nitroarginine and Myocardial-Infarction

Several clinical studies have shown the beneficial cardiovascular effects of fibrates in patients with diabetes and insulin resistance. The ligands of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) reduce ischemia-reperfusion injury in nondiabetic animals. We hypothesized that the activation of PPAR-alpha would exert cardioprotection in type 2 diabetic Goto-Kakizaki (GK) rats, involving mechanisms related to nitric oxide (NO) production via the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. GK rats and age-matched Wistar rats (n >or= 7) were given either 1) the PPAR-alpha agonist WY-14643 (WY), 2) dimethyl sulfoxide (DMSO), 3) WY and the NO synthase inhibitor N(G)-nitro-l-arginine (l-NNA), 4) l-NNA, 5) WY and the PI3K inhibitor wortmannin, or 6) wortmannin alone intravenously before a 35-min period of coronary artery occlusion followed by 2 h of reperfusion. Infarct size (IS), expression of endothelial NO synthase (eNOS), inducible NO synthase, and Akt as well as nitrite/nitrate were determined. The IS was 75 +/- 3% and 72 +/- 4% of the area at risk in the Wistar and GK DMSO groups, respectively. WY reduced IS to 56 +/- 3% in Wistar (P < 0.05) and to 46 +/- 5% in GK rats (P < 0.001). The addition of either l-NNA or wortmannin reversed the cardioprotective effect of WY in both Wistar (IS, 70 +/- 5% and 65 +/- 5%, respectively) and GK (IS, 66 +/- 4% and 64 +/- 4%, P < 0.05, respectively) rats. The expression of eNOS and eNOS Ser1177 in the ischemic myocardium from both strains was increased after WY. The expression of Akt, Akt Ser473, and Akt Thr308 was also increased in the ischemic myocardium from GK rats following WY. Myocardial nitrite/nitrate levels were reduced in GK rats (P < 0.05). The results suggest that PPAR-alpha activation protects the type 2 diabetic rat myocardium against ischemia-reperfusion injury via the activation of the PI3K/Akt and NO pathway.

Topics: Androstadienes; Animals; Blood Glucose; Body Weight; Cardiotonic Agents; Diabetes Mellitus, Type 2; Disease Models, Animal; Enzyme Inhibitors; Hemodynamics; Insulin; Male; Myocardial Contraction; Myocardial Infarction; Myocardial Reperfusion Injury; Myocardium; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; PPAR alpha; Proto-Oncogene Proteins c-akt; Pyrimidines; Rats; Rats, Wistar; Signal Transduction; Wortmannin

Cardiovascular disease and type 2 diabetes mellitus are associated with low plasma concentration of adiponectin. The aim of this study was to investigate whether adiponectin exerts cardioprotective effects during myocardial ischaemia-reperfusion and whether this effect is related to the production of nitric oxide (NO).. Isolated rat hearts were subjected to 30 min of either global or local ischaemia followed by 60 min of reperfusion. The hearts received vehicle, adiponectin (3 microg/mL), the NO-synthase inhibitor nitro-l-arginine (L-NNA) (0.1 mM), or a combination of adiponectin and L-NNA at the onset of ischaemia. Haemodynamics, infarct size, and expression of endothelial NO-synthase (eNOS), AMP-activated protein kinase (AMPK), and Akt were determined. Adiponectin significantly increased left ventricular function and coronary flow during reperfusion in comparison with the vehicle group. Co-administration of L-NNA abrogated the improvement in myocardial function induced by adiponectin. Infarct size following local ischaemia-reperfusion was 40 +/- 6% of the area at risk in the vehicle group. Adiponectin reduced infarct size to 19 +/- 2% (P < 0.01). L-NNA did not affect infarct size per se but abolished the protective effect of adiponectin (infarct size 40 +/- 5%). Phosphorylation of eNOS Ser1177, AMPK Thr172, and Akt Ser 473 was increased in the adiponectin group (P < 0.05).. Adiponectin protects from myocardial contractile dysfunction and limits infarct size following ischaemia and reperfusion by a mechanism involving activation of AMPK and production of NO.

Topics: Adiponectin; AMP-Activated Protein Kinases; Animals; Blotting, Western; Coronary Circulation; Disease Models, Animal; Enzyme Inhibitors; Hemodynamics; Humans; Male; Multienzyme Complexes; Myocardial Contraction; Myocardial Infarction; Myocardial Reperfusion Injury; Myocardium; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Signal Transduction; Time Factors; Ventricular Function, Left

It has been proposed that constitutive expression of endothelial NO synthase (eNOS) protects against myocardial ischemia/reperfusion injury in the naive (unstressed) state and that eNOS plays a critical role in the early phase of ischemic preconditioning (PC). We addressed these issues using both a genetic approach (i.e., eNOS null [eNOS(-/-)]) mice and a pharmacologic approach (with the NOS inhibitor N(omega)-nitro-l-arginine [L-NA]). We found that in the nonpreconditioned state, both of the available strains of eNOS(-/-) mice (C57BL6 and B6129) exhibited infarct sizes similar to the corresponding wild-type (WT) mice (63.3+/-2.2% [group I, n=15] vs. 59.7+/-1.4% [group VI, n=10] of the risk region and 60.9+/-3.6% [group IX, n=14] vs. 68.2+/-2.5% [group X, n=9], respectively). When WT mice were preconditioned with either one or six cycles of 4-min coronary occlusion (O)/reperfusion (R) 10 min prior to the 30-min O, infarct size was markedly reduced (28.5+/-3.3% [group II, one O/R cycle, n=10] and 19.7+/-2.6% [group III, six O/R cycles, n=7] of the risk region, respectively), indicating the development of a robust early PC effect. In eNOS(-/-) mice preconditioned with the same protocol, the reduction in infarct size was similar (24.9+/-2.9% and 15.3+/-2.4% of the risk region, after one [group VII, n=9] or six O/R cycles [group VIII, n=10], respectively), indicating that the PC effect was intact. When WT mice were pretreated with L-NA 30 min before sham PC (group IV, n=7) or PC (group V, six O/R cycles, n=7), infarct size was not different from untreated control and PC groups. We conclude that, in the mouse, basal eNOS activity does not modulate infarct size in the nonpreconditioned state and is not necessary for the cardioprotective effects of early PC. Early PC is not eNOS-dependent, at least in this species.

