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Biomedical subjects

K Harvey

Publications and source records attributed to K Harvey.

At least 37 records · Page 2Linked to original sources
PubMed1999

Diagnostic testing for serious bacterial infections in infants aged 90 days or younger with bronchiolitis.

OBJECTIVES: To describe the different laboratory tests that are performed on young infants aged 90 days or younger with bronchiolitis and to identify historical and clinical predictors of infants on whom laboratory tests are performed. DESIGN: Cross-sectional study whereby information was obtained by retrospective review of medical records from November through March 1992 to 1995 of all infants with a clinical diagnosis of bronchiolitis. SETTING: Urban pediatric emergency department. PATIENTS: Two hundred eleven consecutive infants aged 90 days or younger (median age, 54 days) with 216 episodes of bronchiolitis. MAIN OUTCOME MEASURES: Historical and clinical data on each infant in addition to laboratory data that included a white blood cell count, urinalysis, and blood, urine, and cerebrospinal fluid cultures. RESULTS: Two or more laboratory tests (not including chest radiographs) were obtained in 48% of all infants and 78% of febrile infants. Of the 91 infants with a history of a temperature of 38.0 degrees C or more or temperature on presentation of 38.0 degrees C or more, white blood cell counts were obtained in 77%, blood cultures in 75%, urinalyses in 53%, urine cultures in 60%, and analyses-cultures of cerebrospinal fluid in 47%. Febrile infants were 10 times more likely to get at least 2 laboratory tests than afebrile infants (P<.01). All 6 studies were done in 42 (58%) of 72 febrile infants compared with 7 (16%) of 43 afebrile infants (P<.001). Multiple logistic regression analysis identified a history of a temperature of 38.0 degrees C or more or temperature on presentation of 38.0 degrees C or more (odds ratio [OR] 10.0; 95% confidence interval [CI], 4.8%-21.0%; P<.001), oxygen saturation less than 92% on presentation (OR, 4.7; 95% CI, 1.9%-12.1%; P<.01), and history of apnea (OR, 0.1; 95% CI, 0.02-0.35; P<.001) as significant clinical predictors of whether laboratory studies were obtained. History of preterm gestation, aged younger than 28 days, previous antibiotic use, and presence of otitis media were not associated with obtainment of laboratory studies. No cases of bacteremia, urinary tract infection, or meningitis were found among all infants with bronchiolitis who had blood, urine, and/or cerebrospinal fluid cultures. CONCLUSION: There is wide variability in the diagnostic testing of infants aged 90 days or younger with bronchiolitis. The risks of bacteremia, urinary tract infection, and meningitis in infants with bronchiolitis seems to be low. History or a documented temperature of 38.0 degrees C or more; oxygen saturation of less than 92%, and history of apnea were associated with laboratory testing for bacterial infections.

Bacterial Infections↗
PubMed1999

Development of optimal techniques for cryopreservation of human platelets. I. Platelet activation during cold storage (at 22 and 8 degrees C) and cryopreservation.

