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Biomedical subjects

H F Thomas

Publications and source records attributed to H F Thomas.

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

Effect of the amino acid analog hadacidin on intracellular membrane flow and the cell surface in Dictyostelium discoideum. A transmission- and scanning-electron-microscope study.

We examined the effect of the amino acid analog hadacidin (N-formyl-N-hydroxy glycine) on the process of endocytosis in the slime mold Dictyostelium discoideum. Endocytosis was followed using iron-dextran and transmission electron microscopy. In cells taken from the mid-log growth stage, iron-dextran was found to be distributed in small, medium, and large vesicles at a density lower than that present in the incubation medium, thus suggesting the fusion of small, iron-dextran-containing pinosomal vesicles with intracellular vesicles not containing iron-dextran. In cells treated with hadacidin, more small vesicles were present than in untreated cells, there being a reduction in the number of larger-sized vesicles; in these vesicles, iron-dextran was present at a density similar to that of the medium. This result is consistent with the conclusion that, while pinocytosis had continued, the fusion of vesicles and dilution of the vesicle contents had been inhibited. Also, the large number of small pinosomal vesicles in the drug-treated cells suggested that the recycling of vesicles to the surface had been inhibited. The observation that pinocytosis but not recycling continued after drug treatment raised the question of the origin of the membrane needed for the formation of pinosomes. Measurements of the cell surface revealed no difference between drug-treated and untreated cells, indicating that, when the membrane was internalized for pinosomes, the cell size remained constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Membrane↗
PubMed1985

The dentin-predentin complex and its permeability: anatomical overview.

This paper provides an anatomical overview of the dentin-predentin complex and its permeability. An unique anatomical feature of this complex is the presence of dentinal tubules which extend peripherally from the odontoblast-predentin junction throughout the thickness of the tissue. The permeability of dentin is a consequence of the presence of these tubules. Thus, this review concentrates on the anatomy of dentinal tubules and, in particular, on those studies which in the last decade have increased our knowledge of this anatomy. The structure, size, and number of dentinal tubules and the relationship of these features to the permeability of the tissue are discussed. This is followed by a description of the contents of dentinal tubules, with particular emphasis being paid to the literature concerning the extent of the odontoblast process.

Animals↗
PubMed1985

Doctors' opinions on the prevention of myocardial infarction.

In 1979, 1981 and 1983 random samples of approximately 200 general practitioners, 200 members of the Royal College of General Practitioners and 200 hospital physicians were asked to list, in order of effectiveness, measures which they considered useful in the prevention of myocardial infarction and reinfarction. The overall response rate was 67% and of the responses 77% were eligible for inclusion in the analysis.There was a high degree of concordance between the opinions of the nine doctor-year groups (Kendall's W = 0.89, P < 0.001). Behavioural measures, such as diet, weight control, exercise and cessation of smoking, were mentioned frequently and were ranked above most drug therapies. Overall, opinions concerning the relative utility of different measures did not change between 1979 and 1983 yet there were significant changes in the frequency with which specific therapies were mentioned as useful preventive measures. Beta-blockers, calcium channel blockers, and arteriograms/coronary artery bypass grafting were mentioned more frequently in 1983 than in 1979 while lowering the lipid levels (with drugs) and sulphinpyrazone were mentioned less frequently. The changes in the opinions of doctors are discussed in the context of new therapeutic information published between 1979 and 1983.

Attitude of Health Personnel↗
PubMed1984

Correlation of scanning and transmission electron microscopy of human dentinal tubules.

Areas of human dentine were examined first with the scanning electron microscope (SEM) and subsequently with the transmission electron microscope (TEM). Structures observed in dentinal tubules from outer dentine by SEM were identified by TEM as electron-dense structures lining the tubules and not as odontoblast processes. These structures, termed lamina limitans, correspond to the previously described inner hypomineralized lining of dentinal tubules.

Adult↗
PubMed1984

The lamina limitans of human dentinal tubules.

