Search PubMed⌕ Search

Biomedical subjects

G Cooper

Publications and source records attributed to G Cooper.

At least 109 records · Page 6Linked to original sources
PubMed1995

Abdominal aortic aneurysm: a 12-year experience in the Grampian region, Scotland.

All the 638 new hospital cases of abdominal aortic aneurysm (AAA) diagnosed in the Grampian region of Scotland, over the 12-year period between January 1980 and December 1991, were studied. Information was obtained from the Scottish Morbidity Record Form 1 (SMR1). The number of AAA cases has risen from 19 in 1980 to 84 in 1991 totalling 638 cases in the 12-year study period. Of these, 29% were women, a percentage which remained fairly constant for each year of the study. The mean age of the study population was 73.8 years; higher in women (74.7 in intact and 76.6 in ruptured cases) than in men (71 in intact and 73.1 in ruptured cases). There was a significant increase in the percentage of patients over the age of 75 years (from 31.6% in 1980 to 41.7% in 1991) which was very marked in men (from 25% to 40%). This may indicate that ageing of the population is partly responsible for the apparent increased incidence of the disease. Ruptured AAA constituted 36.5% of all cases of which 76.4% were men. The rate of ruptured cases has dropped from 73.7% in 1980 to 32.1% in 1991 probably owing to operating on more elective cases. Analysis of hospital fatality, including unoperated cases, showed a fatality rate of 8.4% for intact cases as opposed to 46.3% for ruptured cases. Allowing for improved diagnostic techniques and clinical awareness of the disease, the figures suggest a true increase in the incidence of AAA in the Grampian region.

Aged↗
PubMed1995

Effect of intraluminal application of tissue-type plasminogen activator on the fibrinolytic activity of experimental vein grafts.

OBJECTIVE: The aim was to quantify the effect of intraluminally applied tissue-type plasminogen activator (tPA) on the fibrinolytic activity of experimental vein grafts and assess the effect of pretreatment of the vein on early platelet and thrombus formation using histological techniques. METHODS: A pig model of bilateral saphenous venin-carotid artery grafts was used. In each animal one side of the neck was grafted using vein distended to 230 mm Hg and pretreated with tPA (1 mg.ml-1) for a period of 15 min before grafting (treated graft). The perfused in situ for 2 h after implantation and before analysis. Changes in local fibrinolytic activity were quantified using fibrin plate techniques and specific chromogenic assays for tPA and urokinase (uPA) in tissue extract (n = 6 animals). Histological assessment was made using light and scanning microscopy (n = 4 animals). RESULTS: Surgical preparation and distention significantly reduced the fibrinolytic activity of pig saphenous vein in terms of areas of lysis produced on fibrin plates (P < 0.05), tPA activity (P < 0.05), and uPA activity (P < 0.05). Pretreatment of distended vein with tPA before grafting significantly enhanced its fibrinolytic activity after 2 h perfusion compared to control (untreated) grafts, as assessed by areas of lysis on fibrin plates (P < 0.05) and specific tPA activity (P < 0.05). Treated grafts also showed qualitatively less platelet and thrombus formation on histological examination. CONCLUSIONS: Pretreatment of surgically harvested vein by intraluminal application of tPA before grafting enhances its fibrinolytic activity after exposure to 2 h perfusion in vivo. This technique requires further investigation to validate its potential as a means of providing local anticoagulation to veins implanted as arterial grafts thereby reducing the incidence of early graft thrombosis.

Animals↗
PubMed1994

The photocatalytic production of organic-free water for molecular biological and pharmaceutical applications.

The inability of conventional water-purification systems to meet the ultra-high purity needs of molecular biology and biopharmaceuticals reliably was attributed to their almost exclusive utilization of phase-transfer technologies. Water quality may unpredictably degrade when confronted by microorganism blooms or altered feed water characteristics. Photocatalytic point-of-use water-purification systems fed by deionized water were demonstrated to meet the most stringent water-purity needs of the molecular biologist. The reliability of the photocatalytic water-purification technology was attributed to its ability to destroy organic contaminants rather than just effect their phase transfer. Photocatalytically produced water was shown to be free of detectable microorganisms, DNA, endotoxins and RNAses. It is suitable for immunological studies involving tissue and other cell cultures because of its lack of detectable endotoxins. Because DNA was also undetectable, it is suitable for DNA and endotoxin zero-standards as well as pharmaceutical formulation. The photocatalytic water is a reliable substitute for diethyl pyrocarbonate-treated water used in RNA work, compatible with PCR and sufficiently free from other contaminants to be useful for most biochemical and enzymatic assays.