Topics: Animals; Blotting, Western; Genotype; Ischemic Preconditioning; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Mice, Knockout; Myocardial Infarction; Nitric Oxide Synthase Type III; Nitroarginine

Volatile anesthetics induce myocardial preconditioning through a signal transduction pathway that is remarkably similar to that observed during ischemic preconditioning. Nitric oxide-dependent signaling plays an important role in anesthetic and ischemic preconditioning. Therefore, the authors tested the hypothesis that desflurane-induced preconditioning is mediated by nitric oxide.. Barbiturate-anesthetized rabbits were instrumented for measurement of hemodynamics. All rabbits were subjected to 30-min coronary artery occlusion followed by 3 h of reperfusion. Myocardial infarct size was assessed with triphenyltetrazolium chloride staining. Myocardial nitric oxide synthase activity was assessed with a [H]L-arginine-conversion assay. Rabbits were randomized to five separate experimental groups. They received 0.0 or 1.0 minimum alveolar concentration desflurane for 30 min, which was discontinued 30 min before ischemia in the absence or presence of the nitric oxide synthase inhibitor N-nitro-L-arginine (L-NA). L-NA was given either 20 min before or 10 min after desflurane administration, respectively. Data are mean +/- SEM.. Infarct size was 56 +/- 8% in control experiments. Desflurane significantly (P < 0.05) reduced infarct size to 35 +/- 4%. Preconditioning by desflurane was totally blocked by administration of L-NA either during or after desflurane inhalation (58 +/- 4 and 59 +/- 9%, respectively). L-NA alone had no effect on infarct size (56 +/- 7%). Nitric oxide synthase activity was significantly (P < 0.05) increased by desflurane.. The results demonstrate that desflurane-induced preconditioning markedly reduced myocardial infarct size. This beneficial effect was blocked by the nitric oxide synthase inhibitor L-NA either during or after desflurane-administration. These data suggest that early desflurane-induced preconditioning is mediated by nitric oxide.

Topics: Anesthetics, Inhalation; Animals; Desflurane; Enzyme Inhibitors; Hemodynamics; Ischemic Preconditioning, Myocardial; Isoflurane; Male; Myocardial Infarction; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rabbits

Endogenous adenosine is a trigger for ischemic myocardial preconditioning (IPC). Although intravascular administration of adenosine has been used to further unravel the mechanism of protection by IPC, it is questionable whether adenosine and IPC employ the same signaling pathways to exert cardioprotection. We therefore investigated whether the active metabolic barrier of the endothelium prevents an increase in myocardial interstitial adenosine concentrations by intravenous adenosine, using microdialysis, and also the role of NO and activation of a neurogenic pathway in the cardioprotection by adenosine. In pentobarbital-anesthetized rats, area at risk and infarct size (IS) were determined 120 min after a 60-min coronary artery occlusion (CAO), using trypan blue and nitro-blue-tetrazolium staining, respectively. IPC with a single 15-min CAO and a 15-min adenosine infusion (ADO, 200 microg min(-1) i.v.) limited IS to the same extent (IS = 41 +/- 6% and IS = 40 +/- 4%, respectively) compared to control rats (IS = 63 +/- 3%, both P < 0.05). However, IPC increased myocardial interstitial adenosine levels seven-fold from 4.3 +/- 0.7 to 27.1 +/- 10.0 microM (P < 0.05), while ADO had no effect on interstitial adenosine (4.1 +/- 1.2 microM), or any of the other purines. The NO synthase inhibitor N(omega)-nitro-L-arginine (LNNA), which did not affect IS (IS = 62 +/- 3%), attenuated the protection by ADO (IS = 56 +/- 3%; P < 0.05 vs ADO, P = NS vs LNNA). The ganglion blocker hexamethonium, which had also no effect on IS (IS = 66 +/- 3%), blunted the protection by ADO (IS = 55 +/- 4%; P < 0.05 vs ADO and vs hexamethonium). These observations demonstrate that cardioprotection by ADO is dependent on NO, and is primarily mediated by activation of a neurogenic pathway.

Topics: Adenosine; Animals; Cardiotonic Agents; Ganglionic Blockers; Hexamethonium; Infusions, Intravenous; Ischemic Preconditioning; Male; Microdialysis; Myocardial Infarction; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar

Left ventricular (LV) dysfunction caused by myocardial infarction (MI) is accompanied by endothelial dysfunction, most notably a loss of nitric oxide (NO) availability. We tested the hypothesis that endothelial dysfunction contributes to impaired tissue perfusion during increased metabolic demands as produced by exercise, and we determined the contribution of NO to regulation of regional systemic, pulmonary, and coronary vasomotor tone in exercising swine with LV dysfunction produced by a 2- to 3-wk-old MI. LV dysfunction resulted in blunted systemic and coronary vasodilator responses to ATP, whereas the responses to nitroprusside were maintained. Exercise resulted in blunted systemic and pulmonary vasodilator responses in MI that resembled the vasodilator responses in normal (N) swine following blockade of NO synthase with N(omega)-nitro-L-arginine (L-NNA, 20 mg/kg iv). However, L-NNA resulted in similar decreases in systemic (43 +/- 3% in N swine and 49 +/- 4% in MI swine), pulmonary (45 +/- 5% in N swine and 49 +/- 4% in MI swine), and coronary (28 +/- 4% in N and 35 +/- 3% in MI) vascular conductances in N and MI swine under resting conditions; similar effects were observed during treadmill exercise. Selective inhibition of inducible NO synthase with aminoguanidine (20 mg/kg iv) had no effect on vascular tone in MI. These findings indicate that while agonist-induced vasodilation is already blunted early after myocardial infarction, the contribution of endothelial NO synthase-derived NO to regulation of vascular tone under basal conditions and during exercise is maintained.

Topics: Adenosine Triphosphate; Animals; Coronary Circulation; Coronary Vessels; Endothelium, Vascular; Enzyme Inhibitors; Guanidines; Lung; Myocardial Infarction; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Nitroprusside; Physical Exertion; Reproducibility of Results; Swine; Vasodilation; Ventricular Dysfunction, Left

The interaction between the cardioprotective effect of endothelin (ET) receptor blockade and nitric oxide (NO) during ischemia-reperfusion injury was investigated. Anesthetized pigs were subjected to 45 (protocol 1) or 30 min (protocol 2) coronary artery ligation and 4 h reperfusion. In protocol 1, five groups were given vehicle, the ET(A) receptor antagonist LU-135252 (LU), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NNA), L-NNA in combination with LU, or L-NNA in combination with the NO precursor L-arginine (L-Arg) and LU intravenously before ischemia. In protocol 2, two groups were given vehicle or L-NNA. In protocol 1, the infarct size (IS) was 79 +/- 5% of the area at risk in the vehicle group and 93 +/- 2% in the L-NNA group. LU reduced the IS to 43 +/- 7% (P < 0.001). The cardioprotective effect of LU was abolished in the presence of L-NNA (IS 76 +/- 6%), whereas addition of L-Arg restored its cardioprotective effect (IS 56 +/- 2%; P < 0.05 vs. vehicle and L-NNA + LU groups). In protocol 2, the IS was 49 +/- 6% in the vehicle group and 32 +/- 4% in the L-NNA group (P = not significant). Myocardial ET-like immunoreactivity (ET-LI) increased in the vehicle group of protocol 1. ET-LI in the ischemic-reperfused myocardium was lower in the groups given LU (P < 0.01) and L-NNA + L-Arg + LU (P < 0.05) but not in the group given L-NNA + LU compared with the vehicle group. These results suggest that the cardioprotective effect of the ET(A) receptor antagonist is mediated via a mechanism related to NO.

