Jost Müllenheim

Isoflurane Preconditions Myocardium against Infarction via Release of Free Radicals

Background Isoflurane exerts cardioprotective effects that mimic the ischemic preconditioning phenomenon. Generation of free radicals is implicated in ischemic preconditioning. The authors investigated whether isoflurane-induced preconditioning may involve release of free radicals. Methods Sixty-one &agr;-chloralose–anesthetized rabbits were instrumented for measurement of left ventricular (LV) pressure (tip-manometer), cardiac output (ultrasonic flowprobe), and myocardial infarct size (triphenyltetrazolium staining). All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. Rabbits of all six groups underwent a treatment period consisting of either no intervention for 35 min (control group, n = 11) or 15 min of isoflurane inhalation (1 minimum alveolar concentration end-tidal concentration) followed by a 10-min washout period (isoflurane group, n = 12). Four additional groups received the radical scavenger N-(2-mercaptoproprionyl)glycine (MPG; 1 mg · kg−1 · min−1) or Mn(III)tetrakis(4-benzoic acid)porphyrine chloride (MnTBAP; 100 &mgr;g · kg−1 · min−1) during the treatment period with (isoflurane + MPG; n = 11; isoflurane + MnTBAP, n = 9) or without isoflurane inhalation (MPG, n = 11; MnTBAP, n = 7). Results Hemodynamic baseline values were not significantly different between groups (LV pressure, 97 ± 17 mmHg [mean ± SD]; cardiac output, 228 ± 61 ml/min). During coronary artery occlusion, LV pressure was reduced to 91 ± 17% of baseline and cardiac output to 94 ± 21%. After 2 h of reperfusion, recovery of LV pressure and cardiac output was not significantly different between groups (LV pressure, 83 ± 20%; cardiac output, 86 ± 23% of baseline). Infarct size was reduced from 49 ± 17% of the area at risk in controls to 29 ± 19% in the isoflurane group (P = 0.04). MPG and MnTBAP themselves had no effect on infarct size (MPG, 50 ± 14%; MnTBAP, 56 ± 15%), but both abolished the preconditioning effect of isoflurane (isoflurane + MPG, 50 ± 24%, P = 0.02; isoflurane + MnTBAP, 55 ± 10%, P = 0.001). Conclusion Isoflurane-induced preconditioning depends on the release of free radicals.

The noble gas xenon induces pharmacological preconditioning in the rat heart in vivo via induction of PKC-ɛ and p38 MAPK

1 Xenon is an anesthetic with minimal hemodynamic side effects, making it an ideal agent for cardiocompromised patients. We investigated if xenon induces pharmacological preconditioning (PC) of the rat heart and elucidated the underlying molecular mechanisms. 2 For infarct size measurements, anesthetized rats were subjected to 25 min of coronary artery occlusion followed by 120 min of reperfusion. Rats received either the anesthetic gas xenon, the volatile anesthetic isoflurane or as positive control ischemic preconditioning (IPC) during three 5‐min periods before 25‐min ischemia. Control animals remained untreated for 45 min. To investigate the involvement of protein kinase C (PKC) and p38 mitogen‐activated protein kinase (MAPK), rats were pretreated with the PKC inhibitor calphostin C (0.1 mg kg−1) or the p38 MAPK inhibitor SB203580 (1 mg kg−1). Additional hearts were excised for Western blot and immunohistochemistry. 3 Infarct size was reduced from 50.9±16.7% in controls to 28.1±10.3% in xenon, 28.6±9.9% in isoflurane and to 28.5±5.4% in IPC hearts. Both, calphostin C and SB203580, abolished the observed cardioprotection after xenon and isoflurane administration but not after IPC. Immunofluorescence staining and Western blot assay revealed an increased phosphorylation and translocation of PKC‐ɛ in xenon treated hearts. This effect could be blocked by calphostin C but not by SB203580. Moreover, the phosphorylation of p38 MAPK was induced by xenon and this effect was blocked by calphostin C. 4 In summary, we demonstrate that xenon induces cardioprotection by PC and that activation of PKC‐ɛ and its downstream target p38 MAPK are central molecular mechanisms involved. Thus, the results of the present study may contribute to elucidate the beneficial cardioprotective effects of this anesthetic gas.

