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Biomedical subjects

J A Lewis

Publications and source records attributed to J A Lewis.

At least 127 records · Page 7Linked to original sources
PubMed1983

Isolation and preliminary characterization of the Chinese hamster thymidine kinase gene.

The Chinese hamster thymidine kinase (TK) gene has been isolated from a recombinant phage library constructed with genomic DNA from mouse Ltk- cells transformed to Tk+ by transfection with Chinese hamster genomic DNA. The phage library was screened by the Benton-Davis plaque hybridization technique, using as probes, subclones of recombinant phage that were isolated from mouse Ltk+ transformants by the tRNA suppressor rescue method. The Chinese hamster TK gene is contained within 13.2 kilobases of genomic DNA in the isolate designated lambda 34S4. This gene, defined by restriction enzyme sensitivity experiments, homology studies with the chicken TK gene, and mRNA blotting experiments, may extend over 8.5 kilobases. Subclones of the lambda 34S4 isolate used as hybridization probes identified a 1,400-nucleotide polyadenylated RNA as the hamster TK mRNA. The abundance of this mRNA varies dramatically in Chinese hamster cells cultured under various growth conditions, providing direct evidence that the growth dependence of TK activity may be regulated in an important way at the level of cytoplasmic TK mRNA.

Animals↗
PubMed1983

Beta-adrenoceptor blockade and myocardial infarction: when should treatment start and for how long should it continue?

Treatment with oral beta 1 blockade started after recovery from acute myocardial infarction and continued for approximately 2 years reduces total mortality by about 25%. It is unclear how long oral treatment should be maintained, nor is it known if stopping beta blockade increases the risk of sudden death or reinfarction. Acute i.v. administration of beta blockers has been shown to reduce indexes of infarct size. The effect of this reduction on short- and long-term survival is promising, but not conclusive.

Adrenergic beta-Antagonists↗
PubMed1982

Confidence in results of beta-blocker postinfarction trials.

Seventeen published trials of beta-blockers in myocardial infarction were scrutinised for the 95% confidence limits for the reported treatment effects. All the trials were prospective, randomised, and (except when treatment was given intravenously) placebo controlled. For analysis of pooled results the trials were divided arbitrarily according to whether treatment had been given "early" or "late" after the onset of pain. All trials were consistent with a treatment effect of just over 20%, but benefit was more apparent in trials using late intervention with beta-blockers. The pooled results of trials using early intervention showed a positive effect of 8%, whereas those using late intervention showed a 26% reduction in mortality and confidence limits of 17-35%. The results confirm that late intervention with beta-blockers after myocardial infarction reduces mortality but show that the effect of early intervention remains to be determined.

Adrenergic beta-Antagonists↗
PubMed1982

Selective amplification of polymorphic dihydrofolate reductase gene loci in Chinese hamster lung cells.

A series of antifolate-resistant Chinese hamster lung sublines that overproduce either a Mr 20,000 or a Mr 21,000 class of dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3), known to contain amplified DHFR genes, has been analyzed by DNA and RNA transfer techniques. The results suggest that the Mr 20,000 and Mr 21,000 DHFRs are encoded by at least two polymorphic DHFR genes, both of which are expressed in drug-sensitive parental cells. In drug-resistant sublines only one of the two DHFR gene types is amplified, thus accounting for the overproduction of one or the other molecular weight class of DHFR. In addition to the known differences between the DHFRs whose overproduction they direct, these allelic genes differ in restriction endonuclease profiles and in the relative abundances of their multiple mRNA transcripts.

Animals↗
PubMed1982

Gene amplification accompanies low level increases in the activity of dihydrofolate reductase in antifolate-resistant Chinese hamster lung cells containing abnormally banding chromosomes.

Three independently-derived, antifolate-resistant Chinese hamster lung cell lines that exhibit low level increases in dihydrofolate reductase (DHFR) activity, i.e., three- to fivefold vs. controls, have been compared with drug-sensitive cells to determine relative DHFR gene content. With a solution hybridization technique that makes use of genomic DNA and a cloned double-stranded Chinese hamster DHFR cDNA probe, it has been found that the enzyme activity increases are associated with an approximately proportionate amplification of DHFR genes. Trypsin-Giemsa staining techniques and hybridizations in situ further show that the amplified DHFR genes are located within abnormally banding regions along chromosome 2q and also suggest that, in each subline, only one chromosome 2 homolog is initially involved in the amplification process.

Animals↗
PubMed1981

Molecular cloning of Chinese hamster dihydrofolate reductase-specific cDNA and the identification of multiple dihydrofolate reductase mRNAs in antifolate-resistant Chinese hamster lung fibroblasts.

ds cDNA from antifolate-resistant Chinese hamster lung fibroblast subline DC-3F/MQ19 was ligated to Eco RI and Sal I oligonucleotide linkers and cloned into Eco RI and Sal I digested pBR322. Transformed colonies containing dihydrofolate reductase (DHFR)-specific recombinant plasmid were identified by Grunstein Hogness assay using a Chinese hamster DHFR-specific cDNA probe. A recombinant plasmid, pDHFR6, containing a 650 bp HFR insert was isolated and analyzed. This plasmid was used as a molecular probe in a Northern blot analysis of both cytoplasmic and polysomal DHFR, poly A+ mRNAs of the DC-3F/MQ19 subline, which over-produces a 20,000d DHFR 150-fold, and DC-3F/A3 subline, which over-produces a 21,000d DHFR 170-fold. This analysis revealed the presence of three DHFR mRNA species of 1350, 2200, and 3300 nucleotides in both independently-derived cell lines. The relative abundance of each species however varied strikingly between the two cell lines.

Animals↗
PubMed1981

Methods to assess breathlessness in healthy subjects: a critical evaluation and application to analyse the acute effects of diazepam and promethazine on breathlessness induced by exercise or by exposure to raised levels of carbon dioxide.

1. Methods were devised and evaluated for inducing breathlessness by submaximal graded exercise in healthy subjects while objective measurements of cardiorespiratory function were made. Breathlessness was assessed with serial visual analogue scales (VAS), but with various measures to enhance repeatability. 2. A high level of reproducibility was obtained in spite of the subjective nature of the assessment. Individual responses were described by the relationship between breathlessness and ventilation. The sensitivity of the method was demonstrated by the use of inspiratory resistances which disturbed this relationship and caused greater breathlessness for a given level of ventilation. 3. These methods were applied to six healthy subjects to analyse the effects of acute doses of diazepam and promethazine on breathlessness induced by graded exercise or by rebreathing carbon dioxide in a double-blind study. 4. During exercise, diazepam and promethazine did not reduce breathlessness, although there was a minor trend with promethazine. During exposure to elevated levels of carbon dioxide, diazepam and promethazine had no effect on breathlessness. Diazepam and promethazine produced similar levels of sedation, but neither drug had significant effects on the ventilatory response to carbon dioxide. These preliminary findings contrast with those reported for chronic diazepam in 'pink puffers'. 5. Raised levels of carbon dioxide caused greater breathlessness in relation to ventilation than did exercise.

Adult↗