Expression of Cyclooxygenase-1 and Cyclooxygenase-2 Enzymes in Normal Heart and in Myocardial Infarction

Cyclooxygenase (COX) is a key enzyme in prostanoid synthesis which plays an important role in many cell functions. COX exists in two isoforms: COX-1 and COX-2. Our aim was to analyse the expression of both COX isoforms in the normal human heart and in myocardial infarc­tion, with a hypothesis that COX-1 is expressed mostly or exclusively in the normal heart and COX-2 in myocardial infarction. Our study included autopsy samples of heart tissue divid­ed into 2 groups: one consisted of heart tissue samples from 10 healthy persons who died in car accidents, and the other of heart tissue samples from 35 patients with myocardial infarc­tion. Tissue samples were stained with hematoxylline and eosin and immunohistochemistry was used for detection of COX-1 and COX-2. In the normal heart, COX-1 is expressed in blood vessels and endocardium, but not in cardiomyocytes. COX-2 is not expressed in the normal heart or very rarely in occasional myocytes. In contrast, COX-2, but not COX-1 is induced in cardiomyocytes in myocardial infarction. Both isoforms are present in components of gran­ulation tissue and fibrous tissue. COX-1-positivity was intense and almost diffuse, while COX-2 positivity was focal. Our results indicate that COX-1 maintains normal homeostasis in the heart and that inflammatory reaction in myocardial infarction is probably mediated by COX-2. It appears that both COX-1 and COX-2 contribute to the healing processes and scar formation after myocardial infarction.