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Biomedical subjects

M J Lewis

Publications and source records attributed to M J Lewis.

At least 19 recordsLinked to original sources
PubMed1992

Endothelium-derived relaxing factor inhibits platelet adhesion to cultured porcine endocardial endothelium.

By using a simple platelet binding assay, we investigated whether endothelium-derived relaxing factor (EDRF) released from endocardial endothelium influences the adhesion of unstimulated platelets to these cells. Under basal conditions 8.0 +/- 0.32% of total platelets added adhered. The nitric oxide (NO) synthase inhibitor, i.e. NG-nitro L-arginine methyl ester (L-NAME), and the EDRF inhibitor haemoglobin (Hb) increased this adhesion, but another NO synthase inhibitor, NG-monomethyl L-arginine (L-NMMA), did not. The EDRF releasing agent substance P (SP) decreased adhesion, L-NMMA reversed this inhibition, whereas L-NAME and Hb did so only partially. Superoxide dismutase (SOD) caused a marked decrease in adhesion which was fully reversed by L-NMMA, L-NAME and Hb. SOD and SP together showed a cumulative effect on platelet adhesion; this inhibition was significantly reversed by all the EDRF inhibitors, although the levels of adhesion did not return to those seen under basal conditions. These results indicate that EDRF release can inhibit the adhesion of unstimulated platelets to cultured porcine endocardium and that NO synthase inhibitors have differential effects on basal and stimulated EDRF release by these cells.

Animals↗
PubMed1992

Sequence of a second human KDEL receptor.

Retention of luminal endoplasmic reticulum (ER) proteins is mediated via a conserved carboxy-terminal tetrapeptide that serves as a signal for their retrieval from subsequent compartments of the secretory pathway. The signal is recognized by a receptor molecule that is believed to cycle between the Golgi apparatus and the ER. This receptor in Saccharomyces cerevisiae is encoded by the ERD2 gene, and a human cDNA homologue of the gene has been isolated. Binding of ligand by the product of this gene results in a shift of its steady-state location from Golgi to ER, suggesting that retrograde transport has been triggered. Here we report the identification of a related human protein with similar properties. This indicates that there are at least two distinct genes in humans that encode functional KDEL receptors.

Amino Acid Sequence↗
PubMed1992

The effects of flosequinan on endothelin-1-induced changes in inositol 1,4,5-trisphosphate levels and protein kinase C activity in rat aorta.

In rat aorta endothelin-1 (10(-8) M) induces significant increases in inositol 1,4,5-trisphosphate (IP3) levels after a 30 s exposure. An increase in particulate protein kinase C activity is also observed at 30 s with a second peak of activity occurring after 10 min. Flosequinan, at concentrations of 10(-6) M or greater, inhibits these endothelin-1-induced changes in both IP3 and particulate protein kinase C activity in the absence of changes in either cyclic GMP or cyclic AMP. It is likely therefore that flosequinan inhibits the transduction mechanisms between the endothelin-1 receptor and hydrolysis of phosphatidylinositol 4,5-bisphosphate, possibly at the level of a G-protein. These results provide a mechanism to explain the vasodilator effects of flosequinan observed in vitro.

Animals↗
PubMed1992

NMDA-induced release of nitric oxide potentiates aspartate overflow from cerebellar slices.

We report that stimulation of neonatal rat cerebellar slices with N-methyl-D-aspartate (NMDA) release nitric oxide (NO) and also increased the release of aspartate. Inhibition of NMDA receptors with the specific antagonist, 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) prevented the NMDA-induced release of both NO and aspartate. Similar results were obtained with the inhibitor of NO synthase, NG-nitroargine (NG-ARG). The NO scavenger, haemoglobin prevented the release of aspartate. Under calcium-free conditions NMDA-induced aspartate release was abolished and NO release significantly reduced. These results indicate that NO has a physiological role in the release of aspartate.

Animals↗
PubMed1992

Deletions in hydrophilic domains of subunit a from the Escherichia coli F1F0-ATP synthase interfere with membrane insertion or F0 assembly.

