[Is infection a pathogenetic factor in coronary heart disease?]. / Er infeksjon en patogenetisk faktor ved koronar hjertesykdom?

BACKGROUND: Several wellknown risk-factors can contribute to the development of coronary artery disease. A relatively new question is whether infection is also involved in the pathogenesis. Acute and/or chronic infections might affect initiation, progression and instability in coronary artery disease, as well as enhance development of restenosis and transplant atherosclerosis. In clinical studies it is possible to measure the amount of antibodies in blood samples, detect infectious agents in atheromatous lesions, and evaluate potential effects of antibiotic treatment. In animal models it is possible to investigate whether a direct infection can induce atheromatosis. MATERIAL AND METHODS: The aim of this article is to give an updated overview of clinical and experimental results and discuss potential consequences for the treatment of coronary artery disease. Possible cellular mechanisms will be presented. RESULTS: In conclusion, there is an association between coronary artery disease and infection with Chlamydia pneumoniae. Similar results are not obtained for infection with Helicobacter pylori. There is also an association between cytomegalovirus infection and development of restenosis and transplant atherosclerosis. However, a possible direct causal relationship is not fully established. Of special interest is whether antibiotic treatment can prevent acute cardiovascular events. INTERPRETATION: Primary prevention must still be targeted at conventional risk factors. However, in secondary prevention it can be valuable to identify subgroups of patients which may benefit from anti-infection treatment.

Adenosine and cardioprotection during ischaemia and reperfusion--an overview.

Adenosine is a local hormone, with numerous tissue-specific biological functions. In the myocardium, adenosine is released in small amounts at constant basal rate during normoxia. During ischaemia the production of adenosine increases several fold due to breakdown of adenosine triphosphate (ATP). Increased production of adenosine causes coronary vasodilatation. Thus, adenosine couples myocardial metabolism and flow during ischaemia and is called a homeostatic or "retaliatory metabolite". Furthermore, adenosine has electrophysiological effects in supraventricular tissue, causing a decrease in heart rate. In 1985 it was discovered that adenosine also exerts cardioprotective effects directly on cardiomyocytes. The aim of this review is to give an overview of the role of adenosine as a directly cytoprotective agent during myocardial ischaemia and reperfusion. We will focus on its effects on the myocytes, elicited by stimulation of adenosine receptors in sarcolemma, which triggers intracellular signalling systems. We will also address the new aspect that adenosine can influence regulation of gene expression. There is evidence that the myocardium is capable of endogenous adaptation in response to ischaemia, namely "hibernation" and early and late phases of "preconditioning". Endogenous substances produced during ischaemia probably trigger these responses. We will discuss the role of adenosine in these different settings. Adenosine can be given exogenously through intravasal routes; however, this review will also focus on the effects of endogenously produced adenosine. We will discuss pharmacological ways to increase endogenous levels of adenosine, and the effects of such interventions during ischaemia and reperfusion. Finally, we will review results from studies in humans together with relevant experimental studies, and indicate potential therapeutic implications of adenosine.

[Preconditioning--endogenous defence mechanisms of the heart during ischemia]. / Prekondisjonering--hjertets egne forsvarsmekanismer ved iskemi.

BACKGROUND: The term "preconditioning" refers to the paradoxical phenomenon that pretreatment with a potential noxious stress-stimulus can increase cellular tolerance to subsequent noxious stress-stimuli. This was first described in an experimental model in dog hearts in which short-lasting periods of myocardial ischaemia resulted in reduced infarction during a subsequent long-lasting ischaemic period. Similar observations are made in other organs and species. Preconditioning is also used to describe pretreatment with other physical stress-stimuli or pharmacological agents that can increase resistance against cellular damage. This phenomenon probably represents a general adaptive response to cellular stress. MATERIAL AND METHODS: This review focuses on preconditioning in the heart and the possible endogenous mechanisms involved. The potential clinical role of preconditioning is also discussed. RESULTS: It is shown that preconditioning can reduce myocardial infarction in patients. However, protection against reduced contractility without infarction ("stunning") and arrhythmia is more uncertain. Several mechanisms might be involved; these are not fully clarified. INTERPRETATION: Preconditioning is of great interest because its effect is vigorous and reproducible, with a potential for use in patients with coronary heart disease. Preconditioning also illustrates how activation of endogenous defence mechanisms can increase cellular tolerance to ischaemia or other stress stimuli.

