Guro Valen

Inhibition of lipoxygenase and cyclooxygenase augments cardiac injury by H2O2

The role of arachidonic acid metabolites in the cardiac effects of toxic oxygen metabolites (TOM) was investigated in buffer-perfused rat hearts (Langendorff model). Hydrogen peroxide (H2O2, 200 microM) was given for 10 min to generate TOM, followed by 30 min recovery. H2O2 reduced left ventricular developed pressure (LVDP), increased left ventricular end-diastolic pressure (LVEDP), and increased coronary flow (CF). The hydroxyl radical scavenger thiourea inhibited the H2O2-induced effects. Perfusion with three lipoxygenase inhibitors, AA861, BWA4C, and diethylcarbamazine, in addition to H2O2, augmented the decrease of LVDP and the increase of LVEDP induced by H2O2. The cyclooxygenase inhibitor indomethacin had the same effects. The H2O2-induced increase in CF was not influenced by diethylcarbamazine, but inhibited by all other drugs. Control perfusion with drugs alone did not influence cardiac function. In conclusion, inhibition of lipoxygenase and cyclooxygenase augmented the depression of cardiac function induced by TOM. Leukotrienes and prostanoids appear to be protective against H2O2-induced cardiac injury.

Open heart surgery increases the levels of histamine in arterial and coronary sinus blood.

The possible release of histamine into the coronary circulation during reperfusion of the cold, cardioplegic heart was investigated during open heart surgery in 13 patients (cardioplegic arrest 54 (35–120 min) (median (range)), cardiopulmonary bypass (CPB) 96 (65–360) min. Samples were drawn concomitantly from coronary sinus and arterial blood before cardioplegia and during myocardial reperfusion for measurement of histamine (radioenzymatic method). Additional arterial samples were drawn pre-, per- and postoperatively. CPB induced a sustained increase in arterial histamine (from 4.02±2.71 nmol/l preoperatively (mean±SD) to maximum 16.31±7.12 nmol/l,p<0.009). Immediately before cardioplegia histamine levels were higher in arterial than coronary sinus blood (9.24±4.85 versus 4.04±2.07 nmol/l,p<0.002). During myocardial reperfusion coronary sinus histamine increased to levels similar to that of arterial blood. In conclusion, histamine is released during CPB. Before cardioplegic arrest, there is a net uptake of histamine by the heart, which is abolished during reperfusion, possibly due to increased cardiac release of histamine.

Activity of histamine metabolizing and catabolizing enzymes during reperfusion of isolated, globally ischemic rat hearts.

Myocardial ischemia-reperfusion injury increases both tissue levels and release of histamine. To study the possible effects of ischemia-reperfusion on histamine metabolism tissue activities of histidine decarboxylase (HDC), histamine N-methyl transferase (HNMT) and diamine oxidase (DAO) were investigated in isolated rat hearts subjected to either 20 min global ischemia and 40 min reperfusion (n=10) or control perfusion (n=8). Histamine in the coronary effluent increased from 21±4 nmol/min (mean ± SEM) before ischemia to 55±5 and 50±7 nmol/min after 4 and 10 min reperfusion (p<0.004 and p<0.004). Tissue HDC activity did not change during observation in any group. HNMT activity was unchanged in controls, but increased from 0.37±0.04 to 0.84±0.18 and 0.96±0.22 pmol methlylhistamine/mg protein hour after 4 and 10 min reperfusion (p<0.008 and p<0.01). DAO decreased similarily in controls and ischemic-reperfused hearts during observation. In conclusion, the previously observed increase of tissue histamine during reperfusion cannot be explained by increased histamine synthesis or decreased histamine catabolism.

The effects of exogenous histamine in isolated rat hearts

The role of histamine in cardiac physiology and pathophysiology is not clarified, but is dependent on species. The effects of exogenous histamine in Langendorff-perfused rat hearts were investigated. 1 mM, 100, 10, 1 and 0.1 μM of histamine (n=7 each) as 15 min infusions were employed in a dose-response study, and compared to control perfused hearts (n=7). In another experimental series, 100 μM histamine (n=15) was added during reperfusion after 25 min global ischemia, and compared to control ischemia-reperfusion (n=15). The maximal response to histamine in the dose-response study (100 μM) was an increase of left ventricular developed pressure to 126±8% of initial value (mean±SEM, p<0.04), and increase of coronary flow to 152+6% (p<0.02) after 5 min infusion. 100 μM histamine did not significantly influence heart rate or rhythm. The lowest concentration (0.1 μM) did not have effects cardiac performance. Reperfusion with histamine for 2 min after ischemia reduced left ventricular developed pressure to 68±10% of initial value versus 116+17% in ischemic controls (p<0.05), and increased left ventricular end-diastolic pressure to 24±8 mmHg compared to 6±2 mmHg in controls (p<0.04). Left ventricular pressures were similar in hearts reperfused with histamine and in ischemic controls for the rest of the observation. Coronary flow increased during reperfusion in hearts given histamine. Histamine had a dose-dependent positive inotropic and vasodilatory effect in isolated rat hearts. Exogenous histamine had only minor effects on post-ischemic cardiac function.

