LIMITATION OF MYOCARDIAL INFARCT SIZE BY ADENOSINE A(1) RECEPTOR ACTIVATION IS ABOLISHED BY PROTEIN-KINASE-C INHIBITORS IN THE RABBIT

Objective: The aim was to test whether infarct size limitation by adenosine A(1) receptor activation is mediated by protein kinase C. Method: In the first series of experiments, myocardial infarction was induced in rabbits under pentobarbitone anaesthesia by 30 min coronary artery occlusion and 3 h reperfusion. Rabbits were pretreated with no drugs (control), 1 mg.kg(-1) of R(-)N6-2-phenylisopropyl adenosine (PIA), 50 mu g . kg(-1) of staurosporine (Stauro), 2.5 mg . kg(-1) of polymyxin B (PolyB), and a combination of PIA and either Stauro or PolyB. Infarct size and the area at risk were determined by tetrazolium staining and fluorescent particles, respectively. In the second series of experiments, the inotropic response to 4 beta-phorbol 12-myristate 13-acetate (PMA) was assessed in rabbits with and without pretreatment using the same doses of Stauro and PolyB as those in the first series of experiments. Results: Infarct size expressed as percent of area at risk (%IS/AR) was significantly smaller in the PIA treated group than in the control: %IS/AR=19.0(SEM 2.4)% v 37.7(4.0)%, P<0.05. However, %IS/AR in the groups given Stauro [35.0(4.2)%], PolyB [37.9(3.2)%], PIA plus Stauro [34.9(3.9)%], and PIA plus PolyB [36.3(3.3)%] did not differ from the control value. PIMA at the dose of 0.02 and 0.05 mu g . kg(-1) caused a dose dependent increase of the left ventricular dP/dt(max) in the untreated rabbits. Such a positive inotropic response to PMA was not detected in rabbits pretreated with Stauro or PolyB, suggesting that the doses of the protein kinase C inhibitors were appropriate to block protein kinase C in the heart. Conclusions: Infarct size limitation by A(1) receptor stimulation is mediated by activation of protein kinase C in pentobarbitone anaesthetised rabbits.