[Is infection a pathogenetic factor in coronary heart disease?]. / Er infeksjon en patogenetisk faktor ved koronar hjertesykdom?

BACKGROUND: Several wellknown risk-factors can contribute to the development of coronary artery disease. A relatively new question is whether infection is also involved in the pathogenesis. Acute and/or chronic infections might affect initiation, progression and instability in coronary artery disease, as well as enhance development of restenosis and transplant atherosclerosis. In clinical studies it is possible to measure the amount of antibodies in blood samples, detect infectious agents in atheromatous lesions, and evaluate potential effects of antibiotic treatment. In animal models it is possible to investigate whether a direct infection can induce atheromatosis. MATERIAL AND METHODS: The aim of this article is to give an updated overview of clinical and experimental results and discuss potential consequences for the treatment of coronary artery disease. Possible cellular mechanisms will be presented. RESULTS: In conclusion, there is an association between coronary artery disease and infection with Chlamydia pneumoniae. Similar results are not obtained for infection with Helicobacter pylori. There is also an association between cytomegalovirus infection and development of restenosis and transplant atherosclerosis. However, a possible direct causal relationship is not fully established. Of special interest is whether antibiotic treatment can prevent acute cardiovascular events. INTERPRETATION: Primary prevention must still be targeted at conventional risk factors. However, in secondary prevention it can be valuable to identify subgroups of patients which may benefit from anti-infection treatment.

Importance of heart rate for acute hibernation in isolated blood-perfused piglet hearts.

BACKGROUND: Hibernating myocardium may benefit from revascularization. There are several experimental models for acute hibernation. In intact hearts low-flow ischemia causes time-dependent metabolic alterations, termed "metabolic adaptation". In isolated heart preparations metabolic responses to low-flow ischemia vary, and signs of metabolic adaptation are not consistently found. In isolated hearts global ischemia may cause bradycardia unless the hearts are paced. We hypothesized that the lack of consistent metabolic adaptation to low-flow ischemia in isolated hearts might be due to bradycardia during ischemia. In this study we investigated the influence of heart rate on metabolism and function in an isolated heart preparation. METHODS: Isolated blood-perfused piglet hearts were subjected to 120 min 10% flow. In groups A (n=9) and B (n=4) hearts were not paced during ischemia, in groups C (n=5) and D (n=5) hearts were paced at pre-ischemic heart rate during ischemia. RESULTS: Without pacing, heart rate declined to approximately 1/3 during ischemia and anaerobic metabolism showed a slight decline over time. With pacing, production of protons, pCO2 and lactate showed a bell-shaped curve which peaked at 20-25 min of ischemia, followed by a subsequent decline towards the end of ischemia (overall p < 0.001 for all). However, reperfusion revealed impaired recovery of function in paced hearts compared to non-paced hearts (53 +/- 7% vs 77 +/- 4%, p < 0.05) concomitant with higher release of creatine kinase (455 +/- 93 IU/100 g vs 106 +/- 13 IU/100 g, p < 0.01). CONCLUSIONS: When heart rate is allowed to decline during low-flow ischemia in isolated piglet hearts, signs of metabolic adaptation are not evident. When hearts are paced during ischemia time-dependent alterations in anaerobic metabolism occur, resembling observations seen in intact beating hearts. However, paced hearts also show indications of increased cellular injury, indicating that in paced hearts the metabolic consequences are mostly due to increased irreversible cell injury. Thus, the model for acute hibernation with 10% flow in isolated blood-perfused piglet hearts are critically dependent on bradycardia during ischemia.

Elevated levels of endogenous adenosine alter metabolism and enhance reduction in contractile function during low-flow ischemia: associated changes in expression of Ca(2+)-ATPase and phospholamban.

