DOES CARDIOPULMONARY BYPASS ALONE ELICIT MYOPROTECTIVE PRECONDITIONING

Background Brief episodes of ischemia can precondition myocardium. Isc hemic preconditioning (PC) has been proposed as an adjuvant method of improving myocardial protection during cardiac surgery. It is unknown whether CPB without an episode of ischemia generates the PC response. Methods and Results To prove that PC occurs in sheep, groups 1 (non-CP B control) and 2 (non-CPB ischemic PC, three 5-minute episodes of norm othermic regional. ischemia) were studied. Groups 3 (CPB alone), 4 (CP B-alpha receptor blockade, phentolamine 5 mg/kg), and 5 (CPB-adenosine receptor blockade, 8-sulfophenyltheophylline 5 mg/kg) were placed on CPB for 30 minutes and subsequently weaned. All groups underwent 60 mi nutes of normothermic regional ischemia and 150 minutes of reperfusion . The area at risk (AR) was delineated by Monastryl blue pigment, wher eas the infarct size (IS) was determined by tetrazolium staining. Body mass, left ventricular mass, and AR were not different between groups . Ischemic PC was demonstrated in this ovine model by a 54% reduction of IS relative to AR (group 1 versus group 2, P<.01). CPB alone produc ed a similar percentage IS reduction without ischemia (group 3 versus group 1, P<.01) that was prevented by either alpha-adrenergic receptor (group 4 versus group 3, P<.01) dr adenosine receptor (group 5 versus group 3, P<.01) blockade. Conclusions CPB alone appears sufficient to elicit the PC response important for myocardial protection during car diac surgery. These data suggest that myocardial ol-adrenergic recepto r and adenosine receptor stimulation are involved in initiating CPB-in duced PC.