Topics: Animals; Blood Pressure; Coronary Circulation; Endothelin Receptor Antagonists; Endothelin-1; Enzyme Inhibitors; Female; Heart Rate; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenylpropionates; Pyrimidines; Receptor, Endothelin A; Survival Rate; Swine

We investigated whether activation of A(1) or A(3) adenosine receptors (ARs) induces late preconditioning (PC) against infarction in conscious rabbits using the selective AR agonists 2-chloro-N(6)-cyclopentyladenosine (CCPA) and N(6)-3-iodobenzyladenosine-5'-N-methylcarboxamide (IB-MECA). In vitro radioligand binding and cAMP assays demonstrated CCPA to be approximately 200- to 400-fold selective for the rabbit A(1)AR and IB-MECA to be approximately 20-fold selective for the rabbit A(3)AR. We observed that (1) pretreatment of rabbits 24 hours earlier with CCPA (100 microgram/kg IV bolus) or IB-MECA (100 or 300 microgram/kg) resulted in an approximately 35% to 40% reduction in the size of the infarct induced by 30 minutes of coronary artery occlusion and 72 hours of reperfusion compared with vehicle-treated rabbits, whereas pretreatment with the selective A(2A)AR agonist CGS 21680 (100 microgram/kg) had no effect; (2) the delayed cardioprotective effect of CCPA, but not that of IB-MECA, was completely blocked by coadministration of the highly selective A(1)AR antagonist N-0861; (3) inhibition of nitric oxide synthase (NOS) with N(omega)-nitro-L-arginine during the 30-minute occlusion abrogated the infarct-sparing action of CCPA but not that of IB-MECA; and (4) inhibition of ATP-sensitive potassium (K(ATP)) channels with sodium 5-hydroxydecanoate during the 30-minute occlusion blocked the cardioprotective effects of both CCPA and IB-MECA. Taken together, these results indicate that activation of either A(1)ARs or A(3)ARs (but not A(2A)ARs) elicits delayed protection against infarction in conscious rabbits and that both A(1)AR- and A(3)AR-induced cardioprotection involves opening of K(ATP) channels. However, A(1)AR-induced late PC uses an NOS-dependent pathway whereas A(3)AR-induced late PC is mediated by an NOS-independent pathway.

Topics: Adenine; Adenosine; Animals; Binding, Competitive; Cell Line; Consciousness; Decanoic Acids; Humans; Hydroxy Acids; Iodine Radioisotopes; Ischemic Preconditioning, Myocardial; Membranes; Myocardial Infarction; Nitroarginine; Norbornanes; Phenethylamines; Rabbits; Radioligand Assay; Receptor, Adenosine A3; Receptors, Purinergic P1

Endothelium-derived nitric oxide (NO) and endothelin (ET)-1 interact to regulate vascular tone. In congestive heart failure (CHF), the release and/or the activity of both factors is affected. We hypothesized that the increased ET-1 production associated with CHF may result in a reduced smooth muscle sensitivity to NO. The aim of this study was to evaluate the effects of a chronic treatment with the ET(A)-receptor (ET receptor A) antagonist LU-135252 (LU) on cerebrovascular reactivity to sodium nitroprusside (SNP) in the rat infarct model of CHF. Rats were subjected to coronary artery ligation and were treated for 4 wk with placebo (n = 24) or LU (50 mg. kg(-1). day(-1), n = 29). CHF was associated with a decreased (P < 0.05) efficacy of SNP to induce relaxation of isolated middle cerebral arteries. Furthermore, neither NO synthase inhibition with N(omega)-nitro-L-arginine (L-NNA) nor endothelial denudation affected the efficacy of SNP. Thus the endothelium no longer influences smooth muscle sensitivity to SNP. LU treatment, however, normalized (P < 0.05) smooth muscle sensitivity to SNP. Sensitivity of ET-1-induced contraction was increased in CHF only in the presence of L-NNA, whereas contraction induced by ET(B) receptor (receptor B) stimulation was increased (P < 0.05) in endothelium-denuded vessels. LU treatment restored these changes in reactivity and revealed a significant endothelium-dependent ET(B)-mediated relaxation after NO synthase inhibition. In conclusion, CHF decreases and uncouples cerebrovascular smooth muscle sensitivity to SNP from endothelial regulation. The observation that chronic ET(A) blockade restored most of the changes associated with CHF suggests that activation of the ET-1 system importantly contributes to the alteration in vascular reactivity observed in experimental CHF.

Topics: Animals; Cerebral Arteries; Electrocardiography; Endothelin Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Heart Failure; Hemodynamics; In Vitro Techniques; Male; Muscle, Smooth, Vascular; Myocardial Infarction; Nitroarginine; Nitroprusside; Phenylpropionates; Pyrimidines; Rats; Rats, Wistar; Receptor, Endothelin A; Receptors, Endothelin; Vasoconstrictor Agents; Vasodilation; Viper Venoms

Chronic nitric oxide synthase (NOS) inhibition results in hypertension and myocardial injury. In a rapid and severe model of chronic NOS inhibition, we determined the role of angiotensin II in these effects by using angiotensin II receptor blockade and by measuring cardiac angiotensin II concentrations before and during development of cardiac damage. Rats received either no treatment, the NOS inhibitor Nomega-nitro-L-arginine (L-NNA; 500 mg/l), the angiotensin AT(1) receptor antagonist losartan (400 mg/kg chow), or L-NNA plus losartan for 21 days. In the second protocol, five groups of rats received L-NNA (500 mg/l) for 0, 4, 7, 14 and 21 days, respectively. L-NNA increased systolic blood pressure (SBP) (227+/-8 versus 143+/-6 mm Hg; P<0.01), heart weight index (0.44+/-0.02 versus 0.32+/-0.01; P<0.01) and induced coronary vasculitis and myocardial necrosis. Co-treatment with losartan prevented all changes. L-NNA during 4 days decreased cardiac angiotensin II (23+/-4 versus 61+/-15 fmol/g; P<0.05). Although after 7 days, fresh infarcts and after 14 days organized infarcts were present, cardiac angiotensin II was only slightly increased after 21 days (100+/-10 fmol/g; P<0.05). In conclusion, losartan-sensitive cardiac damage due to chronic NOS inhibition is not associated with primary increase of cardiac angiotensin II, suggesting that chronic NOS inhibition increases cardiac sensitivity for angiotensin II.

