Biomedical subjects

M J Lewis

Publications and source records attributed to M J Lewis.

At least 145 records · Page 8Linked to original sources

PubMed1993

Induction of a calcium-independent NO synthase by hypercholesterolaemia in the rabbit.

Endothelium-dependent and -independent relaxation of aortic ring preparations was assessed and nitric oxide (NO) synthase activity measured in the lung, and cerebellum of cholesterol-fed and normal rabbits. Endothelium-dependent relaxation of acetylcholine and ATP was depressed while that to the calcium ionophore, A23187, was unaltered in the cholesterol-fed group. Relaxation to sodium nitroprusside was however greater in aortae from the cholesterol-fed animals. Neither Ca(2+)-dependent nor Ca(2+)-independent NO synthase activity could be detected in aortae or hearts taken from either group of animals. Activity of both enzymes was unaltered in cerebellae from both groups of animals. Activity of the Ca(2+)-independent enzyme was however significantly greater (ca. 2 fold) in lungs from the cholesterol-fed rabbits though the activity of the Ca(2+)-dependent NO synthase was not significantly altered. This finding may account for the increased production of nitrogen oxides previously observed in this model of hypercholesterolaemia.

Amino Acid Oxidoreductases↗

PubMed1993

Porcine ventricular endocardial cells in culture express the inducible form of nitric oxide synthase.

1. We have investigated whether porcine endocardial cells in culture express the inducible, Ca(2+)-independent form of nitric oxide (NO) synthase. 2. NO synthase activity in cytosolic extracts of endocardial cells was measured by estimation of the rate of formation of L-[14C]-citrulline from L-[14C]-arginine. 3. Treatment of the cells in culture with lipopolysaccharide or cytokines induced a Ca(2+)-independent NO synthase activity in the cell cytosol. The combination of tumour necrosis factor (TNF alpha, 10 ng ml-1) and interleukin-1 beta (IL-1 beta, 10 ng ml-1) induced the greatest enzyme activity. 4. The increased Ca(2+)-independent NO synthase activity following exposure to cytokines was paralleled by an increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels in the endocardial cell cytosol. 5. Simultaneous addition of dexamethasone (0.01-1 microM) or cycloheximide (0.03-3 microM) inhibited in a concentration-dependent manner TNF alpha- and IL-1 beta-induced expression of Ca(2+)-independent NO synthase activity. Neither dexamethasone (1 microM) nor cycloheximide (3 microM) had any effect on the activity of the constitutive NO synthase. 6. The possible pathophysiological consequences of endocardial expression of the inducible NO synthase are discussed.

Amino Acid Oxidoreductases↗

PubMed1993

The benefits of telephone-access medical consultation.

A major disadvantage of rural medical practice is the limited reserve of consultative options. To determine the perceived clinical utility and educational impact of the West Virginia University Medical Access and Referral System (MARS), a 24-hour prompt telephone-consultation service, a mailed questionnaire was administered to 303 West Virginia clinicians who had used MARS for infectious disease problems. The overall questionnaire response rate was 62 percent. Callers included family practitioners (35%), medical specialists (32%), surgical specialists (13%), pediatricians (11%), obstetricians (5%), and nonphysicians (4%). Major referral questions posed were therapeutic (60%), diagnostic (48%), and epidemiologic (10%) in nature. On a scale of 1 (not useful) to 5 (very useful), survey responders rated the overall clinical usefulness of MARS as either a 4 (22%) or 5 (76%). Callers felt that MARS consultation assisted in accurate case diagnosis in 80 percent of cases, and aided in successful therapeutic management of 96 percent of cases. An educational benefit was reported by 96 percent of responders. Physicians located in more rural, underserved areas tended to use MARS to a greater degree than colleagues in more populated, medically accessible areas (P < 0.005). These findings suggest that an academic telephone-access consultation program can be a clinically relevant and educational consultative tool for practicing clinicians, especially those located in rural areas.

Academic Medical Centers↗

PubMed1993

A factor released from coronary vascular endothelium inhibits myocardial contractile performance.

The effect of continuous intracoronary infusion of bradykinin (BK; 10(-6) M) on the myocardial contractile performance of isolated Langendorff-perfused ferret hearts was investigated. BK produced a transient but marked inhibition of contractile performance, the changes being fully resolved by 2-3 min. This effect of BK was blocked after disruption of the coronary vascular endothelium with Triton X-100 (0.5%). Prior infusion of the endothelium-derived relaxing factor (EDRF) synthesis inhibitor N omega-nitro-L-arginine (10(-4) M) failed to alter the mechanical effects induced by BK. These changes in contractile performance were reduced, however, by the K+ channel-blocking agent glibenclamide (10(-6) M) but were unaffected by tetrapentylammonium bromide (5 x 10(-5) M) or 4-aminopyridine (10(-3) M). These findings therefore indicate that BK inhibits myocardial contractile performance by opening myocardial ATP-sensitive K+ channels, probably via the release of an endothelium-derived factor unrelated to EDRF.

Animals↗

PubMed1993

SIN-1 reduces platelet adhesion and platelet thrombus formation in a porcine model of balloon angioplasty.

