Background: Induction of protooncogenes such as c-fos, c-jun, and EGR-1 has been implicated in cellular growth and differentiation. Heat-shock proteins (HSPs) such as hsp 70 may mediate resistance to ischemia after heat shock and ischemic preconditioning. The effects of cardioplegia on the regulation of these immediate early genes are unclear.
Methods: Isolated rat hearts were subjected to different cold (5 degrees C) or normothermic (35 degrees C) cardioplegic solutions and reperfused with normothermic Krebs-Henseleit buffer. Right atrial biopsy specimens from patients undergoing coronary artery bypass grafting with cold cardioplegic arrest were taken before and after cardiopulmonary bypass. Analysis of immediate early gene messenger RNAs was performed using Northern blots. Related proteins were localized by immunohistochemistry.
Results: In rat hearts, cold cardioplegia for 40 minutes with Bretschneider or St. Thomas' II solution followed by 40 minutes' reperfusion resulted in a significant increase in left ventricular c-fos, EGR-1, and c-jun messenger RNA levels (4.0-, 3.1-, and 3.0-fold, respectively, with Bretschneider solution and 3.7-, 2.8-, and 2.1-fold, respectively, with St. Thomas' II solution) compared with control hearts perfused at 35 degrees C with Krebs-Henseleit buffer. Normothermic cardioplegia with St. Thomas' II solution was without effect, whereas sequential perfusion with Krebs-Henseleit buffer at 5 degrees C and 35 degrees C resulted in a similar increase in protooncogene messenger RNA levels. Only cold Bretschneider solution was related to a 5.2-fold induction of hsp 70 messenger RNA levels. Likewise, rat atrial tissues and samples from patients after cardiopulmonary bypass displayed a significant induction of these immediate early genes. Monoclonal antibodies against c-FOS and HSP 70 proteins stained nuclei and perinuclear spaces of endothelial cells and cardiac myocytes.
Conclusions: Cold cardioplegic arrest and normothermic reperfusion are potent triggers for immediate early gene induction. Hypothermia emerged as the prime stimulus for the examined protooncogenes. In contrast, hsp 70 induction was dependent on the cardioplegic solution.