Topics: Angiotensin II; Angiotensin Receptor Antagonists; Animals; Blood Pressure; Cardiomegaly; Dose-Response Relationship, Drug; Enzyme Inhibitors; Heart; Losartan; Male; Myocardial Infarction; Myocardium; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Vasculitis

Although isoform-selective translocation of protein kinase C (PKC) epsilon appears to play an important role in the late phase of ischemic preconditioning (PC), the mechanism(s) responsible for such translocation remains unclear. Furthermore, the signaling pathway that leads to the development of late PC after exogenous administration of NO in the absence of ischemia (NO donor-induced late PC) is unknown. In the present study we tested the hypothesis that NO activates PKC and that this is the mechanism for the development of both ischemia-induced and NO donor-induced late PC. A total of 95 chronically instrumented, conscious rabbits were used. In rabbits subjected to ischemic PC (six 4-minute occlusion/4-minute reperfusion cycles), administration of the NO synthase inhibitor Nomega-nitro-L-arginine (group III), at doses previously shown to block the development of late PC, completely blocked the ischemic PC-induced translocation of PKCepsilon but not of PKCeta, indicating that increased formation of NO is an essential mechanism whereby brief ischemia activates the epsilon isoform of PKC. Conversely, a translocation of PKCepsilon and -eta quantitatively similar to that induced by ischemic PC could be reproduced pharmacologically with the administration of 2 structurally unrelated NO donors, diethylenetriamine/NO (DETA/NO) and S-nitroso-N-acetylpenicillamine (SNAP), at doses previously shown to elicit a late PC effect. The particulate fraction of PKCepsilon increased from 35+/-2% of total in the control group (group I) to 60+/-1% after ischemic PC (group II) (P<0.05), to 54+/-2% after SNAP (group IV) (P<0.05) and to 52+/-2% after DETA/NO (group V) (P<0.05). The particulate fraction of PKCeta rose from 66+/-5% in the control group to 86+/-3% after ischemic PC (P<0.05), to 88+/-2% after SNAP (P<0.05) and to 85+/-1% after DETA/NO (P<0.05). Neither ischemic PC nor NO donors had any appreciable effect on the subcellular distribution of PKCalpha, -beta1, -beta2, -gamma, -delta, - micro, or -iota/lambda; on total PKC activity; or on the subcellular distribution of total PKC activity. Thus, the effects of SNAP and DETA/NO on PKC closely resembled those of ischemic PC. The DETA/NO-induced translocation of PKCepsilon (but not that of PKCeta) was completely prevented by the administration of the PKC inhibitor chelerythrine at a dose of 5 mg/kg (group VI) (particulate fraction of PKCepsilon, 38+/-4% of total, P<0.05 versus group V; particulate fraction of PKCeta, 79+/-

Topics: Alkaloids; Animals; Benzophenanthridines; Enzyme Activation; Enzyme Inhibitors; Hemodynamics; Ischemic Preconditioning, Myocardial; Isoenzymes; Male; Myocardial Infarction; Myocardial Stunning; Myocardium; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Penicillamine; Phenanthridines; Polyamines; Protein Kinase C; Rabbits; Subcellular Fractions

Nitric oxide (NO) and prostacyclin (PGI2) are putative cardioprotective agents. Evidence indicates that there may be a reciprocal relationship involved in the synthesis of NO and PGI2, so that inhibiting the release of one mediator may promote the synthesis of the other. Therefore, we investigated the effects of concomitantly inhibiting NO and PGI2 synthesis, using NG-nitro-L-arginine (L-NOARG) or indomethacin, respectively, on infarct size. Langendorff-perfused rabbit hearts were assigned randomly to one of five treatment groups of n=6: control L-NOARG 100 micromol/l; indomethacin 3 micromol/l L-NOARG 100 micromol/l + indomethacin 3 micromol/l; or L-NOARG 100 micromol/l + L-arginine 1 mmol/l. After 30 min regional ischaemia and 120 min reperfusion, infarct size was assessed by tetrazolium staining. Infarct size was reduced significantly in hearts treated with L-NOARG (20.8+/-1.3%) compared to control hearts (34.7+/-0.4%). This reduction in infarct size was abolished by co-perfusing with a 10-fold excess of L-arginine (30.7+/-1.7%). While indomethacin alone had no effect (33.4+/-2.3%), perfusion with both L-NOARG and indomethacin resulted in a significant increase in infarct size (44.0+/-1.9%) compared to controls. Treatment with L-NOARG alone increased 6-keto PGF1alpha in coronary effluent prior to ischaemia (30.5+/-1.2 vs 16.6+/-1.3 pg/min/g in controls, P<0.05). This effect was reversed by co-perfusion with either L-arginine or indomethacin. These results indicate that the reduction in infarct size by L-NOARG may be due to increased PGI2 release. Concomitant administration of indomethacin negated this effect and revealed an adverse effect of NO synthase inhibition on infarct size.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arginine; Cyclic GMP; Cyclooxygenase Inhibitors; Enzyme Inhibitors; Hemodynamics; In Vitro Techniques; Indomethacin; Male; Myocardial Infarction; Myocardial Reperfusion; Nitric Oxide Synthase; Nitroarginine; Rabbits

Myocardial ischaemia followed by reperfusion (I/R) is associated with impaired endothelial function including diminished release and/or effects of nitric oxide (NO) which may contribute to the development of I/R injury. The aim of the present study was to investigate the role of the L-arginine/NO pathway in myocardial I/R injury. In isolated rat hearts subjected to global ischaemia followed by reperfusion L-arginine and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP), but not D-arginine, significantly enhanced the recoveries of mycardial performance and coronary flow, and reduced the area of no-reflow and creatine kinase outflow. The NO synthase inhibitor NG-nitro-L-arginine (L-NNA) abolished the protective effects of L-arginine. Endothelium-dependent vasodilatation after I/R was preserved in L-arginine treated but not in vehicle hearts. Following I/R Ca2+-dependent NO synthase activity was reduced by 90% in comparison with non-ischaemic hearts. L-arginine but not D-arginine significantly increased NO synthase activity. In anaesthetized pigs, L-arginine given by local coronary venous retroinfusion reduced myocardial infarct size induced by 45 min of coronary artery ligation and 4 h of reperfusion to 35% of the area at risk from 76% in controls. The protective effect of L-arginine was blocked by L-NNA. Acetylcholine-induced coronary vasodilatation following I/R was attenuated in controls but not in L-arginine treated pigs. It is concluded that L-arginine or the NO donor SNAP reduces I/R-induced myocardial and endothelial injury. The protective effect of L-arginine seems to be mediated through maintained production of NO by preserving the function of Ca2+-dependent NO synthase in the heart.