Adenosine has several potentially cardioprotective effects including vasodilatation, reduction in heart rate and alterations in metabolism. Adenosine inhibits catecholamine-induced increase in contractile function mainly through inhibition of phosphorylation of phospholamban (PLB), the main regulatory protein of Ca(2+)-ATPase in sarcoplasmic reticulum (SR), and during ischemia it reduces calcium (Ca2+) overload. In this study we examined the effects of endogenous adenosine on contractile function and metabolism during low-flow ischemia (LFI) and investigated whether endogenous adenosine can alter expression of the Ca(2+)-ATPase/PLB-system and other Ca(2+)-regulatory proteins. Isolated blood-perfused piglet hearts underwent 120 min 10% flow. Hearts were treated with either saline, the adenosine receptor blocker (8)-sulfophenyl theophylline (8SPT, 300 micromol/l) or the nucleoside transport inhibitor draflazine (1 micromol/l). During LFI, 8SPT did not substantially influence metabolic or functional responses. However, draflazine enhanced the reduction in heart rate, contractile force and MVO(2), with less release of H+ and CO2. Before LFI there were no significant differences between groups for any of the proteins (Ca(2+)-ATPase, ryanodine-receptor, Na+/K(+)-ATPase) or mRNAs (Ca(2+)-ATPase, PLB, calsequestrin, Na+/Ca(2+)-exchanger) measured. At end of LFI mRNA-level of PLB was higher in draflazine-treated hearts compared to both other groups (P<0.01 vs both). Also, at end of LFI protein-level of Ca(2+)-ATPase was lower in draflazine-treated hearts (P<0.05 vs both), and a parallel trend towards a lower mRNA-level was seen (P=0.11 vs saline and P=0.43 vs 8SPT). During LFI tissue Ca2+ tended to rise in saline- and 8SPT-treated hearts but not in draflazine-treated hearts (at end of LFI, P=0.01 vs 8SPT). We conclude that the amount of adenosine normally produced during LFI does not substantially influence function and metabolism. However, increased endogenous levels by draflazine enhance downregulation of function and reduce signs of anaerobic metabolism. At end of LFI associated changes in expression of PLB and Ca(2+)-ATPase were seen. The functional significance was not determined in the present study. However, altered protein-levels might influence Ca(2+)-handling in sarcoplasmic reticulum and thus affect contractile force and tolerance to ischemia.

Microembolization in pigs: effects on coronary blood flow and myocardial ischemic tolerance.

Coronary microembolization has been reported to increase coronary blood flow (CBF) through adenosine release. Because adenosine may increase ischemic tolerance against infarction, we tested the hypothesis that myocardial microembolization, a common finding in patients with ischemic heart disease, induces cardioprotection. Additionally, because the use of microspheres is a common tool to measure tissue perfusion, the effects of small amounts of microspheres on CBF were examined. Using anesthetized pigs, we measured CBF with a transit time flow probe on the left anterior descending coronary artery (LAD). In six pigs the relationship between the amount of injected microspheres (0-40 x 10(6), 15 micrometer in diameter, left atrial injections) and the effect on CBF was examined. Coronary hyperemia occurred, which was linearly related to the amount of microspheres injected: maximal increase in CBF (%) = 2.8 +/- 1.5 (SE) + (5.8 +/- 0.7 x 10(-7) x number of injected microspheres). Because injection of 40 x 10(6) microspheres induced a long-lasting hyperemic response, which could be blocked by 8-p-sulfophenyl theophylline, ischemic tolerance was examined in five other pigs after two injections, each of 40 x 10(6) microspheres, at a 30-min interval. Six control pigs had no injections. Ischemic tolerance was evaluated by measuring infarct size (tetrazolium stain) as the percentage of area at risk (fluorescent particles) after 45 min of LAD occlusion followed by 2 h of reperfusion. Pretreatment by microspheres increased infarct size from 60 +/- 3% of area at risk in control animals to 84 +/- 6% (P < 0.05). The injection of microspheres induced a significant hyperemic flow response without causing necrosis by itself. We conclude that microembolization, evoking coronary hyperemia, does not improve but reduces myocardial ischemic tolerance against infarction in pigs.

A new approach to normalize myocardial temperature in the open-chest pig model.

To prevent unphysiological temperature fluctuations in the myocardium in the open-chest model, we constructed a thermocage. Five pigs under pentobarbital sodium anesthesia underwent repetitive left anterior descending (LAD) coronary artery occlusions. Myocardial temperature was measured without any thoracic temperature-controlling device and in the presence of either a heating lamp or the thermocage. Without any thoracic temperature-controlling device, the temperature at 5-mm myocardial depth was 1.28 +/- 0.33 degrees C below the intra-abdominal temperature (P < 0.05). During a proximal 5-min LAD occlusion, myocardial temperature decreased by 1.86 +/- 1.02 degrees C in the ischemic area (P < 0.05). Both the heating lamp and the thermocage abolished the difference between intra-abdominal and myocardial temperatures and prevented the decrease in myocardial temperature during ischemia. Only the thermocage minimized myocardial temperature fluctuations due to air currents and prevented epicardial exsiccation. We conclude that either a thermocage or a heating lamp may be used to normalize myocardial temperature in the open-chest pig model. However, the thermocage is superior to the lamp in minimizing temperature fluctuations and preventing epicardial exsiccation.

