Endothelin-1 is involved in plasma mediated stimulation of neutrophil adherence during coronary artery bypass grafting

Stimulation of neutrophil activation during coronary artery bypass grafting: comparison of crystalloid and blood cardioplegia

BACKGROUND

During myocardial ischemia, activation of polymorphonuclear neutrophils (PMNs) results in the production of free oxygen radicals, which increase myocardial injury. It has been shown that PMNs also produce nitric oxide. It is not clear whether PMNs become activated as a result of their direct contact with ischemic/reperfused myocardium or if PMN activation and free oxygen radical production are effects of specific stimuli released during coronary artery bypass grafting (CABG). The aim of the current study was to evaluate plasma-mediated neutrophil stimulation and production of superoxide anion (O2) and nitric oxide in patients undergoing CABG, and to verify whether crystalloid and blood cardioplegia can modify such stimulation.

METHODS

Coronary sinus, peripheral arterial, and venous plasma samples were collected from 50 patients who underwent CABG and were divided into 2 equal groups which received either crystalloid or blood cardioplegia: directly before myocardial ischemia and aortic cross-clamping; at the beginning of reperfusion after aortic clamp release; and 30 minutes after reperfusion. O2 and nitric oxide production by PMN was evaluated by standard methods.

RESULTS

There was a significant (p < 0.05) increase in O2 production by PMN incubated with plasma obtained from the coronary sinus immediately after reperfusion in patients receiving crystalloid cardioplegia compared to blood cardioplegia. No difference was observed in plasma stimulation of nitric oxide production by PMN in the 2 groups of patients at different times during the procedure.

CONCLUSIONS

Cardioplegia may affect release of neutrophil-oriented stimuli from ischemic myocardium and modify neutrophil activation during coronary artery bypass grafting.

Myocyte endothelin exposure during cardioplegic arrest exacerbates contractile dysfunction after reperfusion

Transient left ventricular (LV) dysfunction can occur after cardioplegic arrest. The contributory mechanisms for this phenomenon are not completely understood. We tested the hypothesis that exposure of LV myocytes to endothelin (ET) during simulated cardioplegic arrest would have direct effects on contractile processes with subsequent reperfusion. LV porcine myocytes were randomly assigned to three groups: 1) CONTROL: normothermic (37 degrees C) cell media (n = 204); 2) Cardioplegia: simulated cardioplegic arrest (K(+) 24 mEq/L, 4 degrees C x 2 h) followed by reperfusion and rewarming with cell media (n = 164); and 3) Cardioplegia/ ET: simulated cardioplegic arrest in the presence of ET (200 pM) followed by reperfusion with cell media containing ET (n = 171). Myocyte contractility was measured by computer-assisted video microscopy. In a subset of experiments, myocyte intracellular calcium was determined after Fluo-3 (Molecular Probes, Eugene, OR) loading by digital fluorescence image analysis. Myocyte shortening velocity was reduced after cardioplegic arrest compared with controls (52 +/- 2 vs 84 +/- 3 microm/s, respectively; P < 0.05) and was further reduced with cardioplegic arrest and ET exposure (43 +/- 2 microm/s, P < 0.05). Intracellular calcium was significantly increased in myocytes exposed to cardioplegia compared with normothermic control myocytes and was further augmented by cardioplegia with ET supplementation (P < 0.05). Exposure of the LV myocyte to ET during cardioplegic arrest directly contributed to contractile dysfunction after reperfusion. Moreover, alterations in intracellular calcium may play a role in potentiating the myocyte contractile dysfunction associated with ET exposure during cardioplegic arrest.