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Biomedical subjects

H F Thomas

Publications and source records attributed to H F Thomas.

At least 55 records · Page 3Linked to original sources
PubMed1992

Investigation of the role of Von Korff fibers during murine dentinogenesis.

The existence and significance of Von Korff fibers during early dentinogenesis are still very controversial. The purpose of the present study was to re-examine the questions of the existence, nature and significance of Von Korff's fibers using light microscopy and immunohistochemistry. Specimens were obtained from 3 days-old CD-I mice and mandibles were carefully dissected under constant irrigation and immediately fixed in 10% neutral buffered formalin for light microscopy. Sections were treated or not with collagenase prior to silver staining. For immunohistochemistry, specimens were fixed in 95% ethanol and embedded in paraffin. Sections were reacted with goat anti-human-bovine type I or type III collagen and a rhodamine (RITC) labelled rabbit anti-goat IgG was then reacted as a secondary antibody. Slides were then examined under a Zeiss II photomicroscope equipped with epifluorescence. Our results have confirmed the presence of argyrophilic material concentrated at the periphery of the dental papilla and stretching from the subodontoblastic layer to the future dentino enamel junction. The distribution of type III collagen was very similar to the distribution of the silver staining at the cervical loop area. Type I collagen distribution was different and concentrated in areas where odontoblasts were fully differentiated. Our study showed that Von Korff fibers are not artefactual. We have established the presence of an apical compartment containing type I collagen fibers and a basal compartment containing type III collagen to explain the image of continuous silver staining crossing the entire thickness of the odontoblast layer.

Animals↗
PubMed1991

Audit of an ophthalmology waiting list.

The hospital case notes of 209 (98%) of the 213 patients placed on an adult ophthalmic surgical waiting list between mid 1984 and mid 1985 were reviewed. Information on referral sources, previous eye surgery, outpatient visits, and treatment up to the end of 1987 was recorded. The vital status of patients up to the end of 1988 was also ascertained. Waiting list patients (123 women, 86 men) were elderly (73% over 65 years) and most (70%) were listed for cataract surgery. By the end of 1987 (30-42 months after waiting list entry) 64% of all patients (and 56% of cataract patients) had received surgery under the care of the health authority. The remainder had either died (12%), received surgery elsewhere (7%), were still on the waiting list (7%), no longer wanted or were unfit for surgery (6%), or had left the district (4%). By the end of 1988 (42-54 months after waiting list entry) 28% of the original waiting list population had died.

Adolescent↗
PubMed1991

A survey of dog bites in Salisbury.

A recent survey of patients attending an Accident and Emergency (A&E) department serving several economically depressed Thanet coastal towns found that around 3 per 1000 of the resident population attended each year for the treatment of dog bite injuries (Thomas and Banks, 1990). We report a study of dog bite injuries treated in the A&E department serving Salisbury, a small prosperous Cathedral city, and surrounding villages. In comparison with Thanet, age specific incidence rates for dog bites show a similar pattern but only about half the overall incidence. Some reasons for these findings are suggested and extrapolations for national treatment figures are made.

Adolescent↗
PubMed1991

How well do family practitioner committee and general practice records agree? Experience in a semi-rural practice.

General practice notes may be inaccurate for various reasons. A study was carried out in one semi-rural practice to investigate the agreement between records held by the family practitioner committee and those kept in the practice. Details on the practice notes and the family practitioner committee list were compared for 800 patients. The details examined included name, sex, date of birth, address and National Health Service number. While 58% of records agreed, discrepancies occurred in 339 records (42%). The most common discrepancies concerned the patient's address (30.6%), date of birth (9.4%) and NHS number (8.0%). Nearly 5% of the practice notes appeared to be for patients who were no longer on the practice list or dependent on its care. These findings have implications under the new general practitioner contract where screening programmes, target related payments, and increased capitation fees require accurate practice records.

Documentation↗
PubMed1989

Differentiation of odontoblasts in grafted recombinants of murine epithelial root sheath and dental mesenchyme.

