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Biomedical subjects

D Allan

Publications and source records attributed to D Allan.

At least 19 recordsLinked to original sources
PubMed1992

Two separate pools of sphingomyelin in BHK cells.

In BHK cells labelled to equilibrium with [3H]choline and treated with sphingomyelinase the surface pool of sphingomyelin is degraded very rapidly (half-time 10 min) but the internal pool of sphingomyelin which accounts for about 30% of the total is only degraded slowly (half-time about 80 h) showing that the internal pool does not normally reach the surface. In [3H]choline incorporation experiments the internal pool begins to accumulate radioactivity at about the same time as phosphatidylcholine (30 min) but label does not enter the surface pool of sphingomyelin for a further 90 min. The internal and external pools reach the same specific activity only after about 20 h. Pulse-chase analysis with [3H]choline shows that radioactivity in each pool of sphingomyelin continues to increase when the specific radioactivity of phosphatidylcholine is decreasing, consistent with both pools being synthesised from a phosphatidylcholine precursor. The results suggest that sphingomyelin in BHK cells is present not only in the plasma membrane but also in a more rapidly labelling pool which does not mix with the surface pool.

Animals↗
PubMed1992

Isolation of plasma membrane exovesicles from BHK cells using merocyanine 540.

Treatment of cultured BHK cells with merocyanine 540 caused the non-lytic release of vesicular material having the phospholipid composition characteristic of plasma membrane. The protein composition of the vesicles closely resembled that of the soluble fraction of the cell, as expected for exovesicles budding from the cell surface. Vesicles prepared from cells surface-iodinated with 125I contained no obvious iodinated membrane polypeptides, suggesting that no major proteins in the plasma membrane of the BHK cell are free to diffuse with lipids. The procedure described should represent a general method, applicable to a wide range of cell types, for isolating plasma membrane vesicles.

Cell Membrane↗
PubMed1992

Flash and pattern reversal visual evoked responses in normal and demented elderly.

P1 and P2 components of visual evoked responses (VERs) to flash stimuli were compared between patients diagnosed as suffering from Senile Dementia of the Alzheimer Type (AD) and elderly controls. Additionally the P100 component of the VER to pattern reversal stimuli at high and low contrast and using large and small check patterns was compared. Significant differences between moderate AD patients and the normal elderly were found for the P2 component of the flash stimulus and for the P100 component of the high spatial frequency pattern reversal stimuli at low contrast. These findings suggest a deficit in primary visual processing and a selective deficit in secondary visual processing in moderate cases of dementia. This indicates that visual processing capacities of AD patients decline as the disease progresses in line with the continual degeneration of neuronal populations involved with vision.

Aged↗
PubMed1991

Etretinate and visual function: a 1-year follow-up study.

Concern has been expressed in the literature that the drug etretinate may be potentially retinotoxic. Four patients are reported who have received long-term treatment with etretinate and who have undergone detailed evaluation for the development of visual dysfunction over a 1-year period. Despite prolonged treatment and high total doses no evidence of ocular toxicity attributable to the drug was found in any of the patients.

Ectodermal Dysplasia↗
PubMed1990

Restricted diffusion of integral membrane proteins and polyphosphoinositides leads to their depletion in microvesicles released from human erythrocytes.

The protein and phospholipid composition of microvesicles released from normal human erythrocytes after ATP depletion, on aging or by treatment with merocyanine 540, dimyristoyl phosphatidylcholine or Ca2+/ionophore A23187 has been compared with the composition of the original cell membrane. It has been shown that these microvesicles are depleted of band 3, glycophorin and phosphatidylinositol 4,5-bisphosphate relative to phospholipid by 40% or more. These data are interpreted to mean that less than half of these membrane components are free to diffuse laterally in the lipid bilayer. Acetylcholinesterase was found to be enriched 2-3-fold in microvesicles, possibly because the removal of non-diffusing proteins from the vesiculating region of the lipid bilayer allows more space for freely diffusing proteins like acetylcholinesterase to enter the microvesicle membrane.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1990

Relationship between arachidonate generation and exocytosis in permeabilized mast cells.

Using rat mast cells permeabilized with streptolysin O we show that release of arachidonate generally occurs under similar but not identical conditions to those that cause exocytosis of beta-N-acetylglucosaminidase (hexosaminidase). Thus, hexosaminidase secretion and arachidonate release both require provision of Ca2+ together with a guanine nucleotide but exocytosis occurs at lower concentrations of both effectors. The kinetics of both processes are similar, with a delay in onset only when ATP is present. Arachidonate release occurs largely from a pool of arachidonyl phosphatidylcholine which appears to represent less than 1% of the total phosphatidylcholine of the cells. Despite the general similarity of the conditions causing exocytosis and arachidonate release, our results show that under some circumstances it is possible to obtain exocytosis without measurable release of arachidonate and that therefore phospholipase A2 activation is not an essential precursor of secretion.