Fractured coronal surfaces of both fixed and unfixed human teeth were examined by scanning electron microscopy following HCl demineralization and collagenase digestion. This treatment removed a considerable amount of matrix from the surface of dentin. Tubular structures, termed lamina limitans, were not affected by this treatment and remained on the surface of the tissue. The lamina limitans extended from the pre-dentin-dentin junction to the dentin-enamel junction. Further enzymatic digestion of unfixed specimens with hyaluronidase resulted in the complete removal of the lamina limitans. The susceptibility of the lamina limitans to hyaluronidase digestion indicates a high content of glycosaminoglycan, suggesting that they are extracellular in nature. These data provide further evidence that lamina limitans are not odontoblast processes.

Adolescent↗
PubMed1983

The effect of various fixatives on the extent of the odontoblast process in human dentine.

Unerupted but fully formed human third molar teeth were prepared for ultrastructural examination using three different fixatives; glutaraldehyde, a mixture of glutaraldehyde and p-formaldehyde and a picric acid-formaldehyde solution. These fixatives have reportedly differing rates of penetration of tissue. Odontoblast processes were found to be limited to the inner-third of crown dentine in all teeth, irrespective of the fixative used.

Adult↗
PubMed1983

A scanning electron microscope study of dentinal tubules from un-erupted human teeth.

Twelve fully-formed human third molars were obtained immediately after extraction, the roots removed, the crowns split into buccal and lingual portions fixed in Karnovsky solution and either left in the mineralized state or demineralized in a formic/citric acid solution. Specimens were dehydrated, critical point dried and examined by SEM. Demineralization of the teeth resulted in the loss of peritubular dentine and the appearance within each tubule of a sheet-like structure which extended from the predentine-dentine junction to the dentine-enamel junction. This sheet-like structure, here termed the lamina limitans, may play a role in the control of peritubular dentine formation.

Adult↗
PubMed1982

Bladder tumours among rodent operatives handling ANTU.

The rodenticide ANTU (alpha-naphthylthiourea) was used in the United Kingdom mainly in the late 1940s and early 1950s. The product then contained up to 0.2% of beta-naphthylamine as an impurity, and it was finally withdrawn in 1967 as a suspected carcinogen. Fourteen cases of urothelial tumours among rodent operatives exposed to ANTU are reported: in one district four out of 27 staff were affected, and in another area two out of 10. These cases strongly suggest that the early ANTU manufactured in the United Kingdom posed a cancer hazard to users. ANTU is still made or used in various countries, though the current product may be relatively pure and no longer contaminated by beta-naphthylamine. Recent laboratory evidence shows that even pure ANTU is mutagenic in the Ames test, and the safety of this rodenticide may need review.

Adult↗
PubMed1982

Safe as 2, 4, 5-T?

Explore the source record for details and available documents.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1982

Mortality of flax workers.

A total of 2528 workers in flax mills in Northern Ireland were followed up for 16 years. Follow-up was 97% complete. Deaths were identified and date and cause ascertained. Expected deaths were calculated on the basis of age and sex specific rates for Northern Ireland. Both male and female workers had fewer deaths than expected, and mortality showed no clear relationship with type of work. There was a small excess in the mortality of the workers who had had byssinosis at the time of the original survey, but there was no evidence that the more severe grades of byssinosis were associated with higher mortality than the less severe grades. Workers who smoke are known to have an increased risk of developing byssinosis, and cigarette smoking may be responsible for most of the excess deaths in the workers with byssinosis.

Adult↗
PubMed1982

Further follow-up study of workers from an asbestos cement factory.

A further follow-up traced 1970 workers employed at an asbestos cement factory for at least six months between 1936 and 1977. At the beginning of this period some crocidolite was used in the factory but by the end of 1936 chrysotile had become the only type of asbestos in use. Only 378 women were employed during the period concerned, and of the 30 who had died, none had a cause of death that is generally associated with exposure to asbestos. The mortality experience of the men was examined separately for all workers, all workers alive after 15 or more years after first exposure, and a smaller group of workers who were employed in 1935-6 and may have been exposed to crocidolite. In none of the three groups was there an appreciably raised standardised mortality ratio (SMR) for the causes of death investigated. These were: all causes, all neoplasms, cancers of the lung and pleura, and cancers of the gastrointestinal tract. An excess of lung cancers noted in the first follow-up study in 1964 was not found in this study. Two pleural mesotheliomas were identified but in both cases the men had worked at the factory before 1936 and therefore had been exposed to crocidolite. No cancers of the larynx were found.

Asbestos↗