Maintained geometry, elasticity and contractility of human saphenous vein segments stored in a complex tissue culture medium.

OBJECTIVE: Improved maintenance of endothelial function and higher viability of saphenous vein grafts stored in a complex tissue culture medium (TCM) have been demonstrated. This article studies the biomechanical properties of saphenous vein segments. DESIGN: Biomechanical properties of 72 saphenous vein segments remaining from coronary bypass grafting of 32 patients have been studied after different storage procedures. MATERIALS: The materials studied included fresh segments, segments stored in a cooled conventional physiological salt solution (normal Krebs-Ringer (nKR)) for 1-2 weeks, segments stored in a cooled chemically defined TCM (X-Vivo) for 1,2,3 and 4 weeks and segments cryopreserved for a few weeks. METHODS: Specimens were cannulated at both ends and pressure-diameter curves were recorded in the 0-85-mmHg range in nKR with 10 microM norepinephrine added to induce maximum smooth muscle contraction, as well as in Ca(2+)-free medium to induce full relaxation. Tensile strength was checked at 300 mmHg. Distensibility, elastic modulus and active strain were computed. RESULTS: Segments stored in nKR dilated morphologically, their distensibility decreased and they lost their ability to contract (1.5+/-0.7% from 10.1+/-1.5% of control) in 1 week. The TCM-stored segments preserved their contractility until 1 week, and this parameter only slowly decreased afterwards (first week, 11.5+/-7.3%; fourth week, 3.9+/-0.6%). There was a slight decrease in wall thickness but the lumen diameter was not affected. The elastic parameters of these segments were practically identical to those of fresh segments. Cryopreserved segments narrowed morphologically, their wall thickened and contractility diminished. CONCLUSIONS: Storage in TCM helps preserve the passive and active biomechanical properties of human saphenous vein segments. Such properties can be expected to improve graft tissue viability.

The effect of atrial dilatation on the genesis of atrial arrhythmias.

The effect of atrial stretching on the genesis of atrial arrhythmias was studied in 26 dogs. Left atrial dilatation was produced by inflation of a balloon catheter. Electrophysiological studies were performed by programmed electrical stimulation of the atrium and ventricle. The irritability of the atrium markedly increased when it was distended and atrial arrhythmias (sustained or non-sustained atrial tachyarrhythmias) could regularly be induced by administration of an early extrastimulus or--more rarely--by atrial burst pacing. In 10 cases spontaneous atrial tachycardia appeared during atrial balloon dilatation. The atrial effective refractory period shortened and the atrial conduction time lengthened on atrial stretching, while other electrical variables (cycle length, sinus node recovery time, atrioventricular conduction time, intraventricular conduction, ventricular refractory period, QT interval) remained unchanged. Atrial balloon dilatation was not accompanied by marked haemodynamic changes, and the left ventricular pressure curve, the contractility of the left ventricle and the central venous pressure did not change significantly on atrial stretching. The experimental data suggest that the atrial dilatation plays an important part in the pathogenesis of atrial arrhythmias.

Intrapericardial infusion of endothelin-1 induces ventricular arrhythmias in dogs.