Characterization of metabolic responses to low-flow ischemia in intact pig hearts and isolated blood-perfused neonatal pig hearts.

UNLABELLED: There are different well established experimental models of low-flow ischemia. We examined metabolic variables during reduced coronary blood flow (CBF) in intact pig hearts and isolated neonatal pig hearts, producing similar degrees of postischemic dysfunction without infarction. The isolated hearts were perfused with red blood cell enriched buffer. In eight open-chest pigs mid-LAD flow was reduced to 70% for 60 min, followed by 120 min reperfusion. Myocardial segment lengths were recorded and regional coronary venous blood was sampled. In isolated piglet hearts CBF was reduced to 50% (n = 4), 25% (n = 4), and 10% (n = 17). Only when flow was reduced to 10% did hearts show signs of anaerobic metabolism. Mechanical function was recorded by a balloon in the left ventricle and coronary venous blood was sampled. Intact pig hearts showed release of protons, CO2, and lactate which peaked after 5-10 min of ischemia and thereafter stabilized at reduced levels. In contrast, in isolated neonatal hearts exposed to 10% CBF releases of protons, CO2, and lactate were stable during ischemia with no adaptational changes over time. In a separate group (n = 4), repetitive biopsies revealed no adaptational changes over time for adenosine triphosphate and creatine phosphate during 10% CBF. Contractile function was stably reduced during ischemia in both models. CONCLUSION: During reduced CBF "metabolic adaptation" occurs in intact pig hearts. In contrast, this feature is not present in isolated blood-perfused piglet hearts. The mechanisms responsible for these differences are uncertain. However, differences in metabolism between adult and neonatal hearts and different loading conditions during ischemia might contribute.

Importance of nitric oxide in hepatic arterial blood flow and total hepatic blood volume regulation in pigs.

The importance of nitric oxide in regulating basal arterial blood flow has been examined in several different vascular beds by intra-arterial infusion of inhibitors of nitric oxide synthesis, but not in the arterial vascular bed of the liver. In the present study, N(G)-nitro-L-arginine (L-NNA), in a dose of 0.5 and 1.0 mumol mL-1 of hepatic arterial blood flow, was infused for 5 min into the hepatic artery in seven pigs anaesthetized with pentobarbital sodium. The haemodynamic effects observed by the first infusion were not further enhanced by the second infusion. Hepatic arterial resistance increased by 143 +/- 38% and hepatic arterial blood flow declined by 38 +/- 10%. A systemic effect due to 'spillover' was observed, as evidenced by an increase in mean aortic blood pressure of 24 +/- 4 mmHg. However, no significant increase in arterial mesenteric resistance was observed and total liver blood flow remained unchanged. Hepatic arterial vasodilation in response to occlusion of the portal vein, the arterial buffer response, remained intact after inhibition of nitric oxide synthesis. Liver lobe thickness, measured by an ultrasonic technique, was not found to change with inhibition of arterial nitric oxide synthesis, excluding a significant direct effect of arterial nitric oxide on liver capacitance. In conclusion, nitric oxide is an important regulator of hepatic arterial resistance, but does not mediate the hepatic arterial buffer response and was not found to play any significant role in total hepatic capacitance regulation.

Importance of endogenous adenosine during ischemia and reperfusion in neonatal porcine hearts.

