ISCHEMIC PRECONDITIONING IS PROTEIN-KINASE-C DEPENDENT BUT NOT THROUGH STIMULATION OF ALPHA-ADRENERGIC OR ADENOSINE RECEPTORS IN THE ISOLATED RAT-HEART

Objective: The aim was (1) to clarify whether a adrenoceptor and adenosine receptor stimulation is involved in the anti-infarct effect of ischaemic preconditioning in the rat heart, and (2) to test the hypothesis that signal transduction through membrane bound protein kinase C is essential for the protection. Methods: Isolated, buffer perfused rat hearts were subjected to 30 min of regional ischaemia and 120 min of reperfusion. The risk zone was determined by fluorescent particles, and infarct size was determined by staining with triphenyltetrazolium chloride. Results: Ischaemic preconditioning with three cycles of 5 min ischaemia plus 5 min of reperfusion significantly reduced infarct size as compared to non-preconditioned group [4.5(SEM 0.6)% of the risk zone v 45.5(5.7)%, P<0.001]. Blockade of a adrenoceptors alone and simultaneous blockade of alpha adrenoceptors with phenoxybenzamine (10 mu M) and adenosine receptors with sulphophenyltheophylline (100 mu M) did not prevent the protective effect of ischaemic preconditioning [infarct size = 2.4(0.4) and 5.6(1.9)% respectively, NS v the non-treated preconditioned group]. Blocking either the membrane binding of protein kinase C with polymyxin B (1 mu M) or direct inhibition of protein kinase C activity with chelerythrine (2 mu M) completely abolished the infarct size reducing effect of ischaemic preconditioning [32.4(3.3)% and 48.2(4.0)% respectively, P<0.005 v non-treated preconditioned group; NS v the non-preconditioned group]. Conclusions: In the rat heart infarct model the protective effect of ischaemic preconditioning is not mediated through stimulation of alpha adrenoceptors alone or the combined stimulation of alpha adrenergic and adenosine receptors, and it is dependent on activation of membrane bound protein kinase C.