Base Sequence↗
PubMed1994

Comparison of TechLab Clostridium difficile Tox-A enzyme immunoassay and Bartels Prima system toxin-A EIA.

We evaluated the Bartles Clostridium difficile toxin A test and the TechLab Tox-A test to detect C. difficile toxin A in stool. The results were compared with C. difficile cytotoxicity assays. Of the 463 specimens tested 82 (17.7%) tested positive by cytotoxicity assay. The sensitivity, specificity, and positive and negative predictive values of the TechLab EIA were 86.6%, 93.7%, 74.7%, and 97.0%, respectively. For the Bartels Prima EIA, sensitivity, specificity, and positive and negative predictive values were 95.1%, 95.5%, 82.1%, and 98.9%, respectively. The differences in sensitivity were statistically significant. Indeterminate results requiring repeat testing were more common with the TechLab EIA than with the Bartels Prima EIA. Of the two kits, the Bartels EIA is preferable, primarily because of its increased sensitivity.

Bacterial Toxins↗
PubMed1994

Monosaccharide and oligosaccharide analysis of isoelectric focusing-separated and blotted granulocyte colony-stimulating factor glycoforms using high-pH anion-exchange chromatography with pulsed amperometric detection.

In this study, a sensitive, straightforward technique is developed for the analysis of glycoprotein O-linked oligosaccharides. Specifically, O-linked oligosaccharides of granulocyte colony-stimulating factor (G-CSF) are analysed by separating charged glycoforms using isoelectric focusing, electroblotting to polyvinylidene difluoride, releasing monosaccharides and oligosaccharide alditols from the blotted glycoprotein bands, and producing chromatographs using high-pH anion-exchange chromatography with pulsed amperometric detection. Using this technique, the O-linked structures of G-CSF produced by recombinant Chinese hamster ovary (CHO) cells are deduced by comparison with monosaccharide and oligosaccharide standards. Lectin blotting and peptide sequencing support the identities of the presumed G-CSF glycoforms. The two major glycoforms determined using this methodology correspond to those determined previously for CHO-produced G-CSF using NMR. Additional glycoforms are also identified in this study, presumably resulting from the presence of N-glycolyneuraminic acid in place of N-acetylneuraminic acid. The utility of this analytical approach is then demonstrated in an analysis of the effect of the extracellular environment on the O-linked glycosylation of G-CSF by recombinant CHO cells. Increasing the level of ammonium ion in the culture medium is shown to reduce the percentage of G-CSF produced with sialic acid linked alpha (2,6) to N-acetylgalactosamine.

Amino Acid Sequence↗
PubMed1994

Native beta-adrenergic support for left ventricular dysfunction in experimental mitral regurgitation normalizes indexes of pump and contractile function.

BACKGROUND: It is generally accepted that the adrenergic nervous system provides inotropic support for the failing heart. However, the magnitude of this support has never been studied extensively. The present study was performed to test the hypothesis that the adrenergic nervous system is capable of maintaining indexes of pump and contractile function in the normal range despite significant innate myocardial depression. METHODS AND RESULTS: We used our model of experimental canine mitral regurgitation, which produces left ventricular dysfunction after 3 months of volume overload. We studied indexes of contractile function on and off beta-blockade at baseline and again on and off beta-blockade 3 months after chronic mitral regurgitation had induced significant contractile dysfunction. At baseline, acute beta-blockade caused insignificant reductions in the mass-corrected slope of the end-ejection stress-volume relation (EESVR), the end-systolic stiffness constant, and the ejection fraction-end-systolic stress and the mean velocity of circumferential fiber shortening (VCF)-end-systolic stress relations. After 3 months of chronic mitral regurgitation, all indexes of contractile function were normal in the unblocked state except for the VCF-stress relation, which was mildly reduced. However, after acute beta-blockade after 3 months of chronic mitral regurgitation, the EESVR fell to 303 +/- 27 versus 443 +/- 24 during acute beta-blockade before mitral regurgitation was created (P < .05), and the end-systolic stiffness constant was reduced to 2.54 +/- 0.15 versus 3.27 +/- 0.11 (P < .05). Only after beta-blockade was the ejection fraction-stress relation significantly reduced for dogs with chronic mitral regurgitation. The VCF-stress relation became markedly more abnormal. The viscosity-velocity relation of myocytes isolated from the ventricles of the dogs with mitral regurgitation confirmed that substantial innate contractile depression was present. CONCLUSIONS: After 3 months of chronic mitral regurgitation, the adrenergic nervous system was able to maintain most indexes of contractile function in the normal range despite significant depression in innate contractile function. Thus, in the absence of beta-blockade, significant innate contractile depression may be obscured by adrenergic support.

