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Biomedical subjects

G M Thompson

Publications and source records attributed to G M Thompson.

At least 37 records · Page 2Linked to original sources
PubMed1994

Does topical flurbiprofen affect the pupillary response to acetylcholine?

Pre-operative topical non-steroidal anti-inflammatory drugs (NSAIDs) are known to be effective in maintaining pupillary dilation during cataract surgery. However, previous studies have suggested that pre-treatment with these agents interferes with the miosis produced by intraoperative acetylcholine injection. This study was designed to determine whether the pupillary response to acetylcholine injection is reduced following pre-operative topical flurbiprofen 0.03%. Pupil diameters were measured with a millimetre rule, and the measurements verified using computerised image analysis of digitised video images. Eyes treated with flurbiprofen were compared with controls. There was no significant difference in pupillary diameter before corneal incision, but following aspiration of soft lens matter and insertion of intraocular lens the pupil was significantly larger in the flurbiprofen group (p = 0.002). At 1.0, 2.5 and 5.0 minutes following injection of acetylcholine no significant difference in the degree of miosis was detected. This study confirms that topical flurbiprofen maintains dilation during cataract surgery, and does not find any evidence to suggest that intra-operative response to acetylcholine is reduced.

Acetylcholine↗
PubMed1993

The relationship between clinical classification of cataract and lens hardness.

'Hardness' of the cataractous lens is one of the major factors influencing the suitability of a patient for phacoemulsification. Surgeons should be able to estimate hardness when choosing patients for this method of cataract extraction. The aims of the study were to investigate the relationship between the clinical appearance of cataracts and their hardness. Ninety-one lenses were studied from patients undergoing endocapsular cataract extraction. Lenses were assessed using a classification based on the Lens Opacities Classification System II and hardness was assessed using an automated lens guillotine. The degree of nuclear sclerosis and the age of the patient were found to influence lens hardness. Regression analysis showed that 56% of the variation in hardness could be explained in terms of age and the degree of nuclear sclerosis. The presence of posterior subcapsular and cortical cataract did not influence hardness. These findings confirm our clinical suspicions and enable surgeons to make a more objective analysis of hardness prior to phacoemulsification.

Adult↗
PubMed1992

Mutation analysis of the Cys-X2-Cys-X19-Cys-X2-Cys motif in the beta subunit of eukaryotic translation initiation factor 2.

Recessive lethal mutations in the beta subunit of eIF-2 that restore HIS4 expression in the absence of an AUG start codon were isolated from diploid Saccharomyces cerevisiae strains. DNA sequence analysis of these alleles and of eIF-2 beta suppressor alleles isolated from haploid strains, identified point mutations that altered one of six amino acids that map to a Cys-X2-Cys-X19-Cys-X2-Cys "zinc finger" motif and immediately adjacent residues. Five of the affected amino acids are identical in the human and yeast eIF-2 beta protein. Together with earlier studies (Donahue et al., 1988), these point mutations implicate the zinc finger domain of eIF-2 beta in start-site selection during the scanning process. We have supplemented the mutations obtained by genetic selection with an additional set of constructed mutations in this region. Our studies indicate that the cysteine residues and the intervening amino acids of this motif are essential for eIF-2 beta function in translation initiation in vivo. However, the effects observed in cells containing a copy of eIF-2 beta with a deletion of this motif suggest that this mutated form is still able to associate with other components of the initiation complex, imparting defects on translation initiation. Thus, this motif may be required only for later events that lead to initiator codon recognition. Alterations in defined positions, as found in our suppressor alleles, could lead to recognition of non-AUG codons.

Alleles↗
PubMed1989

The human lens epithelium; morphological and ultrastructural changes associated with steroid therapy.

A distinct disturbance to the structure of the lens epithelium was observed in cataract patients receiving steroid medication. Of those cataract patients receiving steroids, 83% exhibited a reticulated pattern of intercellular clefts compared to 5% in the control group. The reticulated pattern was shown to be due to the presence of gaps between the lateral borders of the epithelial cells by electron microscopy. A significant correlation between steroid therapy and epithelial disruption was demonstrated. The significance of such epithelial disruption to cataract formation is discussed.

Adrenal Cortex Hormones↗
PubMed1988

Human retinal extract stimulates the proliferation of human lens epithelial cells.

The proliferation of lens epithelial cells remaining attached to the capsule after extracapsular cataract extraction represents a potential cause of posterior capsule opacification. In view of the reported mitogenic effects of eye derived growth factors on lens epithelial cells in animal studies, we determined to establish whether the human retina produces a factor capable of inducing a similar response in human lens epithelial (HLE) cells. We report that an extract of the human neural retina is capable of increasing the proliferative capacity of HLE cells in culture by 50%. The possible mechanisms are discussed. The presence of such a growth factor in the human eye would have important consequences for the epithelial cells remaining after cataract surgery.

Cell Division↗
PubMed1988

The human anterior lens capsule--an attempted chemical debridement of epithelial cells by ethylenediaminetetracetic acid (EDTA) and trypsin.