Using the current blood bank storage conditions at 22 degrees C, the viability and function of human platelets can be maintained for only 5 days. This does not allow for the necessary and extensive banking of platelets needed to treat patients afflicted with thrombocytopenia, a side effect of many invasive surgeries such as cardiopulmonary bypass or bone marrow transplantation. The development of optimal techniques for long-term cryopreservation and banking of human platelets would provide the ability to greatly extend the viable life of the platelet and would fulfill an increasing and urgent need in many clinical applications. To determine the optimal techniques for platelet preservation, the expression of an activation marker, phosphatidylserine, on the platelet membrane during storage at 22 and 8 degrees C as well as during the different freezing preservation processes was examined using flow cytometry and annexin V binding assay. Human platelets were identified by both CD41 and light scatter in flow cytometry. In cryopreservation experiments, effects of the following factors on platelet activation were evaluated: (a) cryoprotective agents (CPAs) type: dimethyl sulfoxide (Me2SO), ethylene glycol (EG), and propylene glycol (PG), (b) CPA concentration ranging from 0 to 3 M, and (c) ending temperatures of a slow cooling process at -1 degrees C/min. Our results demonstrated that (a) approximately 50% of platelets were activated on days 7 and 16 at 22 and 8 degrees C, respectively; (b) platelets were not significantly activated after 30-min exposure to 1 M Me2SO, EG, and PG at 22 degrees C, respectively, and (c) there was a significant difference in cryoprotective efficacy among these three CPAs in preventing platelets from cryoinjury. After being cooled to -10 degrees C, 74% of the cryopreserved platelets survived (nonactivated) in 1 M Me2SO solution, while in 1 M EG and 1 M PG solutions, 62 and 42% of the platelets survived, respectively. Using the information that Me2SO consistently yields higher percentages of nonactivated platelets and does not seem to be cytotoxic to platelets for 30-min exposure time, this was found to be the optimal cryoprotective agent for platelets. In addition, significant Me2SO toxicity to platelets was not noted until Me2SO concentrations exceeded 2 M. Finally, a concentration of 1 M Me2SO proved to be the most effective at all cryopreservation ending temperatures tested (-10, -30, -60, and -196 degrees C). In conclusion, under the present experimental conditions, a storage temperature of 8 degrees C appeared to be much better than 22 degrees C. Although the potential chemical toxicity of 1 M Me2SO, EG, or PG is negligible, 1 M Me2SO was found to be optimum for cryopreservation of human platelets. PG has the least cryoprotective function for low-temperature platelet survival.

Blood Platelets↗
PubMed1999

Comparison of the distribution of progenitor cells in G-CSF-mobilized peripheral blood and steady-state bone marrow after counterflow centrifugal elutriation.

Blood-derived progenitor cells obtained following mobilization with granulocyte colony-stimulating factor (MoPBSC) are increasingly being used as an alternative to bone marrow (BM) in allogeneic stem cell transplantation. The higher numbers of mature T lymphocytes in MoPBSC grafts may increase the risk of (chronic) graft-vs.-host disease. Counterflow centrifugal elutriation (CCE) is an effective method for T-cell depletion of BM grafts. The elutriation characteristics of steady-state BM and MoPBSC were compared using a CCE procedure in which fractions were obtained after small incremental increases in flow rate with constant centrifugal force. Counterflow centrifugal elutriation experiments with MoPBSC from six healthy volunteers showed that 54% of all cells collected were recovered in the < or = 15 mL/minute fractions, whereas experiments with mononuclear BM cells from five healthy volunteers resulted in recovery of 52% of collected cells from the > or = 19 mL/minute fractions. The peak concentrations of CD34+ cells were found in the same fraction (18 mL/minute), but more CD34+ cells from MoPBSC were recovered from the small (< or = 16 mL/minute) fractions (54% for MoPBSC, 26% for BM; p = 0.08). The small CD34+ cells from BM were more frequently lacking CD38 and human leucocyte antigen-DR expression than the small CD34+ cells from MoPBSC. Mature T-cells (CD3+) in BM and MoPBSC samples had similar CCE features, as did early (long-term culture initiating cells, high-proliferative potential colony-forming cells) and more mature (colony-forming units granulocyte/macrophage, BFU-e) hematopoietic progenitor cells. The results of this study suggest that T-cell depletion by CCE of MoPBSC as compared to BM products, may lead to a greater loss of CD34+ cells, but not of immature hematopoietic progenitor cells.

Adult↗
PubMed1999

Induction of neutrophil calcium mobilization by phosphatidic acid-enriched plasma membranes.

The purpose of this investigation was to determine if phosphatidic acid (PA) confined to biological membranes could induce physiological responses similar to those induced by exogenous PA. Plasma membranes were treated with phospholipase D (PLD) to increase concentrations of PA within the membranes. Membranes were also treated with other phospholipases including phospholipase A2 (PLA2), and phospholipase C (PLC), which degrade phospholipids without generating PA. A phosphatidylinositol (PI) 3'-kinase inhibitor, LY294002, strongly and selectively inhibited intracellular calcium mobilization induced by PLD-treated membranes. This study suggests that PA-enriched plasma membranes, which exert their effects by activating a unique signaling pathway mediated by PI 3'-kinase, are potent, physiologically relevant initiators of neutrophil activation.