Xenon administration during early reperfusion reduces infarct size after regional ischemia in the rabbit heart in vivo.

The noble gas xenon can be used as an anesthetic gas with many of the properties of the ideal anesthetic. Other volatile anesthetics protect myocardial tissue against reperfusion injury. We investigated the effects of xenon on reperfusion injury after regional myocardial ischemia in the rabbit. Chloralose-anesthetized rabbits were instrumented for measurement of aortic pressure, left ventricular pressure, and cardiac output. Twenty-eight rabbits were subjected to 30 min of occlusion of a major coronary artery followed by 120 min of reperfusion. During the first 15 min of reperfusion, 14 rabbits inhaled 70% xenon/30% oxygen (Xenon), and 14 rabbits inhaled air containing 30% oxygen (Control). Infarct size was determined at the end of the reperfusion period by using triphenyltetrazolium chloride staining. Xenon reduced infarct size from 51% ± 3% of the area at risk in controls to 39% ± 5% (P < 0.05). Infarct size in relation to the area at risk size was smaller in the xenon-treated animals, indicated by a reduced slope of the regression line relating infarct size to the area at risk size (Control: 0.70 ± 0.08, r = 0.93; Xenon: 0.19 ± 0.09, r = 0.49, P < 0.001). In conclusion, inhaled xenon during early reperfusion reduced infarct size after regional ischemia in the rabbit heart in vivo. Implications Xenon might be a suitable volatile anesthetic in an ischemia-reperfusion situation.

Ketamine, but Not S (+)-ketamine, Blocks Ischemic Preconditioning in Rabbit Hearts In Vivo

BackgroundKetamine blocks KATP channels in isolated cells and abolishes the cardioprotective effect of ischemic preconditioning in vitro. The authors investigated the effects of ketamine and S (+)-ketamine on ischemic preconditioning in the rabbit heart in vivo. MethodsIn 46 &agr;-chloralose–anesthetized rabbits, left ventricular pressure (tip manometer), cardiac output (ultrasonic flow probe), and myocardial infarct size (triphenyltetrazolium staining) at the end of the experiment were measured. All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. The control group underwent the ischemia–reperfusion program without preconditioning. Ischemic preconditioning was elicited by 5-min coronary artery occlusion followed by 10 min of reperfusion before the 30 min period of myocardial ischemia (preconditioning group). To test whether ketamine or S (+)-ketamine blocks the preconditioning-induced cardioprotection, each (10 mg kg−1) was administered 5 min before the preconditioning ischemia. To test any effect of ketamine itself, ketamine was also administered without preconditioning at the corresponding time point. ResultsHemodynamic baseline values were not significantly different between groups [left ventricular pressure, 107 ± 13 mmHg (mean ± SD); cardiac output, 183 ± 28 ml/min]. During coronary artery occlusion, left ventricular pressure was reduced to 83 ± 14% of baseline and cardiac output to 84 ± 19%. After 2 h of reperfusion, functional recovery was not significantly different among groups (left ventricular pressure, 77 ± 19%; cardiac output, 86 ± 18%). Infarct size was reduced from 45 ± 16% of the area at risk in controls to 24 ± 17% in the preconditioning group (P = 0.03). The administration of ketamine had no effect on infarct size in animals without preconditioning (48 ± 18%), but abolished the cardioprotective effects of ischemic preconditioning (45 ± 19%, P = 0.03). S (+)-ketamine did not affect ischemic preconditioning (25 ± 11%, P = 1.0). ConclusionsKetamine, but not S (+)-ketamine blocks the cardioprotective effect of ischemic preconditioning in vivo.

Morphine induces late cardioprotection in rat hearts in vivo: the involvement of opioid receptors and nuclear transcription factor kappaB.

