Yozo Uriuda

Local overflow and enhanced tissue content of endothelin following myocardial ischaemia and reperfusion in the pig: modulation by L-arginine

OBJECTIVE The local myocardial overflow and tissue content of endothelin-like immunoreactivity (ET-LI) during ischaemia and reperfusion as well as the coronary vascular effects of endothelin were characterised in anaesthetised pigs. METHODS Ischaemia was induced by ligation of the left anterior descending coronary artery for 45 min followed by 4 h of reperfusion. ET-LI was analysed in plasma from the anterior interventricular coronary vein and aorta for estimation of local overflow and in myocardial tissue. Endothelin analogues were given in the coronary artery for determination of local vascular effects. RESULTS During reperfusion, but not during ischaemia, the veno-arterial concentration difference of ET-LI increased, resulting in a significantly increased overflow at between 10 and 120 min of reperfusion. The tissue concentration of ET-LI in the left ventricle was seven times higher in the ischaemic/reperfused area than in the non-ischaemic area: 161(SEM 30.5) v 25.3(3.8) fmol.g-1, P < 0.05. The increase in myocardial ET-LI was attenuated by 70% (P < 0.01) by coronary venous retroinfusion of the nitric oxide substrate L-arginine, whereas the overflow was unaffected. Chromatographic characterisation of the myocardial ET-LI showed that it was similar to endothelin-1. Intracoronary administration of endothelin-1, endothelin-3, and the endothelin ETB receptor agonist [Ala1,3,11,15]ET-1 evoked dose dependent coronary vasoconstriction, and reductions in left ventricular dP/dt and arterial blood pressure. Endothelin-1 was two times more potent than endothelin-3 and 10 times more potent than [Ala1,3,11,15]ET-1. CONCLUSIONS Myocardial ischaemia/reperfusion evokes enhanced local overflow of ET-LI during the reperfusion period combined with an increased tissue concentration of ET-LI which is is attenuated by L-arginine. Endothelin evokes potent coronary vasoconstriction via activation of both ETA and ETB receptors.

Myocardial Release of Endothelin (ET) and Enhanced ETA Receptor-Mediated Coronary Vasoconstriction After Coronary Thrombosis and Thrombolysis in Pigs

We investigated changes in vascular reactivity to endothelin (ET) and local release of ET-like immunoreactivity (ET-LI) induced by myocardial ischemia and reperfusion in a pig model of coronary thrombosis and thrombolysis and studied the possible mechanisms producing the changed vascular reactivity to ET-1. We induced coronary thrombosis by inserting a copper coil into the left anterior descending coronary artery (LAD) and achieved thrombolysis with tissue plasminogen activator (t-PA). Vascular reactivity to ET-1 in the nonischemic and ischemic/reperfused LAD diagonal branches was evaluated in vitro. ET-LI was analyzed in plasma from the great cardiac vein and aorta for estimation of local release. The vasoconstrictor response to ET-1 was enhanced twofold (p < 0.01) in the ischemic/reperfused arteries as compared with the nonischemic arteries. The vasoconstriction induced by the ETB receptor agonist [Ala 1,3,11,15] ET-1 or serotonin was not significantly affected by ischemia/reperfusion. The ETA receptor antagonist BQ-123 reversed the ET-1-induced vascular contraction to a similar degree in ischemic/reperfused and control arteries. The ET-1-induced vasoconstriction of control arteries was not affected by inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine (L-NNA) or cyclooxygenase with indomethacin. During reperfusion, the myocardial venoarterial plasma concentration difference of ET-LI and blood flow increased, resulting in an increased overflow of ET-LI. Our results demonstrate that coronary thrombosis and thrombolysis evokes enhanced local release of ET-LI during the reperfusion period and increases the vasoconstrictor effects of ET-1 through a mechanism related to ETA receptor activation but unrelated to altered endothelial function. These changes may play a role in the development of ischemic/reperfusion injury and no-reflow phenomenon.