OBJECTIVES: Recently, extremely high levels of endothelin-1 (ET-1) were detected in the pericardial fluid of patients with heart disease; however, the pathophysiological importance of this finding is not known. The present study was designed to characterize ET-1 levels in canine pericardial fluid and to investigate the effects of local high concentrations of exogenous ET-1 in vivo. METHODS: In anesthetized, open-chest dogs ET-1 (Groups 1 and 2: 11 and 33 pmol.kg-1.min-1; n = 6 and 6, respectively) or physiological saline (Group 3, n = 5) were infused into the closed pericardial sac for 40 min. In serial pericardial fluid and aortic blood plasma samples, ET-1 levels were measured by radioimmunoassay, and analysed by high-performance liquid chromatography (HPLC). Systemic arterial blood pressure, heart rate, cardiac output (CO), standard ECG and right ventricular endocardial monophasic action potentials (MAPs) were recorded. RESULTS: Basal pericardial fluid ET-1 levels were significantly higher than respective plasma levels (342 +/- 210 vs. 8.0 +/- 5.2 pmol.l-1, n = 14, P < 0.001. In HPLC analysis pericardial fluid ET-1 was indistinguishable from ET-1(1-21). Infusion of exogenous ET-1 into the pericardial space induced ventricular arrhythmias in all instances, which were associated with 9.7-fold increase in pericardial fluid ET-1 levels. Ventricular tachycardias developed in 9 of 12 animals. The arrhythmogenic effect of ET-1 was more apparent in dogs with the larger dose. Before the onset of arrhythmias, intrapericardial infusion of ET-1 increased QT time (Group 1: 207 +/- 18 to 230 +/- 23 ms, P < 0.01; Group 2: 220 +/- 12 to 277 +/- 17 ms, P < 0.01) and MAP duration at 90% repolarization (at 300 ms cycle length) (Group 1: 192 +/- 9 to 216 +/- 9 ms, P < 0.01; Group 2: 205 +/- 9 to 255 +/- 9 ms, P < 0.001). Hemodynamic variables did not change significantly prior to the onset of ventricular tachyarrhythmias. In Group 3, arrhythmias were not observed and all electrophysiological and hemodynamic parameters remained unchanged. CONCLUSIONS: Administration of exogenous ET-1 into the pericardial space induces ventricular arrhythmias associated with prolongation of QT time and MAP duration. Whether pericardial fluid ET-1 under pathophysiological conditions can ever reach sufficiently high levels to induce ventricular arrhythmias remains to be elucidated.

The effect of superoxide dismutase in the myocardium during reperfusion in the dog.

The aim of the study was to investigate the pathological role of free radicals during myocardial reperfusion. Low (0.5 mg/kg body weight) and high doses (5 mg/kg) of superoxide dismutase (SOD) were infused into the left atrium of mongrel dogs for 4 min starting 29 min after ligation and 1 min before reperfusion of the left anterior descending coronary artery (LAD). Arterial blood pressure, heart rate, electrocardiogram, and the regional contractile force of the left ventricle were monitored throughout the ligation (30 min) and reperfusion periods (20 min). Concentrations of creatine kinase (CK) and malondialdehyde (MDA) in the coronary sinus blood were determined before (0 min) and during ligation (15 and 25 min) and during reperfusion of the LAD (2, 7, and 20 min). In other groups of dogs, the effect of the two doses of SOD on epicardial blood flow was investigated during ligation and reperfusion by the measurement of epicardial temperature using a thermocardiograph. Experimental subjects were mongrel dogs of either sex (n = 25), weight 10-35 kg. Compared to controls (mean +/- SEM, 43.1 +/- 1.2; n = 7), the number of ventricular extrasystoles during the first 5 min of reperfusion was significantly (p < .001) decreased in dogs treated with the high dose (15.01 +/- 2.14; n = 5), but not in those receiving the low dose of the drug (34.6 +/- 5.66; n = 5). The concentrations of CK increased gradually until the end of reperfusion without differences among the different groups. Plasma MDA was the highest in control dogs 7 min after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct renovascular effect of somatostatin in the dog.

Recently, effects of somatostatin on the renal function have been described and the vasoactive properties of the peptide were proposed to contribute to this action. However, the available data on its effect in the renal vascular bed are very controversial. Therefore, we investigated the effect of local intaarterial somatostatin boluses in a wide range of doses (5 x 10(-11) - 5 x 10(-5) g) on the renal blood flow (RBF) in anesthetized dogs. RBF was measured by an electromagnetic flow probe. Somatostatin did not influence blood pressure or heart rate. RBF exhibited a significant, dose-dependent fall (ranging from 11.6 +/- 11.9% to 31.9 +/- 17.3%), with a threshold at a dose of 5 x 10(-10) g. These results offer conclusive evidence for the contribution of somatostatin-induced direct renal vasoconstriction to its renal effects, in addition to the demonstrated modulation of other vasoactive systems and tubular functions.

Characterization and stimuli for production of pericardial fluid atrial natriuretic peptide in dogs.

