8-bromocyclic-gmp and Myocardial-Infarction

It is unknown if cardiac ischemia has any deleterious effect on the contractile properties of nonischemic, peripheral vascular beds. Thus, the objective of the present study was to determine whether acute myocardial ischemia results in peripheral vascular dysfunction.. This study characterized force maintenance and the sensitivity to acetylcholine (ACh)-mediated smooth muscle (SM) relaxation of tertiary (3rd) mesenteric arteries from Sprague-Dawley rats following 30 min of myocardial ischemia. Both the phosphorylation of nonmuscle (NM) light chain (LC) and SM-LCs as well as the expression of myosin phosphatase targeting subunit 1 (MYPT1) were also determined. Our data demonstrate that acute myocardial ischemia resulted in vascular dysfunction of 3rd mesenteric vessels, characterized by decreases in force maintenance, ACh- and cGMP-mediated SM relaxation, the phosphorylation of NM-LCs and SM-LCs, and MYPT1 expression. Ischemia was also associated with an increase in protein polyubiquitination, suggesting that during ischemia MYPT1 is targeted for degradation or proteolysis.. Acute myocardial ischemia produces peripheral vascular dysfunction; the changes in LC phosphorylation and MYPT1 expression result in a decrease in both tone and the sensitivity to NO-mediated SM relaxation of the peripheral vasculature.

Topics: Acetylcholine; Acute Disease; Animals; Biomechanical Phenomena; Cyclic GMP; Enzyme Induction; Male; Membrane Potentials; Mesenteric Arteries; Muscle, Smooth, Vascular; Myocardial Infarction; Myosin Light Chains; Nitric Oxide; Phosphorylation; Potassium Chloride; Protein Phosphatase 1; Protein Processing, Post-Translational; Rats; Rats, Sprague-Dawley; Ubiquitination; Vasodilation

Hyperlipidaemia interferes with cardioprotective mechanisms, but the cause of this phenomenon is largely unknown, although hyperlipidaemia impairs the cardioprotective NO-cGMP system. However, it is not known if natriuretic peptide-cGMP-protein kinase G (PKG) signalling is affected by hyperlipidaemia. Therefore, we investigated the cardioprotective efficacy of cGMP-elevating agents in hearts from normal and hyperlipidaemic rats.. Male Wistar rats were rendered hyperlipidaemic by feeding with 2% cholesterol-enriched chow for 12 weeks. Hearts isolated from normal and hyperlipidaemic rats were perfused (Langendorff mode) and subjected to 30 min occlusion of the left main coronary artery, followed by 120 min reperfusion. 8-Br-cGMP (CG, 10 nM), B-type natriuretic peptide-32 (BNP, 10 nM), S-nitroso-N-acetyl-penicillamine (SNAP, 1 microM) were perfused from 10 min prior to coronary occlusion until the 15th min of reperfusion. Infarct size (% of ischaemic risk zone) was determined by triphenyltetrazolium staining.. Treatment with CG, SNAP or BNP decreased infarct size significantly in normal hearts from its control value of 41.6 +/- 2.9% to 15.5 +/- 2.4%, 23.3 +/- 3.0% and 25.3 +/- 4.6%, respectively (P < 0.05). Protection by BNP was abolished by co-perfusion of PKG inhibitors KT5823 (600 nM) or Rp-8pCPT-PET-cGMPs (1 microM), confirming its PKG dependence. In hearts from hyperlipidaemic rats, CG, SNAP or BNP failed to decrease infarct size. Hyperlipidaemia did not alter basal myocardial PKG content, but decreased its activity as assessed by phosphorylation of cardiac troponin I.. This is the first demonstration that defects in the cardioprotective cGMP-PKG system could be a critical biochemical anomaly in hyperlipidaemia.

