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Biomedical subjects

A Wong

Publications and source records attributed to A Wong.

At least 163 records · Page 9Linked to original sources
PubMed1993

The incidence of obstructive apneas in preterm infants with and without bronchopulmonary dysplasia.

We tested the hypotheses that (1) preterm infants with bronchopulmonary dysplasia (BPD) have an increased incidence of obstructive apneas as compared to those without BPD (control) and (2) the respiratory pattern during obstructive apneas may be associated with more pronounced hypoventilation. Ventilation was measured with a flow-through system. We examined 2929 total apneas in 12 infants with BPD and 4366 apneas in 12 control infants matched for study weight (1.51 +/- 0.11 kg in the BPD group and 1.62 +/- 0.12 kg in the control group, P = 0.6) and for postconceptional age (33.3 +/- 0.8 weeks in the BPD group compared with 33.4 +/- 0.7 weeks in the control group, P = 0.6). The incidence of central apneas predominated in the BPD group (2551/2929, 87%) and in the control group (4188/4366, 96%). Obstructive apneas were more frequent in the BPD group (378/2929, 13%) than in the control group (178/4366, 4%, P = 0.004). The increased incidence of obstructive apneas in infants with BPD was observed in Quiet sleep (9.1 vs. 1.6%, P = 0.03) and in REM sleep (14.2 vs. 3.6%, P = 0.009). This increased incidence of obstructive apneas was applicable to short apneas (< 10 s, 10.9 vs. 2.7%, P = 0.003) and long apneas (> 10 s, 27.5 vs. 16.4%, P = 0.01). There were no significant changes in ventilatory pattern that could be uniquely attributed to one type of apnea. The findings suggest: (1) the great variability in the incidence of obstructive apneas reported in the literature relates, at least in part, to the clinical status of the infants and (2) ventilatory pattern is not a useful predictor of either type of apnea.

Apnea↗
PubMed1993

Multidose use of exametazine for leukocyte labelling: a new approach using tin enhancement.

Reconstituted exametazime is inherently unstable due to the rapid oxidation of the small amount (7.6 micrograms) of stannous chloride present in the kit. A novel approach has been used to improve the shelf-life of reconstituted exametazime based on the premise that tin lost through oxidation should be replaced by further amounts of tin. Freshly prepared stannous solution, 0.1 ml (0.66 microgram Sn2+), was mixed with 0.3 ml (25 micrograms) exametazime solution followed by 400-500 MBq pertechnetate. Mixed leukocytes from 50 ml of patients' blood were labelled with 99Tcm-exametazime which had been prepared by the tin enhancement. One hundred and fourteen patients were investigated. The median labelling efficiency was 72%, range 30-96%. The exametazime had been reconstituted up to 5 months previously. Because of the small volumes of the exametazime solution used, up to 15 doses for leukocyte labelling could be prepared from one vial.

Butanones↗
PubMed1993

Human monoclonal rheumatoid factor derived from rheumatoid synovial cells monospecific for rabbit IgG.

Rheumatoid factors (RF) in rheumatoid arthritis (RA) are polyclonal autoantibodies directed against antigenic epitopes located in the Fc portion of the IgG molecule. Hybridoma technology has overcome the difficulty of their polyclonality, so that monoclonal RF (mRF) can be examined for their individual binding specificities and genetics. We isolated a monoclonal IgM RF secreting hybridoma (designated H4) from the rheumatoid synovial cells (RSC) of a patient with RA. H4 bound specifically with rabbit IgG (RIgG) and had no human IgG (HIgG) reactivity. By direct binding ELISA and absorption experiments, 6% of the RIgG reactive RSC RF in this patient with RA was monospecific for RIgG. H4 was tested against RIgG F(ab')2 and pFc' fragments, and bound only to the pFc' fragment (CH3 domain). Moreover, H4 mRF had high avidity for RIgG in a capture ELISA. Total RNA was extracted and the variable region heavy (VH) and light (VL) chain cDNA were amplified using polymerase chain reaction technology. Sequence analysis of the IgM RF VH and VL chain genes indicated usage of the VH26 germline gene (VhIII gene family) and a new V lambda germline gene. Our results suggest preferential use of restricted germline genes in the formation of autoantibodies in human autoimmune diseases. The pathological significance of RIgG specific RF is still unclear. However, this finding suggests that all RSC RF production may not necessarily be induced by autologous IgG.