Benzoquinones↗
PubMed1999

Prevalence and predictors of parasuicide in chronic psychosis. UK700 group.

OBJECTIVE: This study estimates the prevalence of and risk factors for parasuicide in a large community-based sample of patients with chronic psychosis. METHOD: A total of 704 subjects with chronic psychosis were interviewed using a battery of instruments. The 2-year prevalence of parasuicide was estimated and a comparison was made between attempters and nonattempters on a wide range of sociodemographic and clinical variables. RESULTS: The 2-year prevalence of parasuicide was 18.8%. Attempters were significantly more likely to be younger, of white ethnic origin, to have a diagnosis of affective disorder, to be currently depressed, to have experienced more auditory hallucinations and to have received treatment with antipsychotic drugs for a longer period. CONCLUSION: Parasuicide was found to present a considerable clinical problem in this group. Continual risk assessment is essential to reduce this unacceptably high rate.

Adolescent↗
PubMed1999

Prevalence and characteristics of patients with severe mental illness and borderline intellectual functioning. Report from the UK700 randomised controlled trial of case management.

BACKGROUND: Low cognitive ability and developmental delays have been implicated in the causation of mental illness. AIMS: To examine the prevalence, socio-demographic characteristics, psychopathology and social functioning profiles of people with low intelligence and recurrent psychotic illness. METHOD: A multi-centre randomised controlled trial of case management provided the opportunity to explore associations between mental illness and borderline intellectual functioning (assessed using the National Adult Reading test). RESULTS: Overall prevalence of borderline intelligence was 18%. Significant positive associations were shown with: being Black Caribbean; having a father who worked in a manual occupation; lower educational achievement; having had special education; longer course of illness. Those with borderline intelligence had greater disability and were more likely to suffer extrapyramidal side-effects and show evidence of negative symptoms. Educational achievement, history of special education and social class were the best socio-demographic predictors of intellectual level. CONCLUSIONS: Many patients who attend generic psychiatric services have considerable intellectual deficits. This may lead to difficulties in other domains of adaptive functioning, and merits further investigation as well as clinical vigilance.

Adolescent↗
PubMed1999

Interleukin-8: An autocrine inflammatory mediator.

Interleukin-8 (IL-8), a pro-inflammatory chemokine, induces trafficking of neutrophils across the vascular wall. The release of IL-8 is triggered by inflammatory signals from a large variety of cells. The diversity in the cellular source indicates pleiotropy of its functions. IL-8 plays a key role in host defense mechanism through its effects on neutrophil activation, but a continued presence of IL-8 in circulation in response to inflammatory conditions may lead to a variable degree of tissue damage. Like most of the peptide hormones or mediators, IL-8 transmits its signals through distinct cell surface receptors. The membrane spanning heptahelical IL-8 receptor is coupled with the effector enzyme(s) through the intermediacy of heterotrimeric GTP-binding regulatory proteins. A growing number of studies demonstrated regulation of IL-8 activity by pertussis toxin treatment, implying a role of pertussis toxin sensitive G proteins (Gi), in IL-8 induced effects. IL-8 induced activation of G-protein results in activation of phospholipase C b2 (PLCb2). This enzyme catalyzes the hydrolysis of membrane phosphoinositides to yield diacylglycerol (DAG) and inositol 1,4,5 trisphosphate (IP3), which in turn activates protein kinase C (PKC) and mobilizes the intracellular Ca2+, respectively. Neutrophils activation of phospholipase D (PLD) and superoxide generation in response to IL-8 have also been demonstrated. Furthermore, IL-8-mediated activation of mitogen activating protein kinase (MAPK) and tyrosine phosphorylation of cellular proteins have been observed. It appears that the signalling pathways induced by IL-8 are subject to fine modulations by the demand and presence of IL-8. The presence of IL-8 in various pathophysiological condition implies that blockade of its actions could be exploited for therapeutic purposes.