&dgr;1-opioid receptor agonists can induce cardioprotection by early and late preconditioning (LPC). Morphine (MO) is commonly used for pain treatment during acute coronary syndromes. We investigated whether MO can induce myocardial protection by LPC and whether a nuclear transcription factor &kgr;B (NF-&kgr;B)-dependent intracellular signaling pathway is involved. Rats were subjected to 25 min of regional ischemia and 2 h of reperfusion 24 h after treatment with saline (NaCl; 0.9% 5 mL), lipopolysaccharide of Escherichia coli (LPS; 1 mg/kg), or MO (3 mg/kg). LPS is a trigger of LPC and served as positive control. Naloxone (NAL) was used to investigate the role of opioid receptors in LPC and was given before NaCl, LPS, or MO application (trigger phase) or before ischemia-reperfusion (mediator phase). Infarct size (percentage area at risk) was 59% ± 9%, 51% ± 6%, or 53% ± 10% in the NaCl, NAL-NaCl, and NaCl-NAL groups, respectively. Pretreatment with MO reduced infarct size to 20% ± 6% after 24 h (MO-24h), and this effect was abolished by NAL in the trigger (NAL-MO, 53% ± 14%) and in the mediator (MO-NAL, 60% ± 8%) phases. Pretreatment with LPS reduced infarct size to 23% ± 8%. NAL administration in the trigger phase had no effect on infarct size (NAL-LPS 30% ± 16%), whereas NAL during the mediator phase of LPC abolished the LPS-induced cardioprotection (LPS-NAL 54% ± 8%). The role of NF-&kgr;B in morphine-induced LPC was investigated by Western blot and electrophoretic mobility shift assay. Morphine and LPS treatment increased phosphorylation of the inhibitory protein &kgr;B, leading to an increased activity of NF-&kgr;B. Thus, MO induces LPC similarly to LPS and it is likely that this cardioprotection is mediated at least in part by activation of NF-&kgr;B. Opioid receptors are involved as mediators in both MO- and LPS-induced LPC but as triggers only in MO-induced LPC.

Sevoflurane confers additional cardioprotection after ischemic late preconditioning in rabbits

BACKGROUND: Sevoflurane exerts cardioprotective effects that mimic the early ischemic preconditioning phenomenon (EPC) by activating adenosine triphosphate-sensitive potassium (KATP) channels. Ischemic late preconditioning (LPC) is an important cardioprotective mechanism in patients with coronary artery disease. The authors investigated whether the combination of LPC and sevoflurane-induced preconditioning results in enhanced cardioprotection and whether opening of KATP channels plays a role in this new setting. METHODS: Seventy-three rabbits were instrumented with a coronary artery occluder. After recovery for 10 days, they were subjected to 30 min of coronary artery occlusion and 120 min of reperfusion (I/R). Controls (n = 14) were not preconditioned. LPC was induced in conscious animals by a 5-min period of coronary artery occlusion 24 h before I/R (LPC, n = 15). Additional EPC was induced by a 5-min period of myocardial ischemia 10 min before I/R (LPC+EPC, n = 9). Animals of the sevoflurane (SEVO) groups inhaled 1 minimum alveolar concentration of sevoflurane for 5 min at 10 min before I/R with (LPC+SEVO, n = 10) or without (SEVO, n = 15) additional LPC. The KATP channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) was given intravenously 10 min before sevoflurane administration (LPC+SEVO+5-HD, n = 10). RESULTS: Infarct size of the area at risk (triphenyltetrazolium staining) was reduced from 45 +/- 16% (mean+/-SD, control) to 27 +/- 11% by LPC (P < 0.001) and to 27 +/- 17% by sevoflurane (P = 0.001). Additional sevoflurane administration after LPC led to a further infarct size reduction to 14 +/- 8% (LPC+SEVO, P = 0.003 vs. LPC; P = 0.032 vs. SEVO), similar to the combination of LPC and EPC (12 +/- 8%; P = 0.55 vs. LPC+SEVO). Cardioprotection induced by LPC+SEVO was abolished by 5-HD (LPC+SEVO+5-HD, 41 +/- 19%, P = 0.001 vs. LPC+SEVO). CONCLUSIONS: Sevoflurane administration confers additional cardioprotection after LPC by opening of KATP channels.

