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 adeno sine receptor stimulation is involved in the anti-infarct effect of is chaemic preconditioning in the rat heart, and (2) to test the hypothes is 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 r eperfusion. The risk zone was determined by fluorescent particles, and infarct size was determined by staining with triphenyltetrazolium chl oride. Results: Ischaemic preconditioning with three cycles of 5 min i schaemia plus 5 min of reperfusion significantly reduced infarct size as compared to non-preconditioned group [4.5(SEM 0.6)% of the risk zon e v 45.5(5.7)%, P<0.001]. Blockade of a adrenoceptors alone and simult aneous 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 [infarc t size = 2.4(0.4) and 5.6(1.9)% respectively, NS v the non-treated pre conditioned group]. Blocking either the membrane binding of protein ki nase C with polymyxin B (1 mu M) or direct inhibition of protein kinas e C activity with chelerythrine (2 mu M) completely abolished the infa rct size reducing effect of ischaemic preconditioning [32.4(3.3)% and 48.2(4.0)% respectively, P<0.005 v non-treated preconditioned group; N S v the non-preconditioned group]. Conclusions: In the rat heart infar ct model the protective effect of ischaemic preconditioning is not med iated through stimulation of alpha adrenoceptors alone or the combined stimulation of alpha adrenergic and adenosine receptors, and it is de pendent on activation of membrane bound protein kinase C.