin dose is likely related to prompt cessation of the drug once signs of toxicity occur. The possible association of toxicity with abnormal initial neurological signs has not previously been reported and may possibly define a population at risk if validated by prospective research in additional populations.

Adult↗
PubMed1996

Sensitive and specific electrochemical sensors for charge-diffuse cations: use of lipophilic cyclodextrins and an enzyme relay for the determination of acetylcholine.

Lipophilic, alkylated cyclodextrins (CDs) are aromatic hosts which are excellent ionophores for reversibly binding size-matched, charge-diffuse cations. The application of lipophilic beta-CDs as ionophores for sensing acetylcholine chloride using a potentiometric ISE and an amperometric biosensor is described. Potentiometric ISEs, using 2,6-didodecyl-beta-CD as ionophore, showed a Nernstian response with a limit of detection -log[C] = 5.0 and selectivity coefficient -logKijPot = 4.2 (in serum levels of Na+, K+ and Ca2+). A Nernstian response is maintained in the presence of bovine serum albumin for a PVC- and a polyurethane-based electroactive membrane on initial contact. However, on prolonged contact, the polyurethane-based membranes showed a lower shift in Einitial0 (the bias potential on initial contact with analyte solution) than PVC. Amperometric biosensors were assembled by modifying screen-printed electrodes with a ferrocenyl charge shuttle, enzymes (horseradish peroxidase, choline oxidase and/or acetylcholine esterase) and a thin film comprising a polyurethane matrix, 2,3,6-triethyl-beta-CD, a plasticizer and a large anionic salt. The resulting sensor, which was capable of detecting subpicomolar levels of acetylcholine, was highly specific and was stable to storage in air and in solution. Interference from endogenous electroactive compounds was minimal.

Acetylcholine↗
PubMed1996

Phosphorylation of CREB at Ser-133 induces complex formation with CREB-binding protein via a direct mechanism.

We have characterized a phosphoserine binding domain in the coactivator CREB-binding protein (CBP) which interacts with the protein kinase A-phosphorylated, and hence activated, form of the cyclic AMP-responsive factor CREB. The CREB binding domain, referred to as KIX, is alpha helical and binds to an unstructured kinase-inducible domain in CREB following phosphorylation of CREB at Ser-133. Phospho-Ser-133 forms direct contacts with residues in KIX, and these contacts are further stabilized by hydrophobic residues in the kinase-inducible domain which flank phospho-Ser-133. Like the src homology 2 (SH2) domains which bind phosphotyrosine-containing peptides, phosphoserine 133 appears to coordinate with a single arginine residue (Arg-600) in KIX which is conserved in the CBP-related protein P300. Since mutagenesis of Arg-600 to Gln severely reduces CREB-CBP complex formation, our results demonstrate that, as in the case of tyrosine kinase pathways, signal transduction through serine/threonine kinase pathways may also require protein interaction motifs which are capable of recognizing phosphorylated amino acids.

3T3 Cells↗
PubMed1996

Antigen capture ELISA for the heat shock protein (hsp60) of Chlamydia trachomatis.

AIMS: To develop an indirect ELISA using the heat shock protein (hsp60) of Chlamydia trachomatis as antigen. METHODS: The hsp60 gene was amplified by PCR, expressed in the vector pDEV-107 and transformed into Escherichia coli. The recombinant protein, expressed as a beta-galactosidase fusion product, was captured onto a solid phase using a monoclonal antibody directed against beta-galactosidase. Following incubation with goat anti-human antibody conjugated to peroxidase and colour development on addition of peroxidase substrate, antibody recognition of antigen was quantified by optical density at 492 nm. RESULTS: A sensitive and relatively specific ELISA to detect hsp60 has been produced, which can be exploited to determine the antibody response to C trachomatis hsp60. CONCLUSIONS: This assay will permit the future investigation of the immunopathogenesis of persistent inflammation following C trachomatis infection.

Blotting, Western↗
PubMed1996

Electrogenic pump and a Ca(2+)- dependent K+ conductance contribute to a posttetanic hyperpolarization in lamprey sensory neurons.