Antithrombotic activity of inogatran, a new low-molecular-weight inhibitor of thrombin, in a closed-chest porcine model of coronary artery thrombosis

OBJECTIVE To characterize the antithrombotic activity of inogatran per se in a porcine model of copper-coil-induced coronary artery thrombosis and to compare its effect with that of heparin and ASA. METHODS Forty-eight pigs were assigned to one of the following groups: (1) saline; (2) heparin, (a) 75 and (b) 150 IU/kg/h; (3) acetylsalicylic acid (ASA), 12.5 mg/kg; (4) ASA 12.5 mg/kg + inogatran, 0.06 mg/kg/h; (5) ASA 12.5 mg/kg + inogatran, 0.30 mg/kg/h; (6) inogatran, 0.30 mg/kg/h; (7) inogatran, 0.60 mg/kg/h; (8) inogatran, 1.5 mg/kg/h. Computerized vectorcardiography was applied to monitor coronary occlusion and reperfusion. RESULTS Cumulative time in which coronary arteries were patent, expressed as a percentage of the treatment time (i.e., 90 min) in heparin- and ASA-treated pigs, was 8 +/- 6 and 14 +/- 7%, respectively. This is not significantly different from placebo-treated pigs. Inogatran-treated pigs showed a dose-dependent antithrombotic effect, and the average patency rates were 34 +/- 39, 54 +/- 37 and 80 +/- 32%, in groups 6, 7 and 8, respectively. Combined treatment with inogatran and ASA did not significantly improve the antithrombotic effect. A partial antithrombotic effect of inogatran was maintained for, on average, at least 150 min after the end of treatment, as evidenced by patency rates of 31 +/- 43, 52 +/- 48 and 62% +/- 44, in groups 6, 7, and 8, respectively. CONCLUSION Inogatran inhibits the formation of arterial thrombosis more effectively than heparin or ASA. Inhibition of clot-bound thrombin and thrombin-induced platelet activation may be the mechanisms behind this effect. Our findings also suggest that a thrombus formed in the presence of inogatran is more susceptible to spontaneous endogenous fibrinolysis.

Ischemic and nonischemic tissue concentrations of felodipine after coronary venous retroinfusion during myocardial ischemia and reperfusion: an experimental study in pigs.

Tissue and plasma concentrations of felodipine, a dihydropyridine (DHP) calcium antagonist, retroinfused through the coronary venous system were studied in 27 pigs. The animals underwent 45-min myocardial ischemia followed by 4-h reperfusion. Felodipine (7 nmol/kg body weight) was administered in the coronary vein for 30 min, 5 min before reperfusion. Concentrations of felodipine in the ischemic and nonischemic myocardium and in plasma were determined by gas chromatography. In the ischemic area, felodipine concentration at start of reperfusion was 304 +/- 285, 171 +/- 160, and 52 +/- 47 nmol/kg (mean +/- SD) in the subepicardial, midmyocardial, and subendocardial layer, respectively. Corresponding concentrations in the nonischemic area were 15 +/- 13, 17 +/- 14, and 16 +/- 15 nmol/kg (p < 0.05 vs. ischemic area). Subepicardial concentration was highest at start of reperfusion, whereas concentrations in other layers peaked at the end of retroinfusion. The transmural concentration gradient of felodipine in the ischemic area decreased progressively during the reperfusion period. The nonischemic tissue concentration increased slightly during the reperfusion period. The plasma concentration was very low throughout the study (peak = 3.2 +/- 1.4 nM at 30 min). Coronary venous retroinfusion of felodipine resulted in profound accumulation of the drug, specifically in ischemic myocardium. The plasma concentration was low and did not affect systemic hemodynamics. Coronary venous retroinfusion is considered an advantageous technique for selective drug delivery.

The effect of nitric oxide synthase inhibitor on reperfusion injury of the brain under hypothermic circulatory arrest

The effect of nitric oxide synthase inhibitor-NG-nitro-L-argine methyl ester (L-NAME)-on reperfusion injury of the brain under deep hypothermic circulatory arrest was experimentally investigated in sixteen piglets weighing about 30 kg. Cardiopulmonary bypass was established and animals were cooled to a brain temperature of 20 degrees C and circulatory arrest was performed for 60 minutes followed by reperfusion of 120 minutes. The value of nitric oxide (NO) within the brain was measured with a needle electrode which was inserted into the brain. In the treatment group L-NAME was administered with a intravenous injection of 1.5 mg/kg at the beginning of the reperfusion followed by a 60-minute continuous venous infusion of 1.5 mg/kg/hour. In the control group the value of NO after 120 minutes reperfusion increased significantly compared with pre-circulatory arrest, but in the treatment group it did not. There was significant difference between the groups regarding the NO value after 120 minutes reperfusion. Blood pressure after 120 minutes reperfusion in the treatment group was a little higher than the control group, but there was no significant difference between the groups regarding cerebral blood flow, excess lactate and cerebral tissue water content. However, recovery of SEP after 120 minutes reperfusion was detected in all 8 cases of the treatment group, but only in one of the control group (p < 0.001). This data suggests that L-NAME protects the brain against the reperfusion injury under deep hypothermic circulatory arrest.