Adenosine Triphosphate↗
PubMed1990

A hand-held OKP chart for the screening of glaucoma: preliminary evaluation.

Oculo-kinetic perimetry (OKP) uses controlled movements of the patient's eye to position a static test stimulus in the visual field. The test chart consists of a white tangent screen with 23 numbered fixation points located eccentrically at strategic points in relation to a central black spot, which is the test stimulus. As the patient looks at each number in turn, the spot stimulates the retinal areas that are most likely to show early glaucomatous damage. The result is positive if one or more numbers make the spot disappear. Ninety-eight eyes of 54 patients attending a hospital glaucoma clinic were tested with a prototype OKP glaucoma screener and by conventional perimetry. Visual fields plotted conventionally were independently categorised as normal, equivocal and glaucomatous by the perimetrist and the ophthalmologist and these results were further categorised as normal, equivocal or glaucomatous according to whether they were considered abnormal by none, one or both of the observers respectively. The OKP test was positive in (i) 93% of 27 eyes with glaucomatous defects, (ii) 69% of 32 eyes with equivocal loss, (iii) 41% of 39 eyes without previously recognised field loss but having ocular hypertension, a suspicious disc, or contralateral glaucoma, (iv) 9% of 116 eyes from 60 age matched persons accompanying the patients to hospital. If the results were considered in terms of patients not eyes, the OKP test was positive in 85% individuals with glaucomatous field loss in their worse eye and in 12% of the controls. A hand-held OKP chart testing a small set of points and using a constantly exposed stimulus could be a useful tool for the detection of glaucoma in the community.

Evaluation Studies as Topic↗
PubMed1990

Brightness discrimination and contrast sensitivity in chronic glaucoma--a clinical study.

The visual acuity, the difference in sensitivity of the two eyes to light (brightness ratio), and contrast sensitivity were assessed in 28 patients with chronic open angle glaucoma and compared with those of 41 normal controls of similar ages and visual acuity. The results obtained were related to the results of Tübingen visual field analysis in patients with glaucoma. Twenty-four of the 28 glaucoma patients (86%) had a significant disparity in brightness ratio between the two eyes. This was found to match the frequency of visual field loss. Moreover, there was a significant relationship between the interocular differences in brightness sense and the difference in the degree of visual field loss between the two eyes. Of the glaucoma patients 39% had sum contrast sensitivities outside the normal range for age-matched normal controls. No significant correlation was found between the interocular difference in brightness sense and the visual acuity or the interocular difference in sum contrast sensitivity. It is concluded that, in the presence of a normal visual acuity, the brightness ratio test warrants evaluation as a potential screening test for chronic open angle glaucoma.

Adult↗
PubMed1989

Echinocytosis and microvesiculation of human erythrocytes induced by insertion of merocyanine 540 into the outer membrane leaflet.

Echinocytosis and release of microvesicles from human erythrocytes treated with the impermeant fluorescent dye merocyanine 540 (MC540) has been correlated with the extent of dye binding to intact cells and ghosts. At 20 degrees C binding appeared to saturate at about 9.3.10(6) molecules per cell (3.6 mol/100 mol phospholipid), equivalent to an expansion of the outer leaflet lipid area of about 2.7%. Stage 3 echinocytes were formed upon binding of (3-4).10(6) molecules of MC540/cell (about 1.3 mol/100 mol phospholipid), equivalent to an expansion of the outer leaflet lipid area of about 1.0%. Negligible release of microvesicles was observed with MC540 at 20 degrees C. Binding of MC540 to permeable ghosts was approximately twice that to cells suggesting that there was no selective binding to the unsaturated (more fluid) phospholipids which are concentrated in the inner lipid leaflet of the membrane. At 37 degrees C apparent maximal binding of MC540 was about 3.2 mol/100 mol phospholipid and correlated with the maximal release of microvesicles from the cells as measured by release of phospholipid and acetylcholinesterase. These results are discussed in relation to the bilayer couple hypothesis of Sheetz and Singer (Proc. Natl. Acad. Sci. USA 71 (1974) 4457-4461).

Erythrocyte Membrane↗
PubMed1989

The detection of glaucomatous visual field defects by oculo-kinetic perimetry: which points are best for screening?