Animals↗
PubMed1998

Fundamental cryobiology of human hematopoietic progenitor cells. I: Osmotic characteristics and volume distribution.

While methods for the cryopreservation of hematopoietic stem cells are well established, new sources of progenitor cells, such as umbilical cord blood, fetal tissue, and ex vivo expanded progenitor cells, may require refined protocols to achieve optimal recovery after freezing. To predict optimal protocols for cryopreservation of human hematopoietic progenitors, knowledge of fundamental cryobiological characteristics including cell osmotic characteristics, water and cryoprotectant permeability coefficients of cell membrane, and activation energies of these coefficients is required. In this study, we used CD34+CD33- cells isolated from human bone marrow as hematopoietic progenitor cell models/representatives to study the osmotic characteristics of the progenitor cells. Volume distribution and osmotic behavior of the CD34+CD33- cells were determined using two different methods: (a) a shape-independent electronic sizing technique and (b) a shape-dependent optical image analysis. The cell diameter was measured to be 8.2 +/- 1.1 microns (mean +/- SD, n = 1,091,475, the number of donors = 8) using the electronic sizing technique or 8.7 +/- 1.2 microns (mean +/- SD, n = 1508, the number of donors = 6) by image analysis at initial (isotonic) osmolality, 325 mosm/kg. The cell volume change was measured after the cells were exposed and equilibrated to different anisosmotic conditions. The cell volume was found to be a linear function of the reciprocal of the extracellular osmolality (Boyle van't Hoff plot) ranging from 163 to 1505 mosm/kg. The volume fraction of intracellular water which is osmotically active was determined to be 79.5% of the cell volume. It was concluded that human CD34+CD33- cells osmotically behave as ideal osmometers. This information coupled with cell water and cryoprotectant permeability coefficients as well as their activation energies (to be determined in the ongoing research projects) will be used to design optimum conditions for cryopreservation of human hematopoietic progenitor cells.

Antigens, CD↗
PubMed1997

Counterflow centrifugal elutriation as a method of T cell depletion may cause loss of immature CD34+ cells.

Counterflow centrifugal elutriation (CCE) is capable of separating cells on the basis of size. CCE has been used successfully to deplete allogeneic bone marrow (BM) grafts of T lymphocytes to decrease the risk of acute graft-versus-host disease. Previous studies have shown that more immature CD34+ cells in human BM tend to be smaller than more mature CD34+ cells. Human BM was subjected to CCE with the 4 ml standard chamber at constant rotor speed (2300 r.p.m.) and increasing flow-rate (14-23 ml/min, rotor-off). The eleven fractions collected were assayed for CD34+ and CD3+ cells, and for CFU-GM, HPP-CFC and long-term culture initiating cells (LTC-IC). The CD3+ T cells were enriched in the early (small-cell) fractions 14-17 ml/min. CD34+ cells were enriched in fractions 17-21 ml/min, and CFU-GM were concentrated in the same fractions. HPP-CFC and LTC-IC showed nearly identical CCE profiles, with enrichment in fractions 16-18 ml/min. When fraction < or = 17 ml/min was chosen as cut-off, the small-cell fraction contained 94.0% of all CD3+ cells, 44.4% of total cells, 33.2% of CD34+ cells and 34.7% of CFU-GM; however, 67.6% of HPP-CFC and 72.4% of LTC-IC were recovered in this small-cell fraction. These data suggest that T cell depletion through CCE as used by us, while losing only minor proportions of CD34+ cells and CFU-GM, carries the risk of losing the majority of more immature progenitor cells. This may lead to an increased risk of graft failure, in particular in HLA-mismatched transplants.

Antigens, CD34↗
PubMed1997

Lineage commitment of HLA-DR/CD38-defined progenitor cell subpopulations in bone marrow and mobilized peripheral blood assessed by four-color immunofluorescence.

