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W Schaper

Publications and source records attributed to W Schaper.

At least 19 recordsLinked to original sources
PubMed1992

Proto-oncogene expression in porcine myocardium subjected to ischemia and reperfusion.

The molecular basis of myocardial adaptation to ischemia and reperfusion is poorly understood. It is thought that nuclear proto-oncogenes act as third messengers, converting cytoplasmic signal transduction into long-term changes of gene expression. We studied the expression of six nuclear proto-oncogenes (Egr-1, c-fos, fosB, c-jun, junB, and c-myc) in myocardium subjected to ischemia and reperfusion in anesthetized pigs. Stunning was achieved by two 10-minute left anterior descending coronary artery occlusions separated by 30 minutes of reperfusion. Hearts were excised after the first occlusion, after the first reperfusion, and at 30, 120, 150, and 210 minutes of reperfusion after the second occlusion. Total RNA was prepared from stunned as well as normally perfused myocardial tissue and subjected to Northern blotting. The response of the six nuclear proto-oncogenes varied.fosB gene expression was never detected. The c-myc gene was expressed, but its level was unchanged by ischemia. c-jun expression was slightly increased by ischemia (3.1 +/- 0.6-fold). The c-fos, Egr-1, and junB genes were highly induced, being fivefold to sevenfold higher in experimental than in control tissue. In three animals pretreated with the beta 1-antagonist metoprolol and then subjected to the above experimental protocol, the induction of proto-oncogenes was similar to that in nonblocked controls. Our results show that the myocardial adaptive response to ischemic stress includes the induction of at least four transcription factors that may be further operative in repair processes and angiogenesis.

Animals↗
PubMed1992

Molecular biology of the coronary vascular and myocardial responses to ischemia.

To understand the complex mechanism(s) involved in molecular responses to ischemia, we developed two experimental models in pigs. In a "stunning" model of repetitive ischemia and reperfusion, we studied the mRNA expression of immediate early genes like c-fos, c-myc and heat shock protein-70 (HSP-70). Myocardial stunning was achieved by two cycles of 10-min left anterior descending coronary artery (LAD) occlusion and 30 min reperfusion. We observed several-fold enhanced expression of c-fos and HSP-70 mRNA in the stunned myocardium as compared with the control, whereas c-myc mRNA levels remained almost unchanged. In the second model, we examined the expression of the peptide mitogens heparin-binding growth factor 1 (HBGF-1) and transforming growth factor beta 1 (TGF-beta 1) after a chronic coronary artery occlusion leading to myocardial collateralization. Progredient stenosis of the circumflex coronary artery was induced by implanting a hygroscopic ameroid constrictor ring around it and occlusion was verified by in vivo angiography. Using polymerase chain reaction (PCR) and Northern hybridization techniques, we observed significantly enhanced expression of HBGF-1 and TGF-beta 1 in collateralized myocardium as compared with normal. In situ techniques revealed the localization of HBGF-1 transcripts in the blood vessel wall, and TGF-beta 1 in cardiac myocytes and Purkinje cells. Our results clearly indicate that myocardial stunning stimulates the expression of transcription factors which might be involved in regulation of certain growth factors like HBGF-1 and TGF-beta 1 which may play a significant role in the development of a collateral circulation.

Animals↗
PubMed1991

Amplification and sequencing of mRNA encoding acidic fibroblast growth factor (aFGF) from porcine heart.

Progredient stenosis of coronary arteries can induce angiogenic processes, which are probably regulated by polypeptide growth factors like aFGF. Using applications of reverse transcription-polymerase chain reaction, we amplified and sequenced an mRNA encoding aFGF in the porcine myocardium. A DNA fragment of expected size encoding aFGF was amplified with human and bovine aFGF specific oligonucleotide primers in porcine heart. Identity of amplified PCR product to aFGF sequence was confirmed by internal reamplification, Southern hybridization and sequencing of asymmetrically amplified PCR products. The nucleotide sequence analysis of porcine aFGF revealed a homology of 94% to the human and 92% to the bovine cDNA sequences respectively. The amino acid sequence was homologous to the known sequences except for three alterations in the human and thirteen in the bovine aFGF sequences.