Recently high immunoreactive atrial natriuretic peptide (ir-ANP) levels have been found in the pericardial fluid of patients undergoing cardiac surgery. The present study was designed to characterize pericardial fluid ANP in anesthetized dogs. Pericardial fluid ir-ANP levels were 3.4-fold higher than plasma levels and the molecular form, revealed by high performance liquid chromatography, was indistinguishable from ANP[99-126]. Elimination of [125I]ANP was 5-fold slower in the pericardial space than in plasma. Activity of the major ANP degrading enzyme, neutral endopeptidase (NEP, EC 3.4.24.11), was 15-times higher in the pericardial fluid than in plasma. Right atrial balloon distension and rapid right ventricular pacing induced maximally 2.3-fold and 1.5-fold increases of pericardial fluid ir-ANP, respectively. Pericardial fluid ir-ANP concentrations and right atrial pressure values showed significant correlation during the stimuli. Our present results show that high concentrations of ir-ANP can be found in the dog pericardial fluid even under unstimulated conditions. Slow elimination of ANP from the pericardial fluid compartment may contribute to the high peptide levels. However this slow elimination cannot be attributed to a lower NEP activity. High basal levels of ANP in the pericardial fluid could be further increased by atrial balloon stretch and rapid ventricular pacing. The increase of pericardial fluid ir-ANP appeared to be a stretch-dependent response. ANP released into the pericardial fluid may be involved in the regulation of cardiac function and coronary vascular tone.

Presence of immunoreactive endothelin-1 and atrial natriuretic peptide in human pericardial fluid.

This study was undertaken to characterize endothelin-1 (ET-1) and atrial natriuretic peptide (ANP) concentrations in human pericardial fluid, blood plasma, right atrial appendage and papillary muscle by use of specific radioimmunoassays. In patients undergoing cardiac surgery (n=16) pericardial fluid mean immunoreactive (ir-) ET-1 and ir-ANP levels were 36-fold and 4-fold higher than corresponding plasma levels, respectively. In high performance liquid chromatography (HPLC) pericardial fluid ir-ET-1 was indistinguishable from human ET-1[1-21] and the majority of pericardial fluid ir-ANP coeluted with human ANP[99-126]. Atrial tissue ir-ET-1 and ir-ANP concentrations were 17-fold and 870-fold higher than in ventricular tissue. Our present study demonstrated for the first time the presence of ir-ET-1 in the pericardial fluid in humans. Human pericardial fluid contained far the highest concentrations of ET-1 among all biological fluids tested thus far. The functions of pericardial fluid ET-1 and ANP on cardiac performance and coronary vascular tone require further investigations.

Enhanced accumulation of pericardial fluid adenosine and inosine in patients with coronary artery disease.

Adenosine and inosine are believed to have cardioprotective effects. However, little is known about their possible role in the metabolic autoregulation of human coronaries and in pathologic conditions with supply/demand imbalance of the heart such as coronary artery disease. Since these low molecular weight nucleosides freely diffuse through the monolayer of the visceral pericardium, adenosine and inosine concentrations in pericardial fluid may well reflect the conditions in cardiac interstitium. The pericardial fluid and systemic venous blood adenosine and inosine concentrations were measured in 98 human subjects undergoing heart surgery for coronary artery disease or valvular heart disease. Adenosine and inosine concentrations were measured by HPLC with UV detection. In subjects with coronary artery disease pericardial fluid nucleoside concentrations were significantly higher than in patients with valvular heart disease (adenosine: 1545 (996-3146) nmol/L [median (25th-75th quartiles)] vs. 738 (390-2527) nmol/L, P<0.01; inosine: 658 (321-1331) nmol/L vs. 347 (159-1037) nmol/L, P<0.05), while in both patient groups pericardial fluid nucleoside concentrations were higher by an order of magnitude than in venous plasma. Our results show the enhanced release of adenosine and inosine by the ischemic myocardium as a marker of supply/demand imbalance and support the hypothesis that these cardiac nucleosides may have an important role in the adaptation of coronary blood flow in human coronary artery disease.

Lymphatic arteriopathy: damage to the wall of the canine femoral artery after lymphatic blockade.

The effect of lymph stasis on the histological, biochemical, and elastic properties of the femoral artery were studied after regional lymphatic blockade in 36 dogs. Dogs were sacrificed 4-21 days after operation. Histologic changes of the femoral arterial wall (interstitial edema, degeneration in the muscle layer or media, thickened adventitia with dilated lymph vessels, and fibrosis) developed after regional lymphatic blockade. Characteristic metabolic alterations of the arterial wall (anaerobic catabolism of carbohydrate, increased lactate and glycosamine content) accompanied the morphological changes. Distensibility of the femoral artery decreased and greater elastic stiffness developed after regional lymphatic blockade. These results in conjunction with other experimental and clinical data support the concept that insufficient lymphatic transport within the blood vessel wall may contribute to the genesis and progression of arteriopathies.