Amino Acid Sequence↗
PubMed1992

Stimulation of leukotriene production and membrane translocation of 5-lipoxygenase by cross-linking of the IgE receptors in RBL-2H3 cells.

Recent studies in rat basophilic leukemia cells (RBL-2H3) have shown that two pharmacological agents, ionomycin and thapsigargin, induce leukotriene C4 production and translocation of 5-lipoxygenase from cytosol to membrane, primarily by causing an influx of extracellular calcium. In the present study, we investigate the induction of these events by receptor activation. Cross-linking of high-affinity IgE receptors (Fc epsilon RI) by antigen in RBL-2H3 cells leads to leukotriene C4 production and membrane translocation of 5-lipoxygenase. As in the ionomycin-stimulated cells, leukotriene C4 production in antigen-stimulated cells is calcium-dependent since the amount of leukotriene C4 produced correlates quantitatively with the increase in intracellular free calcium concentration ([Ca2+]i). However, the increase in [Ca2+]i required for equivalent leukotriene C4 production by antigen is not as high as it is using ionomycin. In addition, no threshold [Ca2+]i level is required for leukotriene production by antigen, which is in contrast to the ionomycin stimulation that a [Ca2+]i level of 300-400 nM is required. Furthermore, antigen causes an additive increase in leukotriene C4 production in cells stimulated by the ionomycin. These results suggest that another as yet unidentified intracellular pathway acts in conjunction with Ca2+ for leukotriene synthesis in antigen-stimulated cells. Antigen stimulation causes 20-30% of the total cell 5-lipoxygenase to associate with membranes (compared with 10% in unstimulated cells) as demonstrated by enzyme activity assay and by Western Blot using antibodies to 5-lipoxygenase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Recombinant alpha-interferon inhibits colony formation of bone marrow fibroblast progenitor cells (CFU-F).

Alpha-Interferon (IFN-alpha) has been shown to inhibit colony formation of hematopoietic progenitor cells, including colony-forming unit-granulocyte, erythroid, macrophage, megakaryocyte (CFU-GEMM), day 7 colony-forming unit granulocyte-macrophage (CFU-GM), day 14 CFU-GM, burst-forming unit erythroid (BFU-E), pluripotent stem cells (CFU-S), and colony-forming unit megakaryocyte (CFU-MK). The present study was designed to see whether IFN-alpha also has inhibitory effects on bone marrow fibroblast progenitors (CFU-F). We found that IFN-alpha exerted a significant inhibitory effect on both rabbit and human CFU-F formation. Inhibition of human marrow CFU-F formation by alpha interferon was unaffected by removal of 98% of monocytes/macrophages and T lymphocytes from light density marrow cells. This finding suggests that IFN-alpha probably exerts a direct inhibitory effects.

Animals↗
PubMed1992

Hepatitis D virus superinfection remains a rare occurrence in non-drug abusers in Hong Kong.

Recent studies from Taiwan reported an increased prevalence of hepatitis D virus (HDV) superinfection as well as a spread of HDV infection to non-drug abusers. We examined the current prevalence of HDV superinfection in Hong Kong by testing sera from a large cohort of patients with acute and chronic hepatitis B virus (HBV) infection, collected between January 1988 and December 1990, for IgG antibody to HDV (anti-HDV). Anti-HDV was detected in 13 (93%) of 14 parenteral drug abusers who had HBV-related chronic liver disease. However, anti-HDV was detected in only one (0.15%) of 664 non-drug abusers who had chronic HBV infection and none of 31% patients with acute hepatitis B. We concluded that HDV superinfection remains a rare occurrence in non-drug abusers in Hong Kong.

Cohort Studies↗
PubMed1992

The effect of acetylsalicylic acid on orthodontic tooth movement in the guinea pig.