Amino Acid Sequence↗
PubMed1991

Angiogenesis in the adult heart.

We have studied the development of the collateral circulation in the heart in response to gradual and progressive coronary artery occlusion. When the coronary stenosis becomes critical, tissue ischemia occurs, which we believe leads to the production (and probably to release from storage sites) of tissue hormones (mitogens) that lead to mitosis of endothelial and smooth muscle cells. We have identified from hearts several known mitogens (aFGF, bFGF), non-mitogenic angiogenic factors (TGF-beta), a new anti-mitogen, and a new myocyte-derived growth factor (structures of the last two not yet elucidated). An important principle in the development of collaterals is the remodeling of pre-existing small vessels into the much larger vascular structure. To accommodate new cells old structures have to be removed by controlled proteolysis (tPA, uPA, elastase).

Animals↗
PubMed1991

Molecular mechanisms in "stunned" myocardium.

In a recent overview on stunning, Bolli listed the three pillars on which theories on stunning rest: its causation by oxygen radicals, the amplification of damage by Ca2+ overload, and the resulting excitation contraction uncoupling. Our own experiments with SOD and catalase do not convince us that stunning is caused by free radicals, because we and others were unable to show improvement. An important pathway of radical generation, i.e., xanthine oxidase, does not exist in the hearts of several families of mammals, but stunning can of course be produced in these species. We agree with Bolli that stunning represents a disturbance of electromechanical coupling, but we acknowledge the controversy that exists with regard to the subcellular seat of the defect. Our results would support hypotheses that pinpoint the defect to the sarcoplasmic reticulum. However, the possibility of multiple defects should also be considered: Our finding of altered Ca2+ ATPase expression and Kusuoka's finding of altered myofibrillar Ca2+ sensitivity are not necessarily mutually exclusive but may be complementary, or may represent different stages of ischemic damage. Our finding of decreased myosin expression may help to explain the long persistence of the contractile defect. From the available evidence, the hypothetial possibility evolves that stunning is not just an injury, but rather the unmasking of a regulatory mechanism to protect the heart against premature or further damage. The observation that coronary occlusion causes both stunning and preconditioning by a parallel, and not by a sequential, mechanism and that a multitude of genes alter their expression in order to protect the myocyte argue for a regulatory change.

Animals↗
PubMed1991

In situ localization of transforming growth factor beta 1 in porcine heart: enhanced expression after chronic coronary artery constriction.

We investigated the expression of transforming growth factor beta 1 (TGF-beta 1), a polypeptide differentiation factor probably associated with angiogenic properties in chronically hypoperfused heart tissue. A slowly swelling ameroid constrictor was implanted around the coronary circumflex artery (CX) of young domestic pigs. Two to three weeks after, significant CX stenosis of more than 90% and coronary collateralization could be demonstrated angiographically. The CX dependent experimental myocardial tissue (E) was investigated, with the LAD dependent area of the same pig serving as a control (C). We found significantly enhanced TGF-beta 1 mRNA expression by northern blot hybridization in the experimental myocardium (E) of those pigs with demonstrable coronary collaterals in the absence of a major myocardial infarction. The presence of TGF-beta 1 protein could be demonstrated quantitatively in extracts of the experimental and the control area by immunoblot analysis. By in situ techniques, TGF-beta 1 mRNA and protein could be localized predominantly in cardiac myocytes. We conclude that one adaptive mechanism of the pig heart in chronic coronary artery constriction is the enhanced expression of TGF-beta 1. Cardiac myocytes are a major source of TGF-beta 1. The observed coronary collateralization could be mediated-at least in part-by the angiogenic properties of TGF-beta 1.

Adaptation, Biological↗
PubMed1990

Molecular biologic concepts of coronary anastomoses.

