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T Ehring

Publications and source records attributed to T Ehring.

15 recordsLinked to original sources
PubMed1995

Stunned myocardium and the attenuation of stunning by calcium antagonists.

Myocardial "stunning" is characterized by a reversible postischemic contractile dysfunction despite full restoration of blood flow. The underlying mechanisms are not clearly understood. Inadequate energy supply and impaired sympathetic neurotransmission may have been excluded. Potential mechanisms, which are not mutually exclusive, may include damage to membranes and enzymes by free radicals, an increase in free cytosolic calcium during ischemia and reperfusion, and a lower calcium sensitivity of myofibrils. The equally pronounced increases in regional contractility in normal and stunned myocardium during postextrasystolic potentiation and the infusion of calcium or the calcium-sensitizing agent AR-L-57, however, suggest an unchanged calcium sensitivity in reperfused myocardium. Pretreatment with calcium antagonists before ischemia attenuates myocardial stunning. This effect is probably related to a lessened myocardial calcium overload during early ischemia. The potential benefit of treatment with calcium antagonists after reperfusion is established remains controversial.

Animals↗
PubMed1995

Cholinergic and alpha-adrenergic coronary vasomotion [corrected] with increasing ischemia-reperfusion injury.

Ischemia-reperfusion-induced injury of the coronary vasculature could result in an attenuated vasodilator or increased vasoconstrictor tone that might impact on myocardial recovery and viability. In 30 open-chest dogs the left circumflex coronary artery was occluded for 15 or 60 min and then reperfused, and responses to intracoronary acetylcholine, the alpha 1-adrenergic agonist methoxamine, and the alpha 2-adrenergic agonist BHT-933 (n = 10 each) were measured. In the experiments with 60 min of occlusion, triphenyltetrazolium chloride (TTC) staining was used to distinguish reversibly (TTC+) and irreversibly (TTC-) injured myocardium. After 15 min of occlusion, the vasodilator response to acetylcholine was not altered but was significantly reduced in TTC+ subendocardium and midmyocardium after 60 min of occlusion and was further reduced in TTC- subendocardium, midmyocardium, and also in subepicardium. The vasoconstrictor responses to methoxamine and BHT-933 were not altered after 15 or 60 min of occlusion in both TTC+ and TTC- myocardium. Posterior wall thickening was not affected by acetylcholine, methoxamine, or BHT-933. Thus, in reversibly injured myocardium after 15 min of occlusion, cholinergic and alpha-adrenergic coronary vasomotor responses are unchanged. With increasing duration of ischemia, reversibly and even more so irreversibly injured reperfused myocardium are characterized by an impaired cholinergic coronary vasodilation but not an enhanced alpha-adrenergic coronary vaso-constriction.

Acetylcholine↗
PubMed1994

Attenuation of myocardial stunning by the ACE inhibitor ramiprilat through a signal cascade of bradykinin and prostaglandins but not nitric oxide.

