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Purpose: Ceruloplasmin (CP), an important serum antioxidant, was previously found to reduce the incidence of ventricular fibrillation (VF) induced by ischemia and reperfusion in isolated rat hearts. The present study investigated whether CP sterilized by gamma-irradiation maintains its antiarrhythmic capacity and in vitro antioxidant properties., Materials and Methods: Isolated rat hearts submitted to regional ischemia (15 min), were reperfused (10 min) with native CP or with CP irradiated at various doses (1-3 kGy) in the absence or presence of tyrosine (Tyr)., Results: All untreated hearts showed VF at reperfusion, which were all irreversible ventricular fibrillation (IVF). No IVF were found in hearts treated with native CP or gamma-irradiated CP. Cardioprotection afforded by irradiated CP (with or without Tyr) was slightly higher than that obtained with native CP. No VF at all (100% prevention) was found in hearts treated with CP irradiated alone or in the presence of tyrosine at 3 kGy. Tyrosine and irradiated tyrosine had no cardiotoxic or protective effects on reperfusion-induced arrhythmias. The Oxygen Radical Absorbing Capacity (ORAC), measured in vitro with beta-phycoerythrin (beta-PE) fluorescent indicator, was slightly higher for gamma-irradiated CP in the presence of Tyr., Conclusions: Ceruloplasmin sterilized by gamma-irradiation maintains antioxidant and antiarrhythmic effects in the post-ischemia reperfused isolated rat heart.

1. This study was carried out to investigate novel cardioprotective effects of urea and the underlying mechanisms. The cardiac functions under oxidative stress were evaluated using Langendorff perfused isolated heart. 2. Isolated dogfish shark hearts tolerated the oxidative stress generated by electrolysis (10 mA, 1 min) of the perfusion solution (n=4), and also showed normal cardiac functions during post-ischaemia reperfusion (n=4). The high concentration of urea (350 mM) in the heart perfusate was indispensable for maintaining the normal cardiac functions of the shark heart. 3. Urea at 3 - 300 mM (n=4 for each group) protected the isolated rat heart against both electrolysis-induced heart damage and post-ischaemia reperfusion-induced cardiac injury. 4. A concentration-dependent scavenging effect of urea (3 - 300 mM, n=4 for each group) against electrolysis-induced reactive oxygen species was also demonstrated in vitro. 5. Urea derivatives as hydroxyurea, dimethylurea, and thiourea had antioxidant cardioprotective effect against the electrolysis-induced cardiac dysfunction of rat heart, but were not as effective as urea in suppressing the post-ischaemia reperfusion injury. 6. Our results suggest that urea and its derivatives are potential antioxidant cardioprotective agents against oxidative stress-induced myocardium damage including the post-ischaemia reperfusion-induced injury.

Vasoactive intestinal polypeptide (VIP) was either injected intravenously (300 pmol.kg-1) or perfused (1 nmol in 1 min) into the sinus node artery (SNA) in anesthetized dogs to study its effect on subsidiary atrial pacemakers. Isochronal maps were obtained from 128 unipolar electrograms recorded on the epicardial surface of both atria in nine animals. When VIP was perfused into the SNA or injected intravenously, heart rate increased by 29 +/- 16% and 12 +/- 12%, and blood pressure decreased by 16 +/- 15 mmHg (1 mmHg = 133.3 Pa) and 24 +/- 18 mmHg, respectively. No significant change in heart rate (3 +/- 6% decrease) accompanied a similar decrease in blood pressure after an intravenous sodium nitroprusside perfusion. The perfusion of VIP into the SNA as well as the intravenous injection of VIP induced a shift of the pacemaker site to the region of Bachmann's bundle in a third of the preparations, while the pacemaker remained in the sinus node area in two thirds. A perfusion of isoproterenol into the SNA produced a similar heart rate increase (32 +/- 14%, NS vs. VIP), and shifted the pacemaker site rostrally within the sinus node in three of five preparations, or to the region of Bachmann's bundle in two of five preparations. The response to VIP in the location of the pacemaker was significantly different from the response to isoproterenol. Repeated perfusions of VIP into the SNA after 10-, 25-, 40-, and 60-min intervals produced 2 +/- 13% (p < 0.005 vs. the effect of first VIP administration), 14 +/- 12% (p < 0.05), 10 +/- 12% (p < 0.05) and 30 +/- 13% (NS) heart rate increases, respectively, thereby demonstrating a tachyphylactic effect. In conclusion, VIP seems to exert its positive chronotropic effect directly (probably via specific VIP receptors), although the phenomenon of tachyphylaxis may suggest an indirect sympathomimetic mechanisms.

The present study was designed to identify the free radicals generated during the electrolysis of the solution used to perfuse isolated rat heart Langendorff preparations. The high reactivity and very short half-life of oxygen free radicals make their detection and identification difficult. A diamagnetic organic molecule (spin trap) can be used to react with a specific radical to produce a more stable secondary radical or "spin adduct" detected by electron spin resonance (ESR). Isovolumic left ventricular systolic pressure (LVSP) and left ventricular end diastolic pressure (LVEDP) were measured by a fluid-filled latex balloon inserted into the left ventricle. The coronary flow was measured by effluent collection. Electrolysis was performed with constant currents of 0.5, 1, 1.5, 3, 5, 7.5, and 10 mA generated by a Grass stimulator and applied to the perfusion solution for 1 min. A group of experiments was done using a 1.5 mA current and a Krebs-Henseleit (K-H) solution containing free radical scavengers (superoxide dismutase (SOD): 100 IU/ml or mannitol: 50 mM). Heart function rapidly declined in hearts perfused with K-H buffer that had been electrolyzed for 1 min. The addition of mannitol (50 mM) to the perfusion solution had no effect on baseline cardiac function before electrolysis while SOD (100 IU/ml) increased the coronary flow. However, SOD was more effective than the mannitol in protecting the heart against decreased of cardiac function, 5 min after the end of electrolysis. Samples of the K-H medium subjected to electrolysis were collected in cuvettes containing a final concentration of 125 mM 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and analyzed by spectroscopy. The ESR spectrum consisted of a quartet signal (hyperfine couplings aN = aH = 14.9 G) originating from the hydroxyl adduct signal, DMPO-OH. The intensity of the DMPO-OH signal remained stable during the 60 s of electrolysis and the quantity of free radicals induced by electrolysis was directly proportional to the intensity of the current. The addition of mannitol and SOD to the perfusate scavenged the hydroxyl radicals present in the solution, suggesting that both hydroxyl and superoxide radicals were formed during electrolysis.