The discovery that collateral development after progressive coronary stenosis proceeds by means of DNA synthesis, mitosis and proliferation of endothelial and smooth muscle cells in preformed small interconnecting arterioles (canine heart) and capillaries (porcine heart) has stimulated research into the molecular mechanisms of vascular growth. Growth is tightly controlled under physiologic conditions, and several factors must act in concert to overcome control. Because the result of growth is a much larger orderly structure of complex design, we expect the existence of a genetic blueprint for its construction. Peptide growth factors have recently been isolated from a variety of organs, including the heart. We have provided experimental evidence that the heparin-binding growth factor beta-ECGF shows an increased transcription in growing pig collateral vessels. Because the chain of events probably originates in the ischemic cardiac myocyte, it appears logical to search there for the initiating factor. In addition to local production, growth factors can also be transported into ischemic myocardium by blood-borne cells. Monocytes adhere to altered endothelium in a potentially ischemic region and start to produce growth factors in situ. Platelets are rich sources of transforming growth factor-beta (TGF-beta), platelet-derived endothelial cell growth factor (PDECGF) and platelet-derived growth factor (PDGF), all of which are known angiogenic factors or mitogens.

Adaptation, Physiological↗
PubMed1990

Ischemic preconditioning reduces infarct size in swine myocardium.

We evaluated the hypothesis that stunning swine myocardium with brief ischemia reduces oxygen demand in the stunned region and increases tolerance of myocardium to longer periods of ischemia. Wall function was quantified with ultrasonic crystals aligned to measure wall thickening, and stunning was achieved with two cycles of left anterior descending coronary artery (LAD) occlusion (10 minutes) and reperfusion (30 minutes), after which the LAD was occluded for 60 minutes and reperfused for 90 minutes. Infarct size (as a percent of risk region) was then determined by incubating myocardium with para-nitro blue tetrazolium. Regional oxygen demand was measured as myocardial oxygen consumption before the 60-minute LAD occlusion in the stunned region; tracer microspheres were used to determine blood flow, and blood from the anterior interventricular vein and left atrium was used to calculate oxygen saturations. After the second reperfusion period, wall thickening in the stunned region was reduced to 1.4 +/- 2.4% compared with 36.7 +/- 2.5% (mean +/- SEM) before ischemia (p less than 0.001). Regional myocardial oxygen consumption after stunning (3.1 +/- 0.7 ml O2/min/100 g) was no different from regional myocardial oxygen consumption before stunning (3.7 +/- 0.6 ml O2/min/100 g). In the nine pigs "preconditioned" by stunning, infarct size was 10.4 +/- 6.3% of the risk region compared with 48.0 +/- 12.7% in the six control pigs subjected to 60 minutes of ischemia without prior stunning (p less than 0.005). The risk regions were similar (14.4 +/- 1.5% vs. 14.6 +/- 1.9% of the left ventricle, preconditioned vs. control pigs, respectively). We conclude that stunning swine myocardium with two cycles of a 10-minute LAD occlusion followed by reperfusion increases ischemic tolerance but that changes in regional demand in stunned myocardium do not predict the marked reduction in infarct size that follows a subsequent 60-minute period of ischemia.

Animals↗
PubMed1989

Isolation of heparin-binding growth factors from bovine, porcine and canine hearts.

Fresh bovine, porcine and canine hearts were homogenized and mitogens for mesoderm-derived cells were purified in three different steps. Extraction by two different ammonium sulfate precipitations was followed by cation-exchange chromatography and by heparin-Sepharose affinity chromatography. A heparin-Sepharose fraction from heart (eluted at 1.1 M NaCl) increased mitotic activity in serum-deprived cultures of porcine aortic endothelial and smooth muscle cells, and in human fibroblasts. This mitogenic activity is potentiated by heparin and inhibited by gamma-interferon. The heart mitogenic fraction showed one double peak on HPLC at A215 and one polypeptide band on SDS/PAGE. These peaks and bands were identical to those obtained from bovine brain. The heart acidic fibroblast growth factor (aFGF) showed a positive signal in Western blots using antibodies raised against brain aFGF. Gas-phase amino acid sequencing established that the mitogens were identical to aFGF and the N-terminally truncated aFGF. Extraction in the presence of a protease inhibitor (pepstatin A) produced a higher-molecular mass form of aFGF with a blocked amino terminus. Another mitogen, eluted at 1.6 M NaCl from heparin-Sepharose, reacted with polyclonal antiserum against human recombinant basic fibroblast growth factor (bFGF) and showed a 66% (12 from 18 amino acids determined by gas-phase sequencing) similarity with bFGF. This polypeptide increased the mitotic activity of the same cell lines but was more potent than aFGF.

