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Biomedical subjects

P J Simpson

Publications and source records attributed to P J Simpson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Evaluation of activated protein C on canine infarct size in a nonthrombotic model of myocardial reperfusion injury.

Myocardial infarct size has been measured after 1 hr of mechanical occlusion of the circumflex coronary artery and 5 hr of reperfusion in control dogs infused with saline, and in dogs infused with activated protein C (aPC) (1mg/kg/hr i.v.). Infusion of aPC during reperfusion produced a sustained doubling of activated partial thromboplastin time and no change in thrombin time at a final plasma parent drug concentration of 1.25 +/- 0.11 mug/ml. aPC infusion did not alter systolic arterial pressure, cardiac rate or the rate pressure product when compared to time-related alterations observed in control dogs. ST-segment deviation and the intensity and duration of cardiac arrhythmias associated with reperfusion of ischemic myocardium also were similar between groups. Resultant infarct sizes were 34.8 +/- 3.9 and 33.2 +/- 6.2% of the left ventricular mass placed at risk of necrosis in control and aPC-treated dogs. respectively. aPC infusion was associated with a small reduction in leukocytosis in response to myocardial ischemic injury, but did not alter the localization of leukocytes within ischemic and infarcted myocardium. In vitro concentrations of aPC (0.3, 1 and 3 mug/ml), comparable to the plasma concentration that inhibited blood coagulation in dogs, did not alter superoxide production or CD11b/CD18-mediated adhesion of chemotactic factor f-Met-Leu-Phe-stimulated neutrophils. Present data indicate that aPC lacks cardioprotectant activity at an infusion rate inhibiting coagulation. Apart from inhibition of thrombin generation, no evidence of an anti-inflammatory effect of aPC was observed.

Animals↗
PubMed1995

Eclosion hormone-stimulated cGMP levels in the central nervous system of Manduca sexta: inhibition by lipid metabolism blockers, increase in inositol(1,4,5)trisphosphate and further evidence against the involvement of nitric oxide.

Previous studies have shown that the neuropeptide, eclosion hormone, stimulates a nitric oxide-independent increase in the levels of cGMP in the nervous system of Manduca sexta. By contrast, recent results in Bombyx mori suggest that eclosion hormone increases cGMP via the production of nitric oxide. In view of these conflicting results we have carried out additional studies to test whether nitric oxide is involved in this process in Manduca. Evidence presented here supports our earlier observations that in Manduca the eclosion hormone-stimulated increase in cGMP is nitric oxide- and carbon monoxide-independent. In addition, we show that a wide variety of inhibitors of lipid metabolism block the eclosion hormone-stimulated cGMP increase. This supports the hypothesis that the activation of the guanylate cyclase is mediated by a lipid messenger. We also show that eclosion hormone stimulates an increase in the levels of inositol(1,4,5)trisphosphate. The time-course of this increase is consistent with the hypothesis that eclosion hormone stimulation of a phospholipase C is an early event in the cascade that results in an increase in cGMP. Receptor-mediated lipid hydrolysis is often mediated by G protein-coupled receptors. Experiments using pertussis toxin show that the eclosion hormone-stimulated increase in cGMP is not mediated by a pertussis toxin-sensitive G protein.

Animals↗
PubMed1995

Detecting 'hidden' exchange events within X-ray-induced aberrations using multicolour chromosome paints.

In a recent series of papers we pointed out that any complex exchange (an interaction involving three or more breaks) can yield a wide range of aberration configurations. If these aberrations are detected with a single chromosome paint and total centromere probe, the majority will be scored as either 'simple' exchanges, apparently derived from two breaks, which we term pseudosimples, or as complexes which appear to have fewer breaks than were actually involved, which we term reduced complexes. In this study, metaphases from X-irradiated human fibroblasts were hybridized to two distinctly labelled composite probes (paints) for chromosomes 1 and 2. All centromeres were marked by differential 4',6-diamidino-2-phenylindole (DAPI) staining. Aberrations derived from exchanges involving both paints were characterized. With this method, we are able to identify some of the additional exchange events, so confirming the existence of these two classes of aberration. Ultimately we believe it can be used to estimate their frequency.

Cells, Cultured↗
PubMed1995

Estimating the true frequency of X-ray-induced complex chromosome exchanges using fluorescence in situ hybridization.