1. Tetanic stimulation of lamprey sensory dorsal cells resulted in a posttetanic hyperpolarization (PTH). The amplitude and duration of the PTH were dependent on the stimulus duration and frequency. The PTH was not reversed at membrane potentials negative to -100 mV, whereas the afterhyperpolarization following single action potentials reversed at approximately -85 mV. There was also a biphasic effect on the input resistance during the PTH, with an early reduction that recovered to control before the PTH had decayed. 2. The amplitude and duration of the PTH were increased in Ringer solution containing tetraethylammonium and 4-aminopyridine, both of which broadened single action potentials, but were reduced after intracellular injection of Cs+. Ca(2+)-free Ringer solution, Cd2+, and Co2+ also reduced the PTH, suggesting the involvement of a Ca(2+)-dependent K+ conductance. However, the PTH was not reduced in Ba2+ Ringer solution, or by the Ca(2+)-dependent K+ channel antagonists apamin and charybdotoxin. 3. The cardiac glycoside ouabain reduced the amplitude and duration of the PTH, as did substitution of Na+ with choline or Li+. K(+)-free Ringer solution also reduced the PTH, whereas high-K+ Ringer solution had more variable effects. The amplitude and duration of the PTH were also dependent on temperature. These results support the involvement of an ouabain-sensitive Na-K pump in the PTH. 4. The PTH was reduced by the tachykinins substance P and physalaemin, and by 5-hydroxytryptamine, which blocks apamin-sensitive Ca(2+)-dependent K+ channels in the lamprey. However, gamma-aminobutyric acid, which has been reported to reduce a Ca(2+)-dependent K+ conductance in the dorsal cells, did not reduce the PTH. 5. These results suggest that a Ca(2+)-dependent K+ conductance and an Na-K electrogenic pump underlie the PTH. The PTH reduces the excitability of the dorsal cells, suggesting that it may act as a mechanism to gate sensory information entering the spinal cord.

Action Potentials↗
PubMed1996

Tachykinin-mediated modulation of sensory neurons, interneurons, and synaptic transmission in the lamprey spinal cord.

1. Tachykinin-like immunoreactivity is found in the dorsal roots, dorsal horn, and dorsal column of the lamprey. The effect of tachykinins on sensory processing was examined by recording intracellularly from primary sensory dorsal cells and second-order spinobulbar giant interneurons. Modulation of synaptic transmission was examined by making paired recordings from dorsal cells and giant interneurons, or by eliciting compound depolarizations in the giant interneurons by stimulating the dorsal root or dorsal column. 2. Bath application of tachykinins depolarized the dorsal cells. This effect was mimicked by stimulation of the dorsal root, suggesting that dorsal root afferents may be a source of endogenous tachykinin input to the spinal cord. The depolarization was reduced by removal of sodium or calcium from the Ringer, or when potassium conductances were blocked, and was not associated with a measurable change in input resistance. Dorsal root stimulation also caused a depolarization in the dorsal cells, and this effect and that of bath-applied substance P, was blocked by the tachykinin antagonist spantide. 3. The tachykinin substance P could reduce inward and outward rectification in the dorsal cells, the effect on outward rectification only being seen when potassium conductances were blocked by tetraethylammonium (TEA). 4. Substance P increased the excitability of the dorsal cells and giant interneurons, shown by the increased spiking in response to depolarizing current pulses. The increased excitability was blocked by the tachykinin antagonist spantide. 5. Substance P modulated the dorsal cell action potential, by increasing the spike duration and reducing the amplitude of the afterhyperpolarization. The spike amplitude was not consistently affected. 6. Stimulation of the dorsal column resulted in either depolarizing or hyperpolarizing potentials in the giant interneurons. The amplitude of the depolarization was increased by substance P, whereas the amplitude of the hyperpolarization was reduced. These effects occurred independently of a measurable change in postsynaptic input resistance, suggesting that the modulation occurred presynaptically. Paired recordings from dorsal cells and giant interneurons failed to reveal an effect of substance P on dorsal cell-evoked excitatory postsynaptic potentials (EPSPs), suggesting that the potentiation of the dorsal column-evoked depolarization was due to an effect on other axons in the dorsal column. Dorsal root-evoked potentials could also be increased in the presence of substance P, although this effect was less consistent than the effect on dorsal column stimulation. 7. These results suggest that tachykinins modulate sensory input to the lamprey spinal cord by increasing the excitability of primary afferents and second-order giant interneurons, and also by modulating synaptic transmission. Tachykinins may result in potentiation of local spinal reflexes and also modulation of descending reticulospinal inputs to the spinal locomotor network as a result of potentiation of spinobulbar inputs.

Action Potentials↗
PubMed1996

Effect of cessation of short-term therapy with ipratropium bromide on lung function and airway responsiveness.