Coronary arteriopathy after lymphatic blockade: an experimental study in dogs.

The effects of lymph stasis on the histological and biochemical properties of the coronary arterial wall and on the coronary circulation were studied in 72 dogs. Cardiac lymph stasis was produced in 52 dogs by cardiac lymphatic blockade whereas in 20 dogs only a sham operation was performed. Blockade of cardiac lymph drainage promoted characteristic injury to the coronary arteries including subendothelial edema with plasma inbibition, interstitial and intracellular edema in the tunica media with degeneration in the smooth muscle layer, swelling of the adventitial space with dilated lymph vessels and, later, fibrosis. The biochemical properties of the coronary arterial wall also were adversely affected by cardiac lymph stasis. Thus, the collagen and hexosamine content of the coronary arteries increased and the metabolism of the coronary wall shifted in an anaerobic direction. Whereas coronary blood flow was slightly decreased with lymph blockade, the coronary circulatory reserve capacity and the adaptability of the coronary vascular system was markedly reduced. The histological changes were most apparent in the smaller coronary arteries. The coronary microvasculature was also pathologically altered with the development of numerous coronary arteriovenous microshunts. These findings in conjunction with other experimental and clinical information suggest that impaired cardiac lymph drainage contributes to the pathogenesis and progression of coronary artery disease.

Reversal of isoproterenol-induced calorigenic action in the heart during myocardial ischemia.

With the aid of infrared thermography, a powerful new tool for studying the biological state of cardiac regulatory mechanisms, the reversal of the isoproterenol-induced calorigenic action in the in situ dog heart was demonstrated after establishing acute myocardial ischemia. The thermographic manifestations indicated a modified activity pattern of the cardiac (coronary) beta-mechanism with a preserved sensitivity to its specific pharmacologic blockade. Results provide new evidence of the transformation (plasticity) of adrenoceptor qualities under pathologic circumstances.

[Effect of regional hypothermia on cerebrospinal fluid parameters during thoracoabdominal aorta clamping in dogs]. / Regionális gerincveló hypothermia hatása a liquor összetételére thoracoabdominalis aortakirekesztés során állatkísérletben.

The most feared complication of thoracoabdominal clamping is the paraplegia or paraparesis following ischemic injury of the spinal cord. Early intraoperative recognition of this complication has not been solved yet. In our earlier experiment we found significant alterations of CSF glucose, lactate, pCO2 and Neuron Specific Enolase (NSE) levels during 60 minutes thoracoabdominal aortic clamping in dogs. The analysis of these parameters proved to be proper to follow metabolism of the spinal cord during this type of surgery. In our present paper we studied protective effect of regional hypothermia using peridural cooling by registration of above parameters. Statistical analysis of our data showed prevention of production of anaerobe metabolites in animals with icy peridural irrigation. The biochemical approach is appropriate for monitoring effectiveness of regional hypothermia of the spinal cord during aortic surgery.

Factors influencing the vascular action of dopamine in the canine mesenteric bed.

The effect of dopamine on the mesenteric arterial bed was investigated in dogs anaesthetized with pentobarbital sodium. The vascular responses to dopamine in a branch of the superior mesenteric artery supplying a segment of the small intestine were measured with a flowmeter probe and visualized by infrared telethermography or, in a separate series of dogs, were obtained by the direct determination of arterial resistance--changes during perfusion with constant flow. It was found that the mesenteric action of dopamine (given i.v. in the submaximal dose of 16 micrograms.kg-1.min-1 or intraarterially up to a dose of 40 micrograms.min-1) is primarily mediated via dopaminergic vasodilator and a alpha-adrenergic vasoconstrictor receptors, the net result of this competition usually being moderate vasodilation under natural conditions. The contribution of beta-adrenergic vasodilation to the mesenteric dopamine action is minimal as evidenced by beta-blockade with oxprenolol. By blocking the alpha-component with phentolamine (1.0 mg.kg-1) an almost threefold increase of the vasodilation was obtained in resistance. Because of the concomitant reversal of the systemic hypertensive dopamine action to hypotension, the net flow increase remained essentially unchanged. It was concluded that unless the degree of alpha-stimulation is restrained and proper control of blood pressure is ensured, it is not possible to recommend that dopamine be used in the therapy of mesenteric vascular disorders.

