Search PubMed⌕ Search

Biomedical subjects

R Wilkinson

Publications and source records attributed to R Wilkinson.

At least 91 records · Page 5Linked to original sources
PubMed1995

Computed tomography evaluation of renal parenchymal volume in patients with chronic pyelonephritis and its relationship to glomerular filtration rate.

The measurement of renal parenchymal volume using a calibrated computed tomography image processing method has been evaluated clinically on a cohort of patients with chronic pyelonephritis. Comparison of renal volume with function as assessed by 99Tcm DTPA renography demonstrated a simple linear relationship in patients who were normotensive and aproteinuric. The implications of this result on the interpretation of prognostic factors determining declining renal function in chronic pyelonephritis are discussed.

Chronic Disease↗
PubMed1994

Confocal laser scanning microscopy (CLSM) for the study of collagen sponge microstructure.

This study uses confocal laser scanning microscopy (CLSM) to assess the microstructure of collagen sponges providing an accurate quantification of porosity under conditions similar to those experienced by cells growing on the sponges during culture. CLSM offers several advantages over scanning electron microscopy (SEM) and conventional optical microscopy for this kind of study, the most important of which is probably the absence of artifacts associated with the extensive preparation of samples required for the latter two methods. When the "pan-side" surface of collagen sponges was studied, it was found that the pore sizes increased with increasing depth into the sponge. Collagen sponges frozen in a -70 degrees C freezer had a more open structure than ones frozen on the stage of a tissue dryer. These different pore sizes are thought to reflect different freezing rates in the samples.

Animals↗
PubMed1994

Membrane fluidity is different in intact erythrocytes and ghost membranes.

The fluorescence anisotropy of 1,6-diphenylhexatriene (DPH) and trimethylammonium-DPH in the membranes of intact human erythrocytes and ghost membranes was compared. The anisotropy of fluorophores is significantly higher in intact erythrocytes compared to that in ghost membranes. Perturbation of membranes by heating at 47 degrees C and use of a rotating stirrer affected the anisotropy of fluorophores in intact erythrocytes only. These results suggest that: (a) spectrin has a significant modulating effect on membrane fluidity, and (b) the physical properties of the cell membrane are different between intact erythrocytes and erythrocyte ghost membranes.

Erythrocyte Membrane↗
PubMed1994

Thallium-technetium-subtraction scintigraphy in secondary hyperparathyroidism.

Between 1983 and 1992 thallium-technetium subtraction scintigraphy (TTS) was performed on 74 patients with clinical and biochemical evidence of hyperparathyroidism. Twenty-five of the 53 investigations since 1988 were conducted on patients with renal failure with a suspicion of secondary hyperparathyroidism. In a retrospective study we have evaluated radioisotope scintigraphy for patients with adenoma and for renal failure patients with possible parathyroid hyperplasia. Thirty of 74 patients underwent neck exploration. Scintigraphy detected 17 of 24 parathyroid adenomas (sensitivity 71%). In contrast, in six renal patients who came to operation, scintigraphy localised only 5 of 20 hyperplastic parathyroid glands (sensitivity 25%) and in one renal patient we localised a parathyroid adenoma. A review of the literature shows low detection rates for hyperplasia by TTS to be a common observation. Based on these findings a rational approach is offered for parathyroid localisation in renal patients prior to neck exploration.

Adenoma↗
PubMed1994

Erythrocyte sodium-lithium countertransport activity is related to membrane fluidity in IDDM patients.

Sodium-lithium countertransport (SLC) activity at a standard physiological sodium concentration is raised in uncomplicated IDDM, for which the kinetic mechanism is a raised maximum velocity (Vmax). Diabetic patients with nephropathy do not have raised values for Vmax but a low Michaelis constant (km). Transporter activity could be influenced by its membrane lipid environment. This was assessed in 21 control subjects, 32 uncomplicated diabetic patients, 17 patients with diabetic nephropathy and 11 patients with non-diabetic nephropathy by measuring the fluorescence anisotropy of DPH and TMA-DPH to assess different membrane regions. Standard SLC was higher in all the patient groups compared to the control subjects: 0.307 +/- 0.020 mmol Li/h x 1 cells in uncomplicated IDDM; 0.300 +/- 0.032 in diabetic nephropathy patients and 0.276 +/- 0.019 in non-diabetic nephropathy patients vs 0.216 +/- 0.011 mmol Li/h x 1 cells in control subjects (p < 0.001, p < 0.05, p < 0.05, respectively). This was due to raised Vmax values in the uncomplicated group: 0.528 +/- 0.035 vs 0.385 +/- 0.022 mmol Li/h x 1 cells in control subjects (p = 0.001) and low values for km in the diabetic nephropathy group: 58 (27-170) vs 106 (81-161) mmol/l in control subjects (p < 0.001). Raised SLC in the non-diabetic nephropathy group was largely due to raised Vmax: 0.460 +/- 0.030 mmol Li/h x 1 cells; p = 0.053, with no difference in km: 99.5 (74-137).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Further characterisation of the immune response of the koala.

