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D M Taylor

Publications and source records attributed to D M Taylor.

At least 127 records · Page 7Linked to original sources
PubMed1991

Proton transport at the monolayer-water interface.

It is shown that when monolayers of stearic acid, palmitic acid, DPPC, or DPPS are compressed above some critical area Ac a lateral conduction mechanism is initiated at the monolayer/water interface. The interfacial conductance increases on further increasing the molecular packing density in the monolayer. All compounds also show major changes in surface potential at Ac the potential becoming more positive in all cases. It is argued that this is a consequence of structural reorganisation at the headgroup/water interface causing a significant reduction in the local permittivity. The critical area, Ac, is approximately double the molecular areas estimated from the pressure-area isotherm, and experiments with stearic acid monolayers show that Ac decreases significantly when the chaotropic ion SCN-, which is known to disrupt the molecular structure of water, is added to the subphase. It is likely, therefore, that the structural changes occurring at Ac involve the formation of a hydrogen bonded network between monolayer headgroups and adjacent water molecules at the monolayer/water interface. It is suggested that the conduction mechanism initiated at Ac arises from proton hopping along this hydrogen-bond network.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1991

Inactivation of the unconventional agents of scrapie, bovine spongiform encephalopathy and Creutzfeldt-Jakob disease.

Scrapie, bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob disease (CJD) are the best known of the transmissible degenerative encephalopathies (TDE) that affect animals and man. Among the unusual properties of the unconventional causal agents is their relative resistance to standard decontamination procedures, and this has resulted in accidental transmission. Scrapie in sheep is the most common of these diseases and, through laboratory studies, is the best understood. As the model for the group, scrapie agent has been used in experiments to devise general standards for decontamination of the agents of the TDE.

Animals↗
PubMed1991

Resistance of the ME7 scrapie agent to peracetic acid.

Mouse brain infected with the ME7 strain of scrapie agent was exposed for 24 h to a range of concentrations of PAA, either as fragments of intact brain or as supernates of homogenised brain. Two % PAA inactivated the infectivity in intact tissue but not in a supernate. None of the concentrations tested (up to 19%) was effective with supernates, and this was considered to result from the protection afforded by aggregation of infectivity-containing particles.

Animals↗
PubMed1991

Effectiveness of DTPA treatments following the injection of particulate plutonium.

A limited long-term experiment has been completed in which the chronic toxicity resulting from a single intravenous injection of 31.4 kBq of a poly-disperse 239Pu colloid sol per kg of body weight was tested in Beagle dogs. The Pu deposited mostly in the phagocytic cells of liver, spleen and to a lesser degree in lung and bone marrow. Slow solubilization of the Pu particles by endogenous ligands caused translocation of the nuclide and redeposition mostly as monomeric Pu in the skeleton and in liver hepatocytes. Thus, the deposit behaved as expected from a pulmonary or wound contamination in humans with a moderately soluble depot of Pu such as Class W hot particles. Therefore, this type of deposit provided the basis for a practical model to study the ensuing radiation effects under various experimental conditions. The dogs were divided into three groups of four animals each, and the following conditions were applied: (a) no further treatment was given, allowing free translocation of the Pu to its secondary deposition sites; (b) interception of the Pu translocation by weekly injections of 30 mumol of Ca-DTPA/kg of body weight (Ca-chelate of diethylene-triaminepentaacetic acid); and (c) interception of translocation by daily injections of 30 mumol/kg body weight of Zn-DTPA. For each of the groups (b) and (c), three dogs were used in a lifetime study, and one was sacrificed for nuclide distribution studies. Free translocation and subsequent deposition in the skeleton resulted in the death of each of the non-chelated dogs from osteosarcoma between 1267 and 1594 days after injection. Weekly treatment with Ca-DTPA reduced the total Pu burden significantly, but these dogs also died with osteosarcoma between 1462 and 1783 days. Daily injections with Zn-DTPA reduced the total Pu burden more efficiently than Ca-DTPA and prevented continuous deposition of solubilized Pu on bone surfaces. The mean post-injection survival of these dogs was 3520 days or about 2.1 times that of the animals receiving Ca-DTPA, while the latent period for bone tumour induction was about 2.6 times longer. This treatment reduced the severity of liver lesions and eliminated the occurrence of persistent leukopenia, but it did not prevent the formation of bone cancer.

