Jan Frässdorf

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.

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.

Effects of nitrous oxide on the rat heart in vivo : Another inhalational anesthetic that preconditions the heart?

Background:For nitrous oxide, a preconditioning effect on the heart has yet not been investigated. This is important because nitrous oxide is commonly used in combination with volatile anesthetics, which are known to precondition the heart. The authors aimed to clarify (1) whether nitrous oxide preconditions the heart, (2) how it affects protein kinase C (PKC) and tyrosine kinases (such as Src) as central mediators of preconditioning, and (3) whether isoflurane-induced preconditioning is influenced by nitrous oxide. Methods:For infarct size measurements, anesthetized rats were subjected to 25 min of coronary artery occlusion followed by 120 min of reperfusion. Rats received nitrous oxide (60%), isoflurane (1.4%) or isoflurane–nitrous oxide (1.4%/60%) during three 5-min periods before index ischemia (each group, n = 7). Control animals remained untreated for 45 min. Additional hearts (control, 60% nitrous oxide alone%, and isoflurane–nitrous oxide [0.6%/60%, in equianesthetic doses]) were excised for Western blot of PKC-ϵ and Src kinase (each group, n = 4). Results:Nitrous oxide had no effect on infarct size (59.1 ± 15.2% of the area at risk vs. 51.1 ± 10.9% in controls). Isoflurane (1.4%) and isoflurane–nitrous oxide (1.4%/60%) reduced infarct size to 30.9 ± 10.6 and 28.7 ± 11.8% (both P < 0.01). Nitrous oxide (60%) had no effect on phosphorylation (2.3 ± 1.8 vs. 2.5 ± 1.7 in controls, average light intensity, arbitrary units) and translocation (7.0 ± 4.3 vs. 7.4 ± 5.2 in controls) of PKC-ϵ. Src kinase phosphorylation was not influenced by nitrous oxide (4.6 ± 3.9 vs. 5.0 ± 3.8; 3.2 ± 2.2 vs. 3.5 ± 3.0). Isoflurane–nitrous oxide (0.6%/60%, in equianesthetic doses) induced PKC-ϵ phosphorylation (5.4 ± 1.9 vs. 2.8 ± 1.5; P < 0.001) and translocation to membrane regions (13.8 ± 13.0 vs. 6.7 ± 2.0 in controls; P < 0.05). Conclusions:Nitrous oxide is the first inhalational anesthetic without preconditioning effect on the heart. However, isoflurane-induced preconditioning and PKC-ϵ activation are not influenced by nitrous oxide.

Xenon Induces Late Cardiac Preconditioning In Vivo : A Role for Cyclooxygenase 2?

BACKGROUND:Xenon induces early myocardial preconditioning of the rat heart in vivo, but whether xenon induces late cardioprotection is not known. Cyclooxygenase-2 (COX-2) has been shown to be an important mediator in the signal transduction of myocardial ischemic late preconditioning (i-LPC). We investigated whether xenon induces late preconditioning (Xe-LPC) and whether COX-2 activity and/or expression are involved in mediating this effect. METHODS:Anesthetized male Wistar rats were instrumented with a coronary artery occluder. After 7 d of recovery, animals were randomized to 1 of 5 groups each containing 8 animals. The i-LPC group underwent 5 min of coronary occlusion to induce i-LPC. Xe-LPC was achieved by administration of xenon (70 volume%) for 15 min. Additional rats were pretreated with the COX-2 inhibitor NS-398 (5 mg kg−1 body weight i.p.) with and without Xe-LPC. A group of sham operated animals not undergoing i-LPC or Xe-LPC served as controls (Con). After 24 h, all animals were anesthetized and underwent 25 min of myocardial ischemia induced by tightening of the coronary artery occluder followed by 2 h of reperfusion. Myocardial infarct size was assessed by triphenyltetrazolium chloride staining. In additional experiments, hearts were excised at different time points after preconditioning to investigate COX-2 mRNA and protein expression by polymerase chain reaction and infrared Western blot, respectively. RESULTS:Both i-LPC and Xe-LPC reduced myocardial infarct size (% of the area at risk) compared with Con (i-LPC: 29 ± 7%; Xe-LPC 31 ± 8%, both P < 0.05 vs Con 64 ± 6%). NS-398 abolished the cardioprotective effect of Xe-LPC (61 ± 6%, P < 0.05 vs Xe-LPC). COX-2 mRNA and protein expression was only increased in the i-LPC group, but not in the Xe-LPC group. CONCLUSION:Xenon induces late myocardial preconditioning that is abolished by functional blockade of COX-2 activity. In contrast to i-LPC, Xe-LPC did not lead to an increased expression of COX-2 mRNA and protein. These data suggest differences in COX-2 regulation in i-LPC and Xe-LPC.

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.