This study examined the influence of acetylsalicylic acid an inhibitor of prostaglandin synthesis, on orthodontic tooth movement induced with light spring forces in the guinea pig. The animal model was shown to permit reliable and accurate recording of tooth movement up to 28 days. Tooth movement was found to be highly correlated with spring forces, indicating that the model provided a sensitive test of the effect of aspirin on tooth movement. Aspirin was administered orally at the rate of 65 mg/kg per day in three divided doses and was found to effectively inhibit prostaglandin synthesis at the level of the bronchioles. However, aspirin did not appear to significantly affect tooth movement. Thus prostaglandins may not be the only mediators of the bone resorption associated with tooth movement induced by light orthodontic forces under these experimental conditions.

Analysis of Variance↗
PubMed1992

Prognostic factors in patients with metastatic colorectal cancer receiving 5-fluorouracil and folinic acid.

We have reported that 5-fluorouracil (5-FU) and folinic acid increased response rate and survival in patients with metastatic colorectal cancer. Now we have analysed prognostic factors for response, toxicity, survival and time to progression. The variables used for survival and response were treatment centre, treatment, age, sex, Eastern Cooperative Oncology Group (ECOG) performance status (PS), site of disease, previous radiotherapy, site of primary, disease-free interval, initial alkaline phosphatase (AP), albumin (A), lactate dehydrogenase (LDH) and aspartate aminotransferase (SGOT). The significant independent variables for survival were PS of 2 or more, initial albumin and SGOT, and treatment received, in order of importance. The relative risk of death when patients received 5-FU/folinic acid was 60% of that of patients receiving 5-FU alone. The variables predictive of response were treatment and PS. The variables used for analysis of toxicity were age, treatment centre, treatment, sex, tumour response, PS, number of courses, SGOT, AP and albumin. Treatment was found to be predictive of toxicity. Thus, baseline albumin and SGOT, and 5-FU/folinic acid treatment are significant determinants of survival, 5-FU/folinic acid and PS of 2 or more are major determinants of response and no clinical parameter could be identified as a predictor of toxicity.

Adult↗
PubMed1992

Desferrithiocin is an effective iron chelator in vivo and in vitro but ferrithiocin is toxic.

The efficacy and toxicity of the siderophore desferrithiocin (DFT), which has shown potential application in iron chelation therapy, were assessed in vivo and in vitro. DFT was evaluated in vivo in two ways: firstly, by measuring the effect of a single dose of DFT (10-100 mg/kg) on 59Fe excretion in iron-loaded rats labelled with 59Fe; and secondly, by examining the effect of the daily oral administration for 2 weeks of DFT (10-25 mg/kg/d) on the growing rat. DFT and its ferric complex, ferrithiocin (FT), were assessed in vitro from their effects on transferrin and iron uptake and mobilization from rat hepatocytes in culture using transferrin doubly labelled with 125I and 59Fe. Both oral and subcutaneous DFT were highly effective in promoting iron excretion in vivo, but showed evidence of toxicity after oral administration for 2 weeks at 25 mg/kg/d. In addition, DFT was much more effective than desferrioxamine or pyridoxal isonicotinyl hydrazone in reducing hepatocyte iron in vitro. However, FT was cytotoxic, causing membrane disruption and release of intracellular aspartate aminotransferase. It was concluded that DFT should not be considered for chronic iron chelation therapy without extensive further evaluation.

Administration, Oral↗
PubMed1992

Characterization of a DNA probe for detection of Mycobacterium tuberculosis complex in clinical samples by polymerase chain reaction.

We cloned and sequenced a DNA fragment from Mycobacterium tuberculosis for use in the identification of members of the M. tuberculosis complex. The DNA probe for culture confirmation had a sensitivity and a specificity of 100%. By using primers developed from this probe, the polymerase chain reaction detected 20 mycobacteria by ethidium bromide staining. This polymerase chain reaction system demonstrated 98% sensitivity and 100% specificity for detection of the M. tuberculosis complex in 200 sputum specimens.

Bacteriological Techniques↗
PubMed1992

[Diagnostic and prognostic value of umbilical and cerebral Doppler velocimetry in intrauterine growth retardation].

The diagnostic and prognostic value of Doppler velocimetry in delayed intrauterine growth was investigated in a series of 105 abnormal pregnancies. The diagnostic value of the umbilical Doppler velocimetry, whether alone or combined with simultaneous exploration of the umbilical and cerebral vessels was very limited. In contrast, the simultaneous exploration of the umbilical and cerebral vessels was of considerable prognostic value, since with regard to the risk of fetal distress, the sensitivity was 86.6%, the specificity 80% and the positive predictive value 63%. The negative predictive value was 95% and the prevalence 28.5%. The authors' experience also confirms the prognostic seriousness of the absence of diastolic flow or of reverse flow (2 perinatal deaths out of 6 cases). The interval between the changes in Doppler velocimetry and fetal distress is variable, however, ranging from two days to three weeks or more in these cases.