The addition of edetic acid (EDTA) or trypsin to the infusion during a simulated extracapsular cataract extraction on cadaver eyes facilitates the removal of lens epithelial cells from the anterior capsule. Modification of the chemical composition of infusions used during extracapsular surgery may maximise lens epithelial cell removal and hence reduce the incidence of opacification of the posterior capsule after cataract extraction.

Cataract Extraction↗
PubMed1987

The human anterior lens capsule: cell density, morphology and mitotic index in normal and cataractous lenses.

The morphology, cell density and mitotic index of human lens epithelial cells were determined according to the region of the opacity as follows: (1) nuclear; (2) posterior subcapsular; (3) cortical; (4) nuclear and posterior subcapsular; (5) cortical and posterior subcapsular. Epithelial abnormalities, consisting of enlarged, polymorphous cells and intercellular clefts, were found in cataractous lenses involving posterior subcapsular and/or cortical opacities. In contrast to the normal pattern of cell density, the cell density of cataractous epithelia in these categories decreased from the central to the peripheral epithelium. This decrease in cell density was due to the presence of swollen cells and intercellular clefts. The central and pre-equatorial mitotic index of cataractous lens epithelia was not significantly different (range 0.002-0.008%) and no correlation was found between cataract type and mitotic index (no information was available for the equatorial region). The low mitotic index observed reflects the mature age range of cataractous lenses and in one normal lens epithelium from a 23-yr-old donor, a higher value of 0.015% was found. The relevance of these epithelial abnormalities to the normal function of the epithelium is discussed.

Adult↗
PubMed1987

The effects of steroids on the human lens epithelium.

A study of anterior capsules from cataractous lenses revealed that there are marked abnormalities in epithelial structure associated with cataract. In certain cases a distinctive reticulated pattern was observed in whole mounts of the anterior capsule and of these a higher number than expected were from patients receiving steroid medication. In tissue culture experiments it was found that the presence of steroids in the growth medium (10 microM prednisolone) adversely affected the growth of human lens epithelial cells. These observations are consistent with the hypothesis that steroid-induced cataracts are the result of effects on anterior lens epithelial cell function.

Adult↗
PubMed1987

Morphological changes in the human corneal epithelium associated with surgical corneal clouding.

Light microscopy and electron microscopy were used to define morphological changes occurring in human corneal epithelium during surgery. No correlation was established between preoperative medication or peroperative fluids and corneal epithelial clouding. It is suggested that the changes we observed in relation to epithelial clouding were the direct result of disturbance to endothelial pump functions.

Cell Nucleus↗
PubMed1987

Cytological factors relating to posterior capsule opacification following cataract surgery.

Simulated extracapsular cataract extractions on cadaver eyes were performed which demonstrated that the cells of the anterior capsule remain largely intact and that only a small amount of cortical lens matter remains postoperatively. Human lens epithelial cells from normal and cataractous lenses were grown in culture. There was no appreciable difference in growth rate between cells from normal and those from cataractous lenses or between equatorial and central capsule cells. The cells grew from the cut edges of the capsule, suggesting that release from contact inhibition is an important factor in stimulating proliferation. The daughter cells became increasingly abnormal and metaplastic in successive generations, but there was no evidence of differentiation into fibroblasts within the 35-day culture period, suggesting that a retinal growth factor may be involved with the fibrosis occurring in opacification of the posterior capsule. A small anterior capsulotomy will release fewer cells from contact inhibition and hence reduce cell proliferation after extracapsular cataract extraction.

Cataract↗
PubMed1986

Molecular cloning of partial cDNAs for rabbit liver apolipoprotein B and the regulation of its mRNA levels by dietary cholesterol.

Apolipoprotein B (apoB) is the major protein of plasma very low density lipoprotein (VLDL) and low density lipoprotein (LDL). Here we report the molecular cloning of cDNAs for rabbit liver apoB, by use of the expression vector lambda gt11, and the use of these cDNAs to study the regulation of apoB mRNA levels by dietary cholesterol. The beta-galactosidase-apoB fusion proteins expressed by recombinant clones were identified with guinea pig anti-rabbit LDL antibodies. The cloned cDNAs hybridized to an 18-kilobase mRNA that was present in liver and intestine. Slot blot analysis showed that this mRNA was not present in other tissues studied, with the possible exception of kidney. When rabbits are fed a high-cholesterol diet, they develop severe hypercholesterolemia. Most of the excess cholesterol is contained in beta-VLDL, a cholesteryl ester-rich lipoprotein that contains apoB and apoE. We addressed the question of whether increased apoB mRNA levels, and by inference increased apoB synthetic rates, are responsible for the accumulation of beta-VLDL. A comparison of apoB mRNA levels showed that cholesterol-fed rabbits had lower liver apoB mRNA levels than control rabbits. We suggest that the accumulation of plasma beta-VLDL in cholesterol-fed rabbits is not due to an increased production of beta-VLDL but solely due to a suppression of hepatic LDL receptors.