The effect of type 1 diabetes mellitus on hypoxia-induced coronary vasodilation was studied in isolated perfused rabbit hearts. Four groups of hearts were compared: control hearts from normal rabbits perfused with physiological buffer (5 mM glucose and 2 mM pyruvate added), hearts from alloxan-induced diabetic rabbits (same perfusion as control), hyperglycemic hearts from normal rabbits perfused with 22 mM glucose and 2 mM pyruvate, and hyperosmotic hearts from normal rabbits perfused with 5 mM glucose, 2 mM pyruvate, and 8.5 mM choline chloride. Hypoxia was produced by perfusion with a mixture of N2- and O2- saturated solutions. Endothelium-dependent and -independent dilators were also tested. Papaverine-induced coronary vasodilatation was unaltered, whereas that of serotonin and adenosine was significantly reduced in hyperglycemic and hyperosmotic hearts but not in diabetic hearts perfused with normoglycemic buffer. Hypoxia (PO2 from 515 +/- 86 to 131 +/- 24 mmHg; 1 mmHg = 133.3 Pa) caused a significant coronary vasodilatation in normal hearts (-66 +/- 3%). This vasodilatation was reduced slightly in diabetic (-45 +/- 7%, p < 0.05) and severely in hyperglycemic (-21 +/- 5%, p < 0.05) and hyperosmotic (-24 +/- 5%, p < 0.05) hearts. The adenosine-receptor antagonist 8-phenyltheophylline (10 microM) reduced hypoxia-induced vasodilatation in normal and diabetic hearts. However, inhibition of prostaglandin synthesis with diclofenac (1 microM), which reduces hypoxia-induced vasodilatation in normal hearts, had no effect in diabetic hearts. In conclusion, alloxan-induced type 1 diabetes mellitus in rabbits is accompanied by a reduced coronary vasodilator response to hypoxia. The contribution of adenosine in this response is unaffected. However, the abated contribution of cyclooxygenase products may account for the reduced vasodilatation during hypoxia in this particular model.

We have previously shown that bradykinin (BK) can modulate the release of noradrenaline (NA) in a model of metabolic anoxia in the rat isolated atria. In this study, we tested the effect of an inhibitor of NA reuptake, desipramine, on the modulatory action of BK on NA release in this experimental model. Atria were isolated from Wistar rats and inserted into a perfusion system. After an equilibration period of 20 min, the perfusate was collected every 5 min for a period of 85 min, during which the atria were field stimulated (5 Hz, 2 ms, 50 mA, 60 s) at 10 (S1) and 75 (S2) min. Desipramine (1 microM) was present throughout the experimental procedures. The metabolic anoxia was started 40 min before S2 by replacing O2 with N2 and by removing glucose. The drugs were added 20 min before S2, and their effects were assessed by the ratio S2/S1. The spontaneous release of NA was not changed by the anoxic procedure, which significantly increased the electrically stimulated induced (S-I) release of NA. BK (30 nM) significantly increased the S-I release of norepinephrine under normoxic conditions. However, following anoxia, both BK and the B1 receptor agonist des-Arg9-BK (100 nM) significantly inhibited the S-I release of NA. The inhibition induced by BK was prevented by selective antagonists for B1 and B2 receptors. These observations contrast with the results obtained without desipramine, where BK, but not des-Arg(9)-BK, inhibited the S-I release of NA during anoxia. Therefore, blockade of NA reuptake during metabolic anoxia appears to alter the modulatory effect of kinins on NA release via the B1 receptor in the rat isolated atria.

A model of metabolic anoxia was used to investigate the modulatory effect of bradykinin (BK) on the release of noradrenaline (NA) in isolated rat atria. Atria were isolated from Wistar rats and inserted into a perfusion system. After an equilibration period of 20 min, the perfusate was collected every 5 min for a period of 85 min, during which the atria were field stimulated (5 Hz, 2 ms, 50 mA, 60 s) at 10 (S1) and 75 (S2) min. The metabolic anoxia was started 40 min before S2 by replacing O2 with N2 and by removing glucose. The drugs were added 20 min before S2, and their effects on NA release were assessed by the ratio S2/S1. The spontaneous and electrically stimulated induced (S-I) releases of NA were significantly increased by the anoxic procedure. BK (30 nM) significantly increased the S-I release of NA under normoxic conditions. However, under anoxia, BK had no effect on the S-I release of NA but inhibited its spontaneous release. BK coadministered with HOE-140 (100 nM), a B2 receptor antagonist, significantly increased the S-I release of NA during anoxia, whereas the coadministration of BK with Leu3-des-Arg9-BK (100 nM), a B1 receptor antagonist, significantly inhibited that release. Administration of des-Arg9-BK (100 nM) had no effect on the S-I outflow of NA following anoxia, although its coadministration with a B1 antagonist resulted in a significant inhibition of the S-I outflow of NA. The present results suggest that BK inhibits NA release through the activation of a B2 receptor following a 40-min period of metabolic anoxia. Because this inhibition can be observed only in the presence of a B1 receptor antagonist, this could imply that B1 receptor activation, revealed by the anoxia, is involved in the facilitation of NA release.