BACKGROUND: Attenuation of myocardial stunning by several angiotensin-converting enzyme (ACE) inhibitors has been demonstrated. However, the signal cascade mediating such protective effect has not been analyzed in detail so far. METHODS AND RESULTS: In a first protocol, we addressed the role of bradykinin and analyzed the effect of the ACE inhibitor ramiprilat without and with added bradykinin B2 receptor antagonist HOE 140 on regional myocardial blood flow (colored microspheres) and function (sonomicrometry). Thirty-two enflurane/N2O-anesthetized open-chest dogs were subjected to 15 minutes of occlusion of the left circumflex coronary artery (LCx) and 4 hours of subsequent reperfusion. Eight dogs served as placebo controls (group 1), and 8 dogs received ramiprilat (20 micrograms/kg IV) before LCx occlusion (group 2). Eight dogs received a continuous intracoronary infusion of HOE 140 [0.5 ng/(mL.min) IC] during ischemia and reperfusion (group 3), and in 8 dogs HOE 140 was infused continuously during ischemia and reperfusion, starting 45 minutes before the administration of ramiprilat (group 4). Mean aortic pressure was kept constant with an intra-aortic balloon, and heart rate did not change throughout the experimental protocols. Under control conditions and during myocardial ischemia, posterior transmural blood flow (BF) and systolic wall thickening (WT) were not different in the four groups of dogs. However, at 4 hours of reperfusion, WT was still depressed in groups 1 (-10 +/- 20% of control [mean +/- SD]), 3 (-18 +/- 12% of control), and 4 (-12 +/- 21% of control), whereas WT in group 2 had recovered to 55 +/- 20% of control (P < .05 versus group 1). BF at 4 hours of reperfusion was not different in the four groups of dogs. Thus, the beneficial effect of ramiprilat on the functional recovery of stunned myocardium was obviously mediated by bradykinin. Since bradykinin stimulates the formation of both prostaglandins and nitric oxide, we tested in a second protocol which of these mediators was further involved in the beneficial effects of ramiprilat. Twenty-four additional dogs were subjected to 15 minutes of LCx occlusion and 4 hours of reperfusion. Six dogs received the cyclooxygenase inhibitor indomethacin (10 mg/kg IV) (group 5) and 6 dogs a combination of indomethacin with ramiprilat (group 6) before LCx occlusion. Six dogs received the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg IV) (group 7) and 6 dogs a combination of L-NAME with ramiprilat (group 8) before LCx occlusion. BF and WT before and during myocardial ischemia were not different in groups 5 and 6 and groups 7 and 8. However, at 4 hours of reperfusion, WT was still depressed in groups 5 (-10 +/- 38% of control), 6 (-7 +/- 18% of control), and 7 (-12 +/- 14% of control), whereas WT in group 8 had recovered to 47 +/- 28% of control (P < .05 versus group 7). BF at 4 hours of reperfusion was not different in the four groups of dogs. CONCLUSIONS: In summary, the attenuation of stunning by the ACE inhibitor ramiprilat involves a signal cascade of bradykinin and prostaglandins but not nitric oxide.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1993

A proischaemic action of nisoldipine: relationship to a decrease in perfusion pressure and comparison to dipyridamole.

OBJECTIVE: The calcium antagonist nisoldipine has recently been reported to induce rather than to attenuate ischaemia in some patients with stable angina. The aim of the study was to investigate the mechanisms underlying this proischaemic effect. METHODS: In 20 anaesthetised dogs systemic haemodynamic variables, regional myocardial blood flow (coloured microspheres), and systolic wall thickening (sonomicrometry) were measured during control conditions and following severe stenosis on the left circumflex coronary artery, before and after intravenous administration of equihypotensive doses of either nisoldipine (group I, n = 10) or dipyridamole (group II, n = 10). Finally, measurements were performed while the drug induced decreases in mean aortic pressure--18 (SD 6) mmHg in group I and 14(6) mm Hg in group II--were reversed by inflation of an intra-aortic balloon. RESULTS: The stenosis decreased posterior wall thickening to 50% of control, and posterior subendocardial blood flow from 1.48(0.27) to 0.61(0.19) ml.min-1.g-1 in group I and from 1.49(0.23) to 0.62(0.18) ml.min-1.g-1 in group II. Subendocardial blood flow was further decreased after administration of either nisoldipine [0.37(0.20) ml.min-1.g-1, p < 0.05 v stenosis] or dipyridamole [0.22(0.11) ml.min-1.g-1, p < 0.05 v stenosis]. Regional myocardial blood flow in the anterior region was increased. The drug induced reduction of subendocardial blood flow decreased posterior wall thickening further from 9.3(2.1) to 6.2(3.9)% (p < 0.05 v stenosis, group I) and from 9.1(1.7) to 4.3(2.4)% (p < 0.05 v stenosis, group II). When the drug induced decrease in aortic pressure was reversed, subendocardial blood flow again increased in group I [0.63(0.19) ml.min-1.g-1, p < 0.05 v stenosis and nisoldipine] whereas in group II it remained decreased [0.40(0.29) ml.min-1.g-1, NS v stenosis and dipyridamole]. There was restoration of posterior wall thickening in group I [10.4(3.8)%, p < 0.05 v stenosis and nisoldipine], but not in group II [5.2(3.5)%, NS v stenosis and dipyridamole]. CONCLUSIONS: Nisoldipine and dipyridamole decrease subendocardial blood flow and contractile function distal to a severe stenosis when aortic pressure is decreased. No aggravation of ischaemia by nisoldipine is seen when hypotension is prevented. In contrast, dipyridamole in the absence of hypotension still induces a redistribution of flow at the expense of the ischaemic region.

Animals↗
PubMed1993

Impact of alpha-adrenergic coronary vasoconstriction on the transmural myocardial blood flow distribution during humoral and neuronal adrenergic activation.