BACKGROUND: Nitric oxide inhibits platelet adhesion and platelet aggregation in vivo. In this study, we investigated the effects of the nitric oxide donor SIN-1 on platelet adhesion and platelet-thrombus formation following experimental angioplasty. METHODS AND RESULTS: Bilateral carotid angioplasty was performed in 20 anesthetized pigs. Animals received either SIN-1 (3-morpholino-sydnonimine; 10 micrograms/kg/min; n = 8) or placebo (n = 8) before and during angioplasty. An additional control group of pigs received trimetaphan (n = 4), which induced hemodynamic changes similar to those that followed treatment with SIN-1. Platelet deposition was quantified by the injection of autologous 111In-labeled platelets. SIN-1 reduced platelet deposition after deep arterial injury compared with placebo (mean +/- SEM, 10.870 +/- 2.415 versus 40.326 +/- 9.889 platelets x 10(6)/cm2, p < 0.05). SIN-1 reduced platelet adhesion after superficial injury compared with both placebo and trimetaphan (2.231 +/- 0.333 versus 5.278 +/- 0.606 versus 5.022 +/- 1.136 platelets x 10(6)/cm2, respectively; p < 0.005). Scanning electron microscopy confirmed that platelets were deposited in the form of an adherent monolayer following superficial endothelial denudation and were reduced in number following treatment with SIN-1. The effects of SIN-1 on platelet function were associated with a significant increase in platelet cyclic GMP concentration from baseline (3.15 +/- 0.88 versus 1.58 +/- 0.73 pmol/10(9) platelets, p < 0.005). CONCLUSIONS: SIN-1 reduces platelet adhesion and platelet-thrombus formation following experimental angioplasty. The antiadhesive effects of SIN-1 are independent of changes in systemic hemodynamics. These results imply that the administration of a nitric oxide donor may prove effective in modifying the pathophysiological response to angioplasty injury.

Angioplasty, Balloon↗

PubMed1993

Prevention of bovine mastitis by a premilking teat disinfectant containing chlorous acid and chlorine dioxide.

The objective of this study was to evaluate the efficacy of a premilking teat disinfectant for the prevention of mastitis in dairy cows under natural exposure conditions. Predipping was compared with a negative control using a split udder experimental design. All teats were dipped after milking with the same teat dip. Percentage of quarters newly infected by major mastitis pathogens was 34% lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. New IMI by Streptococcus uberis and Staphylococcus aureus were significantly lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Differences in incidence of clinical mastitis between treatment groups approached significance. Predipping and postdipping were no more effective against Gram-negative bacteria, coagulase-negative Staphylococcus species, and Corynebacterium bovis than postdipping only. No chapping or irritation of teats was observed, and no adverse effects were noted using the test product as a premilking and postmilking teat disinfectant. Results of this study suggest that predipping and then postdipping with the test product was a more effective procedure against major mastitis pathogens than postdipping only.

Animals↗

PubMed1993

Influence of recombinant bovine somatotropin (sometribove) on mononuclear cells during the nonlactating period.

Recombinant bST was evaluated as a potential immunoenhancer of bovine peripheral blood and mammary gland mononuclear cells during the nonlactating period. Cows (n = 4 per group) were assigned to one of four treatments: 1) untreated, 2) treated with recombinant bST during lactation only, 3) treated with recombinant bST during the nonlactating period only, and 4) treated with recombinant bST during lactation and the nonlactating period. Recombinant bST treatment during the nonlactating period had no effect on proliferation of bovine blood or mammary gland mononuclear cells in response to stimulation by mitogens or allogeneic cells. Recombinant bST treatment during the nonlactating period enhanced interleukin-2 secretion by mononuclear cells isolated from cows treated also with recombinant bST during lactation. However, recombinant bST treatment during the nonlactating period had little effect on interleukin-2 secretion by mononuclear cells from cows not treated with recombinant bST during lactation. Results of this study suggest that recombinant bST alters effector functions rather than proliferation of bovine mononuclear cells.

Animals↗

PubMed1993

The role of endocardial endothelium in the modulation of myocardial contraction in the isolated whole heart.

Selective damage to the endocardial endothelium in isolated papillary muscle preparations has been shown to produce an abbreviation of contraction, changes which were also observed following an increase in myocardial cyclic GMP in those preparations. In the present study we have investigated the effects of removing the endocardium and increasing myocardial cyclic GMP on contractile parameters in isolated Langendorff perfused ferret hearts, where the myocardial mass underlying the endocardium is much greater. Selective damage to left ventricular endocardial endothelium without damaging the underlying myocardium was achieved by brief exposure to a weak detergent solution (Triton X-100 0.005% v/v). This resulted in a significant abbreviation of the left ventricular pressure-time curve due to the earlier onset of relaxation, but there was little effect on early systole. The direct intraventricular infusion for 15 minutes of 10 microM sodium nitroprusside, a donor of nitric oxide, or of 1 microM substance P, to stimulate release of endothelium-derived relaxing factor, did not increase myocardial cyclic GMP levels or alter left ventricular contractile performance. Myocardial cyclic GMP levels were significantly increased by 15 minute intracoronary infusions of 10 microM nitroprusside and 1 microM substance P, approximately ten-fold and two-fold respectively. Intracoronary nitroprusside induced an abbreviation of the left ventricular pressure-time curve with an earlier onset of relaxation, but contraction was unaltered by intracoronary substance P. These results show that, in the isolated Langendorff perfused ferret heart, both selective removal of endocardial endothelium and an increase in myocardial cyclic GMP cause an abbreviation of left ventricular pressure and an earlier onset of relaxation with little change in early systole.

Animals↗

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↗