Previous studies have demonstrated that transient ischemia inhibits the release of norepinephrine (NE) following a sustained ischemia. However, the mechanism underlying this inhibition is unknown. Therefore, this study was designed to investigate whether bradykinin (BK) may be involved in the inhibition of NE release following ischemic preconditioning. The effects of transient ischemia, exogenous BK, and kinin receptor blockers on NE release after a prolonged ischemia were tested in the isolated rat heart preparation. Three cycles of 5-min ischemia and reperfusion resulted in the reduction of NE release from 115.3 +/- 14.5 to 51.6 +/- 9.3 pmol.g-1 (p < 0.05) after 30 min of subtotal global ischemia. This effect was not prevented by the administration of either Lys-[Leu8]-des-Arg9-BK (1 mumol.L-1), a B1 antagonist, or HOE-140 (1 mumol.L-1), a B2 antagonist. Three cycles of 5-min BK or des-Arg9-BK infusion also resulted in a dose-dependent inhibition of NE release after 30 min of ischemia. The inhibitory effects of BK (1 mumol.L-1) or des-Arg9-BK (0.5 mumol.L-1) were blocked by Lys-[Leu8]-des-Arg9-BK (1 mumol.L-1), but not by HOE-140 (1 mumol.L-1). The results show that transient ischemia and BK protect sympathetic nerve endings in the isolated rat heart. The inhibition of NE release by pretreatment with BK is mediated by the activation of B1 receptors, whereas preconditioning provided by transient ischemia may be mediated by a different, yet unknown, mechanism in the rat heart.

The relative contribution of ventricular receptors and sinoaortic baroreceptors to the reflex release of adrenaline upon coronary occlusion was studied in anaesthetised rats submitted to a 30-min occlusion of the left coronary artery. Arterial adrenaline concentrations, heart rate and blood pressure were evaluated in control and sham-operated rats, and following sinoaortic denervation (SAD), bilateral vagotomy with and without SAD, ventricular application of lidocaine, neonatal treatment with capsaicin and cervical section of teh spinal cord. In all groups submitted to coronary ligation, blood pressure decreased sharply upon ligation and remained significantly reduced throughout occlusion while heart rate changes were not significant. In control rats, arterial adrenaline concentrations were significantly increased 15 and 30 minutes following coronary occlusion. The increase in adrenaline concentrations observed upon coronary ligation following SAD was not different from that of the control group. On the other hand, vagotomy with or without SAD, ventricular application of lidocaine, neonatal capsaicin treatment and spinal section all greatly reduced the increase in plasma adrenaline values. These results suggest that a large part of the reflex release of adrenaline upon coronary occlusion is mediated by ventricular receptors with unmyelinated vagal afferent fibres.

Recently it has been shown that ceruloplasmin presents a protective action against reperfusion-induced arrhythmias in the isolated perfused rat heart, an effect that is lost when the protein is denaturated by heat. The present study was carried out to see whether ceruloplasmin can alter electrophysiological properties such as ventricular effective refractory periods, conduction time, and action potential duration calculated at 50, 75, and 90% levels of repolarization (APD50, APD75, APD90). To check the specificity of the electrophysiological effects of ceruloplasmin, we have also compared them with those of heat-denatured ceruloplasmin, superoxide dismutase, catalase, deferoxamine, and albumin. In isolated rat hearts, ceruloplasmin (0.25-3 microM) (n = 8 for each concentration) was shown to increase the effective refractory period in a concentration-dependent manner by 26 to 89%. Conduction time was not significantly altered. Heat-denatured ceruloplasmin (0.50-3 microM) (n = 8 for each concentration) increased the effective refractory period by 33 to 70% and did not affect the conduction time. In contrast, superoxide dismutase (1-4 microM), catalase (1-2 microM), deferoxamine (500 microM-1 mM), and albumin (1-4 microM) (n = 8 for each substance and for each concentration) had no significant effect on effective refractory period and conduction time at any dose, suggesting that the ceruloplasmin effect might be specific. In rat ventricular preparations, ceruloplasmin (1 microM) also induced a constant prolongation of APD50 (52%), APD75 (64%), and APD90 (41%) after 15 min of infusion (n = 6). The prolongation of effective refractory period and of action potential duration, by native and heat-denatured ceruloplasmin, suggests that this substance has specific class III effects, although this cannot entirely account for its antifibrillatory action at reperfusion in isolated rat hearts.

The ability of ceruloplasmin, an important serum antioxidant, to reduce the vulnerability of the isolated rat heart to reperfusion arrhythmias has been investigated. Bovine plasma ceruloplasmin was purified by chromatography on aminoethyl-agarose. Isolated rat hearts were submitted to 15 min of regional ischemia and 10 min of reperfusion. The dose-effect relationship and the role of ceruloplasmin conformational integrity in cardioprotection were established by treatment of ischemic hearts with ceruloplasmin at various concentrations (0.25, 0.5, 1, and 2 microM) and at different degrees of conformational integrity (A610/A280 = 0.02, 0.04, and 0.06), 5 min before reperfusion. Deferoxamine (20-500 microM) was used as a positive control. As negative controls we used chemically inactivated ceruloplasmin (1 microM), heat-denatured ceruloplasmin (1 microM), and albumin (1-4 microM). In the control group during the first 5 min of reperfusion, the incidence of total ventricular fibrillation was 100% and of irreversible ventricular fibrillation was 83%. The incidence of reversible and irreversible ventricular fibrillation was significantly decreased in the ceruloplasmin-treated groups in both a dose and molecular integrity dependent manner. Ceruloplasmin had no effect on the incidence of ventricular tachycardia. Deferoxamine reduced the incidence of ventricular fibrillation to the same degree as ceruloplasmin but at concentrations much higher than those of ceruloplasmin. Chemically inactivated ceruloplasmin, heat-denatured ceruloplasmin, and albumin had no protective effects on reperfusion-induced arrhythmias.