The a subunit is a membrane component of the F1F0-ATP synthase from Escherichia coli. Regions of a which appear important for membrane insertion or F0 assembly have been identified by analysis of both deletion mutants and fusion proteins which link the mutant a subunits to alkaline phosphatase. This analysis suggests the hydrophilic, amino-terminal domain of a is required for proper membrane targeting and/or insertion of the nascent polypeptide. In addition, the subcellular fractionation of four different a subunit-beta-galactosidase fusion proteins suggests this domain is localized to the periplasm, in agreement with a proposed topological model of the protein (Lewis, M.J., Chang, J.A., and Simoni, R.D. (1990) J. Biol. Chem. 265, 10541-10550). Deletions within the next three putative loops of a appear to have no significant effect on membrane targeting or insertion. Rather, they seem to interfere with the subsequent assembly of a functional enzyme.

Adenosine Triphosphate↗
PubMed1992

Ligand-induced redistribution of a human KDEL receptor from the Golgi complex to the endoplasmic reticulum.

Resident luminal endoplasmic reticulum (ER) proteins carry a targeting signal (usually KDEL in animal cells) that allows their retrieval from later stages of the secretory pathway. In yeast, the receptor that promotes this selective retrograde transport has been identified as the product of the ERD2 gene. We describe here the properties of a human homolog of this protein (hERD2). Overproduction of hERD2 improves retention of a protein with a weakly recognized variant signal (DDEL). Moreover, overexpression of KDEL or DDEL ligands causes a redistribution of hERD2 from the Golgi apparatus to the ER. Mutation of hERD2 alters the ligand specificity of this effect, implying that it interacts directly with the retained proteins. Ligand control of receptor movement may limit retrograde flow and thus minimize fruitless recycling of secretory proteins.

Amino Acid Sequence↗
PubMed1992

The effect of ellagic acid on xenobiotic metabolism by cytochrome P-450IIE1 and nitrosodimethylamine mutagenicity.

Ellagic acid (EA) is an inhibitor of the in vitro mutagenicity of N-nitrosodimethylamine (NDMA) in Salmonella typhimurium strain TA100 using pyrazole-induced rat liver 9000 x g supernatant (S-9). In order to understand this activity, the effect of EA on the metabolic hydroxylation of 4-nitrophenol, a substrate, as is NDMA, for cytochrome P-450IIE1 was studied using pyrazole induced rat S-9 and microsomal protein. It is shown that EA has an inhibitory effect on 4-nitrophenol hydroxylase with both enzyme preparations. This effect on cytochrome P-450IIE1 may be responsible, at least in part, for the inhibition of NDMA mutagenicity by EA.

Animals↗
PubMed1992

Endothelial modulation of myocardial contraction: mechanisms and potential relevance in cardiac disease.

Recent studies in isolated cardiac preparations and the intact heart demonstrate that the endocardial and coronary vascular endothelium modulate myocardial contractile behaviour and cardiac pump function in a novel manner, mainly by influencing the duration of contraction and the onset of relaxation but without major effect on early systolic contractile characteristics. These effects are mediated by the release of at least two diffusible substances from endothelial cells: a) endothelium-derived relaxing factor (EDRF) which shortens contractile duration by elevating myocardial cyclic GMP, and b) a novel substance, provisionally named "endocardin", which prolongs contractile duration. Under physiological conditions these endothelial influences may be particularly important for relaxation and early diastolic filling events in the heart. It is possible that they could influence myocardial growth, interact with other cardiac hormones, and via EDRF inhibit platelet adhesion to endothelial surfaces. The release of the endothelial factors is regulated by stimuli such as circulating neurohumoral substances, increased flow, products of platelet aggregation, and endogenous peptides stored in endothelial cells. Although experimental evidence is still limited, it seems likely that cardiac endothelium may play an important role in the pathophysiology of cardiac disease, e.g. overload-induced hypertrophy. The endothelium could a) influence the development of phenotype change by modulating and mediating transduction of extrinsic signals, b) contribute to contractile and other abnormalities (especially "diastolic" dysfunction) because of loss or impairment of its normal function, and c) be uniquely amenable to therapeutically useful pharmacological manipulation.

Animals↗
PubMed1992

Failure of Ro15-4513 to alter an ethanol-induced taste aversion.