Oculo-kinetic perimetry (OKP) uses the patient's ocular movements to position a test stimulus in the visual field. By virtue of its simplicity and low cost, this test could be useful in the screening of glaucoma. The general purpose OKP chart, however, which tests 100 points in the central 25 degrees field, is too time-consuming for this purpose, taking approximately 4-7 minutes per eye. Accordingly, this study was performed to identify the points most likely to detect patients with glaucoma. Fifty-one eyes with glaucomatous visual field defects and 51 non-glaucomatous eyes of age matched individuals were tested by conventional and oculo-kinetic perimetry. At least one of only six points were missed by 82.4% of glaucomatous eyes and by 9.8% of nonglaucomatous eyes. These results, although falling short of the ideal efficiency, are comparable with data published by other research groups using computerised equipment and suggest that, with further development, a specialised OKP chart testing only a small number of points might be valuable in screening for glaucoma.

Adult↗
PubMed1989

Pseudoexfoliation glaucoma in Greece.

Pseudoexfoliation glaucoma is commonly seen in Greece, however there is little data concerning the prevalence and characteristics of this disorder. Patients undergoing trabeculectomy for open angle glaucoma were investigated both by the appraisal of the case notes and by re-examination. The prevalence of pseudoexfoliation glaucoma in this population was found to be 87.8%. The characteristics of this disease process in the population studied are discussed. These findings indicate that pseudoexfoliation is a major contributor to severe glaucoma in the population of Northern Greece.

Aged↗
PubMed1989

The benefit of early trabeculectomy versus conventional management in primary open angle glaucoma relative to severity of disease.

One hundred and sixteen patients with newly diagnosed primary open angle glaucoma were selected for a randomised, prospective, multicentre trial if the untreated intraocular pressure was over 25 mmHg and there was field loss characteristic of glaucoma. Conventional management of medical therapy followed by trabeculectomy in unsuccessful cases was compared with trabeculectomy at diagnosis followed where necessary by supplementary medical therapy. At a mean follow-up of 4.6 years there was no significant difference in visual acuity between the groups but the conventional management group had significantly greater loss of visual field which occurred during the unsuccessful attempt at medical control. The eyes which lost most visual field were those with least field loss at diagnosis and this paradox was attributed to a prolonged attempt at medical control in these eyes because they were thought to have a lower risk of visual field deterioration.

Chi-Square Distribution↗
PubMed1989

Intracranial pressure monitoring: a study of nursing practice.

Differences exist within neurological centres with regard to the care of the patient with an ICP monitoring device in place. A survey carried out to identify these differences shows that head injury remains the most common diagnosis associated with ICP monitoring and intraventricular catheters the most popular method, although the use of catheter tip pressure transducers appeared to be on the increase. Some centres used more than one method. The type of machinery used to process the data varied enormously. Written guidelines or standards existed in only a few centres and none of these fully covered every aspect of care as quoted in the literature. Many units appeared to rely on in-service or one to one teaching situations with new or learner staff being supervised initially. Some centres restricted the type of nurse who was permitted to care for these patients. Unfortunately, the restrictions were not clearly identified. Calibration of equipment was not considered a nursing procedure but some respondents felt that it should be.

Clinical Nursing Research↗
PubMed1989

Central visual function in patients with resolved central serous retinopathy. A long term follow-up study.

The visual acuity, central retinal sensitivity, macular thresholds, contrast sensitivity and temporal visual acuity were employed to assess the long term visual outcome in 23 patients with a history of central serous retinopathy (CSR). Twenty patients had unilateral CSR, and 3 had had bilateral disease. The unaffected eyes had significantly better visual acuities (P less than 0.014), better retinal sensitivities (P less than 0.006) and lower macular thresholds (P less than 0.008) when compared with affected eyes. The eyes with CSR whose visual acuities were mildly affected (6/9) showed lower sensitivity for the high spatial frequency (P less than 0.0072). There was no significant difference in the temporal visual acuity between eyes with CSR and the non-affected eyes.

Follow-Up Studies↗
PubMed1989

Pulsed neodymium-YAG laser trabeculotomy: energy requirements and replicability.

Short pulsed laser trabeculotomy has been shown to reduce intraocular pressure in patients with primary open angle glaucoma. This study seeks to determine the energy levels required to produce a fistula into the canal of Schlemm for four different Q-switched neodymium-YAG lasers. The laser was fired at fixed human trabecular meshwork specimens at a range of energy settings for each laser and the characteristics and replicability of the lesions produced were analysed. Energy levels between 3 and 5 mJ were sufficient to produce fistulae into the canal of Schlemm with an approximately 50% success rate for each instrument.

Humans↗
PubMed1989

A grand alliance takes shape behind 'Facts for Life'.

Convinced that if parents could be reached with today's health knowledge and supported in putting it into use, child survival and development would experience a great forward surge, WHO, Unicef and Unesco have compiled a ten chapter summary of the essential information parents need. This booklet is Facts for Life, but more than a publication, it is a movement and the handbook of a grand alliance of communicators.

Child↗