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Biomedical subjects

M J Lewis

Publications and source records attributed to M J Lewis.

At least 109 records · Page 6Linked to original sources
PubMed1997

Redistribution of von Willebrand factor in porcine carotid arteries after balloon angioplasty.

von Willebrand factor (VWF) is a well-characterized multimeric glycoprotein present in platelets and plasma and synthesized by vascular endothelial cells and megakaryocytes. Its role in platelet-vessel wall interactions has been studied extensively, but its involvement in intravascular events after balloon angioplasty has not been clarified. VWF antigen is not present in porcine arterial endothelium (except for the pulmonary artery) but is readily detected in porcine venous endothelial cells. We have examined the localization of VWF in porcine vessel walls during neointima formation after bilateral carotid balloon-angioplasty. Endothelium was denuded by balloon injury but regenerated by 7 days and was fully confluent by 42 days. VWF was detected at the site of injury in localized, adherent platelet aggregates at 10 minutes after angioplasty that were not present at later time points. A well-demarcated homogeneous layer of VWF was observed on the luminal surface from 30 minutes to day 7, but there was a progressive shift of positive staining from the lumen to the outer media from days 1 to 7. VWF was also strongly detected at sites proximal and distal to the balloon injury from 30 minutes to day 7, although endothelial disruption was minimal and the monolayer remained substantially intact at these sites. Regrowing endothelial cells appeared to contain granular VWF from days 12 to 21, but this was not readily evident at later time points. The results suggest that balloon injury is associated with deposition and medial absorption of plasma or platelet VWF in this porcine model over a time period that precedes and overlaps vascular smooth muscle proliferation and endothelial recoverage. The findings provide evidence to support the concept of a wider role for VWF in tissue injury responses.

Angioplasty, Balloon↗
PubMed1997

Effects of sulphydryl- and non-sulphydryl-containing ACE inhibitors on left ventricular relaxation in the isolated guinea pig heart.

ACE inhibitors exert both acute and chronic beneficial effects on cardiac function (e.g remodelling, diastolic dysfunction). We have previously reported that the ACE inhibitor captopril induces selective left ventricular (LV) relaxant effects in the isolated ejecting guinea pig heart. The aim of the present study was to further investigate the mechanism of the captopril-induced changes in early LV relaxation by comparing the effects of two sulphydryl and two non-sulphydryl containing ACE inhibitors in the same experimental preparation. Isolated ejecting guinea pig hearts were studied under conditions of constant loading and heart rate. LV pressure was monitored by a 2F micromanometer-tipped catheter transducer inserted in the LV cavity. The sulphydryl-containing ACE inhibitors captopril and zofenaprilat enhanced early LV relaxation, whereas the non-sulphydryl-containing ACE inhibitors lisinopril and quinaprilat did not. The effects of captopril and zofenaprilat were attenuated both by the nitric oxide-scavenger haemoglobin and the bradykinin B2-kinin receptor antagonist HOE 140. Neither the oxygen free-radical scavenger superoxide dismutase nor the sulphydryl-containing compound N-acetyl cysteine administered together with lisinopril had any effect on LV relaxation. These data demonstrate that inhibition of intra-cardiac ACE activity may acutely modulate LV relaxation through increased activity of the bradykinin-nitric oxide pathway. The presence of a sulphydryl group on the relevant ACE inhibitor appears to be essential for this LV relaxant effect.

Acetylcysteine↗
PubMed1996

SNARE-mediated retrograde traffic from the Golgi complex to the endoplasmic reticulum.

Operation of the secretory pathway in eukaryotic cells requires the selective docking and fusion of transport vesicles with the appropriate target organelle. This is mediated in part by integral membrane proteins termed v-SNAREs (on vesicles) and t-SNAREs (on the target membranes). We describe a novel yeast t-SNARE that resides on the endoplasmic reticulum and mediates retrograde traffic from the Golgi complex. Mutation of this protein prevents both the HDEL receptor and a membrane protein bearing a dibasic retrieval signal from recycling to the endoplasmic reticulum. Forward traffic is also blocked, but only indirectly. Comparison with other yeast mutants indicates that Sec21p (gamma-COP) and Sec20p (an endoplasmic reticulum membrane protein) are also involved primarily, if not exclusively, in retrograde transport.

Biological Transport↗
PubMed1996

Feed-back regulation of gibberellin biosynthesis and gene expression in Pisum sativum L.

