| Isoflurane Inhibits Neutrophil - Endothelium Interactions in the Coronary CirculationObjective: Isoflurane protects myocardium during ischemia - reperfusion via a mechanism involving the adenosine triphosphate - sensitive potassium ( KATP) channels. This study tested the hypothesis that an inhibition of the neutrophil - endothelium interactions by isoflurane contributes to this effect.Methods: Polymorphonuclear neutrophils and coronary artery segments were obtained from 35 healthy dogs. Neutrophils were isolated from this blood u-sing standard methods. Superoxide production by neutrophils, stimulated with platelet activating factor ( PAF) was spectrophotometrically determined by measuring the superoxide dismutase (SOD) inhibitable reduction of ferricytochrome c to ferrocytochrome c. Adherence of PAF - activated neutrophils to the endothelium of coronary segments was assessed by direct counting of neutrophils labeled with fluorescent dye under epifluorescent microscopy. Coronary artery rings were exposed to PAF - activated neutrophils, and following washing and preconstric-tion, and endothelial function was evaluated by vasorelaxation responses to ace-tylcholine ( ACh, endothelium - dependent) and sodium nitroprusside ( SNP, endothelium - independent) . Concentration - responses for vascular relaxation, EC50 and maximum relaxant response was determined. Measurements were done in absence and presence of isoflurane (1 and 2 minimum alveolar concentration, MAC) both with and without glibenclamide (10 uM).Results: PAF alone caused a nine - fold increase in superoxide production, which was diminished in a concentration - dependent fashion by isoflurane. Glibenclamide did not alter the isoflurane - induced decreases in superoxide production. PAF caused a pronounced increase in the number of neutrophils adhering to the endothelial surface of the coronary rings, and that this effect wasprevented by both 1.0 and 2.0 MAC isoflurane. Glibenclamide did not alter the isoflurane - induced inhibition of neutrophil adherence. ACh caused concentration - dependent relaxation responses in the control coronary rings. Pre - incubation and subsequent washout of unactivated neutrophils had no effect on these responses. Activating the neutrophils with PAF reduced the relaxation responses of the coronary rings to ACh, which caused a rightward shift in the concentration- response curve, and it reduced the maximum response. The EC50 for ACh responses in rings exposed to PAF - activated neutrophils was greater than that for control rings. Combining the PAF - activated neutrophils with isoflurane reversed the impairment to ACh - induced coronary relaxation caused by the PAF- activated neutrophils alone, and it returned EC50 and the maximal response to control values. The findings for 1.0 and 2.0 MAC isoflurane were similar. Glibenclamide did not alter the ability of isoflurane to inhibit the neutrophil - mediated decreases in ACh responses. The concentration - related vascular relaxation responses to SNP were not affected by neutrophils (with or without PAF) either in the absence or presence of isoflurane. Prior exposure to isoflurane alone did not alter the concentration - related relaxation responses to either ACh or SNP. Pinacidil caused decreases in superoxide production and adherence by neutrophils , and it prevented the neutrophil - induced rightward shift in the concentration - response curve to ACh. Responses to SNP were unaffected. Glibenclamide reversed the effects of pinacidal. Glibenclamide alone had no effect on the ability of PAF to enhance superoxide production by neutrophils and neutrophil adherence to the vascular endothelium, or to cause vascular endothelial dysfunction.Conclusion: Isoflurane had an inhibitory action on neutrophil - endothelium interactions and neutrophil - mediated coronary endothelial dysfunction, effects that may be involved in its cardioprotective action in vivo. These inhibitory actions of isoflurane were not mediated by KATPchannels.
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