This study describes the carioprotective effect of ceruloplasmin (CAS 9031-37-2) against oxygen free radical injury, as indicated by several biochemical indicators and some cardiodynamic variables. Isolated rat hearts (n = 4-8, p < 0.05, for each experimental point) in Langendorff preparation were exposed to oxygen free radicals generated by electrolysis (10 mA) in the absence and the presence of 0.25 mumol/l purified ceruloplasmin and denaturated ceruloplasmin, in Krebs-Henseleit perfusion solutions. Biochemical indicators (noradrenaline, malondialdehyde, creatine-kinase, lactate dehydrogenase, aspartate aminotransferase, Ca2+ and Mg2+) as well as the electrocardiogram and the left ventricular pressure (LVP), were altered by oxygen free radicals formation, denoting major cellular and tissular damages in the nontreated hearts. Ceruloplasmin exhibited a cardioprotective effect and prevented the oxygen free radical-induced release of noradrenaline, indicating that it can also protect the sympathetic nerve endings from oxygen free-radical injury. Purified ceruloplasmin, a circulating extracellular antioxidant and oxygen free radical scavenger, seems to be an effective heart protective agent against myocardial and neuronal injuries generated by oxygen free radicals.

Previous data from our laboratory have shown that electrolysis-induced oxygen free radicals (OFR) and ischemia/reperfusion (I/R) injury both produced a significant decrease of myocardial noradrenaline (NA) stocks in the isolated perfused rat heart. Therefore, we carried out the present study by immuno- and fluorescence histochemistry techniques to demonstrate the possibility that fibers nerve endings of the heart may be injured and to evaluate the subsequent damages. Isolated rat hearts were perfused according to the Langendorff technique and subdivided into i) control; ii) electrolyzed (two platinum electrodes, DC current, 10 mA, 1 min); iii) xanthine and xanthine oxidase (X-XO) perfusion for 30 min, and iv) 30 min global ischemia followed by 5 min reperfusion. Results indicate that in the last three groups myocardial fibers were altered. However, in electrolyzed hearts and those submitted to X-XO perfusion, but not in the I/R model, a disruption of many of the nerve fibers could be noted. Thus, NA leakage may be due to a neural injury when OFR are generated exogenously, whereas in the I/R model NA overflow may be explained by a metabolic dysfunction such as the inversion of the uptake I carrier. The major conclusion of this study is that OFR as generated exogenously (by electrolysis or by X-XO) cannot be considered to closely mimic the conditions of I/R injury, at least as concerns neural injury.

Objective: The aims were: (1) to study the acute effects of captopril on the action potential characteristics of ventricular fibres from the normal rat, (2) to compare the effects of captopril with those of perindoprilat, a non-thiol angiotensin I converting enzyme (ACE) inhibitor, (3) to determine the electrophysiological properties of the peptide substrates of converting enzyme, bradykinin and angiotensin I, and (4) to investigate whether the effects of captopril occurring in the healthy heart also occur in two models of ventricular hypertrophy., Methods: Action potentials were recorded with the standard glass microelectrode technique in right ventricular preparations excised from rat hearts and superfused under baseline conditions and with drug containing or peptide containing Tyrode solution. Ventricular hypertrophy was induced in response to hypertension (unilaterally nephrectomised, DOCA-salt model) or 4 week old left ventricular infarction., Results: In preparations from normal rat hearts, captopril increased action potential duration in a concentration dependent fashion [EC50 = 3.5 x 10(-8) M; maximum effect = 44(SEM 5.1)% prolongation at 10(-5) M for action potential duration at 90% repolarisation, APD90]. Perindoprilat similarly caused a dose dependent increase in action potential duration, but with 100 times greater potency [EC50 = 3.1 x 10(-10) M; maximum effect = 71(11)% prolongation at 10(-5) M for APD90]. SQ 14,534, a stereoisomer of captopril with one hundredth the ACE inhibitor potency, had no significant effect on action potential duration at 10(-5) M. Angiotensin I and bradykinin caused concentration dependent prolongation of action potential, but angiotensin II (10(-6) M) had no effect. Captopril (10(-5) M) had no significant effect in the hypertrophied right ventricle from DOCA-salt hypertensive rats, but significantly increased APD90 [39(4.9)%] in right ventricular preparations from rats with 4 week old anterior left ventricular infarction., Conclusions: In the rat, captopril prolongs action potential duration, an effect possibly due to local accumulation of bradykinin and angiotensin I.

