Browsing by Subject "nitric oxide synthase"
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Item INTERMITTENT HYPOXIA CONDITIONING REDUCES INOS AND ENOS EXPRESSION IN RAT MYOCARDIUM: A MECHANISM FOR PROTECTION FROM ISCHEMIA AND REPERFUSION INJURY(2014-03) Downey, H. Fred; Manukhina, Eugenia B.; Goryacheva, Anna V.; Belkina, Ludmila M.; Terekhina, Olga L.; Mallet, Robert T.During a heart attack, the heart produces excessive amounts of harmful chemicals. This study showed that prior exposure of rats to short cycles of a low oxygen atmosphere reduced production of these chemicals and lessened the damage to muscle and blood vessels of the heart. This procedure may benefit humans at risk of heart attack. Purpose (a): Recently we demonstrated that intermittent, normobaric hypoxia conditioning (IHC) prevented injuries of myocardium and coronary blood vessels induced by myocardial ischemia and reperfusion (IR). This cardio- and vasoprotection of was associated with alleviation of nitric oxide overproduction. The aim of this study was to identify specific NO synthases responsible for the IR-induced NO overproduction and to determine the effects of IHC on these NO synthases. Methods (b): This research was approved by the Animal Care and Use Committee of the Institute of General Pathology and Pathology. IHC of rats was performed in a normobaric chamber (5-8 cycles/d for 20 d, FIO2 9.5 - 10% for 5 - 10 min/cycle, with intervening 4-min normoxia). IR was produced by ligation of the left anterior descending coronary artery for 30 min followed by 60-min reperfusion. The protein nitration marker, nitrotyrosine (3-NT) and neuronal (nNOS), inducible (iNOS), and endothelial (eNOS) nitric oxide synthases were measured by immunoblot. Results (c): IR induced appreciable 3-NT accumulation in the left ventricular free wall, increasing the 3-NT content by 42% (p<0.01), but not in septum. In IHC rats, 3-NT after IR was similar to that of control rats without IR. IHC decreased iNOS by 71% (p<0.05) and eNOS by 41% (p<0.05) in the left ventricular myocardium; the myocardial content of nNOS remained unchanged. Conclusions (d): IHC prevents IR-induced NO overproduction in myocardium by restricting myocardial expression of iNOS and eNOS.Item Opioid and Nitric Oxide Interaction in the Control of Heart Rate(2002-12-01) Farias III, Martin; James Caffrey; Fred H. Downey; Patricia GwirtzFarias III, Martin, Opioid and Nitric Oxide Interaction in the Control of Heart Rate. Doctor of Philosophy (Biomedical Sciences), December 2002, 130 pp, 2 tables, 30 figures. Understanding of the role endogenous opioids play as modulators of parasympathetic function has increased. The endogenous opioid, methionine-enkephalin arginine phenylalanine (MEAP) attenuates vagal control of heart rate when delivered by microdialysis directly in the canine sinoatrial node. This effect was mimicked by the δ-2 agonist, deltorphin-II indicating involvement by a δ-opioid receptor. The nodal delivery of the δ-antagonist naltrindole abolished the effect of deltorphin-II, further supporting the delta character of the receptor. Although the findings suggested that the opioid receptor mediating vagolysis was delta in character, the exact subtype of δ-receptor remained in question. Selective agonist and antagonists for δ-1 and δ-2 opioid receptors were employed to determine which subtype of δ-receptor mediated MEAP vagolysis. In these experiments, vagolysis produced by the nodal delivery of MEAP was unaltered by the highly selective δ-1 antagonist BNTX but abolished by the δ-2 antagonist, naltriben. Nodal delivery of deltorphin-II attenuated vagal bradycardia similar to MEAP while δ-1 agonists, DPDPE and TAN-67 failed to interrupt vagal bradycardia. TAN-67 actually improved vagal transmission and this effect was reversed by BNTX. These data indicate that δ-2 opioid receptors in the sinoatrial node and vagolytic and support the presence of vagotonic δ-1-opioid receptors in the same location. Nitric Oxide/Opioid Interaction. The hypothesis that intranodal nitric oxide synthase (NOS) modulates vagal transmission and that MEAP attenuates vagal bradycardia via the interruption of the NOS-cGMP pathway was tested. The general (L-NAME) and neuronal (7-nitroindazole) NOS inhibitors each attenuated vagal bradycardia and both effects