Treatment of tall and dwarf (3 beta-hydroxylase impaired) genotypes of pea (Pisum sativum L.) with the synthetic, highly active gibberellin (GA), 2,2-dimethyl GA4, reduced the shoot contents of C19-GAs, including GA1, and increased the concentration of the C20-GA, GA19. In shoots of the slender (la crys) mutant, the content of C19-GAs was lower and GA19 content was higher than in those of the tall line. Metabolism of GA19 and GA20 in leaves of a severe (na) GA-deficient dwarf mutant was reduced by GA treatment. The results suggest feed-back regulation of the 20-oxidation and 3 beta-hydroxylation reactions. Feed-back regulation of GA 20-oxidation was studied further using a cloned GA 20-oxidase cDNA from pea. The cDNA, Ps074, was isolated using polymerase chain reaction with degenerate oligonucleotide primers based on pumpkin and Arabidopsis 20-oxidase sequences. After expression of this cDNA clone in Escherichia coli, the product oxidized GA12 to GA15, GA24 and the C19-GA, GA9, which was the major product. The 13-hydroxylated substrate GA53 was similarly oxidized, but less effectively than GA12, giving mainly GA44 with low yields of GA19 and GA20. Ps074 hybridized to polyadenylated RNA from expanding shoots of pea. Amounts of this transcript were less in the slender genotype than in the tall line and were reduced in GA-deficient genotypes by treatment with GA3, suggesting that there is feed-back regulation of GA 20-oxidase gene expression.

Amino Acid Sequence↗
PubMed1996

Identification of three C20-gibberellins: GA97 (2 beta-hydroxy-GA53), GA98 (2 beta-hydroxy-GA44) and GA99 (2 beta-hydroxy-GA19).

Three new C20-gibberellins, GA97 (2 beta-hydroxy-GA53), GA98 (2 beta-hydroxy-GA44) and GA99 (2 beta-hydroxy-GA19), have all been isolated from spinach, GA97 also from tomato root cultures and pea pods, and GA98 from maize pollen. The structures of these compounds were established by GC-mass spectrometric comparisons of the trimethylsilylated methyl esters with authentic samples prepared from gibberellic acid (GA3).

Gibberellins↗
PubMed1996

Alcohol reinforcement and neuropharmacological therapeutics.

The pleasant subjective effects produced by alcohol undoubtedly reinforce drinking behaviour. Alcohol positively reinforces or rewards drinking by producing a mild euphoria. Alcohol also has anxiolytic effects that negatively reinforce drinking. The reinforcing effects of alcohol are mediated by several neurochemical systems, with dopamine and serotonin playing major roles in reward and the gamma-aminobutyric acid-benzodiazepine receptor system playing a major role in negative reinforcement. Research from our laboratory suggests that the behavioural effects of alcohol change when blood alcohol levels are changing and that these changes correspond to alterations of specific neurochemical systems. Behavioural activation and reward effects appear to occur as blood alcohol concentrations (BACs) increase. Depressive and aversive effects of alcohol occur during the period when BACs decrease. The observed correlation between behavioural and neuropharmacological changes and alcohol consumption suggest that alcohol produces a unique cascade over time that may provide clues to its long-sought specific mechanisms of action. In alcohol-dependent individuals, chronic exposure to alcohol may alter the function and communication between the liver, brain and other vital organ systems involved in hunger and the maintenance of nutrition. Under such conditions, the importance of alcohol in the diet may be enhanced such that hunger signals in the alcohol-dependent individual motivate the consumption of alcohol. Therefore, hunger for alcohol may provide an additional source of reinforcement. Endogenous opioid mechanisms may be important in this form of alcohol reinforcement.

Alcohol Deterrents↗
PubMed1996

Alcohol reinforcement and neuropharmacological therapeutics.

The pleasant subjective effects produced by alcohol undoubtedly reinforce drinking behaviour. Alcohol positively reinforces or rewards drinking by producing a mild euphoria. Alcohol also has anxiolytic effects that negatively reinforce drinking. The reinforcing effects of alcohol are mediated by several neurochemical systems, with dopamine and serotonin playing major roles in reward and the gamma-aminobutyric acid-benzodiazepine receptor system playing a major role in negative reinforcement. Research from our laboratory suggests that the behavioural effects of alcohol change when blood alcohol levels are changing and that these changes correspond to alterations of specific neurochemical systems. Behavioural activation and reward effects appear to occur as blood alcohol concentrations (BACs) increase. Depressive and aversive effects of alcohol occur during the period when BACs decrease. The observed correlation between behavioural and neuropharmacological changes and alcohol consumption suggest that alcohol produces a unique cascade over time that may provide clues to its long-sought specific mechanisms of action. In alcohol-dependent individuals, chronic exposure to alcohol may alter the function and communication between the liver, brain and other vital organ systems involved in hunger and the maintenance of nutrition. Under such conditions, the importance of alcohol in the diet may be enhanced such that hunger signals in the alcohol-dependent individual motivate the consumption of alcohol. Therefore, hunger for alcohol may provide an additional source of reinforcement. Endogenous opioid mechanisms may be important in this form of alcohol reinforcement.