Objective: The aim was to study (1) the effects of intracoronary saralasin, an angiotensin II receptor antagonist, on ischaemia induced and reperfusion induced regional cardiac noradrenaline release and ventricular arrhythmias; and (2) the implication of angiotensin II in coronary constriction during myocardial ischaemia., Methods: Eighteen adult mongrel dogs, weight 22.6(SD 1.1) kg, anaesthetised with sodium pentobarbitone, were used for the study. The left anterior descending coronary artery was ligated for 60 min and then reperfused for 30 min. Saralasin (60 micrograms.kg-1, n = 9) or its vehicle (Ringer lactate, n = 9) was injected into the artery at the beginning of the occlusion period. Two epicardial veins, one running parallel to the left anterior descending coronary artery and the other parallel to the circumflex coronary artery, were cannulated for the measurement of their respective blood flows and of noradrenaline, lactate, and creatine kinase release., Results: Saralasin decreased the incidence of ventricular fibrillation during coronary occlusion (from 44% in the vehicle treated group to 0% in the saralasin treated group, p = 0.0412). This effect was accompanied by significant vasodilatation in both epicardial veins during myocardial ischaemia. Neither the increases in noradrenaline, lactate, and creatine kinase release nor the incidence and duration of the ventricular arrhythmias following reperfusion were modified by the administration of saralasin., Conclusions: Intracoronary saralasin in the early phase of myocardial ischaemia increases the epicardial venous blood flow significantly, suggesting that angiotensin II is implicated in coronary constriction during ischaemia. This haemodynamic effect is accompanied by a significant decrease in the incidence of ventricular fibrillation. However, the renin-angiotensin system does not appear to be implicated in the reperfusion induced noradrenaline release nor in the incidence of the ventricular arrhythmias.

In isolated rat hearts subjected to 30 min stop flow followed by 5 min reperfusion, Bradykinin (Bk), 1 and 0.1 microM, significantly decreased ventricular tachycardia and fibrillation, noradrenaline (NA) output at reperfusion as well as myocardial NA loss and lipid peroxidation, and preserved creatine kinase activity. Des-Arg9-Bk 0.1 microM had also similar effects. Hence, the active metabolite des-Arg9-Bk may be involved in the protective action of Bk, partly mediated by its inhibitory effect on NA liberation.

In the present investigation, we used electrolysis as a source of oxygen free radicals to test their possible role in norepinephrine release, as well as in the mechanism of cellular injury, cardiac dysfunction and arrhythmias. In the isolated rat heart perfused under constant pressure, according to the Langendorff technique, electrolysis of the Krebs-Henseleit solution (10 mA d.c. current for 1 min) produced myocardial irreversible dysfunction within 5 min. Fifteen minutes after electrolysis, significant falls in the left ventricular pressure (from 87.5 +/- 6.8 to 33.7 +/- 5.2 mmHg), dP/dt max (from 1230 +/- 90 to 375 +/- 59 mmHg/s), heart rate (from 287 +/- 18 to 119 +/- 13.5 beats/min) and coronary flow (from 14.8 +/- 9 to 3.4 +/- 1.7 ml/min) were observed, along with an increase in left ventricular end diastolic pressure from 10 to 50 +/- 3.5 mmHg (n = 8, P less than 0.01). AV conduction block and/or sinus bradycardia were noted in all preparations. An increase in norepinephrine washout from 298.5 +/- 84 at baseline to 610 +/- 110 pg/min/g 5 min after electrolysis was measured (n = 8, P less than 0.05) and a 44.8 +/- 9.2% and 35 +/- 7.5% reduction, respectively in right and left ventricular tissue norepinephrine content was also found at 30 min (n = 5, P less than 0.05). Pretreatment of the hearts 10 min before electrolysis and throughout the experimental period by superoxide dismutase (SOD; 100 U/ml), catalase (150 U/ml), a combination of SOD + catalase or mannitol (50 mM) partially blocked the deleterious effect of free radicals and permitted a functional recovery of 50 to 60%, mannitol being the more potent protective agent. Furthermore, these scavengers also significantly reduced norepinephrine washout.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of amiodarone (30 mg/kg p.o. each day for 3 weeks) on noradrenaline (NA) overflow into coronary sinus (CS) blood during left stellate stimulation (15 V, 2-ms square waves, 30 s duration at 1, 2, 4, and 8 Hz in random order) was investigated in an open-chest dog preparation. CS blood samples were taken before and during the stimulation period for plasma NA and hematocrit determinations. CS blood flow was monitored (extracorporal circulation with an electromagnetic flow meter) and used for NA output computation. The right atrium was paced throughout the experimental period. However, because AV block occurred at a high pacing rate in some amiodarone-treated dogs, pacing rate was lower in that group than in control dogs (132 +/- 13 vs. 161 +/- 10 min-1, ns). Mean arterial pressure was also lower in the treated group (95 +/- 9 vs. 110 +/- 13 mmHg, but increased in every dog upon stimulation (p less than 0.05). Basal left ventricular dP/dtmax was comparable in the two groups of dogs and increased in a similar fashion upon stimulation (p less than 0.05). The increase in plasma NA concentration upon stimulation was comparable between the control and the amiodarone-treated group (0.38 +/- 0.08 vs 0.40 +/- 0.12 ng/mL at 1 Hz and 12.7 +/- 3.1 vs 11.3 +/- 2.3 ng/mL at 8 Hz, ns). The increase in NA output was also comparable (7.0 +/- 1.6 vs. 10.7 +/- 5.4 ng/min at 1 Hz and 356 +/- 124 vs. 334 +/- 102 ng/min at 8 Hz, ns). Amiodarone did not alter the myocardial NA content. We conclude that amiodarone, administered orally for 3 weeks, does not interfere with neural NA release, or with the positive inotropic response, following sympathetic nerve stimulation in dogs.

