Objectives: Cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) enzymes catalyze the initial step in the formation of prostaglandins, which have a role in the regulation of circulation and in inflammatory reactions. As hypoxia is reported to stimulate the expression of COX-2, we have investigated the effects of bypass circulation and cardioplegic arrest on the expression COX-1 and COX-2 in the myocardium of porcine hearts.
Methods: Anaesthetized pigs were connected to cardiopulmonary bypass and the hearts were arrested by cold crystalloid cardioplegia for 30 min and reperfused thereafter for 90 min. Then the mRNA and protein levels of COX-1 and COX-2 were measured from the transmural specimens of the left ventricular myocardium by Northern and Western blot analyses. Reference specimens were from the hearts of unoperated control pigs and from sham-operated pigs, which were connected to cardiopulmonary bypass for 120 min without any aortic clamping.
Results: COX-1 mRNA was expressed in unoperated control porcine hearts, whereas the expression of COX-2 mRNA was weak in control hearts. The expression of COX-2 mRNA increased to 170% of the control level in the hearts of sham-operated pigs and to 180% in arrested hearts, while the level of COX-1 mRNA was not changed. Both COX-1 and COX-2 proteins were detected by Western blot analysis in the myocardial specimens of control hearts. After cardioplegic arrest, the level of COX-2 protein increased to 280% of the control level in arrested hearts, whereas the level of COX-1 protein remained unchanged.
Conclusions: These results indicate that the expression of the COX-2 gene is stimulated in the ventricular myocardium of the porcine heart after bypass circulation and cardioplegic arrest.