Alcohol Drinking↗
PubMed1995

Endothelial control of arterial distensibility is impaired in chronic heart failure.

BACKGROUND: Vascular tone is a determinant of conduit artery distensibility. The aim of this study was to establish whether endothelium-derived relaxing factor (EDRF) influences the distensibility of conduit arteries and whether endothelium-mediated increases in distensibility are impaired in chronic heart failure (CHF). METHODS AND RESULTS: Conduit artery distensibility was measured by two methods in healthy subjects and in nine patients with CHF caused by dilated cardiomyopathy. In the first method, pulse-wave velocity (PWV) was measured in the right common iliac artery at rest and during local infusions of acetylcholine (10(-7) to 10(-5) mol/L) or adenosine (2 x 10(-7) to 2 x 10(-5) mol/L), with correction for systemic effects. Acetylcholine induced concentration-dependent local reductions of PWV in healthy subjects (-5%, -15%, and -26%) but not in CHF patients (3%, 1%, -4%, P < .01), whereas adenosine induced similar reductions of PWV in healthy subjects and CHF patients. In the second method, brachial artery diameter, blood flow, and blood pressure were measured noninvasively by high-resolution ultrasound, continuous-wave Doppler, and photoplethysmography during reactive hyperemia in the hand and after sublingual glyceryl trinitrate (GTN, 400 micrograms). Hyperemic flow, similar in healthy subjects and CHF patients, was associated with increases in diameter and distensibility in healthy subjects (8.8% and 18.4%, respectively) but not in CHF patients (0.3% and -4.5%), whereas GTN induced similar effects in healthy subjects and CHF patients. CONCLUSIONS: These data indicate that conduit artery distensibility is increased by acetylcholine and increased blood flow in healthy subjects but not in CHF patients, whereas the effects of adenosine and GTN on distensibility are preserved in CHF patients. This implies that EDRF-mediated increases in distensibility are impaired in CHF patients, thus adding to cardiac work.

Acetylcholine↗
PubMed1995

Enhancement of left ventricular relaxation in the isolated heart by an angiotensin-converting enzyme inhibitor.

BACKGROUND: ACE inhibitors exert both acute and chronic beneficial effects on cardiac function (eg, remodeling, diastolic dysfunction) in experimental studies and in patients. They inhibit the formation of angiotensin II as well as the degradation of endogenous bradykinin. We recently reported that bradykinin induces selective left ventricular (LV) relaxant effects in isolated hearts via the release of nitric oxide. The present study examined the direct effects of interaction between the ACE inhibitor captopril and endogenous bradykinin on cardiac contractile function. METHODS AND RESULTS: Isolated ejecting guinea pig hearts were studied under conditions of constant loading and heart rate. LV pressure was monitored by a 2F micromanometer-tipped catheter. Captopril (1 mumol/L, n = 9) caused a progressive acceleration of LV relaxation without significantly affecting early systolic parameters (eg, LV dP/dtmax) or coronary flow. These effects were inhibited by the nitric oxide scavenger hemoglobin (1 mumol/L, n = 5) or by the B2-kinin receptor antagonist HOE140 (10 nmol/L, n = 5). In the presence of captopril, bradykinin (0.1 nmol/L, n = 6) markedly accelerated LV relaxation (significantly more than captopril alone), whereas bradykinin alone (0.1 nmol/L, n = 6) had no effect. CONCLUSIONS: These data indicate that the ACE inhibitor captopril causes an acute and selective enhancement of LV relaxation independent of changes in coronary flow, probably via an endogenous bradykinin/nitric oxide pathway.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

A SNARE-like protein required for traffic through the Golgi complex.

The secretory pathway of eukaryotic cells comprises several distinct membrane-bound compartments which are interconnected by transport vesicles that pinch off from one membrane and fuse with the next. Targeting of these vesicles is mediated in part by interactions between integral membrane proteins on the vesicles and target organelles (soluble NSF attachment protein receptors (SNAREs)), termed v-SNAREs and t-SNAREs, respectively. SNAREs required for endoplasmic reticulum (ER)-Golgi transport and for fusion of vesicles with the plasma membrane are already known. Here we identify two yeast membrane proteins that show genetic interactions with Sed5p, which is the t-SNARE for ER-Golgi traffic. One of these membrane proteins, Sft1p, is structurally similar to the known v-SNAREs and is required for transport from an early to a later Golgi compartment. Our results indicate that a single t-SNARE can control more than one transport step, and provide the first candidate for a SNARE involved in intra-Golgi traffic.