Plasma catecholamines, heart rate, and cardiac sympathetic activity in exercising dogs. Med. Sci. Sports Exercise, Vol. 14, No. 4, pp. 291-285, 1982. The purposes of the study were, 1) to assess the respective roles of locally released norepinephrine in the sinus node and of plasma catecholamines in the control of heart rate during exercise and 2) to verify whether the heart is a source of plasma catecholamines during exercise. Plasma catecholamines (radioenzymatic assay) and heart rate were measured in the last minute of a 5-min exercise period (3.2 km . h-1, 39% slope) in six normal dogs, in six dogs treated with 5 mg . kg-1 sotalol, and in six dogs sympathectomized with 50 mg . kg-1 6-hydroxydopamine. Compared to the exercise heart rate values of the normal dogs (228 +/- 8 beats . min-1) and the sympathectomized dogs (226 +/- 9 beats . min-1), the sotalol-treated dogs had significantly lower rates (148 +/- 6 beats . min-1). However, plasma catecholamine response was higher in the sotalol-treated dogs (7380 +/- 1350 pg . ml-1) and in the sympathectomized dogs (4280 +/- 680 pg . ml-1) than in the normal dogs (1890 +/- 360 pg . ml-1). Since the action of plasma catecholamines on the sinus node is potentiated by denervation hypersensitivity, it is suggested that in exercising normal dogs, heart rate control could be ensured by locally released norepinephrine rather than by plasma catecholamines. Plasma catecholamines were assessed in six normal dogs at rest and at various exercise levels (HR = 90-200 beats . min-1) and in blood sampled simultaneously in the aorta and the coronary sinus. Plasma catecholamines in the coronary sinus and aorta were similar at rest (490 +/- 90 vs 580 +/- 80 pg . ml-1, respectively) and at the low-intensity exercise (710 +/- 140 vs 880 +/- 120 pg . ml-1, respectively). For moderate and severe work loads, plasma catecholamine concentrations in the coronary sinus (960 +/- 160 and 1570 +/- 340 pg . ml-1, respectively) were lower than in the aorta (1380 +/- 260 and 2950 +/- 100 pg . ml-1, respectively). These results suggest that in exercising dogs the heart is not a source of plasma catecholamines.

The properties and determinants of hysteresis during ventricular effective refractory period (VERP) measurements by an extrastimulus technique were determined in 15 anesthetized open-chest dogs as well as in isolated ventricular muscle (n = 6). VERP was determined both by decreasing the S1-S2 interval and also by increasing S1S2. Hysteresis was then calculated by subtracting the VERP obtained with the decreasing S1S2 from the VERP obtained with the increasing S1S2. The effects of basic cycle length, pulse width, stimulation intensity, and the number of basic drives on VERP and hysteresis were evaluated. VERP was shorter for long pulse width, high stimulation intensities, and shorter basic cycle lengths. These modifications were not associated with significant changes of hysteresis. VERP was shorter during decreasing S1S2 than during increasing S1S2. Hysteresis was greater with 6 basic drive cycles than with 12 (P less than 0.001) in both in vivo and in vitro preparations. The data suggest that 1) hysteresis occurs during VERP measurements; 2) hysteresis is independent of stimulation modality; and 3) hysteresis decreases with the number of basic drive cycles.

Plasma epinephrine (E) and norepinephrine (NE) concentrations were measured (radioenzymatic assay) in blood samples simultaneously withdrawn from the aorta (Ao) and coronary sinus (CS) on 10 anesthetized dogs immediately before and during a 1-min period of electrical stimulation of the left stellate ganglion (4 V, 4 ms, 10 Hz). Heart rate and systolic blood pressure significantly increased in response to electrical stimulation (152 +/- 8 to 180 +/- 15 beats/min and 128 +/- 12 to 149 +/- 12 mmHg, mean +/- SE; P less than 0.05). Plasma NE concentrations were not significantly different in the Ao and the CS (432 +/- 110 and 319 +/- 67 pg/ml) before the stimulation, whereas a net removal of E was present across the myocardium (Ao, 172 +/- 61; CS, 71 +/- 22 pg/ml). A large NE spillover in the CS was observed during the stimulation (Ao, 1,555 +/- 513; CS, 10,583 +/- 3,753 pg/ml). A significant output of E from the myocardium was also present (Ao, 165 +/- 42; CS, 291 +/- 74 pg/ml) during the stimulation. Determination of NE and E concentrations by high-performance liquid chromatography in five of the dogs confirmed the observation made with the radioenzymatic assay, i.e., a significant uptake (66%) of blood-borne E was present across the myocardium in the control situation (Ao, 320 +/- 97; CS, 110 +/- 23 pg/ml), whereas plasma E concentrations in the CS (280 +/- 61 pg/ml) were 1.5 times the values found in Ao (184 +/- 56 pg/ml) under electrical stimulation. These observations give further support to the hypothesis that endogenous tissue E can act as a cotransmitter of sympathetic fibers.

Chemical sympathectomy and bilateral vagotomy were used to evaluate the contribution of each division of the autonomic nervous system in the electrophysiological actions of ouabain. Intact and chemically sympathectomized dogs were given successive and cumulative doses of ouabain until toxicity became manifest (ventricular extrasystoles and (or) ventricular tachycardia). An additional group of normal and sympathectomized animals was also submitted to bilateral vagotomy in the presence of a therapeutic dose of ouabain. Sinus cycle length, AH interval of the His bundle electrogram, atrioventricular junctional effective and functional refractory periods were increased by ouabain at therapeutic doses. These effects were no different in sympathectomized dogs than in intact dogs, indicating the absence of any significant contribution of efferent sympathetic neural activity. However, our results suggested that vagal enhancement was the main mechanism whereby ouabain produced sinus bradycardia and depression of atrioventricular conduction. Sympathectomy with 6-OHDA did not modify nor abolish ouabain toxicity. However, toxic doses were significantly higher in sympathectomized animals than in normal animals. Considering that increasing heart rate by cardiac pacing or vagotomy significantly lowered toxic doses of ouabain in both intact and sympathectomized dogs, it is possible that sympathectomy could influence ouabain toxicity by altering heart rate alone.

