Enhanced expression and localization of heme oxygenase-1 during recovery phase of porcine stunned myocardium

Myocardial adaptation to ischemia involves up-regulated expression of a num ber of genes implicated in conferring cytoprotection. We have previously sh own that myocardial ischemia followed by reperfusion leads to a co-ordinate d expression of mRNAs encoding heme oxygenase-1 (HO-1) and ubiquitin in pig s. HO-1 participates in biological reaction leading to the formation of the antioxidant, bilirubin and the putative cellular messenger, carbon monoxid e. In the present study, we examined the expression and cellular localizati on of HO-1 in the heart during myocardial stunning in anesthetized pigs. Af ter thoracotomy, the LAD was occluded for 10 min and reperfused for 30 min (group I, n = 4), again occluded for 10 min and reperfused for 30 min (grou p II, n = 6), 90 min (group III, n = 4), 210 min (group IV, n = 5) and for 390 min (group V, n = 4). Myocardial tissue specimens were collected in 10% formalin as well as in liquid nitrogen and processed for immunohistochemis try and mRNA expression analysis, respectively. In the distribution territo ry of the LAD (experimental, E), systolic wall thickening was significantly decreased (39 +/- 6%) as compared to that of the area perfused by left cir cumflex coronary artery (LCx, control) in group I and remained depressed in all subsequent groups. Northern blot analysis revealed that the expression of a single mRNA species of 1.8 kb encoding HO-1 was significantly induced in E as compared to control in groups II and III with maximum mRNA levels in group II (1.9 +/- 0.4 fold vs. control). Immunoreactive HO-1 was localiz ed in the cytoplasm of cardiomyocytes as well as in the perivascular region s in all groups. Semiquantitative analysis of HO-1 staining showed signific antly enhanced levels of HO-1 in perivascular region in E as compared to re spective controls derived from groups III and IV. These results suggest tha t myocardial adaptive response to ischemia involves up-regulation of HO-1 i n cells of perivascular region indicating that this enzyme may participate in regulating vascular tone via CO and thereby, contributing in pathophysio logically important defense mechanism(s) in the heart.