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Biomedical subjects

R Davenport

Publications and source records attributed to R Davenport.

At least 37 records · Page 2Linked to original sources
PubMed1994

UV-A coexposure enhances the toxicity of aromatic hydrocarbons, munitions, and metals to Photobacterium phosphoreum.

Johnson et al. (1993) showed that coexposure to UV-A between 300-400 nm enhanced the toxicity of nitrotoluenes to Photobacterium phosphoreum, a marine bioluminescent bacteria used in the Microtox test (Microbics Inc.). This paper reports that UV-A photoenhanced the toxicity of polynuclear aromatic hydrocarbons, other types of organic compounds, and some transition metals to P. phosphoreum. Coexposure to 400 muw/cm2 for 15 min increased the toxicity of psoralen, alpha-terthienyl, anthracene, acridine, fluoranthene, TNT, Cu2-, As3-, Ni2, and Cd2+. Phenanthrene was photoenhanced after 30 min coexposure at 400 muw/cm2-, and Mn2+ at 800 muw/cm2 after 15 min. Naphthalene was not enhanced at 800 muw/cm2 for 30 min.

Metals↗
PubMed1994

Reversion of bioluminescent bacteria (Mutatox) to their luminescent state upon exposure to organic compounds, munitions, and metal salts.

Mutatox is a new genotoxicity bioassay which uses as the endpoint the bioluminescence produced on reversion of a dark strain of the marine bacterium Vibrio fischeri +/- S9. Reversion can occur by several mechanisms, including base substitution, frame-shift, SOS induction, and DNA intercalation. For screening, Mutatox provides many advantages over the Salmonella typhimurium (Ames) assay: it requires minimal sterility, employs a shorter incubation period, and does not require culture maintenance. Eighteen organic chemicals (phenol, polynuclear aromatic hydrocarbons, nitrotoluenes, others), Na3PO4, and 4 genotoxic metals (Cu2+, Ni2+, As3+, Cd2+) were tested. Most of the organic compounds positive in S. typhimurium assays were positive in Mutatox. None of the metals was genotoxic in V. fischeri, possibly due to poor uptake from the saline medium.

Luminescent Measurements↗
PubMed1994

Cytokines and erythrocyte incompatibility.

The strong resemblance between the clinical manifestations of hemolytic transfusion reactions and sepsis, in which cytokine production has a central role, suggests that similar pathophysiologic mechanisms are involved. There is an expanding body of clinical and experimental evidence that cytokines, especially interleukin-1, tumor necrosis factor, interleukin-6, and interleukin-8, are principle mediators of immune responses to erythrocyte incompatibility. Recent studies have further suggested that the monocyte chemotactic and activating factor, monocyte chemoattractant protein-1, and the anti-inflammatory cytokine interleukin-1 receptor antagonist are produced in experimental models of hemolytic transfusion reactions. Differing levels and patterns of expression of these cytokines may be seen in models of intravascular hemolysis due to ABO incompatibility and extravascular hemolysis due to Rh incompatibility, which correlate with the recognized clinical differences between these two types of reactions. Furthermore, recent studies have demonstrated that several of these same cytokines are produced during the storage of platelet concentrates, which may account for some febrile reactions that are not prevented by the use of leukocyte reduction filters.

Blood Component Transfusion↗
PubMed1993

Immunohistochemical assessment of proliferative activity in adrenocortical neoplasms.