Fluorescence in situ hybridization (FISH) with a series of composite probes for human chromosomes 1, 4, 5, 7 and 13, applied separately with a total centromere probe, was used to identify X-ray-induced, chromosome-type aberrations in primary untransformed human fibroblasts. Visible complex exchanges, i.e. those involving three or more breaks in two or more chromosomes, were classified with reference to possible complex FISH patterns derived from a set of theoretical interactions. At 4 Gy, approximately 20% of all exchanges we observed were visibly complex. Using an interaction scheme, which allows either loose end of a break to restitute with its partner, or join with any other loose end within the potential complex, we modelled a set of interactions that matched the frequencies of the complex FISH patterns identified. The direct score of visible complex patterns is an under-estimate of the true frequency because some apparently 'simple' two-break exchanges (dicentrics and translocations) are actually derived from three or more breaks. Using the model we estimate that these account for 20% of the simples scored. Taking this into account, we estimate the true frequency of complexes at 4 Gy to be 35% of all exchanges scored and we believe that the majority of these involve five breaks in four chromosomes.

Cell Line↗
PubMed1995

Localization to chromosome 7q36.1 of the human XRCC2 gene, determining sensitivity to DNA-damaging agents.

The identification of genes controlling cellular response to DNA damage is of considerable importance, and cell lines showing hypersensitivity to DNA-damaging agents can be used as vehicles to map and clone these genes. In this study the hamster cell line irs1, showing hypersensitivity to a number of different DNA-damaging agents, was fused to normal human cells to complement the defect. The resultant hybrids were analysed by Alu-PCR, chromosome painting, and with DNA markers to map the complementing gene (named XRCC2) to a specific chromosomal region. These hybrids showed correction of sensitivity to both X-rays and to mitomycin-C, and contained human chromosome 7, often as their only human component. Hybrids showing unstable retention of human chromosomes were sub-cloned to show that loss of chromosome 7 and loss of resistance to mitomycin-C occurred concordantly. Two separate hybrids were found to have a smaller piece of chromosome 7, and specific DNA probes and microsatellite markers defined this as a contiguous region at 7q35-36. Hybrid irradiation-fusion methods were used to further reduce the size of the complementing genomic region and to localize the gene to an approximately 3-5 Mb region at 7q36.1.

Animals↗
PubMed1995

Effects of BMY21190, an inhibitor of cAMP phosphodiesterase, on infarct size and myeloperoxidase activity in the ischemic myocardium of a canine occlusion-reperfusion model.

This study was performed to assess the effect of BMY21190, an inhibitor of cAMP phosphodiesterase, on infarct size using a canine ischemic model that underwent a 90-min occlusion and a 6-hour reperfusion of the left coronary artery. The infarct zone/area at risk of the BMY21190 group was significantly smaller than that of the vehicle group (36.1 +/- 7.8%; 62.4 +/- 4.3%, respectively; p < 0.05). Myeloperoxidase activity, an indicator of neutrophil infiltration, was significantly correlated to infarct size (r = 0.6893, p < 0.02). Myeloperoxidase activity (0.14 +/- 0.07 U/100 mg tissues) measured in the area at risk from hearts of the BMY21190-treated group was significantly lower than that of the vehicle-treated tissue (0.40 +/- 0.08 U/100 mg tissue, p < 0.05). It is suggested that BMY21190 reduces infarct size through the inhibition of neutrophil infiltration in the canine model.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1995

Activated recombinant human protein C does not attenuate recruitment of neutrophils in rat models of acute inflammation.

It has been proposed that the reduction in mortality in animal models of sepsis by activated protein C (APC) is mediated by an antiinflammatory property rather than the well-characterized anticoagulant action. Human recombinant APC was examined for potential antiinflammatory activity in the pentobarbital-anesthetized rat. In the dermal reversed passive Arthus model, APC (20.0 mg/kg/h, i.v.) elevated clotting time 10-fold 3 h after the Arthus challenge, at which time, the wet-weights from Arthus dermal samples in APC rats (120.0 +/- 1.5 mg, n = 10) did not differ from controls (120.1 +/- 1.5 mg, n = 10) but were 30% heavier than remote noninflamed skin (92.0 +/- 2.0 mg, n = 10), indicating that APC treatment did not diminish tissue edema associated with immune-complex deposition. Skin-lesion myeloperoxidase (neutrophil marker enzyme) activities from APC rats were not significantly different from controls but was 21-fold more than remote noninflamed skin, indicating that APC treatment did not diminish dermal recruitment of neutrophils. In the intestinal ischemia/reperfusion model, 1 h complete occlusion of the superior mesenteric artery and an additional 4 h reperfusion was associated with a 2.87-fold increase in lung myeloperoxidase activity compared to sham-operated rats. APC (1.0 mg/kg/h, i.v.) did not diminish the elevation in this index of lung neutrophil sequestration. In conclusion, APC did not produce an antiinflammatory effect in the rat models used.