Animals↗
PubMed1994

Role of microtubules in contractile dysfunction of hypertrophied cardiocytes.

Cardiac hypertrophy in response to systolic pressure overloading frequently results in contractile dysfunction, the cause for which has been unknown. Since, in contrast, the same degree and duration of hypertrophy in response to systolic volume overloading does not result in contractile dysfunction, we postulated that the contractile dysfunction of pressure hypertrophied myocardium might result from a direct effect of stress as opposed to strain loading on an intracellular structure of the hypertrophied cardiocyte. The specific hypothesis tested here is that the microtubule component of the cytoskeleton is such an intracellular structure, which, forming in excess, impedes sarcomere motion. The feline right ventricle was either pressure overloaded by pulmonary artery banding or volume overloaded by atrial septotomy. The quantity of microtubules was estimated from immunoblots and immunofluorescent micrographs, and their mechanical effects were assessed by measuring sarcomere motion during microtubule depolymerization. We show here that stress loading increases the microtubule component of the cardiac muscle cell cytoskeleton; this apparently is responsible for the entirety of the cellular contractile dysfunction seen in our model of pressure-hypertrophied myocardium. No such effects were seen in right ventricular cardiocytes from normal or volume-overloaded cats or in left ventricular cardiocytes from any group of cats. Importantly, the linked microtubule and contractile abnormalities are persistent and thus may be found to have significance for the deterioration of initially compensatory cardiac hypertrophy into the congestive heart failure state.

Animals↗
PubMed1994

Acute changes in myosin heavy chain synthesis rate in pressure versus volume overload.

The left ventricular hypertrophy that develops with the volume overload of mitral regurgitation is relatively less than that which develops with the pressure overload of aortic stenosis even when both lesions are severe. The hypertrophy that develops must be the sum of changes in the rate of myocardial protein synthesis and degradation. In the present canine study, we explored early changes in the synthesis rate of myosin heavy chain in response to severe acute pressure overload versus that of the severe acute volume overload of mitral regurgitation. We tested the hypothesis that in acute overload, the rate of protein synthesis would increase less in the volume-overload model than in the pressure-overload model, a potential partial mechanism for the discrepancy in the eventual total amount of hypertrophy that develops in these two lesions. Acute pressure overload was produced by inflating a balloon in the descending aorta, and acute volume overload was produced by using our closed-chest mitral chordal rupture technique. In both models, the hemodynamic lesion that was created was severe. In eight dogs with pressure overload, the average gradient across the balloon was 119.8 +/- 6.1 mm Hg. In six dogs with volume overload, the average regurgitant fraction was 0.67 +/- 0.06. Six other dogs served as controls. The average rate of myosin heavy chain synthesis in control dogs was 2.7 +/- 0.2% per day, virtually identical to the rate we found in the severe volume-overload model. In contrast, the rate was increased in the pressure-overload model by 30% to 3.5 +/- 0.3% per day (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1994

Effects of chronic beta-adrenergic blockade on the left ventricular and cardiocyte abnormalities of chronic canine mitral regurgitation.

The mechanism by which beta blockade improves left ventricular dysfunction in various cardiomyopathies has been ascribed to improved contractile function of the myocardium or to improved beta-adrenergic responsiveness. In this study we tested two hypotheses: (a) that chronic beta blockade would improve the left ventricular dysfunction which develops in mitral regurgitation, and (b) that an important mechanism of this effect would be improved innate contractile function of the myocardium. Two groups of six dogs with chronic severe mitral regurgitation were studied. After 3 mo both groups had developed similar and significant left ventricular dysfunction. One group was then gradually beta-blocked while the second group continued to be observed without further intervention. In the group that remained unblocked, contractile function remained depressed. However, in the group that received chronic beta blockade, contractile function improved substantially. The contractility of cardiocytes isolated from the unblocked hearts and then studied in the absence of beta receptor stimulation was extremely depressed. However, contractility of cardiocytes isolated from the beta-blocked ventricles was virtually normal. Consistent with these data, myofibrillar density was much higher, 55 +/- 4% in the beta-blocked group vs. 39 +/- 2% (P < 0.01) in the unblocked group; thus, there were more contractile elements to generate force in the beta-blocked group. We conclude that chronic beta blockade improves left ventricular function in chronic experimental mitral regurgitation. This improvement was associated with an improvement in the innate contractile function of isolated cardiocytes, which in turn is associated with an increase in the number of contractile elements.

Adrenergic beta-Antagonists↗
PubMed1994

The effects of complete versus incomplete mitral valve repair in experimental mitral regurgitation.