The ability of Ro15-4513, an imidazobenzodiazepine inverse benzodiazepine agonist, to attenuate/block the acquisition of an ethanol (ETOH)-induced conditioned taste aversion (CTA) was investigated in two experiments. Experiment 1 examined the effects of Ro15-4513 (3 mg/kg) on rats' consumption of a novel saccharin solution under a traditional CTA paradigm. Experiment 2 examined the effects of Ro15-4513 (3 mg/kg) on rats' consumption of a novel saccharin solution under a preexposure CTA paradigm. Under the preexposure paradigm, rats were given Ro15-4513 immediately before each of five daily consecutive preexposure treatments prior to the initial conditioning day. To obtain maximal preexposure and unconditioned stimulus effects, a 2-g/kg dose of ETOH (20% v/v) was used in the present study. As previously reported, animals given ETOH following 20-min access to a novel saccharin solution established moderate to strong aversions, with the degree of aversion being directly related to the number of conditioning days. Experiment 1 showed that Ro15-4513 failed to alter the CTA induced by ETOH. Experiment 2 further showed that Ro15-4513 failed to block the preexposure effect exerted on the ETOH-mediated CTA. The results confirm previous reports regarding the failure of Ro15-4513 to disrupt an ETOH-induced CTA. These data are in agreement with a number of behavioral studies demonstrating the failure of Ro15-4513 to antagonize certain actions of ETOH. Moreover, the present study along with a previous report suggests that ETOH-induced CTA's do not appear to be mediated via actions at the GABA-BDZ receptor complex.

Animals↗
PubMed1992

The influence of endocardial endothelium on myocardial contraction.

A novel unidentified agent, provisionally named 'endocardin', has been shown to be released from endocardial endothelium. Endocardin has a unique prolonging effect on myocardial contraction. In contrast, endothelium-derived relaxing factor released from endocardial endothelium has the opposite effect of abbreviating contraction. Jerry Smith and colleagues discuss the mechanisms of action of these agents and their possible physiology and pathophysiology.

Animals↗
PubMed1992

Action potential duration and endocardial modulation of myocardial contraction in the ferret.

OBJECTIVE: Endocardial endothelium releases substances which modulate myocardial contraction. Selective endocardial removal abbreviates contraction by removing a contraction prolonging substance "endocardin". The aim of the study was to investigate whether changes in action potential duration underlie these contractile effects. METHODS: The contractile effects of shortening the action potential were first characterised, using a potassium channel "opener" cromakalim (3 microM). Transmembrane action potentials were then recorded in isolated ferret papillary muscles before and after endocardial removal. RESULTS: Cromakalim-induced action potential abbreviation reduced contractile twitch duration. Endocardial removal itself however did not alter action potential duration. CONCLUSIONS: Endocardial modulation of cardiac contraction does not involve changes in action potential duration.

Action Potentials↗
PubMed1992

Exogenous nitric oxide inhibits in vivo platelet adhesion following balloon angioplasty.

OBJECTIVES: The aim was to investigate the effects of an exogenous source of nitric oxide on in vivo platelet adhesion at the site of endothelial denudation after balloon angioplasty. METHODS: The study group consisted of 12 anaesthetised Large White pigs. Pigs were randomised to receive SIN-1 (3-morpholino-sydnonimine), an exogenous donor of nitric oxide, or placebo before and during balloon induced vessel wall injury. Platelet deposition was quantified using the injection of autologous 111indium labelled platelets. Platelet function was also monitored by the measurement of bleeding time and ex vivo whole blood aggregometry. RESULTS: Superficial vessel wall injury was confirmed histologically and platelet monolayer formation was demonstrated by scanning electron microscopy. Platelet deposition at the site of endothelial denudation was markedly reduced following SIN-1 administration compared to placebo: 1.266(SEM 0.063) v 1.732(0.060) log platelets x 10(5).cm-2, p = 0.001. SIN-1 raised platelet cyclic GMP concentration, from 4.47(2.48) to 6.14(2.44) pg.platelet-1 (p less than 0.01) and prolonged the bleeding time, from 135(5) to 202(6) s (p = 0.001), but had non-significant effects on ex vivo whole blood aggregometry. CONCLUSIONS: Exogenous nitric oxide, through the activation of platelet soluble guanylate cyclase, inhibits platelet adhesion in vivo following balloon angioplasty.