Acute Disease↗
PubMed1994

FISH "painting" patterns resulting from complex exchanges.

Many of the unusual patterns seen when irradiated chromosomes are FISH painted arise from Complex interchanges. In this paper, we present a method for classifying chromosome-type complex exchanges. Every possible exchange configuration for the first nine complex families has been determined, and for each of these, the expected metaphase pattern forms seen if any one of the participating chromosomes is painted, has been worked out. A total of 65 recognisably different pattern forms emerge, and a simple classification of these is provided for scoring and discussion purposes. 47 of these patterns are unique ("Tell-tale"), in that they are found in, and are diagnostic for, only one complex family or sub-family (of the sub-set analyzed). Analysis of the contingency tables indicates that: (a) The same individual complex exchange can appear in different pattern forms, depending upon which of the participating chromosomes is painted, and the converse-different forms can represent the same exchange. (b) Many different complex exchange configurations, from different families, can give rise to identical pattern forms. (c) If obvious complex forms are at all frequent in a sample, then a lot of the exchanges being scored as "simple" are not. These observations will have considerable repercussions on the numerical assessment of damage when using painted chromosomes at higher radiation doses.

Chromosome Aberrations↗
PubMed1994

Identification of X-ray-induced complex chromosome exchanges using fluorescence in situ hybridization: a comparison at two doses.

Complex chromosome exchanges are defined as interactions between three or more breaks, in two or more chromosomes. In this study, a sequential hybridisation technique was developed to visualize a given chromosome pair: green (chromosomes 1, 5 and 7), all centromeres red and the remaining chromosomes blue. Primary human fibroblasts were irradiated in G1 with 4 and 6 Gy 250-kV X-rays. After 4 Gy, a total of 387 simple aberrations (defined as translocations or dicentrics with fragments) and 116 complex aberrations were identified. After 6 Gy these aberrations numbered 225 and 110 respectively. Using a break-rejoin scheme, which describes interactions between breaks within a complex as independent events we modelled the complex 'mix' present after 4 Gy. At 6 Gy the same model could be used for chromosomes 5 and 7, but chromosome 1 frequencies could only be explained if we biased the interactions, such that two-breaks-in-one-chromosome events occur predominantly in chromosome 1. From these predicted interactions we also calculated the number of apparently simple exchanges that are actually complex derived. These accounted for 20% of those observed after 4 Gy and 33% after 6 Gy. Therefore, with this FISH assay, an estimated 35 and 54% of all exchanges are derived from complexes after 4 and 6 Gy respectively.

Cell Line↗
PubMed1994

5 nanosecond molecular dynamics and NMR study of conformational transitions in the sialyl-Lewis X antigen.

The range of internal motions of the sialyl Lewis-X (SLe(x)) tetrasaccharide (NeuNAc alpha 2-->3Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc) [where Fuc is L-fucopyranose, Gal is D-galactopyranose, GlcNAc is 2-acetamido-2-deoxy-D-glucopyranose and NeuNAc is D-neuraminic acid (sialic acid)] was studied by restrained simulated annealing and restrained molecular dynamics (MD) calculations. Transitions between predominantly two conformational states were observed for the NeuNAc alpha (2-->3)Gal linkage, consistent with previous observations for this linkage in sialyl-N-acetyllactosamine. The MD trajectory was simulated for 5 ns of real time, in order to observe a statistically significant number of these relatively low-frequency transitions. The Fuc alpha(1-->3)GlcNAc and Gal beta (1-->4)GlcNAc linkages, however, showed more restricted flexibility within a single energy well (RMS differences for the time-averaged glycosidic torsion angles, and , were 50% lower than for the NeuNAc alpha(2-->3)Gal linkage), and approximate to a rigid conformation. NMR parameters [relative rotating-frame Overhauser enhancement (r.O.e.) and inter-glycosidic 3JCH] back-calculated from the MD simulation were in close agreement with experimentally measured values for the free reducing oligosaccharide in D2O solution.

Carbohydrate Conformation↗
PubMed1993

Effect of activation of ATP-dependent potassium channels with (-)-pinacidil and (-)-3-pyridyl pinacidil on infarct size in a canine model of ischemia-reperfusion injury.