Regular exposure to antimuscarinic drugs would be expected to upregulate airway muscarinic receptors and could cause a transient increase in airways obstruction if treatment was stopped or omitted. We have examined peak expiratory flow rate (PEFR) during treatment and forced expiratory flow in one second (FEV1) and airway responsiveness to three constrictor agonists (as the provocative dose of agonist causing a 20% fall in FEV1, (PD20)) following cessation of regular inhaled ipratropium bromide, in 13 subjects with mild stable asthma. Subjects inhaled placebo and ipratropium bromide, 80 microg q.i.d. for 14 days in a cross-over fashion with a 1 week run-in/wash-out period before and after each treatment period. Subjects recorded symptom scores and PEFR throughout the study, and FEV1 and PD20 to histamine, methacholine and metabisulphite were measured before and after cessation of treatment. When compared to baseline, FEV1 was lower after cessation of ipratropium than after placebo, with a significant difference 30 h after the last dose (difference 190 mL; 95% confidence interval (95% CI) 310-70 mL; p<0.02). FEV1 measured 6-10 days later, did not differ significantly. PEFR was significantly lower after cessation of ipratropium than after placebo on Day 15 (19-37 h after the last dose) (mean difference 4.6%; 95% CI 1.6-7.5%; p<0.01) but not on Day 16. There were no significant changes in PD20 histamine, methacholine and metabisulphite, symptom scores or rescue bronchodilator use after cessation of treatment. Thus, transient bronchoconstriction was found around 30 h after cessation of regular therapy with inhaled ipratropium for 2 weeks. The mechanism is unclear, as no evidence of muscarinic receptor upregulation was found. Although the changes were small and unlikely to be important for most patients, the results of this study indicate that the timing of lung function measurements relative to the last dose of ipratropium is important when interpreting the course of lung function in long-term studies.

Administration, Inhalation↗
PubMed1996

Development of a ceramic device for the continuous local delivery of steroids.

Testosterone has been shown to stimulate bone healing. However, large doses of testosterone have been associated with liver damage and prostate enlargement. Sustained release of testosterone by a device placed next to a bone fracture could deliver effective amounts of the steroid necessary for bone healing without the adverse side effects associated with oral delivery or intramuscular injection. The release of 1 mg of testosterone into 1 ml of 50% ethanol from one-hour calcined hydroxyapatite (HA) ceramics (n = 6) and twelve-hour calcined HA ceramics (n = 6) was measured over four days. The twelve-hour calcined HA ceramics exhibited a consistently slower testosterone release. A 200mg HA/0.1% PLA/gentamicin (1mg) ceramic cylinder containing 0, 0.5, 1.0, or 1.5 mg testosterone was placed adjacent to a 4 x 1 x 1 mm femoral defect created in four equal groups of twenty-seven castrated male Sprague Dawley rats. After four weeks, none of the ceramics contained any residual testosterone. Histological examination showed that the traumatized bone of the animals implanted with testosterone-containing ceramics healed faster for the first four weeks than the controls. This data suggests that the twelve-hour calcined HA should be used to extend the release of testosterone to enhance healing of traumatized bone.

Animals↗
PubMed1996

Metabolic and ventilatory response to cross-country skiing classical and double arm poling exercise.

Nordic skiers place great emphasis on upper body endurance. Therefore, the purpose of this study was to compare oxygen uptake (VO2), minute ventilation (VE), tidal volume (VT), breath frequency (fB), heart rate (HR), and ventilatory anaerobic threshold (Tvan) responses to upper body classical poling (CP) and double poling (DP). Sixteen male master class cross-country ski racers performed DP and CP at similar incremental power outputs at 45 strokes/min on a modified Biokinetic swim bench variable-resistance arm ergometer. Leg VO2peak was measured during a Monark bicycle ergometer graded exercise test. Mean CP VO2peak was 34.8 +/- 9.0 ml kg-1 min-1 compared to 40.3 +/- 10.5 ml.kg-1 for DP (p < 0.05). CP and DP VO2peak was 70 +/- 3.4% and 81 +/- 3.8% respectively of the bicycle test VO2peak. DP VO2peak, and HR peak were significantly (p < 0.05) higher than for CP. CP Tvan appeared at 30.1 +/- 6.9 ml.kg-1.min-1 or 86 +/- 3.2% of CP VO2peak and DP Tvan occurred at 36.6 +/- 9.0 ml.kg-1.min-1 or 92 +/- 3.6% of DP VO2peak (p < 0.01). HR at Tvan was significantly higher for DP than for CP (< 0.05). Values for VT, fB, and VE measured at Tvan for both arm exercise modes were not significantly (p > 0.05) different. At submaximal exercise values for VO2, and HR were significantly different between the arm exercise modes. It is concluded that the mechanisms responsible for these observations may be increased active upper body muscle mass involvement for DP and that Tvan adaptations occur specifically to the exercise mode and recruited muscle groups.

Adult↗
PubMed1996

Self-restraint and self-injury: occurrence and motivational significance.

The occurrence of self-restraint was examined in a sample of 99 adults with severe or profound mental retardation who exhibited self-injury. Results showed that 46% of the sample exhibited self-restraint. A significantly higher occurrence of compulsive behaviors was found for subjects who engaged in self-injury and self-restraint when compared to self-injury subjects without self-restraint. To determine the motivational significance of self-restraint, we assessed the response to brief interruption of this behavior. Subjects who engaged in self-restraint responded more negatively to response interruption than did control subjects. These preliminary findings support the hypothesis that self-injury may be related to a compulsive behavior disorder in some individuals who self-restrain.

Adolescent↗