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Biomedical subjects

R D Evans

Publications and source records attributed to R D Evans.

At least 19 recordsLinked to original sources
PubMed1995

Effect of corrosion products (neodymium iron boron) on oral fibroblast proliferation.

The biological effects of the corrosion products of neodymium iron boron (Nd2Fe14B) magnets are largely unknown. The aim of this study was to identify the types of corrosion product and to evaluate the effect of the corrosion products (CP) of Nd2Fe14B magnets on the proliferation of human oral mucosal fibroblasts. Uncoated Nd2Fe14B magnets were stored in saline at 37 degrees C for 6 months and the corrosion products collected. 100 microL of a cell suspension (human oral mucosal fibroblasts [14 x 10(4) cells/mL]) was aliquoted into 72 wells of a 96-well plate, the remaining plates receiving culture medium only. After 12 h incubation at 37 degrees C, each well then received 100 microL of either (A) culture medium, (B) 100% CP, (C) 50% CP, or (D) 0% CP. The plates were reincubated at 37 degrees C for a further 48, 96, or 144 h. Fibroblast proliferation was assessed using the methylene blue uptake/elution technique. The compounds in the corrosion product were examined using quantitative X-ray analysis. Statistical analysis (ANOVA, Bonferroni's test 0.05, SAS v 6.04), showed that at each time point, the cell numbers in groups B, C, and D were significantly lower than group A. Within groups B, C, and D no significant differences were found, despite the suggestion of a dose response effect. Fibroblast proliferation in the presence of corrosion products was significantly lower than with culture medium. Fibroblast proliferation did occur in the presence of 0, 50, and 100% CP. The actual corrosion products appeared to be salts of iron but 3.2% (+/- 0.6) of neodymium chloride (NdCl3) was found.

Alloys↗
PubMed1995

Micro-spatial variations of heavy metals in the teeth of walrus as determined by laser ablation ICP-MS: the potential for reconstructing a history of metal exposure.

This study explored the possibility of using laser ablation inductively-coupled plasma-mass spectroscopy to measure trace metals and other elements within the annual growth layers of the teeth of walrus harvested from the Canadian Arctic. Using sample ablation "footprints" of 125 microns diameter on transects across the exposed cross-sections of teeth, this technique detected Pb, Cu, Zn and Sr, but not Cd, in tooth cementum. The micro-spatial patterns of elements were consistent among different transects on the same tooth, and revealed subtle differences between animals of different ages. The youngest walrus in the sample (4 yr) contained higher concentrations of Pb and Cu than older animals in the growth layer deposited during the first year of life, while the oldest animal (33 yr) exhibited higher Pb and Zn than younger animals in the outer layer corresponding to the year 1988. The differences between animals and across annual layers may reflect both life history and metal exposure phenomena, including high amounts of metals transferred from mothers to pups in maternal milk. The ability to detect metals in a repeatable fashion within annual growth layers suggests that metal exposure histories accurate to within a year might be re-constructed for the life-times of long-lived animals, and that a series of such individual studies would allow exposure histories covering centuries to be quickly assembled. These data may suggest the most likely explanation for the currently high levels of some metals observed in certain Arctic marine mammals, i.e., natural phenomenon or anthropogenic contamination.

Age Factors↗
PubMed1994

The interface between orthodontics and restorative dentistry in the management of anterior tooth surface loss.

Anterior tooth surface loss is a significant problem, ideally requiring early recognition, diagnosis and prevention of progression. However, when first noted it is often sufficiently advanced to warrant treatment. Management should be aimed at minimizing further tooth surface loss and frequently benefits from an integration of treatment procedures. The problems, aims of treatment, and relevant treatment modalities are discussed, and two illustrative cases presented.

Acids↗
PubMed1994

Macroaggregation of platelets in plasma, as distinct from microaggregation in whole blood (and plasma), as determined using optical aggregometry and platelet counting respectively, is specifically impaired following cardiopulmonary bypass in man.