We tested the hypothesis that opening myocardial ATP-dependent K+ (ATP-K) channels by administration of (-)-pinacidil or (-)-3-pyridyl pinacidil intracoronarily (i.c.) either during ischemia or as pretreatment could decrease infarct size in a canine model of ischemia-reperfusion injury in anesthetized male hounds subjected to 90-min left circumflex coronary artery (LCX) occlusion followed by 5-h reperfusion. Drugs were administered by one of two protocols. In the postocclusion treatment protocol (protocol post), either vehicle or (-)-3-pyridyl pinacidil [0.25 micrograms/kg/min (low dose) or 1 micrograms/kg/min (high dose)] was infused i.c. distal to the site of coronary artery occlusion, through LCX beginning 10 min after LCX occlusion and continuing until 10 min after the beginning of reperfusion. In the preocclusion treatment protocol (protocol pre), vehicle, low dose (-)-3-pyridyl pinacidil, or (-)-pinacidil (1 micrograms/kg/min) was infused i.c. distal to the site of coronary artery occlusion through the LCX beginning 10 min before occlusion and continuing until the end of the experiment. In both protocols, (-)-pinacidil and (-)-3-pyridyl pinacidil failed to demonstrate a decrease in infarct size from that of the vehicle-treated groups. In protocol post, the mean sizes of the infarcts in the vehicle, low-dose, and high-dose (-)-3-pyridyl pinacidil-treated groups were 26.4 +/- 5.0, 35.6 +/- 6.6, and 28.9 +/- 6.1% of the area at risk, respectively. In protocol pre, the mean sizes of the infarcts in the vehicle, (-)-pinacidil, and low dose (-)-3-pyridyl pinacidil-treated groups were 29.4 +/- 1.7, 27.0 +/- 3.9, and 35.6 +/- 4.1% of the area at risk, respectively. Neither subepicardial nor subendocardial blood flow in the ischemic zone, measured by radioactive microspheres, was significantly different among groups in either protocol. In protocol post, however, the endocardial/epicardial blood flow ration in the nonischemic zone was decreased by (-)-3-pyridyl pinacidil. In addition, the ischemic zone (LCX)/nonischemic left anterior descending coronary artery (LAD) zone blood flow ratio in the subepicardial region were decreased by (-)-3-pyridyl pinacidil. These observations suggest that the drug may shift blood flow away from the ischemic zone in general and away from the endocardium in particular. In protocol pre, the LCX/LAD ratio tended to decrease with both drugs, but the difference achieved statistical significance only with (-)-3-pyridyl pinacidil (low dose).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Inhibition of granulocyte cAMP-phosphodiesterase by rolipram in vivo is not sufficient to protect the canine myocardium from reperfusion injury.

The purpose of this study was to determine whether the selective type IV cAMP-phosphodiesterase inhibitor rolipram could reduce the reperfusion injury that occurs during myocardial infarction in the anesthetized dog. This question was tested in pentobarbital-anesthetized dogs subject to 90 min of regional myocardial ischemia and 5 h of reperfusion. Dogs were treated with 1 mg/kg of rolipram (i.v., 15 min before reperfusion) followed by a 1 mg/kg/h infusion over the duration of the 5 h of reperfusion. Rolipram was tested in vitro for efficacy in inhibition of isolated human neutrophil superoxide generation. Rolipram produced significant inhibition of superoxide production over the concentration range of 0.1-100 microM rolipram when neutrophils were stimulated with a 10(-7) M concentration of the chemotactic peptide f-Met-Leu-Phe. Rolipram significantly inhibited superoxide generation from human and canine granulocytes in whole blood stimulated by zymosan. Therapeutic concentrations of rolipram in the blood of dogs were achieved during the course of the experiments with a plasma concentration of 0.761 +/- 0.095 micrograms/ml (2.76 +/- 0.34 microM) at the time of reperfusion, and 0.574 +/- 0.098 micrograms/ml (2.08 +/- 0.36 microM) at the end of the reperfusion period. The relative severity of myocardial ischemia between the two treatment groups was similar as assessed with radiolabeled microsphere measurement of myocardial blood flow. Transmural myocardial blood flows were not significantly different between the two groups after coronary occlusion (control, 0.05 +/- 0.01 ml/min/g, n = 6, vs. rolipram, 0.18 +/- 0.07 ml/min/g, n = 6; p = 0.48).(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1992

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion in murine skin by systemic effects of ultraviolet irradiation.