Although many histologic criteria have been utilized to help distinguish benign from malignant adrenocortical tumors, it still may be difficult to assess the biologic potential of a given tumor. We evaluated 19 adenomas and 15 primary carcinomas with the avidin-biotin complex peroxidase method utilizing formalin-fixed, paraffin-embedded tissues with monoclonal antibodies for proliferating cell nuclear antigen (PC10) and Ki-67 (MIB 1) to determine if staining for these antigens could be used to help differentiate benign from malignant adrenocortical neoplasms. We also evaluated whether these markers could be used as prognostic indicators. Labeling indices for both PCNA and Ki-67 were determined by enumerating 1000 tumor cells, and expressed as a percentage of cells with nuclear staining. A PCNA and a Ki-67 score was obtained by the product of the staining intensity (0-3+) and the extent of nuclear staining, expressed as an estimate of the percentage of cells staining. Both PCNA and Ki-67 score and labeling index were correlated with mitotic counts, histologic diagnosis, and clinical outcome. Follow-up period for patients ranged from 4 months to 12 years with a mean of 25 months. Mitotic counts correlated with histologic diagnosis and clinical outcome. Both Ki-67 score and labeling index were significantly higher in malignant than in benign tumors, and correlated with mitotic counts and clinical outcome. There was a strong correlation between Ki-67 score and labeling index, indicating that Ki-67 score may be a more rapid and equally accurate method of estimating proliferative index of a tumor. PCNA score and labeling index did not correlate with histologic diagnosis or clinical outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗
PubMed1992

Inhibition of protein kinase C by ether-linked lipids is not correlated with their antineoplastic activity on WEHI-3B and R6X-B15 cells.

To test the hypothesis that the action of antineoplastic ether-linked lipids in leukemic cells is associated with their ability to inhibit protein kinase C (PKC), we have compared the effects of two ether-linked lipids, 1-O-hexadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET16-OCH3-GPC) and 1-O-hexadecyl-2-O-methyl-sn-glycero-3-(S-beta-D-1'- thioglucopyranosyl)-sn-glycerol (ET16-OCH3-beta-thio-Glc), on two different leukemic cell lines (WEHI-3B and R6X-B15). ET16-OCH3-GPC killed WEHI-3B cells with an EC50 value of 2.5 microM, whereas it was far less effective against R6X-B15 cells (EC50 = 40 microM). In contrast, the beta anomer of ET16-OCH3-beta-thio-Glc did not kill either cell line at concentrations up to 40 microM. Both ET16-OCH3-GPC and ET16-OCH3-thio-Glc inhibited 12-O-tetradecanoylphorbol 12,13-dibutyrate (TPA)-induced PKC translocation in both WEHI-3B and R6X-B15 cells. When WEHI-3B cells were first exposed to TPA, and then to ET16-OCH3-GPC, no significant decrease in PKC activity in the particulate fraction was noticed. When, however, the cells were first exposed to ET16-OCH3-GPC and then to TPA, the enzyme activity in the particulate fraction was decreased by 20-30%. A phorbol dibutyrate binding assay showed that the decrease in membrane-associated PKC activity and the increase in cytosolic PKC activity did not result from impeded enzyme translocation. These results suggest that the similar PKC inhibitory potency of ET16-OCH3-GPC and ET16-OCH3-beta-thio-Glc: (a) is not correlated with the widely different cytotoxicities of these agents and (b) is probably due to interference with the binding of diacylglycerol/phosphatidylserine or TPA to PKC. Taken together, these results suggest that the ether-linked lipids compete with diacylglycerol/phosphatidylserine or TPA for binding sites on PKC required for enzyme activation.

Antineoplastic Agents↗
PubMed1991

Possible dual effect of synapses that are putatively purely excitatory or purely inhibitory: bases in stability theory and implications for neural network behavior.

Depolarization of an excitable membrane has a dual effect; excitatory in that it causes rapid opening of calcium and/or sodium channels but inhibitory in that it also causes those channels to inactivate. We considered whether apparently paradoxical or dual behavior might be exhibited by excitatory and inhibitory synaptic inputs. We used the classic Hodgkin-Huxley model for voltage-gated channels plus leakage channels of appropriate selectivity for ligand-gated postsynaptic channels. We summarize a model cell's behavior by calculating elicited firing frequency as a function of reversal potential and conductance of summed synaptic inputs, using stability theory and direct simulations. Dual behavior is elicited in the model with reasonable densities of ligand-gated channels. Thus a particular synaptic input to a neuron may be either excitatory or inhibitory depending on simultaneous activity of other synaptic inputs to the cell. This input-output map may give rise to biologically realistic and rich behaviors as an element of computed neural networks, and still be computationally tractable.