Animals↗
PubMed1986

Low vision aids--evaluation in a general eye department.

A review was undertaken of all patients referred for Low Vision Aid (LVA) assessment in the Wandsworth Health Authority over eighteen months. The majority of referrals (72 per cent) could have near visual acuity improved and were prescribed an LVA. Of those prescribed only 23 per cent found the LVA useful at home. Fifty-three per cent of patients preferred a high reading addition or hand magnifier to the prescribed LVA. The most helpful indications to predict success in using an LVA were found to be age of the patient, the type of eye disease and the strength of magnification required.

Age Factors↗
PubMed1985

Beta-very low density lipoproteins in cholesterol-fed rabbits are of hepatic origin.

When rabbits are fed a cholesterol-rich diet they accumulate beta-migrating very low density lipoprotein (beta-VLDL) in their plasma. beta-VLDL are cholesteryl ester-rich lipoproteins which contain apolipoproteins B and E. There are 2 forms of apolipoprotein B in beta-VLDL. About 90% of apolipoprotein B is present as a 320 000-dalton protein and the remainder is present as a 210 000-dalton protein. These apolipoproteins are tissue specific. Lipoproteins secreted by perfused rabbit livers contain only the 320 000-dalton apolipoprotein B while lipoproteins secreted by the intestine contain only the 210 000-dalton apolipoprotein B. The tissue specificity of apolipoprotein B shows that beta-VLDL is largely of hepatic origin and that only a small fraction is of intestinal origin. The composition of VLDL secreted from the livers of cholesterol-fed rabbits is similar to that of plasma beta-VLDL. Both are cholesteryl ester-rich, in contrast to plasma and perfusate VLDL from normal rabbits which are both triglyceride-rich. This indicates that the cholesteryl ester-rich hepatic VLDL is a direct precursor for plasma beta-VLDL.

Animals↗
PubMed1984

A comparison of the low-density-lipoprotein receptor from bovine adrenal cortex, rabbit and rat liver and adrenal glands by lipoprotein blotting.

This paper describes the use of lipoprotein blotting to detect low-density-lipoprotein (LDL) receptors in rat and rabbit liver and adrenal glands and in bovine adrenal glands. Using this technique we show that the rabbit and rat liver LDL receptors have Mr values of 128000 and 145000 respectively. Mr values for the rabbit, rat and bovine adrenal receptors are 131000, 142000 and 132000 respectively. Differences between the bovine adrenal and rat liver receptors are not due to differences in the degree of sialylation. Lipoprotein blotting can be used to detect dietary- and drug-induced changes in the concentrations of LDL receptors. When rabbits are fed on a cholesterol-rich diet, liver LDL receptors cannot be detected, consistent with the suppression of hepatic LDL receptors by cholesterol feeding. Pharmacological doses of 17 alpha-ethinyloestradiol cause a marked increase in hepatic LDL-receptor activity in the rat. This is accompanied by a corresponding increase in the number of LDL receptors detected by lipoprotein blotting. The Mr of the induced receptor is identical with that of the receptor from control rats, which suggests that the induced receptors are produced by the same gene as LDL receptors normally present in the liver.

Adrenal Cortex↗
PubMed1984

Tissue-specific expression of genes encoding apolipoprotein E and apolipoprotein A-I in rabbits.

We determined the site of synthesis of apolipoprotein (apo) E and apo-A-I in rabbit by measuring in vitro translational activity of their mRNAs from the liver and from the intestine. Poly(A+) RNA isolated from liver and intestinal epithelium of rabbits fed either a chow diet or a cholesterol-rich diet was translated in vitro in the rabbit reticulocyte lysate system using [35S] methionine as the labeled precursor. Newly synthesized apolipoproteins were immunoprecipitated with specific antisera and quantitated after electrophoresed on 10% polyacrylamide slab gels in the presence of 0.2% sodium dodecyl sulfate. The levels of liver apo-E and apo-A-I mRNAs from chow-fed rabbits are 0.41 and 0.002% of total translatable mRNA, respectively. The level of liver apo-A-I mRNA in the rabbit is approximately 500-fold lower than the reported level of apo-A-I mRNA in rat and human livers. Rabbit intestinal apo-E and apo-A-I mRNAs levels are 0.0036 and 0.67%, respectively. Our results indicate that in rabbits apo-E is synthesized primarily in the liver and that apo-A-I is synthesized primarily in the intestine. When rabbits are fed a cholesterol-rich diet, liver and intestinal apo-E in mRNA levels and intestinal apo-A-I mRNA levels are not changed. In contrast, the liver apo-A-I mRNA level increases 5-fold in response to the cholesterol-rich diet. However, because the intestinal liver apo-A-I mRNA level is so low, the 5-fold induction only increases liver mRNA levels to 2.7% of the corresponding intestinal apo-A-I mRNA level.

Animals↗