We determined changes in platelet aggregability following cardiopulmonary bypass, using optical aggregometry to assess macroaggregation in platelet-rich plasma (PRP), and platelet counting to assess microaggregation both in whole blood and PRP. Hirudin was used as the anticoagulant to maintain normocalcaemia. Microaggregation (%, median and interquartile range) in blood stirred with collagen (0.6 micrograms/ml) was only marginally impaired following bypass (91 [88, 93] at 10 min postbypass v 95 (92, 96] prebypass; n = 22), whereas macroaggregation (amplitude of response; cm) in PRP stirred with collagen (1.0 micrograms/ml) was markedly impaired (9.5 [8.0, 10.8], n = 41 v 13.4 [12.7, 14.3], n = 10; p < 0.0001). However, in PRP, despite impairment of macroaggregation (9.1 [8.5, 10.1], n = 12), microaggregation was near-maximal (93 [91, 94]), as in whole blood stirred with collagen. In contrast, in aspirin-treated patients (n = 14), both collagen-induced microaggregation in whole blood (49 [47, 52]) and macroaggregation in PRP (5.1 [3.8, 6.6]) were more markedly impaired, compared with control (both p < 0.001). Similarly, in PRP, macroaggregation with ristocetin (1.5 mg/ml) was also impaired following bypass (9.4 [7.2, 10.7], n = 38 v 12.4 [10.0, 13.4]; p < 0.0002, n = 20), but as found with collagen, despite impairment of macroaggregation (7.2 [3.5, 10.9], n = 12), microaggregation was again near-maximal (96 [93, 97]). The response to ristocetin was more markedly impared after bypass in succinylated gelatin (Gelofusine) treated patients (5.6 [2.8, 8.6], n = 17; p < 0.005 v control), whereas the response to collagen was little different (9.3 v 9.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Aprotinin↗
PubMed1994

Changing the appearance of anterior teeth with porcelain veneers: a case report.

A case is described in which porcelain veneers were used to improve the appearance of the upper anterior teeth and disguise a marked dental centre-line asymmetry. This followed the traumatic loss of the upper left central incisor and complete space loss. Four anterior teeth were treated so that the illusion of symmetry might be enhanced, and the rationale behind this approach is discussed.

Child↗
PubMed1993

Periprandial regulation of lipid metabolism in insulin-treated diabetes mellitus.

We have examined the regulation of lipid and glucose metabolism in the postabsorptive and postprandial states in six subjects with insulin-treated diabetes mellitus, and compared them with eight nondiabetic subjects. Blood or plasma concentrations of metabolites and fluxes across forearm and subcutaneous adipose tissue were studied after an overnight fast and for 6 hours after a mixed meal (3.1 MJ, 41% from fat). In the postabsorptive state, regulation of lipid metabolism in the two groups appeared basically similar except that a wider spread of plasma (free) insulin concentrations in the diabetic group led to a wider range of values of plasma nonesterified fatty acid (NEFA) release from adipose tissue, plasma NEFA concentrations, and blood ketone body concentrations. Extraction of ketone bodies across adipose tissue was positively correlated with arterial concentration in both groups (as it was in the forearm), confirming the ability of human adipose tissue to utilize ketone bodies. A single subcutaneous injection of insulin before the meal in the diabetic group produced a plasma free-insulin profile that was blunted and prolonged compared with the postprandial response in the control group. Postprandial forearm glucose uptake followed very closely the plasma (free) insulin concentration. Postprandial suppression of NEFA release from adipose tissue was essentially normal in the diabetic group, and the normal postprandial decrease in plasma NEFA concentrations was reproduced extremely closely. Forearm and adipose tissue blood flow did not differ between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1992

Biopsy of canine ear tissue for detection of Borrelia burgdorferi following Ixodes dammini feeding.

A punch biopsy method was developed to detect and cultivate Borrelia burgdorferi from canine ear tissue. The biopsy procedure was sensitive in that spirochetes were detected in 100% of the dogs upon which infected ticks had fed. B. burgdorferi could be cultured as early as 6 days after tick feeding at which time the organisms could not be concurrently recovered from peripheral blood. The ear punch biopsy provides a reliable method for sampling live canines and should prove useful for detecting early B. burgdorferi infection and for monitoring duration of non-disseminated infection. Additionally, the procedure will aid in the development of an animal model for evaluation of preventive and therapeutic treatment modalities.