Sensitive enzyme immunoassays (EIA) were developed to monitor antibody (Ab) production in the koala, in response to both soluble and particulate antigens (Ag). When compared with a eutherian mammal, the rabbit, both the dynamics and kinetics of Ab production in the koala were found to be severely retarded. In vitro, Ag specific lymphocyte proliferative responses were demonstrated for the first time in this animal by sensitising koalas in vivo with Bacillus Calmet-Guerin (BCG), with the level and timing of this cell mediated immune (CMI) response comparable with those seen in non-metatherian mammals. Levels of circulating B lymphocytes were examined in an attempt to clarify the retarded humoral responses to foreign Ags. In addition, peripheral mononuclear cells (PMC) from koalas, were examined for their reactivity to a range of monoclonal Abs and lectins in an attempt to characterise these cells further. The lectins examined, demonstrated an all or none reactivity with koala lymphocytes and were therefore considered unsuitable as markers for identifying lymphoid subsets in this animal. A monoclonal Ab directed at class II MHC Ags in the mouse, demonstrated cross reactivity with a high percentage of all koala monocytes tested. Using this Ab to probe CMI responses in vitro, it is concluded that immune interactions required for such responses in the koala parallel those seen in other mammals.

Animals↗
PubMed1994

External fixation of the distal radius. A biomechanical study.

External fixation is a useful method of treating unstable fractures of the distal radius. There is a lack of information regarding the behaviour of mini-fixation systems, particularly under cyclical loading, which would be expected to occur at the wrist. This laboratory study was designed to investigate the mechanical characteristics of nine current fixation systems. A programme of loading was devised to mimic forces acting on the distal radius. Wooden dowel was used to mount the fixator. Distraction and compression forces were applied in an Instron rig. Displacement was monitored throughout the load programme. No fixator failed at the loads tested. The small Hoffman rectangular frame proved stiffest in compression and extension, but was heavier than other devices. A trend of progressive, permanent deformation became apparent in those fixators which contain plastic or composite materials. This feature has implications for loss of fracture reduction in the clinical setting.

Biomechanical Phenomena↗
PubMed1994

Prescribed drug therapy and near-fatal asthma attacks.

Inhaled fenoterol has been associated with an increased risk of death in severe asthmatics, when compared to other adrenoceptor agonists. It is plausible that fenoterol may also increase the risk of near-fatal attacks. We have conducted a case-control study to investigate this hypothesis. The cases comprised Intensive Care Unit (ICU) admissions for asthma in the Wellington region during 1977-1988. For each of these cases, two age-matched controls were selected from asthma admissions to the same hospital during the same period. For the 155 cases and 305 controls, information on prescribed drug therapy was collected from the hospital admission records. The relative risk of a near-fatal asthma attack in patients prescribed inhaled fenoterol was 2.00 (95% confidence interval (CI) 1.35-2.97). An increased risk was also observed for oral theophylline (odds ratio (OR) = 1.88; 95% CI 1.26-2.79). For the 65 cases and 104 controls who had a previous admission for asthma in the previous 12 months, information relating to the previous admission was also collected; an increased risk was once again observed for inhaled fenoterol (OR = 2.18; 95% CI 1.10-4.33) and for oral theophylline (OR = 1.18; 95% CI 0.99-3.57). No other asthma drugs showed significantly increased risks. Although the ICU admission cases had generally been prescribed more asthma drugs than the hospital admission controls, and appeared to have more severe asthma, it is possible that the findings reported here are influenced by confounding by severity. We nevertheless estimate that our findings are consistent with the hypothesis that fenoterol increases the risk of near-fatal asthma attacks, and that they complement previous findings on fatal asthma attacks.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1994

A new method for measuring the blood volume of the rat using 113mIndium as a tracer.