The epithelial root sheath (ERS) was isolated from first molars of 5-day-old post-natal CD-1 mice using trypsin. After isolation, ERS cells remained viable in vitro and immunohistochemical examination of cultures confirmed the epithelial phenotype and the absence of mesenchymal contamination. Recombinants of isolated ERS and dental papilla resulted in odontoblast differentiation within cells of the dental papilla, and the formation of root-like fragments of dentine after 2 weeks of intra-ocular grafting. These findings indicate the inductive influence of the ERS on dental papilla cells.

Animals↗
PubMed1988

Mutagenicity and cytotoxicity of N-methyl-2-pyrrolidinone and 4-(methylamino)butanoic acid in the Salmonella/microsome assay.

The industrial solvent N-methyl-2-pyrrolidinone (NMP) and its hydrolysis product, 4-(methylamino)butanoic acid (N-MeGABA), were examined for mutagenicity and cytotoxicity in the Ames Salmonella/microsome assay. In order to detect a broad range of possible mutagenic endpoints, the following strains were used in the assay: base-pair substitution strains TA100, TA102 and TA104; frameshift strains TA97 and TA98; and repair proficient strains TA2638, UTH8413 and UTH8414. In the standard plate incorporation assay, six log-linear doses of each compound were tested; doses ranged from 0.01 to 1000 mumol/plate for NMP, and 0.01 to 316 mumol/plate for N-MeGABA. Neither compound was detectably mutagenic when tested in the presence and absence of metabolic activation by Aroclor-induced rat liver S9. NMP did show significant responses with strains TA102 and TA104 that were less than two-fold over background, but no clear dose-response relationships were evident. A preincubation modification of the assay was also performed, using strains TA98 and TA104. Mutagenic activity was not observed for NMP, while N-MeGABA showed significant responses with TA104 but dose-related mutagenicity was not established. Preincubation testing revealed both NMP and N-MeGABA to be cytotoxic to the test population of Salmonella at the highest treatment doses.

Aminobutyrates↗
PubMed1988

Use of general anesthesia in dental care of the child with sickle cell anemia. A case report.

This article reviews the clinical manifestations of sickle cell anemia and describes the dental management, with the use of general anesthesia, of a child affected by the disease and exhibiting some of its complications. The discussion stresses the vital importance of awareness of the possible complications of sickle cell anemia and sickle cell trait in the safe and successful management of patients requiring dental care that includes the use of general anesthesia.

Anemia, Sickle Cell↗
PubMed1987

Plasmid pKM101 muc(-)- and muc(+)-mediated anthracycline mutagenicity and cytotoxicity in Salmonella typhimurium.

Muc (mutagenesis: UV: chemical) genes of plasmid pKM101, along with the chromosomal gene recA are known to be important constituents for full expression of inducible error-prone DNA repair in Salmonella typhimurium. This study investigates the affects of muc+ pKM101 and three of its derivatives bearing muc- point mutations (pGW1, pGW16, and pGW21) on spontaneous as well as anthracycline-induced back mutation to histidine independence. Different base-substitution and frameshift his- tester strains of S typhimurium were treated with the anthracyclines daunomycin, Adriamycin, carminomycin, and 4-demethoxy-doxorubicin. In many cases the muc- plasmids did mediate dose-dependent anthracycline mutagenicity as measured by His+ reversion. In many of the his- strains, the presence of muc+ pKM101 or muc- plasmids also resulted in a concomitant elevation of spontaneous reversion patterns over those seen with the plasmid-free parent strains. As a result, the sensitivity of most strains to anthracycline mutagenicity (based on His+ revertants/spontaneous background/microgram anthracycline) was not enhanced by muc+ pKM101 or its muc- mutant derivatives. In contrast, the low incidence of spontaneous His+ reversion in strains of the hisD3052 series, along with the inherently greater sensitivities of these strains to anthracycline-induced reversion, demonstrate most dramatically the mutagenesis-enhancing effects of muc+ pKM101 and muc- plasmids. In these and other cases in which muc- plasmid effects on enhancement of strain sensitivity to mutagenesis or cytotoxicity are observed, the overall spectrum of enhancement is the following, in decreasing order: pKM101 greater than pGW16 greater than pGW1 greater than no plasmid approximately equal to pGW21. Possible correlations are drawn between muc- plasmid effects on anthracycline-induced mutagenesis and cytotoxicity.

Anti-Bacterial Agents↗
PubMed1987

Preliminary evaluation of treatment and selection conditions which affect expression of anthracycline mutagenicity in Salmonella typhimurium and a diploid human lymphoblast cell line.