Topics: Animals; Cardiotonic Agents; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Dietary Fats; Disease Models, Animal; Hyperlipidemias; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Natriuretic Peptide, Brain; Phosphorylation; Rats; Rats, Wistar; S-Nitroso-N-Acetylpenicillamine; Troponin I

Congestive heart failure (CHF) is a clinical syndrome, which is the result of systolic or diastolic ventricular dysfunction. During CHF, vascular tone is regulated by the interplay of neurohormonal mechanisms and endothelial-dependent factors and is characterized by both central and peripheral vasoconstriction as well as a resistance to nitric oxide (NO)-mediated vasodilatation. At the molecular level, vascular tone depends on the level of regulatory myosin light chain phosphorylation, which is determined by the relative activities of myosin light chain kinase and myosin light chain phosphatase (MLCP). The MLCP is a trimeric enzyme with a catalytic, a 20-kDa and a myosin targeting (MYPT1) subunit. Alternative splicing of a 3' exon produces leucine zipper positive and negative (LZ+/-) MYPT1 isoforms. Expression of a LZ+ MYPT1 has been suggested to be required for NO-mediated smooth muscle relaxation. Thus, we hypothesized that the resistance to NO-mediated vasodilatation in CHF could be attributable to a change in the relative expression of LZ+/- MYPT1 isoforms. To test this hypothesis, left coronary artery ligation was used to induce CHF in rats, and both the dose response relationship of relaxation to 8-Br-cGMP in skinned smooth muscle and the relative expression of LZ+/- MYPT1 isoforms were determined. In control animals, the expression of the LZ+ MYPT1 isoform predominated in both the aorta and iliac artery. In CHF rats, LVEF was reduced to 30+/-5% and there was a significant decrease in both the sensitivity to 8-Br-cGMP and expression of the LZ+ MYPT1 isoform. These results indicate that CHF is associated with a decrease in the relative expression of the LZ+ MYPT1 isoform and the sensitivity to 8-Br-cGMP-mediated smooth muscle relaxation. The data suggest that the resistance to NO-mediated relaxation observed during CHF lies at least in part at the level of the smooth muscle and is a consequence of the decrease in the expression of the LZ+ MYPT1 isoform.

Topics: Alternative Splicing; Animals; Blotting, Western; Calcium; Carrier Proteins; Coronary Vessels; Cyclic GMP; Dose-Response Relationship, Drug; Heart Failure; Ligation; Muscle, Smooth, Vascular; Myocardial Infarction; Nitric Oxide; Phosphoprotein Phosphatases; Phosphorylation; Protein Isoforms; Protein Phosphatase 1; Protein Processing, Post-Translational; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Ultrasonography; Vasodilation

B-type natriuretic peptide (BNP) has been reported to be released from the myocardium during ischemia. We hypothesized that BNP mediates cardioprotection during ischemia-reperfusion and examined whether exogenous BNP limits myocardial infarction and the potential role of ATP-sensitive potassium (K(ATP)) channel opening. Langendorff-perfused rat hearts underwent 35 min of left coronary artery occlusion and 120 min of reperfusion. The control infarct-to-risk ratio was 44.8 +/- 4.4% (means +/- SE). BNP perfused 10 min before ischemia limited infarct size in a concentration-dependent manner, with maximal protection observed at 10(-8) M (infarct-to-risk ratio: 20.1 +/- 5.2%, P < 0.01 vs. control), associated with a 2.5-fold elevation of myocardial cGMP above the control value. To examine the role of K(ATP) channel opening, glibenclamide (10(-6) M), 5-hydroxydecanoate (5-HD; 10(-4) M), or HMR-1098 (10(-5) M) was coperfused with BNP (10(-8) M). Protection afforded by BNP was abolished by glibenclamide or 5-HD but not by HMR-1098, suggesting the involvement of putative mitochondrial but not sarcolemmal K(ATP) channel opening. We conclude that natriuretic peptide/cGMP/K(ATP) channel signaling may constitute an important injury-limiting mechanism in myocardium.

Topics: Animals; Atrial Natriuretic Factor; Cardiotonic Agents; Cyclic GMP; Dose-Response Relationship, Drug; Heart Ventricles; Ion Channel Gating; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Myocardium; Natriuretic Peptide, Brain; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Sprague-Dawley