Thiopentone does not block ischemic preconditioning in the isolated rat heart

PurposeIschemic preconditioning protects the heart against subsequent prolonged ischemia by opening of adenosine triphosphate-sensitive potassium (KATP) channels. Thiopentone blocks KATP channels in isolated cells. Therefore, we investigated the effects of thiopentone on ischemic preconditioning.MethodsIsolated rat hearts (n = 56) were subjected to 30 min of global no-flow ischemia, followed by 60 min of reperfusion. Thirteen hearts underwent the protocol without intervention (control, CON) and in 11 hearts (preconditioning, PC), ischemic preconditioning was elicited by two five-minute periods of ischemia. In three additional groups, hearts received 1 (Thio 1,n = 11), 10(Thio 10,n = 11) or 100 μg·mL−1 (Thio 100,n = 10) thiopentone for five minutes before preconditioning. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial performance and cellular injury, respectively.ResultsRecovery of LV developed pressure was improved by ischemic preconditioning (after 60 min of reperfusion, mean ± SD: PC, 40 ± 19% of baseline) compared with the control group (5 ± 6%,P < 0.0l) and this improvement of myocardial function was not altered by administration of thiopentone (Thio 1, 37 ± 15%; Thio 10, 36 ± 16%; Thio 100, 38 ± 16%,P=0.87–0.99 vs PC). Total CK release over 60 min of reperfusion was reduced by preconditioning (PC, 202 ± 82 U·g−1 dry weight) compared with controls (CON, 383 ± 147 U·g−1,P < 0.0l) and this reduction was not affected by thiopentone (Thio 1, 213 ± 69 U·g−1; Thio 10, 211 ± 98U·g−1; Thio 100, 258 ± 128 U·g−1,P=0.62–1.0vs PC).ConclusionThese results indicate that thiopentone does not block the cardioprotective effects of ischemic preconditioning in an isolated rat heart preparation.RésuméObjectifLe préconditionnement ischémique protège le cœur contre l’ischémie ultérieure prolongée en ouvrant les canaux potassiques sensibles à l’adénosine triphosphate (KATP). Or, le thiopental bloque les canaux KATP dans des cellules isolées. Nous avons donc recherché les effets du thiopental sur le préconditionnement ischémique.MéthodeDes cœurs de rats isolés (n = 56) ont été soumis à 30 min d’ischémie globale à débit nul, puis de 60 min, à une reperfusion. Treize cœurs ont subi le protocole sans intervention (témoin, TEM) et dans onze cœurs (groupe de préconditionnement, PC) le préconditionnement ischémique a été amorcé par deux périodes de cinq minutes d’ischémie. Dans trois groupes additionnels, les cœurs ont reçu 1 (Thio 1, n = 11), 10 (Thio 10, n = 11) ou 100 μg·mL−1 (Thio 100, n = 10) de thiopental pendant cinq minutes avant le préconditionnement. La pression du ventricule gauche (VG) développée et la libération de créatine kinase (CK) ont été mesurées en qualité de variables de la performance myocardique et de la lésion cellulaire, respectivement.RésultatsLa récupération de la pression du VG développée a été améliorée par le préconditionnement ischémique (après 60 min de reperfusion, la moyenne ± l’écart type : PC, 40 ± 19 % de la mesure de base) comparée au groupe témoin (5 ± 6 %, P < 0,01). Cette amélioration de la fonction myocardique n’a pas été modifiée par l’administration de thiopental (Thio 1, 37 ± 15 %; Thio 10, 36 ± 16 %; Thio 100, 38 ± 16%, P = 0,87 - 0,99 vs PC). La libération totale de CK après 60 min de reperfusion a été réduite par le préconditionnement (PC, 202 ± 82 U·g−1 de poids anhydre) comparé au témoin (TEM, 383 ± 147 U·g−1, P < 0,01) et cette réduction n’a pas été affectée par le thiopental (Thio 1, 213 ± 69 U·g−1; Thio 10, 211 ± 98 U·g−1; Thio 100, 258 ± 128 U·g−1, P = 0,62– 1,0 vs PC).ConclusionCes résultats indiquent que le thiopental ne bloque pas les effets cardioprotecteurs du préconditionnement ischémique dans une préparation de cœur de rat isolé.