Increased heart rate and left ventricular pressure during humoral and neuronal adrenergic activation act to restrict blood flow preferentially in the subendocardium. The hypothesis was advanced that alpha-adrenergic coronary vasoconstriction preferentially in the subepicardium may counterbalance the enhanced extravascular compression in the subendocardium and serve to maintain blood flow transmurally uniform. In 40 anesthetized dogs, regional myocardial blood flow was determined with colored microspheres; wall function, with sonomicrometry. Humoral adrenergic activation (HAA) was induced by a combination of intravenous atropine, intravenous norepinephrine, and atrial pacing during baseline coronary vasomotor tone (group 1, n = 6) and in the presence of maximal coronary vasodilation with intravenous dipyridamole (group 2, n = 6). In an additional group, HAA was induced by intravenous norepinephrine in the presence of dipyridamole but without atropine and atrial pacing in order to increase end-diastolic left ventricular pressure (group 3, n = 6). Measurements were performed at rest, during HAA, and during ongoing HAA with the intracoronary infusion of the alpha-antagonist phentolamine (Phen). At unchanged mean aortic pressure, Phen improved blood flow particularly to the inner layers as follows: from 1.42 +/- 0.40 (mean +/- SD) to 1.90 +/- 0.40 mL/(min.g) (group 1, P < .05), from 4.99 +/- 2.31 to 5.53 +/- 2.56 mL/(min.g) (group 2, P < .05), and from 6.01 +/- 1.41 to 6.29 +/- 1.27 mL/(min.g) (group 3, P < .05), associated with a decrease in outer layer blood flow in groups 2 and 3. In 16 additional dogs, beta-adrenoceptors were blocked by propranolol and muscarinic receptors by atropine. Neuronal adrenergic activation (NAA) was induced by cardiac sympathetic nerve stimulation (CSNS) during baseline coronary vasomotor tone (group 4, n = 8) and in the presence of maximal vasodilation (group 5, n = 8). Measurements were performed at rest, during a first CSNS, and 20 minutes later during a second CSNS+Phen. The reproducibility of two consecutive episodes of CSNS 20 minutes apart was demonstrated in a separate set of experiments (n = 6). At matched mean aortic pressures, Phen improved blood flow to all myocardial layers in group 4, whereas in group 5, Phen induced a redistribution of myocardial blood flow toward subepicardial layers [from 4.44 +/- 0.96 to 4.81 +/- 0.83 mL/(min.g), P < .05] at the expense of inner layers. With the addition of Phen, there was no change in regional wall function in any group of dogs studied. Thus, during HAA, alpha-adrenergic coronary vasoconstriction does not exert a beneficial effect on transmural blood flow distribution. During NAA, a beneficial effect of alpha-adrenergic coronary vasoconstriction becomes apparent only under conditions of maximal coronary vasodilation.

Animals↗
PubMed1993

Diastolic dysfunction of stunned myocardium.

The prolonged regional contractile failure of reperfused myocardium has usually been characterized in terms of systolic function, while only few reports on its diastolic function are available. None of these studies considered changes in the isovolumic diastole and the subsequent filling phase separately. Therefore, in the present study, the velocities of wall excursion during systole (Vsys), isovolumic diastole (Viso) and filling phase (Vfill) were determined in 12 anesthetized dogs. Additionally, post-ejection thickening (Pejt), a marker of left ventricular asynchrony, was determined. Measurements were performed under control conditions, during a 15 minute left circumflex (LCX) coronary artery occlusion (CAO) and at 10 minutes, 4 and 8 hours reperfusion. Heart rate, left ventricular pressure, and Vsys, Viso, Vfill, and Pejt of the anterior myocardium remained unchanged throughout the experiments. During CAO, systolic wall-thickening of the posterior wall was reversed to systolic wall-thinning. Upon reperfusion, Vsys started to recover (2.5 +/- 3.2 mm/s at 10 minutes) and gradually improved over 8 hours of reperfusion (4.6 +/- 3.2 mm/s at 4 hours, 6.4 +/- 1.5 mm/s at 8 hours). Viso became positive during CAO (9.4 +/- 7.1 mm/s vs. -5.6 +/- 3.9 mm/s under control conditions) and was unchanged at 10 minutes reperfusion (7.9 +/- 5.2 mm/s). After 4 hours and 8 hours of reperfusion, Viso recovered to 1.2 +/- 9.2 mm/s and -0.3 +/- 10.7 mm/s, respectively. Vfill also became positive during CAO (1.5 +/- 6.2 mm/s vs. -18 +/- 8.7 mm/s under control conditions). There was a quick recovery of Vfill (-9.4 +/- 7.5 mm/s) with the onset of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Characterization of "hibernating" and "stunned" myocardium with focus on the use of calcium antagonists in "stunned" myocardium.

