To characterize the regulation of the myocardial bradykinin B2 receptor after induction of myocardial infarction (MI), we studied its expression at different time points in the left ventricle (LV), right ventricle (RV) and interventricular septum (S) of the heart.
Male Sprague-Dawley rats were submitted to permanent occlusion of the left descending coronary artery. Six hours, 24 h or 6 days after MI induction or a sham operation, a Millar-tip catheter was placed in the LV. Left ventricular pressure (LVP) and contractility [(dP/dt)max] were measured. The LV, RV and S of all animals were isolated, and total RNA was extracted. B2-receptor expression was analysed by an RNase-protection assay. In addition, Western blot analysis was used to determine protein levels of the B2 receptor in the infarcted area of the LV.
We observed a decrease in LVP and contractility at all time points after MI in comparison with sham-operated animals. Basal B2-receptor expression was detected in the LV and RV, but not in the S of sham-operated rats. In the LV of infarcted hearts, we found a time-dependent up-regulation of the B2-receptor expression, which was increased twofold and fivefold, respectively, 6 h and 24 h after induction of MI compared with controls. This increase was maintained for at least 6 days. Similarly, we also found an up-regulation of the B2-receptor expression in the RV and S. Both reached a peak 24 h after induction of MI. The protein level of the receptor gradually increased up to day 6.
We conclude that myocardial ischaemia triggers B2-receptor up-regulation in both the infarcted and non-infarcted areas of the heart.