Release of histamine from isolated rat hearts during reperfusion is not dependent on length of ischemic insult, or contents of histamine in cardiac tissue

Release of histamine (H) by ischemia-reperfusion injury was investigated in isolated rat hearts (Langendorff model). The effect of 10, 15, 20, 25, 30, 40 and 60 min ischemia (n=10 each) on H in the coronary effluent and in cardiac tissue was studied after 4 min reperfusion. Release of creatine kinase and lactate dehydrogenase in the coronary effluent increased with time of ischemia. Tissue H increased from 95±10 ng/g rat heart (mean±SEM) before ischemia to max 148±10 ng/g after 20 min ischemia (p<0.002), and increased also after 15 (p<0.01), 25 (p<0.01), 25 (p<0.01), and 30 min (p<0.045). H in the coronary effluent increased after 15 (from 16±3 to 26±2 pmol/min,p<0.044), 30 (26±6 pmol/min,p<0.027), and 60 min ischemia (47±6 pmol/min,p<0.0044). Release of H during ischemia-reperfusion is neither dependent on the severity of the ischemic insult, nor on the level of tissue H.

The Effect of Exogenous Adenosine on Functional Injury Caused by Hydrogen Peroxide in the Isolated Rat Heart

Adenosine is an endogenous cardioprotective substance. The present study examines whether exogenous adenosine attenuates cardiac injury induced by oxidative stress. Rat hearts (Langendorff model) were perfused with H2O2 (180 microM) for 10 min, then recovered for 60 min (n = 10). In other groups adenosine 55 microM, 11 0 microM, or 220 microM (n = 10 in each) was given in addition to H2O2 throughout perfusion. Control perfusion with Krebs Henseleit only (n = 7), adenosine 110 microM throughout perfusion (n = 7), and adenosine 110 microM as an intervention (n = 7) was performed. The hearts were paced at 320 beats/min. Left ventricular systolic (LVSP) and end-diastolic (LVEDP) pressures were measured together with coronary flow (CF), and left ventricular developed pressure (LVDP = LVSP - LVEDP) was calculated. H2O2 decreased LVSP from 105 +/- 8 to 60 +/- 5 mmHg (mean +/- SEM) after 10 min infusion (p < 0.008). Adenosine did not attenuate the decrease of LVSP. LVEDP increased from 0 to 59 +/- 10 mmHg (p < 0.004) and 62 +/- 11 mmHg 5 and 15 min after end of infusion of H2O2, respectively. Neither 55 microM nor 220 microM adenosine inhibited the H2O2-induced increase of LVEDP. Adenosine 110 microM attenuated the increase after 15 (15 +/- 4 mmHg, p < 0.004) and 25 min observation (26 +/- 7 mmHg, p < 0.012). Adenosine did not attenuate the reduction of LVDP. CF initially increased during infusion of H2O2, thereafter decreased. Hearts given adenosine had higher basal CF, and CF did not increase after H2O2. Control perfusion with adenosine, given throughout perfusion or as an intervention, increased CF and tended to increase LVSP. In summary, adenosine did not inhibit H2O2-induced depression of contractility or reduction of CF. One concentration of adenosine (110 microM) attenuated H2O2-induced impairment of relaxation. Exogenous adenosine does not have an important influence on functional injury caused by exogenous oxidants.

Adaptation to Ischemia by in vivo Exposure to Hyperoxia—Signalling through Mitogen Activated Protein Kinases and Nuclear Factor Kappa B

We have established a model of adaptation to ischemia by breathing a hyperoxic gas mixture, which may be directly employed in clinical practice. Hyperoxia improves postischemic function and reduces myocardial necrosis in globally and regionally ischemic rat and mouse hearts, protects hearts of animals with severe atherosclerosis, and modulates in vitro reactivity of isolated aortic rings. Hyperoxic preconditioning is most efficient when the inspired oxygen fraction is >80% oxygen, with different exposure times in rats and mice. In rats the protection is both immediate and delayed, while in mice only immediate protection can be evoked. Exposure to hyperoxia causes an oxidative stress evident as increased serum lipid peroxidation products and reduced antioxidant defence. When breathing hyperoxic gas a rapid nuclear translocation of nuclear factor kappa B (NFκB) in the lungs is followed by a cardiac NFκB activation. In conjunction with hyperoxia the mitogen activated protein kinases (MAPK) p38, ERK1/2, and JNK are phosphorylated in the heart. Pharmacological inhibition of NFκB activation abolished the beneficial effects of hyperoxia. During Langendorff-perfusion with induced global ischemia, phosphorylation of MAPK as well as translocation of NFκB is reduced in animals subjected to hyperoxia prior to the experiments, the latter perhaps due to increased formation of the NFκB inhibitor IkBα. A posssible role for the NFκB-regulated gene inducible nitric oxide synthase (iNOS) in the hyperoxia response was investigated in knock out mice, who had no functional or antiinfarct protection of preconditioning by either hyperoxia or classic ischemic preconditioning. However, neither cardiac iNOS nor contents of antioxidants, heat shock protein 70, or endothelial NOS in the heart increased after hyperoxia. Thus, the signal transduction pathways and organ effectors of hyperoxic protection are not fully determined, but appear to involve MAPK and NFκB. Hyperoxia may have a large potential in the pretreatment of patients undergoing not only open heart procedures, but also in front of any major surgery.

Hüperoksia – kas uus võimalus südamelihase kaitseks?

Aeroobsetele organismidele on hapnik elutahtis ja hapniku defitsiit viib organismi kahjustusele. Nii sudamelihase isheemia reperfusioonikahjustuse kui ka isheemilise eelkohastumuse patofusioloogias mangivad olulist osa hapniku reaktiivsed osakesed. Hapniku korge osarohk ja kestev ekspositsioon voivad pohjustada hapniku reaktiivsete osakeste kestva liigproduktsiooni, mis uletab organismi antioksudantse kaitsevoime ja kutsub esile kahjustava oksudatiivse stressi. Samas on hapniku reaktiivsetel osakestel oluline fusioloogiline roll rakkude signaalmolekulidena, mis osalevad rakusiseste adaptatsioonimehhanismide aktivatsioonil. Eesti Arst 2003; 82 (1): 22–28