Biomedical subjects

Guro Valen

Publications and source records attributed to Guro Valen.

24 records · Page 2Linked to original sources

PubMed2003

Preconditioning and cardiac surgery.

Preconditioning is in experimental studies the most powerful mode of cardioprotection known. The signal transduction pathways involve a variety of trigger substances, mediators, receptors, and effectors. The studies of preconditioning in cardiac surgery provide conflicting results but the majority of studies show that ischemic preconditiong is an effective adjunct to myocardial protection. However, ischemic preconditioning with repeated clamping of the aorta will never get widespread use. If the "preconditioning response" is to be exploited in cardiac surgery, targeting the underlying molecular mechanisms must provide easily applicable techniques or drugs, which are shown in large scale clinical studies to be beneficial.

Animals↗

PubMed2003

Hyperoxia elicits myocardial protection through a nuclear factor kappaB-dependent mechanism in the rat heart.

OBJECTIVE: Hyperoxia has been previously shown to protect the heart from ischemia-reperfusion injury. In the present study we investigated whether the cardioprotective effects of hyperoxia were dependent on the redox-sensitive transcription factor nuclear factor kappaB. METHODS: Rats were kept in a hyperoxic (> or =95% O(2)) environment for 60 minutes. Their hearts were isolated immediately afterward, buffer perfused in a Langendorff apparatus, and subjected to 25 minutes of global ischemia and 60 minutes of reperfusion. Cardiac pressures and coronary flow were measured, and infarct size was determined by means of triphenyl tetrazolium chloride staining. Activation of nuclear factor kappaB was assessed by means of the electrophoretic mobility shift assay, whereas the inhibitor IkappaBalpha was evaluated by means of immunoblotting. Pharmacologic inhibition of nuclear factor kappaB was achieved with 2 different agents, SN50 and pyrrolidine dithiocarbamate. RESULTS: Preischemic exposure to hyperoxia improved postischemic recovery of myocardial contractile function and coronary flow and reduced infarct size. Hyperoxia activated pulmonary and myocardial nuclear factor kappaB. Pretreatment with SN50 (400 microg/kg administered intraperitoneally) or pyrrolidine dithiocarbamate (100 mg/kg administered intraperitoneally) before hyperoxia abolished the functional and infarct-limiting protection. Hyperoxia reduced nuclear factor kappaB activation in the heart during sustained ischemia and reperfusion and increased the cytoplasmatic inhibitory factor IkappaBalpha. Administration of pyrrolidine dithiocarbamate or SN50 during ischemia and reperfusion to isolated hearts from normoxic control animals improved postischemic contractile function and coronary flow and reduced infarct size. CONCLUSIONS: Hyperoxia protects the rat heart against ischemia-reperfusion injury. The cardioprotection depends on myocardial activation of the transcription factor nuclear factor kappaB. Our results support evidence for a dual role of nuclear factor kappaB in the heart.

Analysis of Variance↗

PubMed2003

Cellular signalling mechanisms in adaptation to ischemia-induced myocardial damage.

Ischemic heart disease is the major cause of morbidity and mortality in the Western world. Ischemia-reperfusion injury may induce cardiomyocyte cell death by necrosis or apoptosis. The heart can be adapted to tolerate an ischemic event by preceding brief episodes of ischemia and reperfusion, called preconditioning. Preconditioning protects the heart when it is directed towards the heart itself either immediately before or several days before an induced ischemic event. Adaptation by preconditioning can even be achieved in other organs, and preconditioning one organ can protect another organ. Evidence suggests that preconditioning may be a naturally occurring adaptive process in vivo, and in humans unstable angina before acute myocardial infarction may represent the phenomenon. The mechanisms underlying the response are complex and intertwined, and probably differ between acute and delayed. as well as local or remote models. Based on animal experiments, it appears that preconditioning consists of a trigger phase with release of signal substance(s), a signal transduction phase where cascade reactions are induced, and an organ effector phase where mediator(s) ensure organ protection against necrosis and apoptosis. Understanding the underlying mechanisms of action is crucial to making therapeutic use of this powerful mode of myocardial protection.

Adaptation, Physiological↗

PubMed2003

Deficiency of nitric oxide synthase 2 results in increased neointima formation in a mouse model of vascular injury.