Severe mitral regurgitation (regurgitant fraction 0.75 +/- 0.02) was created in eight dogs by our closed-chest chordal rupture technique. After 3 months of chronic mitral regurgitation all indices of contractile function were depressed. Mitral valve repair was then attempted. Postoperative regurgitant fraction was reduced compared with the preoperative value in all eight dogs. Concomitantly, forward cardiac output increased in all dogs and pulmonary capillary wedge pressure fell in all dogs. However, in some dogs, significant regurgitation persisted despite repair. Postoperative regurgitant fraction ranged from 0% to 60%. Postoperative residual regurgitant fraction was related significantly to postoperative cardiac output (r = 0.99), pulmonary capillary wedge pressure (r = 0.77), ejection fraction (r = 0.75), and two indices of contractile function--the mass-corrected end-systolic stress volume relationship (r = 0.87) and end-systolic stiffness (r = 0.93). In general, these parameters returned to their normal values before mitral regurgitation when postoperative regurgitant fraction was less than 30%. Myocytes isolated from the ventricles at the end of study also demonstrated normal contractile function when regurgitant fraction was less than 30%.

Animals↗
PubMed1993

Cytoskeletal role in the contractile dysfunction of hypertrophied myocardium.

Cardiac hypertrophy in response to systolic pressure loading frequently results in contractile dysfunction of unknown cause. In the present study, pressure loading increased the microtubule component of the cardiac muscle cell cytoskeleton, which was responsible for the cellular contractile dysfunction observed. The linked microtubule and contractile abnormalities were persistent and thus may have significance for the deterioration of initially compensatory cardiac hypertrophy into congestive heart failure.

Actin Cytoskeleton↗
PubMed1993

The Saccharomyces cerevisiae SDC25 C-domain gene product overcomes the dominant inhibitory activity of Ha-Ras Asn-17.

The carboxy-terminal part of the Saccharomyces cerevisiae SDC25 gene product (SDC25 C domain) can elicit activation of mammalian Ras proteins. Specifically, SDC25 C domain functions as an exchange factor for cellular Ras proteins in CHO cells. In this study, we used the dominant inhibitory Ha-Ras Asn-17 mutant and SDC25 C domain to further investigate the interaction between cellular Ras proteins and their putative endogenous guanine nucleotide-releasing factors. Transcription from the polyomavirus thymidine kinase gene (Py tk) promoter is strongly inhibited by the expression of Ha-Ras Asn-17 in NIH 3T3 cells. Coexpression of SDC25 C domain overcomes the negative effect of the Ras mutant on the Py tk promoter. On the other hand, transactivation of the Ras-responsive element of the Py tk promoter induced by SDC25 C domain is lost upon coexpression of increasing amounts of Ha-Ras Asn-17. In addition, coexpression of SDC25 C domain overcomes the inhibition of proliferation of NIH 3T3 cells caused by Ha-Ras Asn-17. These results are consistent with the idea that the Ha-Ras Asn-17 mutant functions by titrating an upstream activator of cellular Ras proteins.

3T3 Cells↗
PubMed1993

Cardiocyte contractile performance in experimental biventricular volume-overload hypertrophy.

Previous studies have shown that the right ventricle (RV) appears to tolerate volume overloading better than does the left ventricle (LV). To determine whether this dichotomous response is due to intrinsic differences in the contractile performance of volume hypertrophied RV vs. LV cardiac muscle cells, or cardiocytes, we characterized the contractile performance of cardiocytes isolated from an experimental feline model of biventricular volume overload (n = 7 cats), wherein a peripheral arteriovenous fistula (AVF) produced an identical duration and degree of volume overload for both ventricles; sham-operated cats served as the appropriate controls (n = 7). Cardiocyte contractile function was defined by laser diffraction measurement of sarcomere motion. For the AVF cats, there was a 2.4-fold increase in cardiac output, a significant increase in the RV and LV weight-to-body weight ratios, and a significant increase in cell surface area for the RV and LV cardiocytes. Despite this, cardiocyte contractile function in the AVF cats was entirely normal. Thus there was no significant difference between RV and LV cardiocytes from control cats in the extent or velocity of sarcomere shortening either in 1 cP superfusate or in higher viscosity superfusates, and comparison of RV and LV cells from the AVF cats to those from sham-operated cats again revealed no significant differences. Furthermore, cardiocyte relengthening properties showed no significant differences between AVF and control groups. In summary, this study shows that contractile dysfunction is not an inherent property of either RV or LV cardiac muscle cells hypertrophying in response to substantial volume overloading when preload is increased but afterload is normal.