In the initial seconds after a sudden reduction in coronary blood flow, a temporary mismatch between myocardial energy demand and supply exists. The mechanisms underlying the rapidly ensuing reduction in contractile function in the ischemic myocardium are still unknown. In the presence of some residual blood flow, a state of "perfusion-contraction matching" develops. The metabolic status of such hypoperfused myocardium improves, since myocardial lactate production is attenuated and creatine phosphate (CP), after an initial reduction, returns toward control values. The hypoperfused myocardium responds to inotropic stimulation by dobutamine. The recruitment of an inotropic reserve implies increased energy utilization. During inotropic stimulation, after partial normalization, lactate production is again increased, and CP is decreased again. Thus, a supply-demand imbalance that had been at least partially corrected by the ischemia-induced decrease in regional contractile function is precipitated again. A situation of chronic contractile failure in viable myocardium that normalizes upon reperfusion has been termed myocardial "hibernation." Myocardial "stunning" is characterized by a reversible postischemic contractile dysfunction despite full restoration of blood flow. The details of the underlying mechanisms are not clear. An inadequate energy supply and impaired sympathetic neurotransmission have been excluded. Potential mechanisms, which are not mutually exclusive, may include (a) damage of membranes by free radicals, (b) an increase in free cytosolic calcium during ischemia and reperfusion, and (c) a decrease in the calcium sensitivity of the myofibrils. The equally pronounced increases in regional contractility in normal and "stunned" myocardium during postextrasystolic potentiation and the infusion of calcium or the calcium-sensitizing agent AR-L-57, however, suggest an unchanged calcium sensitivity of reperfused myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1992

The calcium antagonist nisoldipine improves the functional recovery of reperfused myocardium only when given before ischemia.

It is unclear whether the protective effects of calcium antagonists on reperfused myocardium are secondary to increased blood flow during ischemia (anti-ischemic action) or reperfusion (Gregg phenomenon), or are mediated through altered calcium kinetics in ischemic or reperfused myocardium. To study the effect of the calcium antagonist nisoldipine on the functional recovery of stunned myocardium, 32 enflurane-anesthetized dogs were subjected to 15 min of occlusion of the left circumflex coronary artery and subsequent 4 h of reperfusion. Eight dogs served as placebo controls (group I), and eight dogs received nisoldipine (5 micrograms/kg i.v.) before occlusion (group II), eight dogs at 10 min of occlusion (group III), and eight dogs at 4 min of reperfusion (group IV). The mean aortic pressure was kept constant with an intra-aortic balloon, and the heart rate did not change. In group I, posterior systolic wall thickening (WT, sonomicrometry) decreased from 18.3 +/- 2.4% (mean +/- SD) during control conditions to -3.0 +/- 2.0% at 13 min of occlusion. At 10 min of reperfusion, WT was 1.7 +/- 3.9% and did not recover further (-1.2 +/- 3.7% at 4 h of reperfusion). Posterior transmural blood flow (BF, colored microspheres) decreased from 1.42 +/- 0.43 ml/min/g during control conditions to 0.26 +/- 0.08 ml/min/g at 13 min of occlusion. BF was 2.07 +/- 0.93 ml/min/g at 10 min and 0.95 +/- 0.31 ml/min/g at 4 h of reperfusion. In groups III and IV, the WT and BF were not different from those in group I throughout the experimental protocol. In group II, however, the WT, although similar to the WT of group I before and during ischemia, recovered from 2.7 +/- 4.3% at 10 min to 11.8 +/- 6.0% at 4 h of reperfusion (p less than 0.05 vs. groups I, III, and IV). The BF in group II decreased from 2.52 +/- 0.66 ml/min/g after administration of nisoldipine to 0.22 +/- 0.14 ml/min g at 13 min of occlusion. The BF was 1.31 +/- 0.51 ml/min/g at 10 min and 1.33 +/- 0.43 ml/min/g at 4 h of reperfusion. Nisoldipine exerts no beneficial effect when given immediately before or after the onset of reperfusion. The improved functional recovery of reperfused myocardium in dogs pretreated with nisoldipine cannot be attributed to an increased regional myocardial blood flow during ischemia or reperfusion. The better myocardial recovery, therefore, appears to be related to an attenuated myocardial calcium overload during the first few minutes of ischemia.