Angioplasty, Balloon↗
PubMed1992

Pharmacokinetics and pharmacodynamics of verapamil following sublingual and oral administration to healthy volunteers.

1. The pharmacokinetics and pharmacodynamics of verapamil administered via the oral and sublingual routes were compared in a randomised, two-way cross-over study involving six healthy male volunteers. 2. Administered sublingually, a verapamil 40 mg (Securon) crushed tablet produced a significantly higher peak plasma concentration (P less than 0.05), a greater rate of absorption (P less than 0.05), and greater bioavailability (P less than 0.05) when compared with orally administered verapamil 40 mg (Securon). 3. In comparison with oral dosing, PR intervals were significantly (P less than 0.05) prolonged between 30 and 90 min after sublingual verapamil dosing. 4. Correlations between log plasma verapamil concentration and percentage increase in PR interval were greater after sublingual compared with oral dosing in all volunteers.

Administration, Oral↗
PubMed1992

Ethanol self-administration in deprived rats: effects of Ro15-4513 alone, and in combination with flumazenil (Ro15-1788).

Previous work in our laboratory demonstrated that Ro15-4513, a partial inverse benzodiazepine agonist, decreases self-administration of ethanol (ETOH) in rats maintained on a two-bottle regmine of a saccharin ethanol solution (ES) and water over a 35-day consumption period. The present study extended the consumption period to 60 days and examined the effects of Ro15-4513 (2.5 mg/kg), flumazenil (Ro15-1788) (8.0 mg/kg), and Ro15-4513 in combination with Ro15-1788 on the time course of ETOH self-administration. High initial intake of ES observed during the first 4 weeks declined significantly over subsequent weeks. Ro15-4513 pretreatment, however, resulted in significant reduction of ES, while significantly preventing the "normal" reduction of consumption as was observed under control conditions. The antagonistic actions of Ro15-4513 were blocked/attenuated by the benzodiazepine receptor antagonist, Ro15-1788, independent of whether consumption of the ES was low or high. Both Ro15-4513 and Ro15-1788 affected water intake differentially compared with vehicle-injected controls. The results suggest that GABA-benzodiazepine mechanisms may be important in altering chronic ETOH drinking patterns depending upon experience with ETOH, tolerance, or learning.

Alcohol Drinking↗
PubMed1992

Evidence for involvement of nitric oxide in the non-adrenergic non-cholinergic (NANC) relaxation of human lower oesophageal sphincter muscle strips.

Electrical field stimulation of circular muscle strips from human lower oesophageal sphincter reveals a predominant relaxation response. This relaxation is non-adrenergic non-cholinergic (NANC). The nitric oxide synthesis-blocking agent N omega-nitro-L-arginine (10-100 microM) reduces or abolishes this NANC relaxation, suggesting involvement of nitric oxide in the response.

Adrenergic Fibers↗
PubMed1992

Influence of prepartum antibiotic therapy on intramammary infections in primigravid heifers during early lactation.

Jersey heifers were assigned alternately to three groups: 1) negative control (n = 41), 2) intramammary infusion of 200 mg of sodium cloxacillin (n = 38) at 7 d before expected parturition, and 3) intramammary infusion of 200 mg of cephapirin sodium (n = 36) at 7 d before expected parturition. The percentage of mammary glands infected prior to treatment was 62.2, 50.0, and 70.1 for groups 1, 2, and 3, respectively. The percentage of mammary glands infected during early lactation was 44.5, 8.6, and 2.1 for groups 1, 2, and 3, respectively. Most infections (87.1%) were due to Staphylococcus species other than Staphylococcus aureus. Thirty-six of 460 quarters were infected with major pathogens before treatment, 3 of 22 persisted following antibiotic treatment, and 9 of 14 persisted in the control group. Infusion of sodium cloxacillin resulted in antibiotic residues in 17.4% of samples obtained .5 d postpartum. All samples were negative at 3 and 10 d postpartum. Infusion of cephapirin sodium resulted in antibiotic residues in 84.7, 28.2, and 0% of samples obtained at .5, 3, and 10 d, respectively. Prepartum antibiotic therapy was effective in eliminating many IMI, especially those caused by coagulase-negative staphylococci, but there is the potential for antibiotic residues in milk.

Animals↗