Topics: Animals; Arginine; Coronary Circulation; Creatine Kinase; Enzyme Inhibitors; Heart; Hemodynamics; In Vitro Techniques; Myocardial Infarction; Myocardial Ischemia; Myocardial Reperfusion Injury; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Penicillamine; Perfusion; Rats; Rats, Sprague-Dawley; Swine

Despite intense investigation, the effector of the infarct-limiting protection observed during the late phase of ischemic preconditioning (PC) remains unknown. The goal of this study was to test the hypothesis that late PC against myocardial infarction is mediated by the activity of nitric oxide synthase (NOS).. Conscious rabbits underwent a 30-minute coronary occlusion followed by 3 days of reperfusion. In group I (control group, n= 10), infarct size (tetrazolium staining) averaged 56.8+/-5.3% of the risk region, which was decreased to 27.6+/-2.5% (P<0.05) in rabbits preconditioned 24 hours earlier with a sequence of six 4-minute occlusion/4-minute reperfusion cycles (group II, n= 10). When preconditioned rabbits were given the nonselective NOS inhibitor N(omega)-nitro-L-arginine (L-NA, 13 mg/kg i.v. [group III, n=8]) or the selective iNOS inhibitor aminoguanidine (AG, 150 mg/kg SC [group V, n=7]) before the 30-minute occlusion, the protective effect of late PC was completely abrogated; that is, infarct size (59.9+/-4.5% and 65.8+/-3.3%, respectively) was similar to that measured in the control group. Measurements of systolic wall thickening (sonomicrometry) demonstrated that L-NA and AG also abolished the improved recovery of myocardial function effected by late PC in group II. When rabbits were given L-NA or AG without prior PC (group IV [n=8] and group VI [n=6], respectively), infarct size did not differ from that observed in controls (53.8+/-4.3% and 59.8+/-4.3%, respectively), demonstrating that L-NA and AG do not increase the extent of cell death in nonpreconditioned myocardium.. Taken together, these results indicate that in the conscious rabbit, the infarct-sparing effect of the late phase of ischemic PC is mediated by the activity of NOS and suggest that the specific isoform primarily responsible for this cardioprotective phenomenon is iNOS. Thus, NO appears to be a pivotal component of the pathophysiological cascade of late PC.

Topics: Analysis of Variance; Animals; Consciousness; Disease Models, Animal; Enzyme Inhibitors; Guanidines; Heart; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardium; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Rabbits; Time Factors

Abnormalities of vasomotor tone are characteristic of heart failure. This study was designed to assess the effects of chronic heart failure on endothelium-dependent relaxation in both large conduit arteries and small resistance vessels and to determine whether or not impaired nitric oxide (NO) production is involved. Segments of pulmonary artery (PA), abdominal aorta (AA), and small mesenteric artery (MA) were harvested from rats with heart failure resulting from coronary artery ligation and from sham-operated controls. Organ-bath experiments done in the presence of indomethacin to avoid the influence of vasodilatory prostanoids demonstrated that relaxation to acetylcholine (ACh) was impaired in the PA but not the AA or MA of the group with heart failure. Endothelium-independent relaxation to nitroglycerin was not significantly affected by the development of heart failure. Constriction to prostaglandin (PG) F(2alpha) was enhanced in PA but not in AA or MA segments. Preincubation with N(omega)-nitro-L-arginine (NNA) to inhibit the production of NO increased baseline force in vessels from all three beds, but the effect was greatest in the PA. Although relaxation to ACh was significantly diminished by NNA in the PA, it was not completely abolished. Furthermore, ACh-mediated relaxation in the presence of NAA was still impaired in the group with heart failure compared with the sham-operated control group. NNA had only mild effects on ACh-mediated relaxation in MA. These results demonstrate that (a) the mediators of endothelium-dependent relaxation may vary throughout the arterial circulation, (b) the contribution of NO to endothelium-dependent relaxation is substantial in PA and minimal in mesenteric resistance vessels, (c) endothelium-dependent relaxation is not uniformly impaired throughout the arterial bed by the development of heart failure, and (d) although a defect in NO production may account for enchanced vasoconstriction seen in response to PGF(2alpha), it does not account for the diminished vasodilatory response to ACh in this experimental model of heart failure.

Topics: Acetylcholine; Animals; Aorta, Abdominal; Dinoprost; Endothelium, Vascular; Heart Failure; Hemodynamics; In Vitro Techniques; Male; Mesenteric Arteries; Muscle Relaxation; Muscle, Smooth, Vascular; Myocardial Infarction; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroglycerin; Pulmonary Artery; Rats

1. To observe the effect of nitric oxide (NO) on the myocardium, the NO synthesis inhibitor NG-nitro-L-arginine (L-NNA) was administered to hypercholesterolaemic stroke-prone spontaneously hypertensive (SHRSP) rats. 2. Hypercholesterolaemic SHRSP were produced by feeding SHRSP a high fat and high cholesterol diet (HFC) for 2 weeks. The rats were then divided into three groups: (i) the N group, which were fed the HFC diet containing 0.023% L-NNA and 1% NaCl in their drinking water (n = 10); (ii) the NH group, which were fed the HFC diet containing 0.023% L-NNA and 1% NaCl in their drinking water which also contained 80 mg/L hydralazine (n = 10); and (iii) the C group, which were fed the HFC diet and 1% NaCl in their drinking water (n = 10). 3. All rats in the N and NH groups died within 35 days of the initiation of L-NNA administration. Rats in the N and NH groups had significantly increased serum creatine phosphokinase, lactate dehydrogenase, glutamic oxaloacetic transaminase and serum total cholesterol levels compared with rats in the C group. 4. Fibrosis in response to necrosis was histopathologically observed in the hearts of all rats in the N and NH groups without exception. Occlusion or intimal thickening in the arteries adjacent to the necrotic regions was also observed. 5. These results suggest that nitric oxide deficiency induces myocardial infarction in hypercholesterolaemic SHRSP. These NO-deficient hypercholesterolaemic SHRSP offer a new model of myocardial infarction in rats.