BACKGROUND: Adenosine has several potentially cardioprotective effects. We hypothesized that the effects of endogenous adenosine vary with degree of ischemia and that elevating endogenous levels is protective. METHODS AND RESULTS: Isolated blood-perfused piglet hearts underwent 120 minutes of low-flow ischemia (10% flow) or 90 minutes of zero-flow ischemia, all with 60 minutes of reperfusion. Hearts were treated with either saline, the adenosine receptor blocker 8-sulfophenyltheophylline (8SPT, 300 micromol x L(-1)), or the nucleoside transport inhibitor draflazine (1 micromol x L(-1)). In separate groups, biopsies were obtained before and at the end of ischemia. Compared with saline, 8SPT did not significantly alter functional recovery in either protocol. Draflazine significantly improved percent recovery of left ventricular systolic pressure both in the low-flow protocol (92+/-3% versus 75+/-2% [saline] and 73+/-3% [8SPT], P<.001 for both) and in the zero-flow protocol (76+/-3% versus 59+/-4% [saline] and 46+/-9% [8SPT], P<.05 for both). In the zero-flow protocol, draflazine also significantly reduced ischemic contracture and release of creatine kinase. Tissue adenosine at the end of ischemia was elevated by draflazine compared with saline-treated hearts: after low-flow ischemia to 0.10+/-0.05 versus 0.00+/-0.00 micromol x g(-1) dry wt (P<.05) and after zero-flow ischemia to 1.73+/-0.82 versus 0.15+/-0.03 micromol x g(-1) dry wt (P<.05). CONCLUSIONS: In neonatal porcine hearts, endogenous adenosine produced during ischemia does not influence ischemic injury or functional recovery. Elevating endogenous adenosine by draflazine elicits cardioprotection in both low-flow and zero-flow conditions.

Proarrhythmic effects of ischemic preconditioning in anesthetized pigs.

Conflicting data exist on how ischemic preconditioning affects the incidence of arrhythmias during ischemia. The present study was, therefore, performed to clarify if ischemic preconditioning alters the incidence of arrhythmias during the early phase of ischemia in pigs. Twenty-four pigs (23-36.5 kg) in pentobarbital anesthesia were preconditioned by a 10 min LAD-occlusion and 30 min reperfusion prior to a second 10 min occlusion. The first occlusion served as the preconditioning ischemic period, and the second occlusion as the test ischemic period. To verify that the preconditioning protocol induced protection, infarct size was assessed in an additional nine pigs. The arrhythmic index (arrhythmic beats/min) increased from 12+/-3 during the first occlusion to 38+/-8 during the second occlusion (P < 0.05). Four pigs (17%) fibrillated during the first ischemic period, while 10 pigs (42%) fibrillated during the second ischemic period (P < 0.05). All pigs that fibrillated during the first occlusion also fibrillated during the second occlusion. Mean heart rate was 108+/-4 beats/min before the first occlusion and increased to 113+/-4 beats/min before the second occlusion (P < 0.001). There was a positive correlation between heart rate before the second occlusion and occurrence of fibrillation during this occlusion (rs = 0.42; P < 0.05). The preconditioning protocol reduced infarct size, after a subsequent 45 min ischemic period followed by two hours of reperfusion, from 58+/-3% of area at risk to 40+/-5% (P < 0.05). In conclusion, our data show that ischemic preconditioning increases both the arrhythmic index and the incidence of ventricular fibrillation during the early phase of a subsequent ischemic period.

Preconditioning with ischaemia reduces both myocardial oxygen consumption and infarct size in a graded pattern.

We tested the hypothesis that ischaemic preconditioning reduces pre-ischaemic energy demand and thereby reduces the energy supply-demand mismatch imposed by coronary artery occlusion. Experiments were performed in 52 open chest pigs anaesthetised with sodium pentobarbital. One or two cycles, each of 10 min LAD occlusion followed by 30 min reperfusion, served as the preconditioning stimuli. The degree of protection was evaluated by measuring infarct size (tetrazolium stain) as percentage of area at risk (fluorescent particles) after 45 min LAD occlusion followed by 2 h reperfusion. One preconditioning cycle reduced regional myocardial oxygen consumption (MVO2) by 15+/-3% (P<0.05), whereas two cycles of preconditioning reduced MVO2 by 25+/-3% (P<0.05 v one cycle). This reduction was probably due to reduced energy demand, as both coronary blood flow and arteriovenous oxygen differences decreased, without lactate release or reduction in peak hyperaemic flow response. Energy requirements were most likely also reduced during ischaemia since repayment of flow debt after the second ischaemic period was 33+/-7% less than after the first ischaemic period (P<0.001). One preconditioning cycle reduced infarct size from 58+/-3% of area at risk to 40+/-5% (P<0.05), whereas two cycles of preconditioning reduced infarct size to 15+/-4% of area at risk (P<0.05 v one cycle). We conclude that preconditioning with ischaemia reduces energy consumption in a graded pattern. This effect may contribute to the graded protective effect of ischaemic preconditioning.