Effect of sotalol (STL) was compared with that of (+/-)-propranolol, (+)-propranolol (PPL), and acebutolol (ABL) on noradrenaline (NA) release as measured in coronary sinus (CS) blood during postganglionic stimulation (2 Hz, 30 s) of the left cardiac sympathetic nerves in anesthetized dogs. In control dogs receiving saline, increasing responses of CS-NA concentration, mean CS blood flow, and CS-NA output to repetitive stimulation were relatively stable throughout a given experimental period. Both STL (1,2.5, and 5 mg/kg, i.v.) and (+/-)-PPL (0.5 and 2.5 mg/kg, i.v.) diminished the increased CS-NA concentration by approximately 35 (P less than 0.05) to 60% (P less than 0.01) in a dose-dependent fashion. However, (+)-PPL (0.02-2.5 mg/kg, i.v.) and ABL (0.5-5 mg/kg, i.v.) did not significantly alter the increasing response of CS-NA concentration upon stimulation. STL, (+/-)-PPL, and ABL markedly inhibited the CS blood flow response to stimulation at all doses tested, while (+)-PPL did not significantly diminish the flow response even at the highest dose tested. Consequently, CS-NA output decreased significantly (p less than 0.01) in the presence of STL, (+/-)-PPL, and ABL at all doses tested but not with (+)-PPL at any dose tested. The inhibitory effect of STL and (+/-)-PPL on the increasing response of CS-NA concentration upon stimulation could be related to their beta-blocking effect, which exerts presumably on postulated presynaptic beta-adrenoceptors, as (+)-PPL did not at all diminish the response.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of catecholamine-depleting pretreatments, reserpine, and 6-hydroxydopamine (6-OH-DA) on left ventricular pressure (LVP) and the inotropic response to graded doses of ouabain (up to 300 mug/0.05 ml) was studied in isolated perfused rat and guinea-pig hearts. In rats, reserpine and 6-OH-DA depleted the cardiac content of catecholamine, but did not increase initial LVP and did not reduce the inotropic response to the highest dose of ouabain. It is concluded that in isolated rat hearts, these catecholamine-depleting pretreatments nearly abolish the inotropic response to ouabain, and this effect appears to be mediated mainly through an increase in initial LVP. The reason why catecholamine depletion failed to increase initial LVP in guinea pigs remains unexplained.

Fourteen sedentary middle-aged men underwent a chest X-ray, a 12 lead ECG, a VCG, and an echocardiographic examination prior to and following 5 months of training a moderately severe intensity, on a cycle ergometer. No modification in the X-ray cardiac profile was observed following training. Some electrocardiographic (R wave amplitude in V5 and V6 and Sokolow index: SV1 + RV5 or V6) and vectorcardiographic (maximal QRS vector amplitude, maximal spatial QRS vector, and R wave amplitude) indices of left ventricular hypertrophy were slightly but significantly increased following training. The echocardiographic measurements in diastole (septal and posterior wall thickness, left ventricular internal diameter, and left ventricular mass) were unchanged after training. Results suggest that electrical changes may not provide adequate indications of left ventricular morphological modifications. The lack of echocardiographic evidences of left ventricular hypertrophy suggest that: (1) training does not necessarily induce left ventricular hypertrophy; (2) the large heart sometimes observed in athletes may be the result of a genetic factor or of a prolonged and very intensive training pursued since a very young age, over a number of years; and (3) left ventricular enlargement probably plays a minor role in the increase in aerobic capacity following training.

In anesthetized dogs, 60-min occlusions of either the proximal (n = 14), distal (n = 8) left circumflex (LCX), or left anterior descending (LAD, n = 10) arteries were followed by reperfusion. Coronary sinus and aortic norepinephrine and epinephrine plasma concentrations were measured. The ventricular arrhythmias were ventricular premature depolarizations (VPDs), unsustained ventricular tachycardia (VT) (greater than or equal to 3 and less than 20 VPDs), sustained VT (greater than or equal to 20 VPDs), and ventricular fibrillation (VF). A gradual twofold increase (p less than 0.05) in myocardial norepinephrine overflow followed occlusion in all three groups. The increases in the amounts of norepinephrine released in the coronary sinus blood during reperfusion were significant and proportional to the size of the occluded area: proximal LCX, from 0.236 +/- 0.038 to 1.528 +/- 0.490 ng/mL of plasma (p less than 0.001); LAD, from 0.180 +/- 0.027 to 0.795 +/- 0.286 ng/mL (p less than 0.05); distal LCX, from 0.215 +/- 0.039 to 0.404 +/- 0.110 ng/mL (p less than 0.05). Aortic epinephrine concentrations were significantly increased only by LAD occlusion; at 15 min, the value had increased to 0.187 +/- 0.053 ng/mL from an initial value of 0.069 +/- 0.029 ng/mL (p less than 0.001). Two phases of ventricular arrhythmias followed both occlusion and reperfusion. Phase 1 postocclusion was characterized by VPDs and phase 2 by VPDs and unsustained VT. Sustained VT was seen only in phase 1 postreperfusion, whereas unsustained VT was seen in phase 2. VF was seen in 50, 35, and 25% of the dogs with proximal LCX, LAD, and distal LCX occlusion and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

S-2395 is a new, long-acting, non-selective beta-receptor blocking agent without apparent intrinsic cardiodepressive action and no receptor selectivity. Its electrophysiological actions were studied in intact and chemically sympathectomized dogs. In normal dogs, S-2395 very slightly increased atrial monophasic action potential (MAPa) duration, atrioventricular functional (FRP) and ventricular effective (ERP) refractory periods. The onset of the atrial supernormal conduction phenomenon (SNCP) was delayed and the ventricular SNCP was abolished. These results are consistent with the action of low concentrations of beta-blocking agents. In contrast S-2395 reduced the ventricular MAPv and increased the ERP/MAPv ratio of sympathectomized animals. Such modifications are usually seen with concentrations higher than necessary for simple beta-receptor blockade. In conclusion S-2395, like several others beta-blockers, had minor effects on the classical electrophysiological parameters of normal dogs. However, it suppressed ventricular SNCP and had a more pronounced action in sympathectomized dogs who are known to have higher levels of circulating catecholamines and who present post-synaptic supersensitivity. The SNCP has been linked with re-entrant arrhythmias. Considering that beta-blockers prevent arrhythmias specially in hyperadrenergic states, the suppression of the ventricular SNCP by S-2395 could thus be the mechanism by which this drug and possibly other beta-blockers might exert their antiarrhythmic action.