A new method is described for the estimation of blood volume in the rat using 113mIndium chloride. No in vitro labelling step is necessary as the isotope binds specifically to transferrin in vivo. Under anaesthesia, an external jugular vein was cannulated for blood sampling and indium chloride injected directly into a lateral tail vein. Three blood samples of 0.2 ml were taken at short intervals and radioactivity measured under standard conditions. Blood volume was found to be 7.46 +/- 0.14 (mean +/- SEM) ml/100 g body weight. Repeating the study of 5 animals gave similar values for blood volume on the 2 occasions (7.23 +/- 0.26 and 6.95 +/- 0.23 ml/100 g, P > 0.05). The new technique was compared with established methods using 51Cr labelled red blood cells and 125Iodinated albumin. In each animal, the 113mIndium technique produced values approximately 10% higher than those obtained using the sum of plasma and red cell mass, in keeping with the known difference between whole body and large vein haematocrit (Indium, 7.20 +/- 0.19 and Iodine with Chromium, 6.40 +/- 0.34 ml/100 g). Data on blood volume determined using 125Iodine as the tracer on these same animals were identical (Indium, 7.20 +/- 0.19 and iodine, 7.16 +/- 0.34 ml/100 g). The method is simple to perform and appears to be at least as accurate and reproducible as established methods for measuring blood volume.

Animals↗
PubMed1994

Confocal laser scanning microscopy of calcified bioprosthetic heart valves.

Calcification of bioprosthetic heart valves is a major factor limiting their long-term function. Current methods of microscopic examination of calcific deposits require dehydration and processing of the leaflet material, e.g. wax embedding, sectioning, gold coating. Confocal laser scanning microscopy is a new technique which allows serial optical sectioning of thick biological specimens in their normal hydrated state. The current study has examined bovine pericardium and porcine aortic valve materials calcified in vitro under static and dynamic conditions. A series of clinical explants of bovine pericardial and porcine aortic valve types has also been examined. The calcium-specific stain, Alizarin Red S, has been used as a fluorescent marker for calcium deposits. Fluorescent images, generated by Argon ion laser light at 488nm, have been obtained at varying depths into samples. These have been reconstructed to demonstrate the relationship between calcium deposits and autofluorescent collagen fibers. The patterns of calcification were similar in both in vitro and explant valve material. The calcification was of three main patterns: calcium depositing longitudinally on collagen fiber bundles; calcium forming a banded pattern perpendicular to the fiber direction and large, dense, focal deposits obliterating the underlying collagen structure. Involvement of collagen fibers in the calcification pattern was a consistent finding in all sample types. The method is a useful addition to the tools available for study of calcification processes. The potential exists for three-dimensional reconstruction of leaflet architecture and its inter-relationship with calcium deposition, in a normally hydrated state.

Adult↗
PubMed1994

Nephropathy and changes in sodium-lithium countertransport kinetics in type 2 (non-insulin-dependent) diabetes mellitus.

Previous studies of erythrocyte sodium-lithium countertransport activity, a putative genetic marker of essential hypertension, in Type I and Type II diabetic patients with nephropathy have given conflicting results. We have found changes in the maximum velocity (Vmax) and sodium-affinity constant (Km) of sodium-lithium countertransport in Type I diabetic patients with diabetic nephropathy. In this study, sodium-lithium countertransport kinetics were measured in Type II diabetic patients with established diabetic nephropathy, matched uncomplicated Type II diabetic patients, non-diabetic patients with nephropathy and healthy control subjects. Mean standard sodium-lithium countertransport activity was not significantly increased in either of the groups of diabetic patients compared with the non-diabetic control groups. The Type II diabetic patients with nephropathy had a significantly reduced km and Vmax compared with the uncomplicated diabetic patients and non-diabetic control group. These kinetic changes are identical to those observed in Type I diabetic nephropathy patients. There are similar underlying changes in the erythrocyte plasma membrane with the development of nephropathy in both Type I and Type II diabetes.

Antiporters↗
PubMed1993

Characterization of the response of erythrocyte sodium-lithium countertransport to inhibitors.

To clarify the biochemical characteristics of the sodium-lithium countertransporter (SLC) the responses of SLC to two probes of ion transport--4,4'-diisothiocyanostilbene-2,2' disulfonate, and N-ethylmaleimide--were assessed. The results suggest that the SLC transporter is associated with the band 3 protein in the plasma membrane and demonstrate that a sulfhydryl group is essential for transport function.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

Collagen arrangements in ureter.

The collagen fibres of rabbit and human ureter were exposed by digestion with trypsin and hyaluronidase. The fibre structure was examined using an SEM and examples of the inner and outer fibre structures are shown together with the effects of different types of mechanical strain. An interesting difference between the arrangements of the inner fibres of human and rabbit was seen where the human ureter had a cross-ply structure while in the rabbit it was helical.

Animals↗