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Biomedical subjects

M D Lee

Publications and source records attributed to M D Lee.

17 recordsLinked to original sources
PubMed1992

Factors affecting endotoxin release from the cell surface of avian strains of Pasteurella multocida.

Two avian strains of Pasteurella multocida, a vaccine strain and a virulent field isolate, were investigated to determine their propensity to release endotoxin from the cell surface. Both organisms released comparable amounts of endotoxin when plasma complement proteins were present, however the virulent strain did so without the loss of viability that occurred in the vaccine strain. Blocking complement activity decreased the ability of plasma to elicit endotoxin release from the bacteria. When the cells were treated with divalent metal chelators such as trans-1, 2-diaminocyclohexane-N,N,N1,N1-tetraacetic acid (CDTA), more endotoxin was released from the vaccine strain than from the virulent isolate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of purified lipopolysaccharide (LPS) from both strains revealed virtually identical patterns. Both had patterns considered typical of rough LPS. Challenge studies in 8 weeks old turkeys showed that the field strain induced endotoxemia of longer duration than the vaccine strain and produced greater mortality.

Animals↗
PubMed1992

Partial reversal of fluoxetine anorexia by the 5-HT antagonist metergoline.

Experiment 1 showed that the reduction of intake produced by 5 or 10 mg/kg fluoxetine in rats eating either a solid or a liquid meal was partially antagonised by 1 mg/kg of the 5HT1/5HT2 antagonist metergoline but not by 1 mg/kg of the 5HT2 antagonist ketanserin. Experiment 2 examined the meal patterning of rats given 5 mg/kg fluoxetine and 1 mg/kg metergoline. Fluoxetine alone increased the latency to feed, reduced meal size and shifted the inter-pellet interval (IPI) distribution to the right. Metergoline alone had little immediate effect on food intake or other feeding parameters but partially reversed the reduction of food intake produced by fluoxetine. There was a complete reversal of the increased latency to feed and a partial reversal of the depression of meal size. However, the rightward shift of the IPI distribution caused by fluoxetine, which indicated a depression of feeding rate, was more pronounced after combined treatment. We conclude that fluoxetine reduces food intake by enhancing satiety through a serotonergic dependent mechanism but reduces feeding rate through a separate mechanism, whose neurochemical basis remains to be established.

Animals↗
PubMed1992

Free-feeding and free-drinking patterns of male rats following treatment with opiate kappa agonists.

Three experiments investigated the effects of PD117302 and U50,488H on the patterns of food and water intake by male rats. Experiment 1 demonstrated early dose-related suppression of food and water intake after PD117302 (0, 1.25, 2.5, 5 mg/kg). The initial suppression of drinking was followed by a sustained increase 4-12 h after drug administration. Experiment 2 demonstrated that 2.5 mg/kg PD117302 failed to increase food intake whether given at the beginning of the night (high baseline food intake) or the beginning of the day (low baseline food intake). Experiment 3 showed that 0.5 mg/kg U50,488H significantly enhanced meal size but, at doses of 0.5, 1.0, and 2.0 mg/kg, had no effect on overall food intake. U50,488H also produced delayed, dose-related increases in water intake. The results suggest kappa receptors may have limited importance in modulating ad lib food intake and demonstrate the behavioural characteristics of increased drinking after excessive urine output.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1992

CT reconstruction algorithm for a dental panoramic x-ray unit.

A variable Jacobian and weighted backprojection algorithm, used for medical CT, was adapted to perform CT reconstructions on data obtained with a dental panoramic x-ray unit. A detector array, fitted to the unit for the purpose of acquiring digital panoramic radiographs, was used to collect the data. Compensations were made for the incomplete (230 degrees) rotation of the panoramic x-ray unit, the non-fixed centre of rotation, the irregular rotation of the x-ray target and detector, and the resulting variances in magnification. The algorithm was tested on mathematically simulated phantoms and on acquired data. Reconstruction of simulated data proved the success of the algorithm. Real data reconstructions showed some defects as a result of inaccuracies in quantifying the experimental panoramic device.

Algorithms↗
PubMed1991

The gene encoding rat nuclear pore glycoprotein p62 is intronless.

Glycoproteins of the nuclear pore complex are thought to play an important role in the transport of regulatory proteins and ribonucleoproteins across the nuclear envelope. However, the genetic elements and signals that control the expression of nuclear pore glycoproteins are poorly understood. To study the transcriptional regulation of mammalian nuclear pore glycoprotein biosynthesis, we have isolated the gene coding for the major rat nuclear pore glycoprotein p62. The p62 gene consists of a 2941-base pair region that is linear with the full length p62 cDNA with no intervening sequences. Quantitative Southern analysis revealed that the gene is present in single copy. The p62 gene encodes a 525-amino acid open reading frame that directs the synthesis of the 62-kDa pore glycoprotein in vitro and in transfected cultured cells. The 5'-flanking region contains two potential transcription start sites; primer extension analysis revealed that the furthest upstream site is preferentially used in vivo. When linked to a reporter gene, the 5'-flanking region of the p62 gene serves as an active promoter.