Topics: Animals; Blood Pressure; Cerebrovascular Disorders; Coronary Vessels; Enzyme Inhibitors; Fibrosis; Hydralazine; Hypercholesterolemia; Male; Myocardial Infarction; Myocardium; Necrosis; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred SHR

Inducible nitric oxide synthase (iNOS) is activated in cardiac disorders. We investigated the contribution of increased iNOS activity to the development of left ventricular dysfunction after myocardial infarction by selective inhibition of the isozyme.. Male New Zealand rabbits were subjected to myocardial infarction. Animals were treated with either saline, S-methylisothiourea sulfate (SMT) (a selective iNOS inhibitor), or N(omega)-nitro-L-arginine (L-NNA) (a nonselective NOS inhibitor). Inducible and constitutive NOS (cNOS) activity, plasma NO(x), cGMP, hemodynamics, and myocardial blood flow were measured before and 5, 24, and 72 hours after coronary occlusion. Infarction 72 hours after occlusion resulted in increased myocardial iNOS activity, increased cardiac NO(x) production, and elevated cGMP levels. cNOS remained unchanged. Infarction increased left ventricular end-diastolic pressure (LVEDP) and decreased maximum +dP/dt and -dP/dt. L-NNA inhibited iNOS and cNOS activities and plasma NO(x) levels. L-NNA further increased LVEDP and reduced myocardial blood flow. Administration of SMT 72 hours after infarction significantly inhibited iNOS and cardiac NO(x) production but had no effects on cNOS. SMT improved left ventricular maximum +dP/dt and -dP/dt and decreased LVEDP. Myocardial blood flow in the remote myocardium increased.. These findings suggest that induction of iNOS activity 72 hours after infarction exerts negative inotropic effects and contributes to the development of myocardial dysfunction; selective modulation of increased iNOS activity by SMT improves cardiac performance, enhances myocardial blood flow, and may be beneficial in the treatment of acute myocardial infarction.

Topics: Animals; Coronary Circulation; Cyclic GMP; Enzyme Induction; Enzyme Inhibitors; Hemodynamics; Isothiuronium; Male; Myocardial Infarction; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rabbits; Ventricular Function, Left

We tested the hypothesis that late preconditioning (PC) against myocardial infarction is triggered by the formation of nitric oxide (NO). Conscious rabbits underwent a 30-min coronary occlusion followed by 3 days of reperfusion. In group I (control group, n = 10), rabbits were not preconditioned, whereas in group II (n = 10), they were preconditioned 24 h earlier with a sequence of six 4-min occlusion/4-min reperfusion cycles. Myocardial infarct size (tetrazolium staining) was reduced by 50% by PC (28.6 +/- 3.2% of the risk region in group II vs. 56.9 +/- 5.9% in controls, P < 0.05). This reduction in cell death was associated with improved recovery of myocardial function [systolic thickening fraction (by sonomicrometry) at 3 days: 2.0 +/- 11.0% of baseline in group II vs. -20.0 +/- 2.8% in group I, P < 0.05]. Group III rabbits (n = 11) underwent the same protocol as group II except that the rabbits received the NO synthase inhibitor N omega-nitro-L-arginine (L-NNA, 13 mg/kg) before the PC ischemia. In these animals, infarct size did not differ significantly from that observed in control rabbits, indicating that L-NNA completely blocked the development of late PC against myocardial infarction. In group IV (n = 9), rabbits received L-NNA as in group III, but without the six occlusion-reperfusion cycles, and were subjected to the 30-min occlusion 24 h later. In this group, infarct size did not differ from that observed in controls, demonstrating that pretreatment with L-NNA, in itself, did not affect the extent of cell death. Taken together, these results indicate that, in the conscious rabbit, the development of late PC against myocardial infarction is triggered by the generation of NO during the PC ischemia. It is proposed that NO plays a key role in the delayed myocardial adaptation to ischemic stress.

Topics: Animals; Consciousness; Coronary Vessels; Echocardiography; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardial Reperfusion; Nitroarginine; Rabbits; Risk Factors; Systole; Time Factors

Nitric oxide (NO), an unstable radical, is synthesized from L-arginine by the constitutive (cNOS) and inducible (iNOS) forms of NOS. cNOS is present mainly in endothelial cells and plays a role in the regulation of blood flow. iNOS, the dominant enzyme in heart muscle during myocardial infarction, allograft rejection, and cardiomyopathy, is activated in macrophages. We recently described a significant increase of iNOS activity in macrophages of infarcted rabbit myocardium 24 hours after coronary occlusion, with peak activity occurring 3 days following coronary artery ligation. Inhibitors of NOS are L-arginine derivatives that inhibit both cNOS and iNOS; S-methylisothiourea (SMT) and aminoguanidine (AMG) are specific inhibitors of iNOS. Cyclosporin A and dexamethasone inhibit by interfering with protein synthesis. iNOS inhibition by SMT, NG-nitro-L-arginine (L-NNA), AMG, cyclosporin A and dexamethasone was examined in homogenates of normal, risk and infarcted myocardium. Three days after coronary artery ligation, the heart was excised and divided into normal, risk and infarcted regions. The inhibitory effect was calculated as IC50. Results shows that SMT was the most potent inhibitor with the lowest IC50; its effect, as well as the effects of L-NNA and AMG, depended on the location in the myocardium. Inhibition for SMT and AMG was greater in the normal area than in the risk and infarcted regions. AMG induced an initial rise of iNOS followed by gradual decline in the area of risk and infarction. No inhibitory effects in cyclosporin A and dexamethasone were noted.

