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Biomedical subjects

L S Levy

Publications and source records attributed to L S Levy.

At least 73 records · Page 4Linked to original sources
PubMed1986

Investigation of the potential carcinogenicity of a range of chromium containing materials on rat lung.

Twenty one chromium containing materials were examined for carcinogenic activity in a two year study using an intrabronchial pellet implantation system whereby pellets loaded with test material were surgically implanted into the lower left bronchus of rats. The principal aim of the study was to extend our knowledge of the carcinogenic potential of chromium compounds and, in particular, chromates (Cr6+). A statistically significant incidence of treatment related lung tumours was found with some sparingly soluble chromate materials. All tumours were large keratinizing squamous carcinomas of the left lung, except for a single left lung adenocarcinoma and two left lung anaplastic carcinomas. No bronchial carcinomas (0/100) were seen in the negative control group (blank pellet loaded with cholesterol), whereas bronchial carcinomas (22/48 and 25/100) occurred in the two positive control groups which received pellets loaded with 20-methylcholanthrene and calcium chromate respectively. Among the 20 test materials, only three groups gave statistically significant numbers of bronchial carcinomas. Two of these were groups receiving different samples of strontium chromate which gave 43/99 and 62/99 tumours. The third group, zinc chromate (low solubility), gave 5/100 bronchial carcinomas. A further zinc chromate group (Norge composition) produced 3/100 bronchial carcinomas which was not statistically significant. A few lung tumours were observed in other test groups.

Animals↗
PubMed1982

Nonadenylylated mRNA is present as polyadenylylated RNA in nuclei of Drosophila.

The sequence complexity of nuclear total RNA and nuclear poly(A)+RNA from Drosophila third-instar larvae was determined by hybridization of these RNAs to labeled single-copy DNA. At saturation, the nuclear poly(A)+ - and total RNA hybridized to 11% and 22.5% of the single-copy DNA, respectively. The increase in complexity of nuclear total RNA over that observed for nuclear poly(A)+RNA indicates the presence of a discrete class of nonoadenylylated nuclear RNA molecules. The relationship between DNA sequences coding for nuclear RNA and mRNA was then determined by hybridization of nuclear total and poly(A)+RNA to DNA enriched for mRNA coding sequences. The results of these studies show that those single-copy DNA sequences that are represented in either the poly(A)+ - or poly(A)- mRNA population are transcribed into RNA molecules that appear in the nuclear poly(A)+RNA population.

Animals↗
PubMed1981

Complexity and content of the DNA and RNA in Trypanosoma cruzi.

The content and sequence complexity of the nuclear DNA and messenger RNA for epimastigotes of Trypanosoma cruzi were determined. From analysis of nuclear DNA reassociation studies and microspectrofluorometric measurements of laser induced fluorescence of cellular DNA, T. cruzi is found to be a diploid organism with a nuclear DNA content of 2.5 x 10(8) nucleotide pairs (2.8 x 10(-13) g) and a kinetoplast DNA content of 4.9 x 10(7) nucleotide pairs (5.4 x 10(-14) g). Reassociation kinetics of nuclear DNA of average length 0.4 kb reveals three kinetic components: a moderately repetitive component with a reiteration frequency of 5.1 x 10(3) present in 9% of the fragments, a lowly repetitive component with a reiteration frequency of 32 present in 51% of the fragments, and a single-copy component present in 23% of the fragments. By saturation hybridization of total polysomal RNA to 3H-labeled single-copy DNA, it was determined that 68% of the single-copy DNA was represented in the epimastigote polysomal RNA. This corresponds to ca. 12 000 different mRNA species. Of these, ca. 9000 are present as poly(A)+-RNA, while the remaining 3000 appear not to be polyadenylated. Kinetic analysis of the poly(A)+-RNA population indicates it is composed of at least three classes of RNA's of different abundancy levels: two sequences which occur ca. 3000 per cell, ca. 750 sequences which occur about 20 times per cell, and ca. 15 500 sequences which occur 1-2 times per cell.

Animals↗
PubMed1981

Comparative carcinogenicity of alkylating agents: comparisons of a series of alkyl and aralkyl bromides of differing chemical reactivities as inducers of sarcoma at the site of a single injection in the rat.

A series of alkylating and aralkylating bromides was used in a comparative study of chemical reactivity (using 4-(p-nitrobenzyl) pyridine as standard nucleophile), and carcinogenic activity (using single injections by the subcutaneous route in 6-week old female CB-hooded rats). Benzyl, ethyl, isopropyl, and trityl bromides were inactive as carcinogens at doses up to 0.83, 12.5, 8.3 and 0.25 mmol/kg, respectively. 7-Bromomethylbenz[a]anthracene and 7-bromomethyl-12-methylbenz[a]anthracene gave high yields of sarcomas at the injection site (in the right flank); at the highest doses used, 35% yield of tumors was obtained using 0.25 mmol/kg 7-bromomethylbenz[a]anthracene, and 75% yield with 0.056 mmol/kg of the 12-methyl homologue. The order of chemical reactivity was trityl greater than 7-bromomethyl-12-methylbenz[a]anthracenyl greater than 7-bromomethyl-benz[a]anthracenyl greater than benzyl greater than ethyl greater than isopropyl. The relationship suggested between carcinogenicity and reactivity is that the highest reactivity permitted little in vivo penetration to essential cellular receptor sites because of immediate solvolysis, whereas the lower reactivities did not ensure sufficient alkylation of such receptors. The bromomethylbenz[a]anthracenes (of intermediate chemical reactivity) are known to react with DNA in vivo, but so far no differences in reactivity between them can account for their quantitatively different carcinogenic potencies.

Alkylating Agents↗
PubMed1978

A review of the organization of occupational health and safety and occupational hygiene in Britain.

Britain's Health and Safety at Work Act introduced in 1974 marked a change in approach to occupational health and safety which is having important long-term effects on the organization of occupational health and safety in Britain. The purpose of this paper is to outline the broad principles of approach to health and safety at work contained within the 1974 Act; highlight the implications of the new Act for employers, managers, employees, and representative organizations, and discuss the developments in the organization of occupational health and safety as a result of the 1974 Act.

Accidents, Occupational↗