Animals↗
PubMed1993

Electrically stimulated contraction accelerates protein synthesis rates in adult feline cardiocytes.

Cardiocytes were induced to contract via electrical field stimulation with an 8 V/cm electrical square-wave pulse of 5 ms at 0.125-2.0 Hz for up to 6 h. Protein synthesis rates were measured as rate of incorporation of [3H]-phenylalanine into total cell protein. Rates of protein synthesis were accelerated 43 +/- 4%, P < 0.001, by 4 h. The acceleration of total protein synthesis showed a frequency dependence between 0.125 and 0.5 Hz. In addition to accelerating rates of total protein synthesis, electrical stimulation of contraction accelerated fractional rates of synthesis of myosin heavy chain by 42 +/- 8%, P < 0.05. Protein synthesis rates were not accelerated upon electrical stimulation using subthreshold voltages. Addition of 100 ng/ml of actinomycin D had no effect on the ability of electrical stimulation of contraction to accelerate protein synthesis. To uncouple excitation-contraction coupling, 2,3-butanedione monoxime (BDM) was used to block actin-myosin cross-bridge interactions. BDM significantly decreased the ability of electrical stimulation to accelerate protein synthesis rates.

Animals↗
PubMed1993

Rapid expression of the Na(+)-Ca2+ exchanger in response to cardiac pressure overload.

This report identifies a rapid increase in the expression of cardiac Na(+)-Ca2+ exchanger mRNA in response to an acute pressure overload. This enhanced exchanger expression appeared within 1 h after the onset of right ventricular pressure overload in the cat and was sustained during cardiac overloading for at least 4 h. Maintenance of this right ventricular pressure overload for 48 h evoked an increase in the production of exchanger protein. Because of our previous finding that load imposition on the heart initiates cell growth and our hypothesis that this is in response to the enhanced entry of cellular cations, we then examined the effect of Na+ influx into cultured adult cardiac myocytes, or cardiocytes, in terms of early anabolic responses. Pressure overload of the heart and cardiocyte Na+ influx were found to produce a common, rapid result in terms of both enhanced Na(+)-Ca2+ exchanger expression and accelerated synthesis of general and contractile proteins, the hallmarks of cardiac hypertrophy.

Animals↗
PubMed1993

Effects of chronic mitral regurgitation on diastolic function in isolated cardiocytes.

We have previously shown that chronic mitral regurgitation (MR) increases the rate of left ventricular early diastolic filling. These changes in chamber diastolic function were felt to be secondary to alterations in left ventricular loading conditions. Therefore, cellular diastolic function measured in cardiac muscle cells (cardiocytes) isolated from animals with chronic MR (absent alterations in loading conditions) was expected to be normal. However, chronic MR caused a decrease in sarcomere lengthening rate. The purpose of the current study was to define the mechanisms causing this decreased sarcomere lengthening rate in chronic MR cardiocytes and to explain the apparent dichotomy between chamber and cellular diastolic properties. Accordingly, sarcomere motion was measured using laser diffraction techniques in enzymatically isolated cardiocytes from seven control dogs and 11 dogs with chronic MR (produced by closed-chest transection of the mitral chordae). In the MR cardiocytes, there were abnormalities in cellular systolic function (decreased extent and velocity of shortening) and in cellular diastolic function (decreased velocity of sarcomere lengthening). Because studies in papillary muscles have shown that there is a direct relation between abnormal diastolic function (decreased velocity of muscle lengthening) and abnormal systolic function (decreased extent of muscle shortening), it was unclear whether the changes in cellular relaxation rate observed in chronic MR merely reflected a concomitant decrease in the extent of shortening or instead reflected an impairment in intrinsic relaxation properties. To make this distinction, the relation between relaxation velocity (measured as peak sarcomere lengthening rate) and sarcomere shortening extent was examined in MR cardiocytes and compared with that in control cardiocytes. There was a direct relation between sarcomere relaxation velocity and sarcomere shortening extent in both control and MR cardiocytes. Over a wide range of shortening extent, the slopes and y intercepts of this relation were similar in control and MR cardiocytes (slope, 27.7 sec-1 in control cells versus 28.1 sec-1 in MR cells; y intercept, -1.1 microns/sec in control cells versus -1.7 microns/sec in MR cells; p = NS). At any common shortening extent, relaxation velocity was the same in control and MR cardiocytes. To prove that this relation could detect abnormalities in the intrinsic myocardial relaxation process, interventions known to produce primary alterations in the intrinsic myocardial relaxation process were examined: the effects of hypothermia (30 degrees C) and isoproterenol (10(-6) M) on the relaxation velocity-shortening extent relation were studied in normal and MR cardiocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