Animals↗
PubMed1991

A survey of potential virulence markers from avian strains of Pasteurella multocida.

Twenty-four isolates of Pasteurella multocida from clinical cases of fowl cholera and the Clemson University vaccine strain were surveyed for the presence of potential virulence markers. Membrane proteins, enzymatic activity of the membrane proteins, and carbohydrate fermentation patterns were also determined to demonstrate phenotypic relationships within the groups. Few differences were found in these phenotypic characteristics among the isolates. Almost all the organisms produced siderophore and were hemolytic on turkey red blood cells. No extracellular enzyme or bacteriocin activity was detected and little antibiotic resistance was found. However, many organisms contained plasmids and demonstrated some degree of resistance to complement. Both characteristics were correlative markers in Pasteurella multocida isolated from birds with fowl cholera.

Animals↗
PubMed1991

Recombination of automatic processing components: the effects of transfer, reversal, and conflict situations.

This research was conducted to evaluate the effects of compatible and incompatible automatic processes on performance. Subjects were trained for 8400 trials of consistent mapping practice in a semantic category visual search task and then transferred for 2352 trials to conditions that utilized the trained component processes in various ways. Results indicate that if the components were reused in a compatible fashion (target and distractor transfer), there was positive transfer. Target and distractor reversal resulted in equivalent and severe performance disruption that persisted for the entire retraining period. Target conflict produced disruption equivalent to the reversal conditions. Distractor conflict resulted in less initial disruption, which dissipated before the end of the retraining period. The results are discussed in terms of agreement with strength-theoretic views of visual search and in terms of practical training and retraining issues.

Adult↗
PubMed1991

Analysis of ras gene mutations in gastrointestinal cancers.

Point mutations of c-Ki-ras genes were analyzed in 33 samples of human gastrointestinal malignancy. DNA extracted from the frozen tissue was amplified by polymerase chain reaction (PCR) and analyzed by direct sequencing and slot-blot hybridization at codons 12, 13 and 61 of c-Ki-ras. In 7 cases out of 19 colorectal cancers, point mutations were found: 3 cases at codon 12, 1 at codon 13, 2 at codon 61 of c-Ki-ras and one case had double mutations at codon 12 and codon 13. In 11 cases of gastric cancer, 4 showed point mutations: 1 at codon 12 and 3 at codon 13 of c-Ki-ras. In 3 pancreatic carcinomas, 2 had point mutations: one at codon 12 and the other at codon 13 of c-Ki-ras. The results indicate that c-Ki-ras gene point mutations are involved in the tumorigenesis of the human gastrointestinal system.

Adult↗
PubMed1990

The growth factor-like effects of tumor necrosis factor-alpha. Stimulation of glucose transport activity and induction of glucose transporter and immediate early gene expression in 3T3-L1 preadipocytes.

In the present study, the ability of tumor necrosis factor-alpha (TNF) to stimulate hexose transport in quiescent 3T3-L1 fibroblasts has been examined. Activation of transport occurred in a dose- and time-dependent manner, with maximal stimulation (6-8-fold) observed 16 h after exposure to 2.5 nM TNF. Early activation of hexose transport by TNF (2-fold within 30 min) was associated with increased plasma membrane immunoreactive glucose transporters. Prolonged exposure to TNF (16 h) resulted in a 2-fold increase in glucose transporter content of both plasma and inner membrane compartments. The magnitude of increased glucose transport (6-8-fold) was greater than the increased content of plasma membrane glucose transporters (2-fold), suggesting that the TNF-treatment altered the intrinsic activity of the glucose transporters. Increased transcription of the glucose transporter (GLUT-1) gene, as well as several immediate-early genes (c-fos, c-jun, jun-B, and beta-actin) was observed within 15 min of exposure to TNF. Transcriptional activation of immediate-early genes was tightly coupled to subsequent accumulation of their respective mRNAs. However, increased GLUT-1 mRNA (8 h after TNF treatment) was due to an apparent 3-fold increase in the stability of this message and not to increased transcription. The time course of TNF-induced hexose transport occurred concomitant with a 6-fold increase in total RNA synthesis which preceded a 3-fold increase in protein synthesis. Moreover, TNF induced cell-cycle progression through S-phase, as measured by aphidicolin-sensitive thymidine uptake. Phorbol myristate acetate also stimulated hexose transport as well as expression of the GLUT-1 gene and several immediate-early genes in quiescent 3T3-L1 cells. TNF-induced immediate-early gene expression was intact in PMA-pretreated cells (with the exception of GLUT-1 and beta-actin genes where the response was muted), suggesting the involvement of multiple pathways in TNF signal transduction. Our results indicate that TNF initiates mitogenic events in quiescent 3T3-L1 fibroblasts reminiscent of serum-derived growth factors.

Adenosine Triphosphate↗
PubMed1989

Monokine regulation of glucose transporter mRNA in L6 myotubes.