Effects of Ketamine and Its Isomers on Ischemic Preconditioning in the Isolated Rat Heart

BackgroundIschemic preconditioning protects the heart against subsequent ischemia. Opening of the adenosine triphosphate–sensitive potassium (KATP) channel is a key mechanism of preconditioning. Ketamine blocks KATP channels of isolated cardiomyocytes. The authors investigated the effects of ketamine and its stereoisomers on preconditioning. MethodsIsolated rat hearts (n = 80) underwent 30 min of no-flow ischemia and 60 min of reperfusion. Two groups with eight hearts each underwent the protocol without intervention (control-1 and control-2), and, in eight hearts, preconditioning was elicited by two 5-min periods of ischemia before the 30 min ischemia. In the six treatment groups (each n = 8), ketamine, R (−)- or S (+)-ketamine were administered at concentrations of 2 or 20 &mgr;g/ml before preconditioning. Eight hearts received 20 &mgr;g/ml R (−)-ketamine before ischemia. Left ventricular (LV) developed pressure and creatine kinase (CK) release during reperfusion were determined as variables of ventricular function and cellular injury. ResultsBaseline LV developed pressure was similar in all groups: 104 ± 28 mmHg (mean ± SD). Controls showed a poor recovery of LV developed pressure (17 ± 8% of baseline) and a high CK release (70 ± 17 IU/g). Ischemic preconditioning improved recovery of LV developed pressure (46 ± 14%) and reduced CK release (47 ± 17 IU/g, both P < 0.05 vs. control-1). Ketamine (2 &mgr;g/ml) and 2 or 20 &mgr;g/ml S (+)-ketamine had no influence on recovery of LV developed pressure compared with preconditioning (47 ± 18, 43 ± 8, 49 ± 36%) and CK release (39 ± 8, 30 ± 14, 41 ± 25 IU/g). After administration of 20 &mgr;g/ml ketamine and 2 or 20 &mgr;g/ml R (−)-ketamine, the protective effects of preconditioning were abolished (LV developed pressure–recovery, 16 ± 14, 22 ± 21, 18 ± 11%; CK release, 67 ± 11, 80 ± 21, 82 ± 41 IU/g; each P < 0.05 vs. preconditioning). Preischemic treatment with R (−)-ketamine had no effect on CK release (74 ± 8 vs. 69 ± 9 IU/g in control-2, P = 0.6) and functional recovery (LV developed pressure 12 ± 4 vs. 9 ± 2 mmHg in control-2, P = 0.5). ConclusionKetamine can block the cardioprotective effects of ischemic preconditioning. This effect is caused by the R (−)-isomer.

The direct myocardial effects of xenon in the dog heart in vivo

Xenon has minimal hemodynamic side effects, but no data are available on its direct myocardial effects in vivo. We examined myocardial function during the global and regional administration of xenon in the dog heart. Anesthetized (midazolam/piritramide) dogs (n = 8) were instrumented for measurement of left ventricular pressure, cardiac output, and blood flow in the left anterior descending coronary artery (LAD) and circumflex coronary artery. Regional myocardial function was assessed by sonomicrometry in the antero-apical and the postero-basal wall. Hemodynamics were recorded during baseline conditions and during inhalation of 50% or 70% xenon, respectively. Subsequently, a bypass containing a membrane oxygenator was installed from the carotid artery to the LAD, allowing xenon administration only to the LAD-dependent myocardium. No changes in myocardial function were observed during inhalation of xenon. The regional administration of 50% xenon had no significant effect on regional myocardial function (systolic wall thickening and mean velocity of systolic wall thickening). Seventy percent xenon reduced systolic wall thickening by 7.2% ± 4.0% and mean velocity of systolic wall thickening by 8.2% ± 4.0% in the LAD-perfused area (P < 0.05). There were no changes of global hemodynamics, coronary blood flow, and regional myocardial function in the circumflex coronary artery-dependent myocardium. Xenon produces a small but consistent direct negative inotropic effect in vivo.