Analysis of Variance↗
PubMed1991

Postextrasystolic potentiation does not distinguish ischaemic from stunned myocardium.

Myocardial function is impaired by ischaemia, and it remains depressed during reperfusion following short periods of ischaemia (stunned myocardium). We tested whether ischaemic and reperfusion dysfunction, in particular the time course of its recovery, can be distinguished by postextrasystolic potentiation (PESP). In eight open-chest dogs, posterior systolic wall thickening (sonomicrometry) was reduced by graded occlusion of the left circumflex coronary artery (LCX) from 17.4 +/- 6.8% (SD) during control conditions to 10.7 +/- 1.3% (mild ischaemic dysfunction), 7.2 +/- 2.3% (moderate ischaemic dysfunction), 3.6 +/- 1.4% (severe ischaemic dysfunction), and -4.4 +/- 3.6% (complete coronary occlusion). Extrasystoles with constant prematurity and a fully compensated postextrasystolic interval were induced after at least 4 min steady-state ischaemia. After each ischaemic period full recovery of posterior systolic wall thickening was assured. During 8 h of reperfusion following a 15-min LCX occlusion, extrasystoles were induced when posterior systolic wall thickening was comparable to one degree of the preceding ischaemic dysfunction. The increases in posterior systolic wall thickening induced by PESP were 10.5 +/- 5.8% during control conditions, during ischaemia they were 11.5 +/- 3.5% (mild dysfunction), 12.3 +/- 4.6% (moderate dysfunction), 12.6 +/- 4.1% (severe dysfunction) and 10.4 +/- 4.4% (complete coronary occlusion), and during reperfusion they were 12.8 +/- 8.2% (severe dysfunction), 13.0 +/- 9.7% (moderate dysfunction) and 10.7 +/- 2.2% (mild dysfunction).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Felodipine prevents the poststenotic myocardial ischemia induced by alpha 2-adrenergic coronary constriction.

Alpha 2-adrenoceptor-mediated coronary constriction contributes to the precipitation of myocardial ischemia during sympathetic activation. Felodipine is a novel dihydropyridine calcium-channel antagonist with vascular selectivity. In this study, the effect of felodipine on alpha 2-adrenoceptor-mediated poststenotic coronary constriction was investigated. In ten open-chest dogs, the selective alpha 2-adrenoceptor agonist BHT 933 (200 micrograms IC) was infused before and after production of a severe stenosis on the left circumflex coronary artery. BHT 933 increased calculated resistance of the intact left circumflex coronary artery from 1.16 +/- 0.30 (SD) to 2.00 +/- 0.70 mmHg*min*100 g/ml (p less than 0.05) without changing posterior systolic wall thickening (sonomicrometry) (14.2 +/- 2.8% vs. 14.1 +/- 2.7%). In the presence of a severe stenosis, BHT 933 increased poststenotic coronary resistance from 1.59 +/- 0.54 to 2.88 +/- 1.16 mmHg*min*100 g/ml (p less than 0.05) and decreased posterior systolic wall thickening from 11.9 +/- 2.7% to 8.2 +/- 3.1% (p less than 0.05). In contrast, after intravenous pretreatment with felodipine (4 micrograms/kg), intracoronary infusion of BHT 933 did not change coronary resistance (1.69 +/- 0.61 vs. 1.61 +/- 0.64 mmHg*min*100 g/ml) and posterior systolic wall thickening (12.1 +/- 3.0% vs. 12.6 +/- 2.9%). In conclusion, felodipine prevents alpha 2-adrenoceptor-mediated coronary constriction and ischemic regional myocardial dysfunction distal to a severe coronary stenosis.

Adrenergic alpha-Agonists↗
PubMed1990

Left ventricular asynchrony: an indicator of regional myocardial dysfunction.

