INTRAMYOCARDIAL INFUSION OF TOOL DRUGS FOR THE STUDY OF MOLECULAR MECHANISMS IN ISCHEMIC PRECONDITIONING

Many of the new tool drugs useful for the study of molecular mechanism s of ischemic preconditioning (IF) are very valuable in in vitro syste ms but produce undesired side-effects after systemic injection in inta ct animals that limit their applicability. Our aim was to develop an e xperimental in vivo model that allows the use of said drugs in suffici ently high local concentrations, but avoiding at the same time the sys temic side-effects. Several techniques were combined to study regional damage or protection as a result of local drug infusion such as nucle ar staining, NADH fluorescence, fluorescent microspheres and tetrazoli um salts. In open-chest pigs, the intramyocardial infusion (20 mu l/mi n) of the adenosine Al-receptor agonist N6-cyclohexyladenosine (0.3 mm ol) for 10 min prior to a 60-min LAD-occlusion and 120-min reperfusion mimicked IP by exerting a local protection (n = 9, p < 0.001). Krebs- Henseleit buffer (negative control) was without protective effect. IP' s cardioprotection was locally prevented by the intramyocardial applic ation of the adenosine Al-receptor antagonist cyclopentyltheophylline (1 mmol, infused during IP; n = 6, p < 0.001) but not by KHB. The prot ein kinase C (PKC)-inhibitors staurosporine (100 nmol, n = 6) or bisin dolylmaleimide (BIS, 25 mu mol, n = 9) did not prevent IP locally. The PKC activator phorbol myristate acetate (PMA, 1 mu mol, n = 6) was in effective in preventing ischemic injury and increased the amount of ne crosis in IF, whereas BIS exerted a local myocardial protection (n = 9 , p < 0.001). In conclusion, the new model of intramyocardial infusion appears to be useful for the investigation of IP's signal transductio n. Our data support the role of the adenosine A(1)-receptor in IF, but suggest that inhibition instead of activation of PKC may protect isch emic myocardium from infarction.