Cardioprotection against reperfusion injury is maximal with only two minutes of sevoflurane administration in rats

PurposeVolatile anesthetics can protect the heart against reperfusion injury. When sevoflurane is given for the first 15 min of reperfusion, a concentration corresponding to one minimum alveolar concentration (MAC) provides a maximum protective effect. The present study addresses the question of how long sevoflurane has to be administered to achieve the best cardioprotection.MethodsChloralose anesthetized rats were subjected to a 25-min occlusion of a major coronary artery, followed by 90 min of reperfusion. During the initial phase of reperfusion, an end-tidal concentration of 2.4 vol.% of sevoflurane (1 MAC) was given for two (n = 8), five (n = 8) or ten minutes (n =7). Seven rats served as untreated controls. We measured left ventricular (LV) pressure, mean aortic pressure and infarct size (triphenyltetrazolium staining).ResultsAdministration of sevoflurane for two minutes resulted in the greatest reduction of infarct size to 15% (8–22 [mean (95% confidence interval)] of the area at risk compared with controls [51 (47–55) %, P < 0.00 1], Five or ten minutes of sevoflurane administration reduced infarct size to 26 ( 18–34) and 26 ( 18–35) % [P < 0.05], respectively. The cardiodepressant effect of sevoflurane varied with the duration of its administration: LV dP/dt was reduced from 6332 mmHg · sec−1 (5771–6894) during baseline to 4211 mmHg · sec−1 (3031–5391), 3811 mmHg · sec−1 (2081–5540) and 3612 mmHg · sec−1 (2864–4359) after two, five and ten minutes of reperfusion, respectively.ConclusionAdministration of 1 MAC sevoflurane for the first two minutes of reperfusion effectively protects the heart against reperfusion injury in ratsin vivo. A longer administration time had lesser cardioprotective effects in this experimental model.RésuméObjectifLes anesthésiques voiatiis peuvent protéger le cœur contre tes lésions de reperfusion. Lorsque le sévoflurane est administré pendant les 15 premières minutes de la reperfusion, une concentration correspondant à une concentration alvéolaire minimale (CAM) fournit un effet protecteur maximal. Nous voulions déterminer le temps d’administration de sévoflurane nécessaire pour atteindre la meilleure cardioprotection.MéthodeDes rats anesthésiés à la chloralose ont été soumis à 25 min d’occlusion d’une artère coronaire principale, suivie de 90 min de reperfusion. Pendant la phase initiale de reperfusion, une concentration télé-expiratoire de 2,4 vol.% de sévoflurane (1 CAM) a été donnée pendant deux (n = 8), cinq (n = 8) ou dix minutes (n = 7). Sept rats non traités ont servi de témoins. Nous avons mesuré la pression ventriculaire gauche (VG), la pression aortique moyenne et la taille de l’infarctus (coloration au triphényltétrazolium).RésultatsL’administration de sévoflurane pendant deux minutes a donné la plus importante réduction de la taille de l’infarctus à 15 % de l’aire à risque (8–22 [moyenne (intervalle de confiance de 95 %)], comparativement aux témoins [51 (47–55) %, P < 0,001]. Ladministration pendant 5 à 10 min a respectivement réduit l’infarctus à 26 (18–34) et à 26 (18–35) % [P < 0,05]. L’effet cardiodépresseur du sévoflurane a varié avec la durée de l’administration : la dP/dt du VG a été, respectivement, réduite de 6332 mmHg· secr−1 (5771–6894), comme mesure de base, à 4211 mmHg · sec−1 (3031–5391), 3811 mmHg · sec−1 (2081–5540) et 3612 mmHg · sec−1 (2864–4359) après deux, cinqetdix minutes de reperfusion.ConclusionLadministration de 1 CAM de sévoflurane pendant les deux premières minutes d’une reperfusion protège efficacement le cœur contre les lésions de reperfusion in vivo chez des rats. Une administration prolongée produit moins d’effets cardioprotecteurs chez ce modèle expérimental.