We used four-color fluorescence analysis to compare lineage antigen expression in relationship to CD38 and HLA-DR on CD34+ progenitor cells in adult human bone marrow and mobilized peripheral blood. Each of four progenitor cell subpopulations defined by HLA-DR and CD38 intensity (CD38-/HLA-DR-, CD38-/HLA-DR+, CD38+/HLA-DR+, and CD38+/HLA-DR-) were present in both progenitor cell sources in similar ratios. The most prevalent subpopulation consisted of cells that expressed both CD38 and HLA-DR. Virtually all progenitor cells that lacked CD38 also lacked lineage antigens regardless of their HLA-DR expression. In contrast, the majority of the cells within both CD38+ progenitor cell subpopulations possessed either lineage antigens or the proliferation-associated antigen, CD71. Furthermore, CD71 was expressed on three times the number of CD38+/HLA-DR- cells when compared with the CD38-/HLA-DR- subpopulation. Within CD34+ progenitor cell subpopulations defined by the expression of CD38 and HLA-DR, the CD38+/HLA-DR- component appears to be the most mature, based on the expression of CD71 and various lineage-associated antigens, including representative markers characterizing early lymphoid, myeloid, and erythroid precursors. Thus, selection of the most immature CD34+ progenitor cells based solely on the lack of HLA-DR expression results in isolation of two distinct cell populations with markedly different maturation status and resultant growth characteristics.

ADP-ribosyl Cyclase↗
PubMed1997

Differences in CD34+ cell subpopulations between human bone marrow and "mobilized" peripheral blood as determined with counterflow centrifugal elutriation.

Engineering of hematopoietic progenitor cells (HPCs) from bone marrow (BM) or "mobilized" peripheral blood (MoPB) is becoming increasingly important. Counterflow centrifugal elutriation (CCE) has been used to separate cells on the basis of their size. In this study, CCE was applied to evaluate BM and MoPB for differences in their HPC populations. Using a standard 4-mL elutriation chamber at 2300 rpm, CD34+ cells from BM peaked at a flow rate of 19 mL/minute, with 85% of all CD34+ cells recovered from fractions 15-22 mL/minute. The CD34+ cells from MoPB, mobilized with chemotherapy and granulocyte colony-stimulating factor (G-CSF), peaked at 22 mL/minute, with 90% of all CD34+ cells recovered from fraction 19-26 mL/minute. Colony-forming cells (colony-forming units granulocyte/macrophage [CFU-GM] + burst-forming unit-erythroid [BFU-E] + multipotent colony-forming units [CFU-GEMMs]) followed the distribution of CD34+ cells very closely, also with a shift to higher flow-rates for MoPB compared with BM. The lower flow-rate fractions of both BM and MoPB contained an increased proportion of CD34+ cells that did not express HLA-DR and/or CD38 on their surface, suggesting that the earliest CD34+ cells were enriched in the low-flow rate fractions. Although CFU-GMs, BFU-Es, and CFU-GEMMs from BM all peaked in the same fraction (19 mL/minute), high-proliferative potential colony-forming cells (HPP-CFCs) were concentrated in fraction 17 mL/minute, indicating that these earlier progenitor cells were slightly smaller. With MoPB, HPP-CFCs did not appear to be smaller than BFU-Es or CFU-GEMMs. CCE appears to be an attractive method for separating HPCs from BM or MoPB into populations of different maturity. Differences in CD34+ cell populations between BM and MoPB may help explain the differences in repopulation kinetics observed after transplantation.

Antigens, CD34↗
PubMed1995

Phorbol ester-induced priming of superoxide generation by phosphatidic acid-stimulated neutrophils and granule-free neutrophil cytoplasts.