Topics: Animals; Arginine; Cyclosporine; Dexamethasone; Dose-Response Relationship, Drug; Enzyme Inhibitors; Guanidines; Heart; Isothiuronium; Male; Myocardial Infarction; Myocardium; Nitric Oxide Synthase; Nitroarginine; Rabbits

The contribution of increased inducible nitric oxide synthase (iNOS) activity to the development of left ventricular dysfunction after acute myocardial infarction (MI) was investigated New Zealand rabbits (n = 24) were randomly treated with either saline, S-methylisothiourea sulfate (SMT; selective iNOS inhibitor) or N-omega-nitro-L-arginine (NOLA; non-isoform selective NOS inhibitor). Left ventricular hemodynamics and myocardial blood flow were measured before coronary occlusion and on postoperative day 3 (POD 3). MI resulted in left ventricular dysfunction and increased myocardial iNOS activity. SMT and NOLA significantly inhibited iNOS activity; SMT, but not NOLA, significantly improved left ventricular maximum +dP/dt and decreased LVEDP; myocardial blood flow in the remote myocardium significantly increased after SMT. Induction of myocardial iNOS after MI on POD 3 contributes to the development of left ventricular dysfunction; modulation of iNOS activity by SMT improves left ventricular performance and may be beneficial after acute MI.

Topics: Animals; Blood Pressure; Coronary Circulation; Coronary Vessels; Enzyme Induction; Enzyme Inhibitors; Heart Rate; Heart Ventricles; Isoenzymes; Isothiuronium; Male; Myocardial Infarction; Myocardium; Nitric Oxide Synthase; Nitroarginine; Rabbits; Vascular Resistance; Ventricular Function, Left

The effects of NO donor--L-arginine (L-arg) and ischemic preconditioning (IP) on the hemodynamics and myocardial infarct size were examined in the anesthetized rabbit subjected to myocardial ischemia-repefusion to define whether exogenous L-arg could exert a beneficial effect in this pathological model, and whether the L-arg-NO pathway was involved in the cardioprotection provided by IP. The results obtained were as follows: (1) During the course of ischemia (30 min)-reperfusion (180 min), blood pressure, heart rate and myocardial oxygen consumption decreased progressively, and the myocardial infarct size occupied 33.9 +/- 2.4% of the whole left ventricle. (2) The myocardial infarct size could be reduced to 20.1 +/- 2.2% (P < 0.01) by pretreatment with L-arg (300 mg/kg). This myocardial protective effect of L-arg was abolished by NO synthesis inhibitor--Nitro-L-arginine (L-NNA), thereby indicating the involvement of L-arg-NO pathway. (3) IP significantly reduced the infarct size to 21.9 +/- 2.1% (P < 0.01), indicating the prominent cardioprotective effect of such an intervention. Since L-NNA showed no effect on the cardioprotection afforded by IP, it was implied that the L-arg-NO pathway was not involved in the cardioprotective mechanism of IP. (4) Exogenous L-arg might markedly augment cardioprotection provided by IP. The above results strongly suggested that the cardioprotective effect of L-arg on ischemia-reperfused myocardium was mediated by L-arg-NO pathway, which, however, was not involved in the cardioprotection provided by IP.

Topics: Animals; Arginine; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Nitroarginine; Rabbits

Unenhanced hypothermic cardioplegia does not prevent postischemic endothelial and contractile dysfunction in hearts subjected to antecedent regional or global ischemia. This study tested the hypothesis that supplementing blood cardioplegic solution and reperfusion with the nitric oxide precursor L-arginine would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction by the L-arginine-nitric oxide pathway. In 23 anesthetized dogs, the left anterior descending coronary artery was ligated for 90 minutes, after which total bypass was established for surgical "revascularization." In 10 dogs, unsupplemented multidose hypothermic blood cardioplegic solution was administered for a total of 60 minutes of cardioplegic arrest. In eight dogs, L-arginine was given intravenously (4 mg/kg per minute) and in blood cardioplegic solution (10 mmol) during arrest. In five dogs, the nitric oxide synthesis blocker N omega-nitro-L-arginine (1 mmol) was used to block the L-arginine-nitric oxide pathway during cardioplegia and reperfusion. Infarct size (triphenyltetrazolium chloride) as percent of the area at risk was significantly reduced by L-arginine compared with blood cardioplegic solution (28.2% +/- 4.1% versus 40.5% +/- 3.5%) and was reversed by N omega-nitro-L-arginine to 68.9% +/- 3.0% (p < 0.05). Postischemic regional segmental work in millimeters of mercury per millimeter (sonomicrometry) was significantly better with L-arginine (92 +/- 15) versus blood cardioplegic solution (28 +/- 3) and N omega-nitro-L-arginine (26 +/- 6). Segmental diastolic stiffness was significantly lower with L-arginine (0.46 +/- 0.06) compared with blood cardioplegic solution (1.10 +/- 0.11) and was significantly greater with N omega-nitro-L-arginine (2.70 +/- 0.43). In ischemic-reperfused left anterior descending coronary arterial vascular rings, maximum relaxation responses to acetylcholine, the stimulator of endothelial nitric oxide, was depressed in the blood cardioplegic solution group (77% +/- 4%) and was significantly reversed by L-arginine (92% +/- 3%). Smooth muscle function was unaffected in all groups. We conclude that cardioplegic solution supplemented with L-arginine reduces infarct size, preserves postischemic systolic and diastolic regional function, and prevents arterial endothelial dysfunction via the L-arginine-nitric oxide pathway.

Topics: Acetylcholine; Amino Acid Oxidoreductases; Animals; Arginine; Blood; Calcimycin; Coronary Vessels; Creatine Kinase; Dogs; Heart; Heart Arrest, Induced; Hemodynamics; Hypothermia, Induced; In Vitro Techniques; Myocardial Contraction; Myocardial Infarction; Myocardial Reperfusion; Myocardial Reperfusion Injury; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Peroxidase; Sodium Nitrite; Vasodilation