Endotoxin-induced macrophage secretory proteins (monokines) have been shown to stimulate hexose uptake in L6 myotubes (1). In those studies a doubling of the Vmax for hexose uptake was observed which correlated with elevated numbers of glucose transporters (GT) in both plasma and microsomal membranes. To determine if these changes in transporter populations were due to increased GT mRNA, we performed Northern blot analysis using L6 cell RNA and a cDNA to the HepG2 glucose transporter. The L6 myotubes contained a single 2.8 kb species of GT mRNA that increased 2.5-fold after an 8h exposure to the monokine preparation. beta-Actin mRNA levels were unaltered by the treatment, indicating specificity of monokine action. Glucose transporter mRNA content appeared to reach a maximum 8 h after exposure to the monokine. Over the next 16 h the levels of this mRNA gradually decreased, approaching control levels. Data obtained from nuclear transcription run-on assays suggest that increased levels of CT mRNA are due to an increased rate of gene transcription. A second transporter, the insulin-sensitive glucose transporter, was also observed to be expressed in the L6 cells. Monokine treatment resulted in a 60% suppression of the mRNA coding for this protein.

Actins↗
PubMed1989

In vivo transmural potential difference: an early monitor of rejection in small bowel transplantation.

To determine if serial measurements of transmural potential difference (TMPD) can serve as an early monitor of rejection in small bowel transplantation, three groups of rats were studied. The groups are defined as follows: (1) group 1, isolated loop (N = 5): 20 cm of distal jejunum was defunctionalized (Thiry-Vella loop); (2) group 2, isotransplant (N = 5): 20 cm of distal jejunum was isotransplanted between inbred Lewis rats, as a Thiry-Vella loop; the native bowel remained in continuity; (3) group 3, allotransplant (N = 8): allotransplantation as in group 2 but between outbred Sprague-Dawley rats. Using luminal and peritoneal electrodes, TMPD was measured serially every third day. Biopsies of the stoma were taken on the same days for histologic examination of rejection. Group 1 animals (isolated loop) did not show a significant decrease in TMPD from day 1 to day 20. Group 2 (isotransplant animals) had a significant decrease in TMPD as compared with group 1 on day 5 (P less than .01), but by day 8, TMPD returned to baseline. Biopsies in groups 1 and 2 showed no signs of rejection. Group 3 (allotransplant animals) showed a significant decrease in TMPD as compared with group 1 on day 5 (P less than .01). The severity of the histologic signs of rejection parallelled the TMPD decrease throughout the remainder of the study. Monitoring TMPD is a sensitive method of detecting early rejection in small intestine transplantation.

Animals↗
PubMed1989

Calicheamicins, a novel family of antitumor antibiotics. 3. Isolation, purification and characterization of calicheamicins beta 1Br, gamma 1Br, alpha 2I, alpha 3I, beta 1I, gamma 1I and delta 1I.

Novel antitumor antibiotics, calicheamicins beta 1Br, gamma 1Br, alpha 2I, alpha 3I, beta 1I, gamma 1I and delta 1I were recovered from the fermentation broth of Micromonospora echinospora ssp. calichensis by solvent extraction, selective precipitation, normal phase, reversed phase and partition chromatography. The individual components were characterized by their UV, IR, 1H and 13C NMR spectral data.

Aminoglycosides↗
PubMedDate not supplied

Comparison of a quantitative microtiter method, a quantitative automated method, and the plate-count method for determining microbial complement resistance.

A quantitative microtiter method for determining the degree of complement resistance or sensitivity of microorganisms is described. The microtiter method is compared with a quantitative automated system and the standard plate-count technique. Data were accumulated from 30 avian Escherichia coli isolates incubated at 35 C with either chicken plasma or heat-inactivated chicken plasma. Analysis of data generated by the automated system and plate-count techniques resulted in a classification of the microorganisms into three groups: those sensitive to the action of complement; those of intermediate sensitivity to the action of complement; and those resistant to the action of complement. Although the three methods studied did not agree absolutely, there were statistically significant correlations among them.

Animals↗
PubMedDate not supplied

Characterization of Pasteurella multocida mutants of low virulence.

Ten temperature-sensitive mutants of the Clemson University (CU) vaccine strain of Pasteurella multocida have been developed and were characterized by phenotypic attributes such as carbohydrate fermentation, antibiotic resistance, and membrane protein profiles. Some mutants were found to have lost the ability to utilize some substrates, notably xylose and gluconate, whereas others were able to ferment additional carbohydrates such as arabinose and rhamnose. CU was found to be resistant to sulfisoxazole, of intermediate resistance to bacitracin, and sensitive to rifampin; the sensitivity to these three antibiotics varied among the mutant strains, but 60% were resistant to rifampin. Membrane protein profiles demonstrated some changes in major bands, and there was variation in 50% of the mutants in proteins in the 31 kilodalton range. All strains were assayed for the presence of several virulence factors, and many were found to produce siderophore and to exhibit some degree of complement resistance.

Animals↗