There is a marked heterogeneity of myocardial wall thickening within the left ventricle and among different individuals. It is therefore difficult to detect regional myocardial dysfunction from absolute values of systolic wall thickening. We tested whether the extent of left ventricular asynchrony during ischemia and reperfusion can be used to quantify the severity of regional myocardial dysfunction when nonischemic baseline function is not known. In six anesthetized, open-chest dogs regional myocardial wall thickness was measured by means of sonomicrometry under control conditions, at three degrees of ischemic dysfunction (mild, moderate, and severe), and after release of a 15-minute occlusion of the left circumflex coronary artery, when degrees of moderate and mild reperfusion dysfunction similar to the preceding ischemic dysfunction were present. Two indexes of left ventricular asynchrony were calculated: (1) postejection thickening (PET) and (2) the phase difference of the first Fourier harmonic of posterior versus anterior myocardial wall motion (PD). Systolic myocardial wall thickening was decreased from 15.3 +/- 3.1 (standard deviation) % (control value) to 9.7 +/- 1.4% (mild ischemia), 4.2 +/- 1.6% (moderate ischemia), and -3.7 +/- 3.1% (severe ischemia). Conversely PET increased from 0.02 +/- 0.04 mm (control value) to 0.15 +/- 0.22 mm (mild ischemia), 0.19 +/- 0.15 mm (moderate ischemia), and 0.50 +/- 0.26 mm (severe ischemia). PD increased from 9 +/- 28 degrees (control value) to 22 +/- 19 degrees (mild ischemia), 54 +/- 18 degrees (moderate ischemia), and 107 +/- 21 degrees (severe ischemia). After release of the 15-minute left circumflex coronary artery occlusion, PET and PD recovered to 0.34 +/- 0.19 mm and 36 +/- 24 degrees (moderate dysfunction) and 0.25 +/- 0.31 mm and 29 +/- 8 degrees (mild dysfunction), respectively. There were inverse linear relationships between systolic wall thickening and PET (r = -0.86, p less than 0.001) and between systolic wall thickening and PD (r = -0.87, p less than 0.001). Inotropic stimulation by postextrasystolic potentiation increased regional systolic myocardial posterior and anterior wall thickening but did not alter the extent of left ventricular asynchrony. Thus, when normal baseline function is not known, the severity of regional myocardial dysfunction at a given inotropic state can be determined by analysis of left ventricular asynchrony. There was no significant correlation between the extent of PET and PD during ischemia and at early reperfusion and the recovery of contractile function at late reperfusion. Thus PET does not provide a prospective marker for the functional outcome of reperfusion.

Animals↗
PubMed1990

BRL 34915 ameliorates oxygen supply in ischemic myocardium by a simultaneous enhancement of coronary blood flow and a reduction of myocardial function.

In the presence of stenotic coronary arteries, oxygen supply in the poststenotic myocardium is reduced. A counterbalancing poststenotic metabolic vasodilatation is attenuated up to 30% by an alpha 2-adrenoceptor-mediated vasoconstrictor tone. In six open-chest dogs, we determined whether cumulative intracoronary doses (1, 4, and 14 micrograms) BRL 34915, a vasodilator with additional dose-dependent cardiodepressant properties, could enhance coronary blood flow and simultaneously reduce myocardial function in poststenotic myocardium, thereby increasing oxygen supply and decreasing oxygen demand. BRL 34915 increased mean left circumflex coronary blood flow [ml/(min.100 g)] dose-dependently from 59 +/- 12.4 (mean +/- SEM) (no BRL) to 227 +/- 43.9 (14 micrograms BRL) (p less than 0.05) in intact coronary arteries and from 36 +/- 7.2 (no BRL) to 74 +/- 13.2 (14 micrograms BRL) (p less than 0.05) distal to a severe stenosis, respectively. In contrast, posterior systolic wall thickening (%), was significantly decreased only by 14 micrograms BRL from 9.7 +/- 1.82 (no BRL) to 7.8 +/- 2.07 (14 micrograms BRL) (p less than 0.05) when coronary arteries were intact and from 8.7 +/- 2.02 (no BRL) to 4.1 +/- 1.39 (14 micrograms BRL) (p less than 0.05) in poststenotic myocardium. We conclude that BRL 34915 can both enhance coronary blood flow in the poststenotic myocardium and decrease myocardial function simultaneously, potentially narrowing the gap between oxygen supply and demand.

Animals↗
PubMedDate not supplied

Characterization of the inotropic and arrhythmogenic action of the sodium channel activator BDF 9148: a comparison to its S-enantiomer BDF 9196, to its congener DPI 201-106, to norepinephrine, and to ouabain.