Amino Acid Sequence↗
PubMed1988

Enhanced postischemic ATP repletion by pharmacological inhibition of nucleoside washout and catabolism.

We tested the hypothesis that inhibition of adenosine transport by dipyridamole and inhibition of adenosine deamination by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) prevents nucleoside loss and stimulates postischemic ATP-repletion. In an open chest canine model, dipyridamole (0.5 mg/kg/h) and EHNA (5 mg/kg/h) were infused intra-atrially during a coronary occlusion period of 45 min and a reperfusion period of 180 min. Transmural needle biopsies, obtained during the ischemic period and within the reperfusion period, were analyzed using high performance liquid chromatography for adenine nucleotides and adenosine, inosine, xanthine, and hypoxanthine as well as creatine phosphate. During ischemia and under the influence of dipyridamole plus EHNA, 56% of the catabolized adenine nucleotides were recovered stoichiometrically as adenosine, whereas in the untreated group less than 10% of the nucleotides were recovered as adenosine because of rapid deamination to inosine. In the control group, ATP levels decreased during ischemia from control values of 5.25 +/- 0.28 microns/g to 2.01 +/- 0.18 microns/g. In the group treated with dipyridamole and EHNA, ATP levels fell to 2.2 +/- 0.22 microns/g but rose to 3.22 +/- 0.29 microns/g within 180 min of reperfusion, whereas in the untreated control group tissue levels of ATP did not increase. However, a significant proportion of the adenosine accumulated during ischemia under the influence of dipyridamole plus EHNA was not used for the restoration of the ATP level during reperfusion. A significant amount of adenosine was probably trapped in the interstitial space and could not be transported back into the myocytes in the presence of dipyridamole during reperfusion. In both groups, creatine phosphate levels were restored to normal levels during reperfusion.

Adenine Nucleotides↗
PubMed1987

Influence of mioflazine on canine coronary blood flow and on adenine nucleotide and nucleoside content under normal and ischemic conditions.

Intravenous injection of mioflazine, a nucleoside transport antagonist, caused maximal coronary vasodilation in canine hearts. This was completely reversed by intravenous injection of the enzyme adenosine deaminase. Coronary vasodilation was induced again by the adenosine deaminase inhibitor EHNA [Erythro-9(2-hydroxy-3-nonyl)adenine]; however, without previous injection of mioflazine, EHNA did not produce coronary vasodilation. Mioflazine-induced coronary vasodilation was antagonized by theophylline, but it was not associated with increased plasma levels of adenosine. Under the influence of mioflazine, ischemic myocardium contained adenosine and inosine at a ratio of 65:30, which is the reverse of the control ratio. Total nucleoside content following mioflazine showed reduced nucleoside losses as compared with control. A significant amount of the accumulated adenosine is extracellular since it was accessible to exogenous adenosine deaminase. Reperfusion of ischemic myocardium did not result in increased rates of adenosine phosphorylation, another indicator of its extracellular accumulation. The data are best explained by assuming release of adenosine by mioflazine in addition to its known effect of inhibiting nucleoside transport. The adenosine release occurs most probably into the interstitial space where it occupies smooth muscle adenosine receptors. The existence of nonsymmetric transport (uptake is more inhibited than release) is postulated for the myocyte, as well as for the endothelial cell plasma membrane.

Adenine Nucleotides↗