Animals↗
PubMed1992

Adipose tissue metabolism in obesity: lipase action in vivo before and after a mixed meal.

Physiological actions of insulin include suppression of fat mobilization from adipose tissue and activation of adipose tissue lipoprotein lipase. Here, we report measurements of adipose tissue hormone-sensitive lipase (HSL) and lipoprotein lipase (LPL) action in vivo in 10 normal and eight obese subjects, with the latter group having varying degrees of glucose intolerance. HSL and LPL actions (per gram of adipose tissue) were similar in the two groups, after an overnight fast. In the normal subjects, HSL action was suppressed after a meal (by 75% +/- 6% between 60 to 300 minutes, P less than .01), and the action of LPL was increased (clearance of circulating triacylglycerol [TAG] increased by 140% +/- 57% at 300 minutes, P less than .05). Despite hyperinsulinemia, these responses were blunted in the obese subjects (P less than .05 for each change being less than in normal group). The adipose tissue of the obese subjects showed continued nonesterified fatty acid (NEFA) release at a time when NEFA mobilization was completely suppressed in the normal group. Both impaired suppression of HSL and low fractional retention of fatty acids for reesterification within the adipose tissue contributed to this abnormal NEFA release. Impaired activation of LPL was associated with a greater absolute increase in plasma TAG concentration postprandially in the obese. In obese subjects, adipose tissue HSL and LPL fail to respond to immunoreactive insulin postprandially, which may be an important maladaptation in terms of lipoprotein metabolism and risk of coronary heart disease.

Adipose Tissue↗
PubMed1992

Acute administration of tumour necrosis factor-alpha or interleukin-1-alpha does not mimic the hypoketonaemia associated with sepsis and inflammatory stress in the rat.

1. Administration of tumour necrosis factor (cachectin) and of interleukin-1-alpha increased the plasma level of nonesterified fatty acids in fed rats, and in the case of interleukin-1-alpha the blood glycerol level was also increased, suggesting stimulation of adipose tissue lipolysis. There were parallel increases in the plasma level of triacylglycerols. Neither cytokine had significant effects on blood or liver total ketone body (acetoacetate plus 3-hydroxybutyrate) concentrations. 2. In starved rats, the higher plasma non-esterified fatty acid concentration was not increased further by the cytokines. The plasma triacylglycerol level was increased, although the absolute change was less than in fed rats. The ketonaemia associated with starvation tended to be increased by the cytokines, but this was only significant in the case of interleukin-1-alpha. Parallel changes occurred in hepatic ketone bodies. 3. It is concluded that tumour necrosis factor-alpha and interleukin-1-alpha are not responsible for the hypoketonaemia associated with sepsis or other inflammatory states.

Animals↗
PubMed1992

Platelet-activating factor causes hypoketonaemia in starved rats.

1. The aim of this work was to examine whether platelet-activating factor could mimic the hypoketonaemia seen in septic and endotoxic experimental animals. Platelet-activating factor was administered either by the intraperitoneal (high dose) or intravenous (jugular vein, low dose) routes. 2. Intraperitoneal injection of platelet-activating factor (25 micrograms/kg body weight) decreased the blood ketone body concentration (acetoacetate plus 3-hydroxybutyrate) transiently (30 min after injection) in starved rats. Continuous intravenous infusion of platelet-activating factor (40 ng min-1 kg-1 for 5 h) caused comparable hypoketonaemia. 3. The hepatic acetoacetate concentration also decreased transiently after injection of platelet-activating factor and there was an increase in the 3-hydroxybutyrate/acetoacetate ratio. The hepatic ATP concentration decreased at 15 and 30 min after injection of platelet-activating factor. Infusion of platelet-activating factor caused a similar decrease in hepatic ketone body concentration, but no significant change in the 3-hydroxybutyrate/acetoacetate ratio or adenine nucleotide concentrations. 4. Platelet-activating factor administered by infusion, but not by injection, decreased the plasma non-esterified fatty acid concentration. The plasma glycerol concentration also decreased after infusion of platelet-activating factor, suggesting decreased lipolysis in adipose tissue. 5. Changes in plasma insulin concentration or white adipose tissue blood flow did not appear to contribute to the decrease in the plasma non-esterified fatty acid concentration after infusion of platelet-activating factor. However, there was a significant decrease in blood flow to interscapular brown adipose tissue in both the infused and injected groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1991

Effects of platelet-activating factor on lipid metabolism in rats in vivo. Origin of the hypertriglyceridaemia.