Mutagenic potency in the Ames Salmonella test is an important endpoint that can be influenced by biological and technical factors. The ranking of mutagenic activity of a series of anthracyclines was measured using different conditions of exposure and mutation selection. A 20 min preincubation treatment version of the Ames test using a 0.2-2.0 microgram/ml (0.36-3.60 nM/ml) dose range of each of the anthracyclines Adriamycin, Daunomycin, Carminomycin, 4'-O-methyldoxorubicin and 4-demethoxydoxorubicin confirmed the order of mutagenic potency seen with the same compounds under direct plating conditions. Preincubation results also confirm direct-plating results by showing the greater sensitivity of selection to His+ reversion over 8-azaguanine resistance to anthracycline mutagenicity. However, the order of mutagenic potency was changed by lengthening the preincubation treatment time to 2 h or reducing the population density of the treated cell inoculum by ten fold. These results suggest that certain treatment conditions enable the treated cells to diminish the phenotypic expression of anthracycline mutagenicity. For comparative purposes, daunomycin and Adriamycin mutagenicity in response to 0.1-0.2 nM/ml and 0.1-0.3 nM/ml dose ranges, respectively, were assessed in a human cell culture system with 6-thioguanine and 5-trifluorothymidine forward mutation selection. A daunomycin dose of 0.1 nM/ml generated approximately 25-fold and 20-fold increases in mutant fraction with 6-thioguanine and 5-trifluorothymidine selections, respectively. Equivalent dosing with Adriamycin generated approximately a 4-fold increase in mutant fraction with 6-thioguanine selection and little or no increase with 5-trifluothymidine selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibiotics, Antineoplastic↗
PubMed1986

Effects of excision repair and plasmid pKM101 on mutagenic and cytotoxic potencies of anthracycline derivatives in test strains of Salmonella typhimurium.

The effects of excision repair and presence of plasmid pKM101 on the mutagenicities and cytotoxicities of the anthracycline derivatives Adriamycin, daunomycin, carminomycin, and 4-demethoxydoxorubicin were examined in strains of Salmonella typhimurium. Plasmid pKM101 has been shown to mediate inducible error-prone repair in S. typhimurium. While the test compounds were shown to produce a range of mutational responses in excision repair defective (uvrB-), pKM101-bearing strains of different his- backgrounds, proficiency in excision repair generally resulted in the elimination of mutagenic responses in all such strains except those that contain the hisG428 site. In the absence of pKM101, only hisD3052 uvrB- strain TA1538 was shown to be sensitive to anthracycline mutagenicity. A suspension (preincubation) test as well as a direct plating test showed that while proficiency in either excision repair (uvr+) or plasmid pKM101 error-prone repair afforded cellular protection against anthracycline cytotoxicity, plasmid-free uvrB- strains were most sensitive to anthracycline cytotoxicity.

Antibiotics, Antineoplastic↗
PubMed1986

Mutagenic and cytotoxic potencies of a series of anthracycline derivatives as measured by His+ reversion, 8-azaguanine resistance and direct plating cytotoxicity tests in Salmonella typhimurium.

His+ reversion at multiple his- loci, 8-azaguanine resistance, and a previously reported direct plating cytotoxicity test were used to measure the genotoxic potencies of a series of anthracycline derivatives in Salmonella typhimurium. N-demethylated amino sugar monosaccharide anthracyclines reverted most his- tester strains and were positive with 8-azaguanine selection. Reversion of strain TA98 was the most sensitive end point for measuring the mutagenic activity of the N-demethylated anthracyclines. N,N-dimethyl amino sugar derivatives of Adriamycin and daunomycin were negative as measured by His+ reversion in tester strain TA98, but generated positive responses in tester strain TA102 that were equal to or greater than those of the demethylated parent compounds. Similarly, N,N-dimethyl amino sugar derivatives of pyrromycinone and 1-deoxypyrromycinone had no mutagenic activity as measured by His+ reversion except in tester strains TA102 and TA104. These later compounds also gave positive responses with 8-azaguanine selection. In view of these results, the importance of amino sugar dialkylation and anthracycline mechanisms of mutagenesis are discussed.

Anti-Bacterial Agents↗