This study was undertaken to examine the mechanisms involved in polymorphonuclear leukocyte superoxide release stimulated by exogenous phosphatidic acid (PA). Unlike the immediate burst of superoxide release affected by membrane-permeable dioctanoylglycerol (DiC8-DAG), dioctanoyl phosphatidic acid (DiC8-PA) induced superoxide release after a lag period of 5-20 min. This period was considerably reduced or eliminated when cells were primed by substimulatory levels of phorbol myristate acetate (PMA). Granule-depleted neutrophil cytoplasts also responded to DiC8-PA with a burst of superoxide generation. Activation of the cytoplast superoxide generating system in response to DiC8-PA was also significantly faster after cells had been preexposed to substimulatory levels of PMA, indicating that at least a portion of the priming mechanism was independent of PMA-induced degranulation. To further examine the potential mechanism of PMA priming of responses to PA, we evaluated the activity of neutrophil ecto-phosphatidic acid phosphohydrolase (ecto-PA phosphohydrolase), which generates diacylglycerol from exogenous PA. PMA priming had no discernable effect on the activity of this enzyme. In addition, propranolol, an inhibitor of PA phosphohydrolase, did not selectively inhibit PMA priming of neutrophil responses to DiC8-PA, indicating that priming did not result from acceleration of DiC8-PA hydrolysis. We therefore investigated the possibility that activation of protein kinase C was the basis of the primed response. Several semiselective protein kinase C inhibitors (calphostin C, H-7, and acylmethylglycerol) inhibited DiC8-DAG- and DiC8-PA-induced superoxide release as well as PMA-primed responses to approximately the same extent. These results are consistent with the hypothesis that neutrophil responses to phosphatidate are mediated by diglyceride generated by the action of ecto-PA phosphohydrolase. PMA priming does not result from increased catalytic activity of ecto-PA phosphohydrolase but rather seems to result from potentiation of an intermediate involved in the cells' response to multiple stimuli.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Maturation of mobilized peripheral blood progenitor cells: preclinical and phase I clinical studies.

The use of mobilized peripheral blood progenitor cells (PBPC) after high-dose chemotherapy has markedly decreased the period of severe neutropenia. In an attempt to further decrease the duration of neutropenia, the potential of PBPC to mature during in vitro culture was assessed, with special attention being paid to culture medium, growth factors, and cell concentration. Concentrations of 10(6) PBPC/mL resulted in better recovery than 10(7)/mL as far as total cells, CFU-GM, and granulocytes were concerned. The combination of IL-3 + GM-CSF+G-CSF appeared to be better than any of these growth factors alone. Simple media, such as Medium 199, gave poorer cell recovery than more complex media, such as IMDM. With 10(6)/mL nonenriched PBPC in IMDM with IL-3/GM-CSF/G-CSF, on day 15 CFU-GM reached 450% of the initial level. At that point, granulocytes had increased 15-fold. A small phase I study was performed to assess the toxicity of infusing 1000-2000 mL of PBPC cultured for 3 days at 3-10 x 10(6)/mL with IL-3/GM-CSF/G-CSF in LifeCell bags. Although no clear decrease in the duration of neutropenia was observed, the infusions were uncomplicated in 5 of the 6 patients and had minor side effects in the sixth patient. These data suggest that in vitro differentiation of nonenriched PBPC is possible. However, to develop a clinically applicable method, several logistical problems will have to be overcome.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1995

Activation and inhibition of the endogenous opioid system in human heart failure.

BACKGROUND: In a canine model of congestive heart failure beta endorphin concentrations were high and opioid receptor antagonists exerted beneficial haemodynamic effects. In humans previous studies have suggested that opioid peptides may modify the perception of breathlessness and fatigue in heart failure. METHODS: Plasma concentrations of beta endorphin were measured in patients with acute and chronic heart failure and cardiogenic shock. A subgroup of eight patients with New York Heart Association (NYHA) class III-IV heart failure was assessed for acute haemodynamic effects of naloxone, an opioid receptor antagonist. A separate group of 10 patients with class II-III heart failure, was randomised to a double blind placebo controlled study of the effects of intravenous naloxone on cardiopulmonary exercise performance. RESULTS: Plasma concentrations of beta endorphin were usually normal in patients with chronic heart failure and did not correlate with severity as assessed by NYHA class. In 29% of patients with acute heart failure and 71% of those with cardiogenic shock beta endorphin concentrations were high. The median concentration in the cardiogenic shock group was significantly higher than in either of the two heart failure groups and there was some evidence of a relation between beta endorphin concentrations and survival. At the doses tested, naloxone was unable to modify systemic haemodynamics, exercise performance, or symptoms in patients with chronic congestive heart failure. CONCLUSIONS: Circulating concentrations of beta endorphin are usually normal in patients with chronic congestive heart failure. Inhibition of the endogenous opioid system is unlikely to have therapeutic potential in heart failure.