Animals↗
PubMed1991

Inactivation of BSE agent.

Although there are no data reported yet for inactivation of BSE agent it is reasonable in the interim, to draw upon existing data for other transmissible degenerative encephalopathies (TDE), much of which derives from experiments with the scrapie agent. Such studies suggest that no standard chemical or physical decontamination procedure will reliably inactivate the amount of scrapie/BSE infectivity present in worst-case situations but high concentrations of sodium hypochlorite or sodium hydroxide have been shown respectively to be completely effective or almost so. Regarding physical inactivation procedures, it is clear that some infectivity survives exposure to doses of UV and ionising radiations which represent "overkill" for conventional viruses. With dry heat, survival of infectivity is also remarkable, and it is only through autoclaving that apparently secure standards can be achieved for thermal inactivation; even so, autoclaving procedures need to be more rigorous than for conventional microorganisms, and can be compromised by prior chemical treatment of infected material.

Animals↗
PubMed1991

An aqueous paracentesis pipet.

We describe a glass pipet tipped with a short, sharp, 30-gauge needle for performing aqueous paracentesis. The design eliminates the possibility of needle bending and minimizes fractional resistance during limbus penetration; it also allows quicker recovery of aqueous samples. A small plastic bulb at the upper end facilitates removal of aqueous samples from the pipet.

Aqueous Humor↗
PubMed1990

A refractive and histopathologic study of excimer laser keratectomy in primates.

Using a 193-nm excimer laser, we produced wide-area, refractive keratectomies on 18 cynomolgus monkey corneas and followed them up for up to 18 months. All corneas developed some subepithelial haze by one month. Electron microscopy disclosed epithelial thickening, absence of Bowman's layer, and subepithelial activated fibroblasts surrounded by disorganized collagen. By six months, the haze faded to a variable degree, the epithelium regained normal thickness, and the collagen was more organized. Persistent corneal haze at 12 months in some corneas correlated with electronlucent spaces in the subepithelial zone. Corneas were 90 microns thinner centrally two weeks after myopic ablation, but returned to preoperative thickness by six months. Myopic flattening and hyperopic steepening of 6 diopters were targeted, and over 7 diopters of each were achieved initially. Regression of induced curvature stabilized over several months. At 18 months, 4.4 diopters of myopic flattening and 5.2 diopters of hyperopic steepening remained.

Animals↗
PubMed1990

Aminoglycoside volume of distribution in pediatric patients.

Pharmacokinetic parameters of three aminoglycoside antibiotics were studied retrospectively in 218 pediatric patients to determine an apparent volume of distribution (Vd) for this age group and to determine if Vd is significantly different in pediatric patients compared with adults. Data on patients considered for inclusion in the study were obtained from the files of the aminoglycoside monitoring services at Saskatoon University Hospital and Regina General Hospital. Both services use a computer program that calculates pharmacokinetic parameters using the Sawchuk-Zaske method. Children between the ages of 1 and 16 years with normal renal function from whom serum concentration had been obtained were included in the study. Exclusion criteria included abnormal or unstable renal function, cystic fibrosis, and pregnancy. The mean age of the pediatric group was 8.65 +/- 5.37 years. Average values for Vd and half-life were 0.34 L/kg and 2.3 h, respectively. No strong correlation was found between the Vd (L/kg) and age. The patients were subdivided into three age groups: 1-4.9 years, 5-9.9 years, and 10-16 years. Group 1 (1-4.9 years) had a larger Vd than the other groups and the Vd of all three groups were significantly different from the estimated Vd of 0.20 L/kg for adult patients. A "normal" pediatric value for the Vd of aminoglycosides could not be determined; however, the Vd in children is significantly larger than the Vd in adults and dosage regimens should be adjusted accordingly.

Aging↗
PubMed1989

Bovine spongiform encephalopathy and human health.