Surgical reconstruction of an ascending aortic dissection in Takayasu's arteritis

A 45-year-old Japanese woman with Stanford type A dissecting aortic aneurysm underwent a reconstructive operation on the ascending aorta. Histopathological diagnosis was Takayasus arteritis in the chronic and inactive phase. It is very rare that a dissecting aortic aneurysm results from Takayasus arteritis. Long-standing hypertension and fragility of the aortic media due to disruption of elastic fibers were suspected to cause dissection in the entire aorta in this case.

Coronary thrombosis/thrombolysis in pigs: effects of heparin, asa, and the thrombin inhibitor inogatran

UNLABELLED The aim of the present study was to develop a coronary thrombolysis model using the copper coil technique in closed-chest pigs. The first goal (protocol I) was to obtain a reproducible size of myocardial infarction by controlling the coronary occlusion period, a prerequisite for evaluation of myocardioprotective interventions. The second goal (protocol II) was to study if thrombin and platelet aggregation inhibitors influence the rate of thrombolysis, the degree of reocclusion, and the time of coronary patency when added to a thrombolytic regimen (recombinant tissue-type plasminogen activator, rt-PA). Coronary thrombosis was produced by insertion of a thrombogenic copper coil into the LAD of 40 anesthetized pigs. The animals were divided into six groups as follows: Protocol I, group 1: Open-chest, lysis initiated with intracoronary rt-PA (50 mg) concomitant with intravenous heparin and acetylsalicylic acid (ASA) (n=6). Group 2: Closed-chest, lysis initiated with intracoronary rt-PA concomitant with intravenous heparin and ASA (n=10). Protocol II, group 3: Closed-chest, lysis initiated with intravenous rt-PA (n=6). Group 4: Closed-chest, lysis initiated with intravenous rt-PA concomitant with heparin (n=6). Group 5: Closed-chest, lysis initiated with intravenous rt-PA concomitant with inogatran, a low molecular weight thrombin inhibitor (n=6). Group 6: Closed-chest, lysis initiated with intravenous rt-PA immediately after intravenous administration of ASA (n=6). Protocol 1; Reperfusion was achieved in all closed- and open-chest pigs. The time to thrombolysis was 5+/-1.6 and 6+/-3.0 min (mean+/-SD) for closed- and open-chest pigs, respectively. Reocclusions were rare (one in group 1). The size of the ischemic myocardial area was 21+/-11% of the left ventricular area in group 1 and 22+/-6% in group 2. The corresponding values for infarct size as a proportion of the ischemic area were 58+/-10% and 68+/-14%, respectively. The closed-chest model was subsequently used to study the effect of the thrombin and platelet aggregation inhibitors (inogatran, heparin, and ASA) as conjunctive agents to rt-PA-induced thrombolysis (groups 3-6). To mimic its clinical use, rt-PA was administered intravenously. Time to lysis after rt-PA only (group 3) was 33+/-24 min. Concomitant treatment with heparin (group 4), inogatran (group 5), and ASA (group 6) did not significantly influence time to lysis. All adjunctive compounds did, however, prolong the time to reocclusion, which occurred in 100%, 75%, 67%, and 20% of the animals in groups 3, 4, 5, and 6. Thus, concomitant treatment with heparin and inogatran did not shorten time to lysis or reduce the reocclusion rate, and ASA turned out to be the only effective adjunct to rt-PA, significantly reducing both time to and frequency of reocclusion (p < 0.05). CONCLUSION The described closed-chest pig model was feasible as regards the induction and lysis of a thrombus in the left coronary artery, giving reproducible areas of myocardial ischemia and infarction. This model was useful for the evaluation of pharmacological interventions in the thrombolysis process.