To investigate the actions of lidocaine and diltiazem on the ischemic alterations associated with the onset of acute ischemic arrhythmias, the left anterior descending coronary artery was occluded for 6-min periods separated by 30 min of reperfusion, under control conditions and after injection of lidocaine (2.4-3.8 micrograms/mL of plasma) or diltiazem (390-510 ng/mL) in open-chest anesthetized pigs. Sixty-one unipolar electrograms were continuously recorded in the ischemic zone. Isochronal maps and isopotential maps were determined by computer analysis. The magnitude of beat-to-beat alternation of unipolar waveforms was described by the difference between the time integrals subtended by electrograms of consecutive beats. Activation times were prolonged by ischemia and the ST segment became elevated. Delay and ST elevation developed at a faster rate in the presence of lidocaine than under control conditions, but were reduced by diltiazem. ST-T alternation was not significantly different between control and lidocaine occlusions, but the incidence of negative T waves and that of ventricular tachycardia degenerating to fibrillation were higher in lidocaine occlusions than in control occlusions. In contrast, unipolar waveform alternation and negative T waves were virtually abolished by diltiazem, even at fast pacing rates (180-210 beats/min) at which diltiazem did not reduce ST elevation. Ventricular arrhythmias also were abolished by diltiazem. Thus, lidocaine and diltiazem produce opposite effects on the ischemic alterations most closely associated with the initiating mechanism of tachycardia. This could be related to differences between these drugs with regard to their actions on transmembrane currents during repolarization.

Dynamics of circulating catecholamines (CA) were studied at rest (heart rate = 104 +/- 3 beats/min) and during mild treadmill exercise (heart rate = 168 +/- 5 beats/min) in 60 dogs. Plasma epinephrine (E) and norepinephrine (NE) removal from circulation and release into circulation were estimated from plasma CA arteriovenous differences across the regional vascular beds studied (pulmonary, myocardial, hepatosplanchnic, renal, and skeletal muscle vascular beds) and from regional blood flows. Regional plasma E fractional extraction (PEFE) was used as an index of NE removal from plasma. Arterial plasma CA increased significantly from rest to exercise (P less than 0.05). A significant PEFE was observed at rest and exercise across all studied vascular beds but the pulmonary bed. When plasma flow was taken into account, the largest contributors to plasma CA removal were the hepatosplanchnic vascular bed at rest and skeletal muscle vascular beds during exercise. At rest, the hepatosplanchnic vascular bed was a major contributor to the plasma NE pool. During exercise, main contributors to NE release into plasma were skeletal muscle vascular beds. Circulating CA kinetics did not appear to vary from rest to exercise. Clearance and apparent distribution space were estimated to be, respectively, 1.5 l/min and 2 liters for circulating E and 2 l/min and 5 liters for NE at rest and exercise. Circulating E and NE half times were estimated to be approximately 1 and 1.8 min, respectively.

Correlations between the concentration of endogenous catecholamines in coronary sinus blood and various physiological responses to adrenergic stimulation were studied in anesthetized dogs. Plasma catecholamine levels both in coronary sinus and aortic blood were measured by means of a modification of the radiometric-enzymatic assay for tissue catecholamines, and found to be 0.769 +/- 0.110(S.E.) and 0.972 +/-0.127(S.E.) ng/ml, respectively, under basal conditions. Circulating catecholamine levels increased after the intracoronary injection of 6-hydroxydopamine, which has an indirect sympathomimetic action. Both the increment in catecholamine release from the heart and the intensity of physiological response were dose-related. A frequency-dependent increase in coronary sinus blood catecholamine levels occurred during right cardioaccelerator nerve stimulation. Maximum values were observed with a stimulation frequency of 10 Hz, at which maximum physiological responses were obtained. A highly significant correlation was found between endogenous catecholamine levels in coronary sinus blood and the dp/dt of left ventricular pressure (r = 0.750, p less than 0.001), as well as mean coronary blood flow (r =0.706, p less than 0.001). The present preparation may prove to be a reliable means of studying the role of the sympathetic system in regulating cardiac function.

The relationship between the increase in catecholamine levels of the coronary sinus blood and the amplitude of various cardiac responses to adrenergic nerve stimulation was studied in anesthetized dogs. Plasma catecholamine levels in both coronary sinus and aortic blood were measured by a modification of the radiometric enzymatic assay for tissue catecholamines and were found to be 0.622 plus or minus 0.104 (SE) ng/ml and 0.933 plus or minus 0.116 ng/ml, respectively, under basal conditions. The catecholamine levels in coronary sinus blood increased linearly during right cardioaccelerator nerve stimulation up to a frequency of 10 Hz. At this frequency, maximum values were observed in both coronary sinus blood catecholamine levels and cardiac responses. The correlation between the response in heart rate, mean coronary blood flow, and dP/dt of left ventricular pressure and the increase in endogenous catecholamine levels of coronary sinus blood was significant, but the relationship was nonlinear. The present experimental design may prove to be a reliable means of studying the role of the sympathetic nervous system in the regulation of cardiovascular function in vivo.