Effect of atrial dilatation on the tendency of atrial arrhythmias.

The arrhythmogenic effect of atrial dilatation was studied by electrophysiological investigations carried out on 24 dogs. Atrial distension was evoked by increasing the pressure in the right atrium (12 to 14 mm Hg) or by the balloon dilatation of the left atrium. Programmed electrical stimulation of the heart was used for the electrophysiological investigations. In addition to the superficial ECG leads also atrial and ventricular epicardial electrograms were obtained for the ECG recording. Acute atrial dilatation led to shortening of the atrial refractory period, whereas neither impulse conduction of the heart, nor pacemaker activity of the sinus node exhibited any alteration. Atrial dilatation resulted in pathological atrial irritability, and early or frequent atrial stimulation caused atrial tachycardia of shorter (non sustained) or longer (sustained) duration. Repetitive atrial extrasystoles in response to early stimuli could also frequently be observed during atrial dilatation. The obtained results indicate that atrial dilatation is arrhythmogenic and may lead to the development of atrial tachycardia.

Pharmacologic assessment of the functional state in stenosed coronary circulation of the dog.

In open chest dogs under sodium pentobarbital anaesthesia the interaction of mechanical constriction on a large coronary branch and autoregulatory capacity of the relevant small resistance vessels was analyzed. Coronary blood flow (CBF) was measured with an electromagnetic flowmeter. Step-by-step mechanical constriction gradually abolished adenosine-induced coronary vasodilation, whereas the resting level of mean CBF remained unaltered. At this point verapamil (0.2 mg/kg i.v.), a vasodilator with a strong potency of blocking adenosine action, eventually decreased CBF and increased coronary resistance. Similar results were obtained with these drugs injected directly into a bypass established between the carotid and left common coronary arteries. The results suggest that (i) adenosine affects the same coronary segments which accomplish compensatory autoregulation (ii); with critical stenosis verapamil augments indirectly coronary resistance by inhibiting an "intrinsic" adenosine effect (iii); the functional state of stenosed coronaries can be assessed with the aid of these pharmacologic tests.

Experimental investigation of the effect of cardiac glycosides on the ischemic coronary circulation.

The paper presents new evidence of the vasoactivity of cardiac glycosides in the myocardium. Experiments were performed on the in situ dog heart. The present study primarily focuses on the analysis of K-strophantoside induced topo-optical and thermographic alterations in acute myocardial ischemia. The strong binding of K-strophantoside to the coronary vessel wall and the endothelial cells was found to be accompanied by vasoconstriction in the regionally ischemic heart muscle. The potential clinical impact of these findings on therapy is briefly evaluated.

The dopamine-induced coronary vasoconstrictor response is potentiated by adenosine administration in the dog heart.

The ineffectiveness of beta-adrenergic blockade in abolishing adenosine-induced coronary vasodilation was utilized to demonstrate that dopamine (DA) is capable of eliciting very strong coronary vasoconstrictor actions in vivo. In 2 separate groups of dogs anesthetized with pentobarbital, responses to DA were assessed either by flowmeter recordings or by computer-aided infrared thermography, which senses coronary blood flow-dependent heat emission from the epicardium. In untreated controls, submaximal DA infusions (16 micrograms.kg-1.min-1 iv) elicited a coronary vasodilator response. The thermographic equivalent of this hemodynamic action was an increased epicardial temperature. Pretreatment with oxprenolol (0.5 mg.kg-1 iv) preserved both basic heart activity and cardiac heat emission at levels which were comparable to the control state, but prevented DA mediated excitation of cardiac and coronary beta-adrenoceptors. In this state, DA infusion constricted the coronary arteries and tended to decrease heart emission. However, both types of effects were moderate, and only the hemodynamic effect was statistically significant. If DA was given after the coronary bed had been dilated submaximally by adenosine (30 micrograms.kg-1.min-1 infused into the left heart), the flow-reducing effect of DA became a dramatic phenomenon, and the DA-induced epicardial cooling was significantly potentiated. The results show that after eliminating conventional beta-effects, DA affects the coronary arteries through vasoconstrictor mechanisms. This finding suggests that the DA-induced constriction is limited in undilated coronary arteries by the metabolic autoregulatory capacity of the vessels.