Because bovine spongiform encephalopathy (BSE) has probably been caused by accidental transmission of the transmissible agent of sheep scrapie there is concern that humans may be at risk from BSE. Epidemiological and experimental evidence is examined which suggests that this is unlikely.

Animals↗
PubMed1989

The biodistribution and toxicity of plutonium, americium and neptunium.

In the nuclear fuel cycle the transuranic radionuclides plutonium-239, americium-241 and neptunium-237 would probably present the most serious hazard to human health if released into the environment. Despite differences in their solution chemistry the three elements exhibit remarkable similarity in their biochemical behaviour, apparently sharing similar transport pathways in blood and cells. After entering the blood the elements deposit predominantly in liver and skeleton, where retention appears to be prolonged, with half-times of the order of years. The principal late effects of all three radionuclides are the induction of cancers of bone, lung or liver. For the latter tumours the induction risk per unit radiation dose appears similar for the three radionuclides. But in bone there are indications that, due to microscopic differences in the distribution of the alpha-particle radiation dose, the efficiency of bone cancer induction may increase in the order americium-241 less than plutonium-239 less than neptunium-237. No case of human cancer induced by these radionuclides is known.

Americium↗
PubMed1989

Effects of continuous exposure to 239Pu-alpha rays on Co631 cells.

Exposure of Co631 cells to 239Pu-citrate leads to continuous irradiation and results in increasing cell death which depends on dose and incubation time of the metal. The D37 is calculated to be 0.13 Gy. Plutonium-239 induces the amplification of the integrated SV40 sequences of the Co631 cells. Other cellular genes such as the alpha-actin gene were not amplified, indicating that the SV40-gene amplification is a selective process. Southern blot analysis of genomic DNA shows that not all S40 sequences are equally amplified. Excised sequences of the SV40 genome only appear after an exposure time of 4 days.

Animals↗
PubMed1989

Scrapie agent decontamination: implications for bovine spongiform encephalopathy.

Bovine spongiform encephalopathy probably results from the use of commercial diets containing scrapie-contaminated ingredients. Of all the chemical and physical decontamination procedures which are effective against conventional viruses, only high temperature autoclaving, high concentrations of sodium hypochlorite, and possibly molar sodium hydroxide, are useful against the group of unconventional transmissible agents which includes scrapie. The implications of this problem for the rendering industry and farm practice are discussed.

Animal Feed↗
PubMed1989

Two models for screening chelating agents for cadmium removal.

The effectiveness of some chelating agents to mobilize cadmium from Chinese hamster ovary cells after chronic exposure (20 hr), as well as from cytosolic metallothionein, was studied. In the first protocol, the most effective substance was 2,3-dimercaptopropanol, followed by 2,3-dimercaptopropane-1-sulfonate and 2,3-dimercaptosuccinic acid, whereas CaNa3-diethylenetriamine pentaacetic acid X 5 H2O showed less effect. Simultaneous incubation of cells with cadmium and the chelating agent resulted in a different order of effectiveness: CaNa3 DTPA prevented cadmium uptake almost totally, 2,3-mercaptopropanol by 75% and 2,3-dimercaptopropane-1-sulfonate by 35%. Neither CaNa3-diethylenetriamine pentaacetic acid X 5 H2O nor 2,3-dimercaptosuccinic acid had altered the distribution of cadmium between the cytosolic protein fractions after a 2 hr incubation of cells, whereas after this period, 2,3-dimercaptopropanol had removed all cadmium from metallothionein, and 2,3-dimercaptopropane-1-sulfonate about 50%. None of the chelating agents had reduced the amount of Cd bound to high molecular weight proteins. In the cell-free system, 2,3-dimercaptopropanol and 2,3-dimercaptopropane-1-sulfonate were equally effective and removed all cadmium from metallothionein within ten minutes. CaNa3-diethylenetriamine pentaacetic acid X 5 H2O, however, even after 60 min, had removed only 50% of the cadmium. The remaining cadmium was found distributed to the high molecular weight and lower molecular weight protein fractions.

Animals↗