Positive inotropic substances which enhance the myocardial cAMP level or inhibit the Na+/K(+)-ATPase are known for their proarrhythmic side-effects. This study was performed to investigate the inotropic and arrhythmogenic action of the Na(+)-channel activator BDF 9148 (racemate) in comparison to its S-enantiomer BDF 9196, its congener DPI 201-106 (racemate), to norepinephrine, and to ouabain. In 30 open-chest dogs, the effects of these substances on the first derivative of left ventricular pressure (dP/dt, Millar-tip catheter) and anterior systolic wall thickening (AWT, sonomicrometry) were studied. Concomitantly, myocardial excitability, conduction times, and refractory period were assessed with a transmural, three-dimensional, 16-electrode array in the anterior wall. For the study of the Na(+)-channel activators, alpha- and beta-adrenergic and muscarinic receptors were blocked. A first set of measurements was performed during normoperfusion with administration of BDF 9148 (1 mg/kg, n = 8), BDF 9196 (0.5 mg/kg, n = 8), and DPI 201-106 (1 mg/kg, n = 8), respectively. A second set of measurements was performed with administration of the threefold dosage of either substance. With a severe stenosis on the left anterior descending coronary artery, a final set of measurements was performed, again using the higher dosage of either substance. For the study of norepinephrine (0.5 micrograms/kg/min i.v., n = 6) and ouabain (40 micrograms/kg i.v., n = 4), measurements were performed during normoperfusion in additional animals. Under normal conditions, either Na(+)-channel activator induced increases in dP/dtmax (lower dosage: 45-84%, higher dosage: by 93-117%) and AWT (lower dosage: by 24-37%, higher dosage: by 19-56%). Under ischemic conditions, either drug increased dP/dtmax by 60-98% and AWT by 45-102%. Excitability, conduction times, and refractory period did not change significantly in response to the Na(+)-channel activators, neither under normal nor under ischemic conditions. There was no significant difference in the incidence of spontaneous ventricular extrasystoles before and after administration of either Na(+)-channel activator. In contrast, an equi-inotropic dosage of norepinephrine (increases in dP/dtmax by 148% and AWT by 42%) increased excitability, decreased conduction times and refractory period, and increased the incidence of spontaneous ventricular extrasystoles. Ouabain induced only a moderate increase in dP/dtmax by 56% and AWT by 24%, but elicited sustained and complex ventricular arrhythmias. Excitability was markedly increased, whereas conduction times and refractory period changed only little.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗
PubMedDate not supplied

Three-dimensional analysis of regional mechanical function, blood flow and electrophysiological parameters during early myocardial ischemia in dogs.

Ventricular arrhythmias are primarily responsible for sudden cardiac death early after the onset of acute myocardial ischemia. We designed an experimental model to simultaneously characterize regional myocardial function, myocardial blood flow, and electrophysiological parameters, and to determine predisposing factors for the development of early ventricular arrhythmias (EVA). The left circumflex coronary artery was occluded in six anesthetized (n = 2 piritramide/N2O, n = 4 chloralose/urethane) mongrel dogs. Systolic wall thickening (%WT) in a control zone and in the central ischemic zone was measured with sonomicrometry and regional myocardial blood flow (RMBF) with colored microspheres. Excitability and relative refractory period at the stimulus electrode and conduction times to all other electrodes were determined with a three-dimensional transmural multi(16)-electrode assay using a computer algorithm. In three of six dogs spontaneous EVA occurred 4 to 6 min after coronary occlusion, degenerating to ventricular fibrillation in two of these dogs. The three dogs developing EVA were not distinguished from those not developing EVA, neither by the kind of anesthesia nor by ischemic % WT (-6.6 +/- 3.8 [SD] vs -7.8 +/- 1.6, ns). Also, dogs with and without EVA did not differ significantly in excitability and relative refractory period. In contrast, dogs with EVA were characterized by a greater mass of severely ischemic myocardium, i.e., exhibiting a RMBF reduction to less than 0.1 ml/(min.g) (18 +/- 3 g vs 7 +/- 4 g, p less than 0.05), and by an increase in subendocardial conduction times of greater than 100% above the respective pre-ischemic values (120 +/- 18% vs 66 +/- 9%, p less than 0.05). Dogs with and without EVA were not as clearly distinguished by the increases in subepicardial (81 +/- 22% vs 46 +/- 15%, ns) and transmural (98 +/- 31% vs 67 +/- 14%, ns) conduction times. The development of EVA is associated with a greater mass of severely ischemic myocardium and a greater increase in subendocardial conduction times.

Animals↗