Coronary venous drug infusion in the ischaemic-reperfused isolated rat heart

OBJECTIVES Coronary venous retroinfusion (CVR) has been used experimentally in large animals for selective drug delivery into ischaemic myocardium. It would be an advantage if CVR could also be used in isolated perfused rat heart models. The aim of the present paper is to develop a regional ischaemic model in the isolated perfused rat heart combined with CVR. METHOD Pharmacokinetic study: The spatial distribution of retrogradely infused felodipine (used as a tracer) during regional myocardial ischaemia was investigated. Following occlusion of the left coronary artery, felodipine was administered over a period of 5 min by CVR. Ischaemia-reperfusion study: Following 30 min of stabilisation, 14 rat hearts were subjected to 60 min of regional ischaemia followed by 60 min of reperfusion. Felodipine (0.7 nmol/kg, n = 7) or vehicle (n = 7) was administered by means of CVR. The infusion was given during the last 5 min of ischaemia at a rate of 0.6 ml/min. RESULTS Pharmacokinetic study: By means of CVR, the compound was distributed specifically into the ischaemic myocardium. The highest tissue concentration was obtained when the coronary vein was occluded during CVR. The maximal concentration in the ischaemic myocardium was 20-70 times that in the non-ischaemic areas. A transmyocardial gradient was noted with higher drug concentration in the subepicardial zone. Ischaemia-reperfusion study: At the end of reperfusion, the recovery of coronary flow, left ventricular developed pressure and double product (DP; LVDP x HR) was 101 +/- 7% (mean +/- s.e.m.), 99 +/- 8% and 98 +/- 4% of the pre-ischaemic values, respectively. This was significantly different from the vehicle group (78 +/- 5, P < 0.05, 74+/- 6, P < 0.01 and 78 +/- 3, P < 0.05). CONCLUSION CVR could easily be accomplished in the isolated perfused rat heart. The drug was specifically delivered into the ischaemic myocardium. Felodipine exerted a myocardioprotective effect in isolated rat hearts subjected to 60 min of regional ischaemia followed by 60 min of reperfusion.

Beneficial Effects of H290/51, a New Lipid Peroxidation Inhibitor, on Functional Recovery After Ischemia and Reperfusion in Isolated Cold-Arrested Rat Hearts

Lipid peroxidation is one of the major mechanisms involved in free radical-mediated postischemic myocardial injury. In the present study, a newly synthetized lipid peroxidation inhibitor H290/51 [cis-7metyl-9-methoxy-5,5a,b,10b-tetrahydroindeno(2,l-6 indole)] was evaluated for its effects on myocardial functional recovery during reperfusion after 30-min global ischemia in isolated cold-arrested rat hearts. Administration of 200 and 800 nM H290/51 at initiation of global ischemia markedly improved the functional recovery, whereas 50 nM H290/ 51 had no significant effects. The percent recovery of cardiac output (CO), left ventricular developed pressure (LVDP), and LVdP/dtmax at the end of the 30-min reperfusion period in the working mode was much higher in the groups receiving 200 and 800 nM H290/51 than that in vehicle group (CO 73 ± 5 and 60 ± 5 vs. 23 ± 7%; LVDP 79 ± 5 and 73 ± 8 vs. 43 ± 10%; LV dP/dtmax78 ± 5 and 69 ± 4 vs. 45 ± 10%). The indenoindole compound H290/ 51 reduced ischemia/reperfusion-induced cardiac dysfunction.

Protective Effects of Intrathecal Lidocaine Administration on Ischemic Injury of the Spinal Cord

The protective effects of intrathecal lidocaine administration on experimental ischemic spinal cord injury following aortic cross-clamping (AXC) were studied. Twelve mongrel dogs were divided into two groups, six animals in an intrathecally saline-administered group (control group) and the other six in an intrathecally lidocaine-administered group (lidocaine group). The dose of lidocaine administration was determined by the change of somatosensory-evoked potential traces generated by brachial nerve stimulation. Following administration of the agents, all dogs underwent cross-clamping of the thoracic aorta and the left subclavian artery for 60 minutes. Mean proximal aortic pressure during AXC remained in a similar range to baseline pressure until 40 minutes after AXC in the lidocaine group, while it increased significantly in the control group. The ratio of mean distal aortic pressure to mean proximal aortic pressure during AXC (D/P), which was calculated for estimation of collateral blood flow changes, gradually increased in the lidocaine group, but did not change in the control group. Four of six dogs had spastic paraplegia in the control group, but none in the lidocaine group (p < 0.05). Histological examination revealed that extensive infarction of the gray matter was noticed in the control group, but changes in the lidocaine group were only slight. From these results, it was concluded that intrathecal lidocaine administration controlled proximal hypertension effectively, increased D/P during AXC, and diminished neurological damages following AXC.