Systemic effects of UVB irradiation (280-320 nm) have been shown to prevent subsequent chemical tumorigenesis induced by an initiation-promotion protocol. The present investigation was designed to determine whether initiation or promotion is prevented by UV irradiation. Groups of 25 B6D2F1/J mice received 12 weeks of intermittent dorsal UVB radiation treatments administered before, or 3 weeks after, initiation with a single application of 7,12-dimethylbenz[a]anthracene on the ventral skin. All mice were promoted ventrally with 5 micrograms 12-O-tetradecanoylphorbol-13-acetate (TPA) applied three times weekly throughout the experiment. UV irradiation consisted of five 30-min exposures per week to a bank of 6 Westinghouse FS40 sunlamps. UV irradiation applied before or after initiation resulted in a decrease of 18-16 tumors per group of 25 mice, for a reduction of 61 and 50%, respectively, at 24 weeks after the first TPA treatment. Thus, prevention of tumor development was similar whether the UV influence was present or not during initiation. This finding suggests that the UV prevention of promotion could account for UV inhibition of skin tumors induced by an initiation-promotion regimen. Consistent with this concept, pretreatment of mice with dorsal UVB radiation was found to reduce DNA synthesis after exposure to TPA by 46%, although it did not decrease tritiated benzo[a]pyrene binding to DNA, in ventral epidermis. Thus, UVB irradiation systemically reduced TPA-induced tumor promotion in murine skin.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

Speech audiometry: digitization effects and the non-equivalence of isophonemic word lists.

Phonetically balanced word lists have many applications, including the field of audiometric testing, as equivalent test material. An experiment designed to assess the effects of digitizing parameters on speech intelligibility has shown, following detailed analysis, that the lists show a degree of non-equivalence. The reasons for this are explored and questions asked about the fundamental principles involved in describing speech forms. Other approaches to this kind of assessment are discussed.

Adult↗
PubMed1991

The role of serotonin (5HT2) receptor blockade in myocardial reperfusion injury: effects of LY53857 in a canine model of myocardial infarction.

The potential protective effects of serotonin receptor antagonism during the process of acute myocardial infarction were studied in anesthetized male dogs, which were subjected to a 90-min left circumflex coronary artery occlusion followed by 5 h of reperfusion. Either vehicle (0.9% NaCl) or the serotonin (5HT2) receptor antagonist LY53857 was infused i.v. at a dose of 0.5 mg/kg, followed by a constant infusion of 2 mg/kg/min beginning 5 min before left circumflex coronary artery occlusion and continuing throughout the duration of the ischemia and subsequent reperfusion. Verification of functional 5HT2 receptor antagonism in the circulating blood of the LY53857-treated dogs was monitored throughout the experiments by periodic assessment of ex vivo platelet reactivity to exogenous serotonin. After 5 h of reperfusion, the hearts were excised and analyzed utilizing histochemical staining with triphenyltetrazolium, which demarcates myocardial infarct size and anatomical area of myocardium at risk of infarction. There was not a significant reduction of infarct size with LY53857 treatment: control infarct/area at risk = 38.6 +/- 4.7%, n = 9 LY53857 infarct/area at risk = 33.4 +/- 3.8%, n = 6. Similarly, when myocardial infarct size was analyzed as a function of myocardial collateral blood flow, there were no significant effects of drug treatment on the relationship between collateral blood flow and infarct size. The effects of 5HT on neutrophil activation were determined by measuring the potential ability of 5HT to enhance the chemotactic peptide-induced production of superoxide. 5HT did not activate human neutrophils in vitro and LY53857 had no effect on neutrophil superoxide production.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Therapeutic defibrination with ancrod does not protect canine myocardium from reperfusion injury.

The purpose of this study was to determine whether normal fibrinogen contributes to the development of myocardial reperfusion injury by acting as a substrate in vivo for neutrophil adhesion. This was tested in a dog model of acute myocardial infarction that used pentobarbital anesthetized dogs subjected to 90 min regional myocardial ischemia and 5 h reperfusion. Dogs were treated with 1 unit/kg Ancrod (venom from the Malayan pit viper, Agkistrodon rhodostoma) or vehicle i.v. 60 min after left circumflex coronary artery occlusion. Therapeutic defibrination was verified in Ancrod-treated dogs by measurements of clottable fibrinogen, alpha-2 antiplasmin and plasminogen, by the activated partial thromboplastin time and by immunoelectrophoresis. Fibrinogen was depleted to below detectable limits of the assay (less than 0.05 mg/ml) after treatment with Ancrod. The defibrination effect was accomplished by the expected activation of the fibrinolytic system: alpha-2 antiplasmin was decreased by 10% and plasminogen activity was decreased by 30% with Ancrod treatment. There were no measureable differences between the two treatment groups in heart rate, mean arterial blood pressure, rate pressure product or circumflex coronary blood flow throughout the 90 min of regional ischemia or during the 5 h of reperfusion. The relative severity of ischemia between the two treatment groups was similar when assessed with radiolabeled microsphere measurement of myocardial blood flow. The accumulation of neutrophils (measured by myeloperoxidase activity) within the myocardium after reperfusion was not reduced by prior depletion of fibrinogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Ancrod↗