Amino Acid Sequence↗
PubMed1995

Kinetics of smooth muscle cell proliferation and intimal thickening in a pig carotid model of balloon injury.

Restenosis as a result of neointimal smooth muscle cell accumulation is an important limitation to the effectiveness of balloon angioplasty as a treatment for end-stage atherosclerosis. Quantitative animal models allow the definition of pathophysiological mechanisms and the evaluation of new therapeutic strategies. In this study we quantified the time course of neointima formation by morphometry, and smooth muscle cell (SMC) proliferation by immunocytochemistry for proliferating cell nuclear antigen (PCNA), in the pig carotid artery 0-28 days following balloon injury. This led to two distinct kinds of injury observed also in clinical studies, namely medial dilatation or deep medial tearing with rupture of the internal elastic lamina. Dilatation injury alone led to medial enlargement and neointima formation by 7 days, which did not increase further up to 28 days. Medial enlargement was similar following rupture of the internal elastic lamina; however the sum of neointima formation plus the area of medial repair ('neomedia') increased progressively up to 21 days after balloon injury. Balloon injury increased the PCNA index of smooth muscle cells in the media underlying an intact internal elastic lamina maximally after 3 days. The PCNA index in the neointima and especially in the neomedia was greater and maximal after 7 days. Endothelial regrowth occurred by 21 days in the presence or absence of medial tears. Our results establish a quantitative pig model of balloon injury which will allow the assessment of new therapeutic strategies directed at two clinically relevant types of injury. Medial tearing is associated with an enhanced and localized proliferative response and may therefore be especially important in human restenosis.

Angioplasty, Balloon↗
PubMed1995

The influence of endothelium-derived nitric oxide on myocardial contractile function.

Nitric oxide released by cardiac endothelial cells modulates myocardial contractile function through elevation of intracellular 3',5'-cyclic guanosine monophosphate (cGMP). In the absence of agonist stimulation, nitric oxide typically enhances myocardial relaxation and reduces diastolic tone, without significantly altering the rate of force or pressure development. This pattern of effect is observed with nitric oxide or with cGMP analogues in isolated rat cardiac myocytes, isolated ferret papillary muscle preparations, and isolated ejecting guinea-pig hearts. In human subjects studied at cardiac catheterisation, low-dose bicoronary infusions of sodium nitroprusside or of substance P induce similar effects on left ventricular systolic and diastolic function. These changes may benefit from cardiac filling and coronary perfusion by increasing the diastolic interval, reducing extravascular compressive forces and increasing the driving pressure for filling, e.g., during exercise. Nitric oxide may also modulate inotropic and chronotropic responses to beta-adrenergic stimulation. Under pathological conditions, overproduction of nitric oxide by an inducible nitric oxide synthase may be detrimental for contractile function. Dysfunction of the constitutive nitric oxide pathway could also contribute to pathophysiology, e.g., in conditions characterised by diastolic dysfunction. The paracrine nitric oxide pathway is likely to be an important regulator of cardiac contractile function, acting in concert and interacting with other regulatory pathways.

Animals↗
PubMed1995

Power spectral analysis of the foetal magnetocardiogram.

The results of power spectral analysis of foetal magnetocardiographic (FMCG) data, acquired using a DC-SQUID-based system, are reported. Similar analyses have been previously reported using foetal electrocardiographic data, but it is believed that our work represents one of the first attempts to analyse, in the frequency domain, the magnetic fields produced by foetal cardiac activity. Analysis of the data in this way may enable the integrity of the foetal nervous system, and thus the status of the foetus as a whole, to be monitored and evaluated during a significant part of the antenatal period. The results obtained are discussed with reference to the probable underlying physiological mechanisms. This preliminary study highlights some of the advantages of FMCG as a novel, non-invasive technique for obtaining clinically useful information. Fourier analysis of the FMCG data is likely to yield new information, not only about cardiac function but also about the foetal central nervous system.

Algorithms↗
PubMed1995

Observations on the effect of raw milk quality on the keeping quality of pasteurized milk.