Restenosis frequently occurs after arterial interventions. The inducible form of nitric oxide synthase (NOS2) may both promote and inhibit neointima formation. This study investigated the role of NOS2 for neointima formation in a mouse model of carotid artery injury. The common carotid artery was ligated in anesthetized mice. Homozygous NOS2 knockout mice were compared with wild-type B6/129 mice or wild-type mice treated with the pharmacologic NOS2 inhibitor aminoguanidine given orally daily after ligation (n = 6-8 in each group). Vessels were harvested for quantification of lesion size 4 weeks later, or serially after ligation for tissue analysis. mRNA for NOS2 increased 1-4 days after ligation of the carotid artery. Cell proliferation could be visualized with an antibody against proliferating cell nuclear antigen. An intimal smooth muscle cell layer, confirmed by an alpha-actin antibody, was observed in the lumen 4 weeks after injury. Inhibition of NOS2 by either pharmacologic or genetic approaches tended to increase the area of intima formation (P = 0.13 or P < 0.05, respectively) and increased the intima/media ratio (P = 0.14 and P < 0.01, respectively). Inhibition of NOS2 by two different approaches increased neointima formation in a mouse model of mechanical vessel injury, indicating that the NOS2 expressed in the injured vessel wall is beneficial.

Animals↗

PubMed2002

Effects of spontaneous or induced brain ischemia on vessel reactivity: the role of inducible nitric oxide synthase.

Short episodes of ischemia and reperfusion in various organs may protect the organ itself, and the heart both as an immediate and a delayed effect. The present study investigates whether a systemic protection of vascular function occurs during adaption to ischemia. Brain ischemia was induced by bilateral ligation of the internal carotid arteries in C57BL6 mice, and 24-36 hours later rings of the thoracic aorta were mounted to study in vitro relaxation and contraction, or proteins were extracted for immunoblotting for endothelial nitric oxide synthase (eNOS) or inducible NOS (iNOS). eNOS decreased, while iNOS increased in the aortic wall after carotid artery ligation. In vitro contraction to increasing concentrations of prostaglandin F(2alpha) (PGF(2alpha)) was attenuated, while relaxation to acetylcholine (ACh) was enhanced. The latter was abolished by the iNOS-inhibitor aminoguanidine. When brain ischemia was induced in iNOS deficient mice, an increase of aortic eNOS was found 24 hours later. The ischemia-induced attenuated relaxation to PGF(2alpha) and enhanced relaxation to ACh were abolished. Aortic rings from mice with severe atherosclerosis (apolipoprotein E and low density lipoprotein receptor double knockout (ApoE/LDLr KO) mice) and spontaneous ischemic events in the heart or brain in vivo were also studied. Spontaneous ischemic events in ApoE/LDLr KO animals did not influence iNOS and eNOS in the vessel wall. A reduced contraction to PGF(2alpha) was observed, but relaxation to ACh was unchanged. These findings suggest that induced brain ischemia as a model of delayed, remote preconditioning protects vessel reactivity, and this protection is mediated by iNOS.

Acetylcholine↗

PubMed2002

Spontaneous ischemic events in the brain and heart adapt the hearts of severely atherosclerotic mice to ischemia.

To investigate if spontaneous ischemic events in mice with severe multi-organ atherosclerosis could adapt to ischemia, apolipoprotein E/LDL receptor knockout mice were fed an atherogenic diet for 7 to 9 months. Signs of spontaneous ischemia occurred. One to two days later, hearts were excised, Langendorff-perfused with induced global ischemia, and compared with mice without signs of disease. In vivo heart or brain infarctions were verified by heart histology and/or increased serum levels of cardiac troponin T and S100B. Hearts of mice with spontaneous ischemic events had improved function and reduced Langendorff-induced infarctions. To investigate the remote preconditioning effect of brain ischemia, bilateral ligation of the internal carotid arteries was performed in C57BL6 mice. Twenty-four hours later, their isolated hearts were protected against induced global ischemia. A possible role of inducible NO synthase (iNOS) was studied in iNOS knock out mice, who were not preconditioned by induced brain ischemia. Cardiac iNOS was unchanged 24 hours after preconditioning, suggesting that NO is a trigger rather than a mediator of protection. These findings suggest that spontaneous ischemic events in the brain and heart adapt the heart to ischemia. This can be mimicked by induced brain ischemia, with iNOS as a key factor of protection.

Animals↗