Administration of platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF) did not alter the rate of triacylglycerol entry into the plasma. The gastrointestinal absorption of [1-14C]triolein was, however, inhibited by PAF, yet there was increased accumulation of [14C]lipid in the plasma and hypertriglyceridaemia. The half-life of injected [9,10(n)-3H]triolein in the plasma increased by 47%, and there was decreased accumulation of [3H]lipid in brown adipose tissue. This was accompanied by a decrease in lipoprotein lipase activity. The hypertriglyceridaemia induced by PAF appears to be mainly due to decreased peripheral removal, one important site affected being brown adipose tissue.

Animals↗
PubMed1991

Comparison of effects of platelet-activating factor and tumour necrosis factor-alpha on lipid metabolism in adrenalectomized rats in vivo.

The acute metabolic effects of platelet-activating factor (PAF) and tumour necrosis factor-alpha (TNF-alpha) were compared in sham-operated and adrenalectomized rats. PAF caused hyperglycaemia in sham-operated rats, whereas with TNF-alpha there was a slight decrease in blood glucose. Both PAF and TNF-alpha resulted in marked hypoglycaemia in the adrenalectomized rats. Plasma insulin was depressed (about 50%) by PAF and TNF-alpha in sham-operated rats, whereas in the adrenalectomized rats the already low plasma insulin concentration was not significantly altered. Liver glycogen content was the same in control and treated sham-operated rats, but was considerably decreased (about 50%) in the adrenalectomized rats. In sham-operated rats, PAF and TNF-alpha increased plasma non-esterified fatty acids and triacylglycerols, suggesting increased lipolysis, whereas in adrenalectomized rats there was no significant increase in non-esterified fatty acids with PAF, although it still occurred with TNF-alpha. This suggests that the lipolytic effect of TNF-alpha may be direct, whereas that of PAF is indirect, possibly via increased catecholamines in the sham-operated rats. The stimulation (about 3-fold) of hepatic fatty acid synthesis in vivo by PAF and TNF-alpha in sham-operated rats was still evident in the adrenalectomized rats, although the absolute increase was smaller. PAF, but not TNF-alpha increased (100%) sterol synthesis in adrenalectomized rats. It is concluded that PAF and TNF-alpha can increase hepatic lipogenesis in vivo in the absence of adrenal hormones and in the presence of a low plasma insulin.

Adrenalectomy↗
PubMed1991

Cadmium concentrations in the freshwater mussel (Elliptio complanata) and their relationship to water chemistry.

Concentrations of cadmium were determined in freshwater mussels (Elliptio complanata) from 21 small lakes in south-central Ontario. The average Cd concentrations ranged from 0.5 to 7.5 micrograms/g dry weight. A poor correlation between the concentration of Cd in lakewater and the concentration of Cd in the organisms was observed. Concentration of Cd in the sediments was not a useful predictor. Thus, it is hypothesized that the availability of the Cd varies among the 21 lakes. In an effort to test this hypothesis, the relationships between organism concentrations and water chemistry parameters that have the potential to alter Cd availability including pH, calcium (Ca), total organic carbon (TOC) and total inorganic carbon (TIC) were examined. The strongest relationship was found between Cd concentration in the mussels and water column pH, suggesting that hydrogen ions are replacing Cd ions in complexes and increasing the amount of free Cd available to the organisms. Correlations between pH and other water chemistry parameters make it difficult to test this hypothesis. A multiple regression model was developed incorporating pH, Ca, TOC, and TIC which explained 69% of the variance in Cd concentrations.

Animals↗