were reversed by adding excess of the NOS substrate, L-arginine. These findings suggested that nNOS was a necessary component of vagal bradycardia in the canine sinoatrial node. Various probes of the NOS-cGMP pathway (L-arginine, SNAP, cGMP, and IBMX) were employed to determine if MEAP interrupted this pathway to produce vagolysis. The delivery of MEAP into the sinoatrial node for sixty minutes exerted a consistent vagolytic effect during vagal simulations. When MEAP was combined with a NOS pathway components, the vagolytic effect was reversed after 15-45 minutes of treatment. These findings suggested that MEAP exerted its effect by interacting with the NOW-cGMP system. The site of convergence maybe cAMP since the phosphodiesterase inhibitor, IBMX (by allowing the accumulation of cAMP) reversed the vagolytic effect of MEAP. To rule out a postjunctional effect, MEAP and the NOS inhibitors were combined with the direct acting muscarinic agonist, methacholine. The bradycardia produced by methacholine was unaltered by MEAP or nNOS inhibitors. This suggested that the effect of NOS inhibitors and MEAP were prejunctional. In summary, the cumulative findings suggest that MEAP, by activating δ-2-opioid receptors, attenuated vagal bradycardia prejunctionally, through modulating the cAMP component of the NOS-cGMP pathway in the canine sinoatrial node.Item Responses of Myocardial Antioxidant Systems to Intermittent Hypoxia and Ethanol Withdrawal(2008-05-01) Schulz, Diana R.; Robert Mallet; H. Fred DowneySchulz, Diana R., Responses of Myocardial Antioxidant Systems to Intermittent Hypoxia and Ethanol Withdrawal. Master of Science, May 2008, 50 pp., 3 tables, 14 figures, bibliography: 38 titles. Introduction: The effects of ethanol intoxication on the heart have been extensively studied over the past century; however the consequences of ethanol withdrawal on the heart have not been documented. Myocardial adaptations to hypoxia can improve contractility, enhance antioxidant defense mechanisms, decrease lipid peroxidation induced by oxidative stress, and bolster cardiac resistance to ischemia-reperfusion. This study was conducted to determine if ethanol intoxication-withdrawal can harm the myocardium, and if intermittent hypoxia conditioning (IHC) can induce antioxidant enzymes and proteins that blunt these effects. Hypothesis: IHC increases myocardial antioxidant enzymes and other stress proteins, which could protect myocardium from ethanol intoxication-withdrawal. Methods: Four month old Sprague Dawley rats (n=61) were divided into 8 groups. Four groups were fed a 6.4% ethanol enriched diet, and the other four were fed an isocaloric dextrin diet. IHC was initiated two weeks after the diets began. The antioxidant N-acetylcysteine (NAC) was injected throughout the IHC and sham conditioning programs to interrogate the role of reactive oxygen species in the effects of ethanol intoxication-withdrawal and IHC on myocardial proteins. Proteins were extracted from snap-frozen myocardium for assays of nitric oxide synthase (NOS), gluthathione peroxidase (GPx) and superoxide dimustase (SOD) activities, and immunoblot analyses of endothelial NOS (eNOS) and heat shock protein 70 (Hsp70). Results: Ethanol withdrawal inactivated myocardial SOD, but did not affect activities of GPx and NOS, or contents of Hsp70 and eNOS. IHC lowered SOD activity by 55% in dextrin-fed rats, but partially protected SOD activity from ethanol intoxication-withdrawal. IHC did not affect myocardial GPx, NOS, and Hsp70 in dextrin and ethanol-withdrawn rats. NAC alone increased SOD activity in dextrin-fed and ethanol withdrawn rats and, when combined with IHC, NAC fully protected SOD activity from ethanol intoxication-withdrawal. Conclusions: Ethanol intoxication-withdrawal had statistically significant effects on the antioxidant enzyme SOD. IHC and NAC selectively protected SOD activity from ethanol intoxication-withdrawal. This specificity suggests that the oxidative stress induced by ethanol intoxication-withdrawal is discrete in comparison to the massive oxidative stress inflicted on the brain under these conditions. The differences in the intensity of oxidative stress could be one of the factors influencing the divergence of results in comparison to previous investigations of ethanol intoxication-withdrawal.