Acute Disease↗
PubMed1994

Regulation of neutrophil responses by phosphotyrosine phosphatase.

By using immunofluorescent flow cytometry, we observed a profound up-regulation of CD45 on the plasma membrane of neutrophils exposed to low levels of a culture supernatant of the Gram-negative pathogen, Fusobacterium nucleatum (FN). Plasma membranes of neutrophils freshly prepared form human blood possessed little enzymatically active phosphotyrosine phosphatase. The activity of this enzyme was markedly potentiated in plasma membranes prepared from cells preexposed to the FN culture supernatant. This activity was vanadate sensitive and could be immunoprecipitated with anti-CD45 Ab. Cells preexposed to the FN culture supernatant were inhibited in their ability to release superoxide when challenged with the bacterial chemotactic factor, FMLP, but not PMA. The tyrosine kinase inhibitor, genistein, likewise inhibited FMLP but not PMA-induced superoxide release. Pretreatment of neutrophils with vanadate reversed FN-mediated inhibition of FMLP-triggered superoxide release but had no effect on genistein-mediated inhibition of FMLP-induced superoxide release. Of several proteins tyrosine phosphorylated in response to treatment of neutrophils with FMLP, Western analysis revealed one (m.w. approximately 93,000) that was lost when FMLP-stimulated cells were exposed to FN. This effect was inhibited when the cells were preexposed to vanadate. These results are consistent with the hypothesis that plasma membrane tyrosine phosphatase modulates FMLP-induced superoxide release by reversing the effects of tyrosine kinases activated in the initial phases of cell stimulation.

Cell Membrane↗
PubMed1994

Failure to reproduce the in vitro cardiac electrophysiological effects of naloxone in humans.

1. Opioid receptor antagonists such as naloxone have shown antiarrhythmic activity in animal models of coronary artery occlusion. Studies have indicated that these effects are stereospecific but both isomers of naloxone prolong action potential duration and refractoriness in guinea-pig and rabbit isolated ventricular myocardium (Class III effect). 2. This study was performed to identify whether this Class III effect of naloxone could be reproduced in human myocardium in vivo. Twenty patients with coronary artery disease received intravenous racemic naloxone (1-40 micrograms kg-1 min-1). Surface electrocardiographic parameters were measured and refractory periods were determined during fixed rate pacing by programmed stimulation. 3. The corrected QT interval during sinus rhythm (SR-QTc) was prolonged by 5(3)% (P = 0.06) at a dose of 20 micrograms kg-1 min-1 and by 9(10)% at 40 micrograms kg-1 min-1 (P = 0.03). These small changes were lost at higher paced heart rates. No significant effects on atrial, atrioventricular nodal or ventricular refractoriness were seen. 4. Plasma naloxone concentrations well into the micromolar range were achieved with both of the higher doses of naloxone administered. Plasma beta-endorphin concentrations invariably increased following naloxone infusion. There was no statistical relationship between peak plasma naloxone concentrations and the absolute or percent prolongation of SR-QTc. 5. It seems unlikely that racemic naloxone would have any clinical utility as an antiarrhythmic agent. Racemic naloxone may enhance cardiac adrenergic nerve activity and this receptor mediated effect may have prevented the demonstration of any nonreceptor mediated prolongation of cardiac refractoriness. Studies with the individual stereoisomers of naloxone would be of interest.

Action Potentials↗