Animals↗
PubMed1986

Control of sensitivity to inactivation by H2O2 and broad-spectrum near-UV radiation by the Escherichia coli katF locus.

Mutations in the Escherichia coli katF gene (hydroperoxidase II) result in sensitivity to inactivation by H2O2 and broad-spectrum near-UV (NUV; 300 to 400 nm) radiation. Another mutation, nur, originally described as conferring sensitivity to inactivation by broad-spectrum and monochromatic NUV, also confers sensitivity to inactivation by H2O2. Genetic analysis via transduction suggests that the nur mutation allele of the katF locus. As previously reported for broad-spectrum and monochromatic NUV wavelengths, the sensitivity of a particular strain to H2O2 inactivation is also independent of the recA and uvrA alleles. Extracts of nur and katF strains lack catalase (hydroperoxidase II) as revealed by polyacrylamide gels stained for such activity, which is consistent with the genetic results.

Alleles↗
PubMed1986

A high performance liquid chromatographic assay for tocainide with alternate application for the determination of lidocaine, procainamide, and N-acetylprocainamide.

We describe a simple, isocratic high-performance liquid chromatographic method for measuring the oral antiarrhythmic agent tocainide in serum. The extraction requires 200 microliters of serum, is performed on a reverse-phase column, and utilizes the drug mepivacaine as the internal standard. This analytical method can also be used to assay procainamide, n-acetylprocainamide, or lidocaine with minor modifications to either the extraction protocol or the wavelength used to monitor column eluant.

Acecainide↗
PubMed1983

The derivation of the gamma-variate relationship for tracer dilution curves.

Tracer dilution curves are useful for describing blood flow through vessels and organs. Empirically determined curves for flow through nonbranching vessels have been shown to correspond to a mathematical function called the gamma variate. This paper presents a derivation of the gamma-variate relationship, discusses some of the properties of the gamma variate and its use in problems involving organ blood flow and recirculation.

Humans↗
PubMed1982

Cyclic AMP does not modulate hexose uptake of serum-deprived BHK-21 fibroblasts.

We have studied the uptakes of the glucose analogs, 2-deoxyglucose (2DG), and 3-O-methylglucose (3OMG) in serum-deprived BHK-21 fibroblasts. Incubation for 4 hours with 0.25 mM 1-methyl-3-isobutylxanthine (MIX) increased cellular cyclic AMP 3 to 15 fold, without affecting the initial rates of uptake of these sugars. Incubation with 100 nM insulin, doubled hexose uptake without affecting cyclic AMP. Insulin did not modify the cyclic AMP response to MIX; nor did MIX alter the hexose uptake response to insulin. There was no effect of 0.1 mM L-isoproterenol (ISO) or 0.1 mM prostaglandin E1 (PGE1) on cyclic AMP. PGE1 slightly stimulated uptake of 2DG but not 3OMG; ISO did not affect hexose uptake. We conclude that cyclic AMP does not directly regulate hexose uptake in these cells.

1-Methyl-3-isobutylxanthine↗
PubMed1980

Monitoring clorazepate dipotassium as desmethyldiazepam in plasma by electron-capture gas--liquid chromatography.

We describe a procedure for determing clorazepate dipotassium as its decarboxylated, pharmacologically active metabolite, desmethyldiazepam, in 100 microL of plasma, with use of electron-capture gas--liquid chromatography and with methylnitrazepam as the internal standard. The procedure is a one-tube, one-step extraction without derivative formation and is accurate, reproducible, and rapid. The sensitivity limit is 20 micrograms/L. Within-run and between-run CV's (concentration, 3.5 mg/L) were 2.9 and 3.5%, respectively. Within-run CV's for 1.5 and 1.0 mg/L concentrations were 3.9 and 4.3%, respectively. For a 1.0 mg/kg per day dose of clorazepate dipotassium, the mean steady-state concentration of desmethyldiazepam in plasma was 1.037 mg/L.

Anti-Anxiety Agents↗