Raw milk was stored for up to 14 d at 4 degrees C and pasteurized on days 1, 3, 4, 7, 9 and 14. Precautions were taken to eliminate post-pasteurization contamination. The pasteurized milks were stored at 4 degrees C and analysed at weekly intervals for standard plate counts (SPC), psychotrophic counts (PC) and aerobic spore counts (ASC). The initial raw milk quality was very good and the keeping quality of all the pasteurized milks tested was greater than 22 d. In some cases the milk still had acceptable SPC after 42 d storage, which shows the keeping quality that can be achieved when the process is well controlled. However, the best keeping quality resulted from milk pasteurized on the third and fourth days. Even milk pasteurized on the seventh and ninth had superior keeping quality to that pasteurized on the first day. The lactoperoxidase anti-microbial system in raw milk may be most active around days 3 and 4.

Animals↗
PubMed1995

Endothelial inhibition of myofilament calcium response in intact cardiac myocytes.

Recent studies suggest that factors released by endothelial cells can modify contraction of isolated cardiac preparations. We compared the effects of 1) coronary effluent collected from Langendorff-perfused rat hearts and 2) cultured vascular endothelial cell superfusate on isolated fura 2-loaded rat ventricular cardiac myocytes. Coronary and cultured cell effluent produced similar effects. Isotonic contraction amplitude was reduced by 31.6 +/- 2.6 and 70.2 +/- 9.1%, respectively; myocyte diastolic length increased by 0.8 +/- 0.2 and 1.5 +/- 0.4 microns, and time to 50% relaxation fell by 6.2 +/- 1.8 and 10.1 +/- 2.0% (all P < 0.05; n = 29 and 15 myocytes, respectively). A small fall in the amplitude of the intracellular Ca2+ transient was observed (8.5 +/- 1.5 and 10.9 +/- 3.5%, respectively; both P < 0.01), insufficient to account for the reduction in twitch amplitude. In intact myocytes tetanized in the presence of thapsigargin, the steady-state myofilament response to Ca2+ was reduced by coronary and cultured cell effluent. These results suggest that both coronary endothelial cells in situ and cultured endothelial cells tonically release a factor(s) that reduces myofilament Ca2+ response.

Actin Cytoskeleton↗
PubMed1995

The effects of exogenous nitric oxide on smooth muscle cell proliferation following porcine carotid angioplasty.

OBJECTIVES: Nitric oxide reduces platelet adhesion and platelet-thrombus formation following angioplasty and inhibits smooth muscle cell (SMC) proliferation in vitro. In this study we investigated the effects of the nitric oxide donor molsidomine on SMC proliferation and intimal growth following experimental angioplasty. METHODS: Bilateral carotid angioplasty was performed in 24 anesthetized pigs. Animals were randomized to receive oral molsidomine (whose active metabolite is SIN-1; 0.3 mg/kg every 8 h; n = 12) or placebo (n = 12) for 48 h before angioplasty and until the arteries were removed either 7 or 21 days (n = 12 each group) later. SMC proliferation was quantified by immunocytochemical staining with an antibody to the proliferating cell nuclear antigen (PCNA) and morphometric changes by computerized planimetry. SMC's were identified by alpha-actin staining. RESULTS: After 3 weeks treatment with molsidomine there was a significant prolongation in bleeding time [mean +/- SEM] (151 +/- 6 to 187 +/- 7 s. P < 0.01) and a sustained increase in arterial wall cyclic GMP (6.57 +/- 1.29 to 13.24 +/- 1.02 pmol/mg protein, P < 0.05). Molsidomine significantly reduced intimal proliferation when compared with placebo in arteries with an intact internal elastic lamina at 7 days (4.3 +/- 0.7 vs. 9.6 +/- 1.9 PCNA index, P < 0.005) and medial proliferation at 7 days (2.4 +/- 0.2 vs. 4.2 +/- 0.7 PCNA index, P < 0.05) and at 21 days (1.3 +/- 0.1 vs. 1.9 +/- 0.2 PCNA index, P < 0.05) after angioplasty. In arteries with rupture of the internal elastic lamina, intimal and medial SMC proliferation were similar in molsidomine- and placebo-treated animals. Intimal cell number and intimal area were uninfluenced by treatment with molsidomine in either the presence or absence of rupture of the internal elastic lamina. CONCLUSIONS: These results show for the first time that exogenous nitric oxide inhibits SMC proliferation following balloon angioplasty in vivo. The antiproliferative effects of nitric oxide are overwhelmed when injury is severe and are not associated with a reduction in intimal thickening. The inhibitory effects of nitric oxide on platelet adhesion and SMC proliferation identify a possible role for high local concentrations of nitric oxide to modify the vascular response to balloon angioplasty.

Angioplasty, Balloon↗