Recent studies suggest that nitric oxide (NO) is deleterious in models of shock and hypoxia-reoxygenation However, the role of endogenous NO in ischaemia-reperfusion injury in vivo remains controversial. We tested the hypothesis that blockade of endogenous NO produced during myocardial ischaemia-reperfusion or during reperfusion alone in vivo increases infarct size after coronary occlusion in the rabbit, and conversely, supplementation with L-arginine would reduce infarct size.. Ketamine-xylazine anaesthetised New Zealand white rabbits were subjected to left coronary artery occlusion for 30 min and reperfusion for 120 min. The rabbits were divided into five groups: (1) saline (VEH); (2) L-nitro arginine (L-NA), a NO-synthase inhibitor, was infused intravenously (15 mg/kg bolus followed by 7.5 mg/kg h-1) before coronary occlusion to block NO synthase activity during ischaemia and reperfusion (IR); (3) L-NA was administered during reperfusion only (R) at the same dose as in the IR group; (4) D-arginine (D-ARG) (25 mg/kg bolus followed by 4 mg/kg min-1), the non-metabolised enantiomer of L-arginine was infused intravenously during reperfusion only; (5) L-arginine (L-ARG) (25 mg/kg bolus followed by 4 mg/kg min-1), the physiological precursor of NO, was infused intravenously during reperfusion only.. L-NA infusion in the IR and R groups caused an increase in mean arterial pressure and a decrease in heart rate; however, no significant change in pressure rate product (PRP) occurred immediately after drug infusion. PRP did not change significantly during the experiment across groups except at the end of reperfusion. The area at risk was comparable in all groups, averaging 29(1)%. The infarct size (triphenyltetrazolium chloride) expressed as a percent of area at risk was 27(2)% for the untreated vehicle group. In contrast, L-NA significantly (P < 0.05) increased infarct size in the IR group, 51(2)%; this augmented infarct size persisted when NO synthase activity was blocked during reperfusion only in the R group, 50(2)%. There was no significant (P < 0.05) difference in infarct size between the IR and the R groups. D-ARG-treated group showed a comparable increase in infarct size 48(2)% versus the IR and R groups. However, supplementation of NO with L-arginine (L-ARG) showed no reduction in infarct size, 24(3)%, over vehicle group (VEH).. We conclude that (1) blockade of NO synthase activity with L-NA increases infarct size, (2) this effect was expressed primarily during reperfusion, (3) D-arginine mimicked the infarct augmentation of L-NA, while (4) L-arginine supplementation did not reduce infarct size. These data imply that endogenous NO production exerts a tonic cardioprotective effect on myocardial infarct following coronary reperfusion.

Topics: Animals; Arginine; Dose-Response Relationship, Drug; Heart; Isomerism; Male; Myocardial Infarction; Myocardial Ischemia; Myocardial Reperfusion Injury; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rabbits

1. Recent experiments suggest that acetylcholine (ACh) may exert myocardial protective effects during ischaemia (I) and reperfusion (R). The present study was designed (i) to assess whether ACh limits infarct size and protects coronary endothelial cells in a rat model of I and R, (ii) to evaluate the role of ATP-sensitive potassium (KATP) channels and nitric oxide (NO) in the beneficial effect of ACh (iii) to evaluate whether the protective effect of ACh also extends to coronary endothelial cells and (iv) to assess whether ACh contributes to the beneficial effect of preconditioning. 2. Anaesthetized rats were subjected to 20 min I (left coronary artery occlusion) and 2 h of R. Infarct size was assessed by triphenyltetrazolium (TTC) staining and expressed as a % of the area at risk (India ink injection). Vascular studies were performed on 1.5-2 mm coronary segments (internal diameter 250-300 micros) removed distal to the site of occlusion and mounted in wire myographs. 3. ACh limited infarct size (from 59 +/- 3 to 26 +/- 5%, P < 0.01), and this was prevented by atropine (46 +/- 7%; P < 0.05 vs ACh), but not by the inhibitor of KATP channels, glibenclamide (29 +/- 8%). The inhibitor of NO synthesis NG-nitro L-arginine did not affect infarct size (54 +/- 5%) but abolished the beneficial effect of ACh (59 +/- 8%; P < 0.05 vs ACh), whereas the NO donor 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1 limited infarct size to the same extent as ACh (28 +/- 6%). Preconditioning also limited infarct size (5 +/- 2%, P< 0.01 vs control), and this was not affected by atropine (6 +/- 2%). I and R induced a significant decrease in the endothelium-dependent relaxations of isolated coronary arteries toACh (maximal response: sham: 58+/-4; I/R: 25+/-5%; P<0.01) and this dysfunction was prevented by prior in vivo treatment with ACh (55+/-7%; P<0.01 vs I/R) or (SIN-1 50+/-5%; P<0.05 vs I/R).4 Thus, in the rat model, ACh is able to stimulate potent endogenous protective mechanisms during I and R, which are evident both at the level of myocardial and coronary endothelial cells, and appear entirely mediated through the production of NO. Pharmacological stimulation of this endogenous protective mechanism may constitute a new approach in the treatment of acute myocaridal ischaemia.

Topics: Acetylcholine; Animals; Arginine; Blood Pressure; Coronary Vessels; Disease Models, Animal; Endothelium, Vascular; Heart Rate; In Vitro Techniques; Male; Molsidomine; Myocardial Infarction; Myocardial Ischemia; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Potassium Channel Blockers; Rats; Rats, Wistar; Vasodilator Agents

The effect of chronic, periadventitial administration of basic (b) fibroblast growth factor (FGF) on endothelial dysfunction in the collateral-dependent and normally perfused coronary microcirculation was examined. Ameroid constrictors were placed on the proximal left circumflex coronary artery (LCX) in 23 pigs. In 11 pigs, bFGF was released from calcium alginate microcapsules into the perivascular space of the proximal left anterior descending coronary artery (LAD) and LCX. After 5-8 wk, coronary arterial microvessels (80-170 microns) were studied in a pressurized (40 mmHg) no-flow state with video microscopy. Receptor-mediated endothelium-dependent relaxations to ADP and serotonin were reduced while contraction to acetylcholine was enhanced in the collateral-dependent LCX microvessels of non-bFGF-treated control hearts. Relaxation of vessels to the non-receptor-mediated, endothelium-dependent agent A-23187; endothelium-independent relaxation to nitroprusside; and contraction to KCl were similar in all groups. Chronic treatment with bFGF normalized responses to ADP, serotonin, and acetylcholine in the collateral-dependent LCX region but had no effect on the responses of vessels in the normally perfused LAD region. Arteriolar density in the collateral-perfused LCX region of bFGF-treated hearts was markedly increased (4-fold compared with that in untreated hearts, suggesting a link between the angiogenic effect of bFGF and its action on endothelial preservation. Thus the periadventitial, sustained delivery of bFGF preserves receptor-mediated, endothelium-dependent responses in the collateral-dependent LCX region but has no effect on responses of microvessels in the normally perfused LAD region or on non-receptor-mediated endothelium-dependent relaxation.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Adenosine Diphosphate; Alginates; Animals; Arginine; Calcimycin; Coronary Circulation; Coronary Vessels; Drug Carriers; Endothelium, Vascular; Female; Fibroblast Growth Factor 2; Glucuronic Acid; Heart; Hexuronic Acids; Indomethacin; Ketanserin; Male; Microcirculation; Muscle Relaxation; Myocardial Infarction; Myocardium; Nitroarginine; Nitroprusside; Potassium Chloride; Prostaglandin Endoperoxides, Synthetic; Sepharose; Serotonin; Swine; Thromboxane A2; Vasodilation