Cerebral Arteries↗
PubMed1991

Influx of extracellular calcium is required for the membrane translocation of 5-lipoxygenase and leukotriene synthesis.

Our studies assessed the effects of increases in intracellular calcium concentrations [( Ca2+]i) on leukotriene synthesis and membrane translocation of 5-lipoxygenase (5LO). The calcium ionophore ionomycin and the tumor promoter thapsigargin stimulated leukotriene production and translocation of 5-lipoxygenase to the membrane. Both agents elicited prolonged rises in [Ca2+]i. Leukotriene C4 production associated with [Ca2+]i in cells stimulated with various concentrations of ionomycin and thapsigargin suggests that a threshold [Ca2+]i level of approximately 300-400 nM is required. In the absence of extracellular Ca2+, both the ionomycin- and thapsigargin-induced rises in [Ca2+]i were transient, indicating that the prolonged [Ca2+]i elevation is due to an influx of extracellular Ca2+. Addition of EGTA to the external medium before, or at different times during, the treatment with ionomycin or thapsigargin instantaneously inhibited 5LO translocation and leukotriene synthesis, indicating that Ca2+ influx plays an essential role in 5LO membrane translocation and leukotriene synthesis. No leukotriene production was detected when cells were stimulated by a physiological stimulus of leukotriene D4. The addition of 100 nM leukotriene D4 triggered peak rises in [Ca2+]i that were comparable to those achieved by the ionomycin and thapsigargin. However, the leukotriene D4 induced rise was transient and rapidly declined to a lower but still elevated steady-state level, which was attributed to Ca2+ influx. Stimulation with 100 nM leukotriene D4 for 15 s increased the cellular levels of 1,4,5-inositol triphosphate (IP3), 1,3,4-IP3, and 1,3,4,5-inositol tetraphosphate (IP4).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Influence of otitis media on the correlation between rectal and auditory canal temperatures.

In a noninterventional, controlled, single-blinded trial, 251 children were examined in a university hospital emergency department setting to study the influence of acute otitis media on the relationship between rectal and auditory canal temperatures. Bilateral auditory canal temperatures were measured using an infrared detection probe and microprocessor by nursing staff blinded to the presence of acute otitis media. Correlation between rectal and auditory canal temperatures in children with (r = .81) and without (r = .75) acute otitis media were not significantly different. There was no significant difference between infected (38.1 degrees C +/- 1.0 degree C) and uninfected ears (38.0 degrees C +/- 1.0 degree C) with unilateral otitis (n = 75). Although significantly higher than in uninfected children, auditory canal temperatures of children with acute otitis media reflected elevated rectal temperatures and not differences in auditory canal temperatures between ears.

Acute Disease↗
PubMed1991

An epizootic of cutaneous zygomycosis in cultured dwarf African clawed frogs (Hymenochirus curtipes) due to Basidiobolus ranarum.

Morbidity and mortality approaching 100% occurred in dwarf African clawed frogs (Hymenochirus curtipes) from a culture facility in central California. Moribund frogs exhibited preference for a terrestrial environment rather than their normal aquatic environment. Affected animals had a slight pallor of the integument but were otherwise grossly unremarkable. Microscopic examination revealed a fungal infection of the integument primarily characterized by the presence of surface and intra-epidermal conidia. Skin cultures of the infected animals yielded an organism identified as Basidiobolus ranarum, based on the formation of conidia in culture with internal cleavage to form sporangiospores. The organism was transmitted to healthy frogs by co-habitation with infected frogs but not by short-term immersion exposure of healthy frogs to homogenized broth cultures of the fungus. Benzalkonium chloride at 2.0 mg l-1 was efficacious in controlling the infection. Although Basidiobolus species are normally found in the intestinal tract of amphibians, the severity of this epizootic indicates that B. ranarum may be an important pathogen of amphibians reared in culture facilities.

Animals↗