Brief preconditioning ischemia alters diacylglycerol content and composition in rabbit heart

In order to give further insight into the potential role of PKC in the bene ficial effects of ischemic preconditioning, we have characterized the produ ction of diacylglycerol, the endogenous activator of PKC, and its molecular species composition in ischemic control and preconditioned hearts. Precond itioning was induced by 1 cycle of 5 min of ischemia followed by 5 min of r eperfusion. In control and preconditioned groups, hearts were harvested und er deep anesthesia at baseline (preischemia) and at 2, 5 and 10 min into th e sustained coronary artery occlusion, i.e., preceding myocyte death. Diacy lglycerol content and fatty acid composition were analyzed by thin-layer ch romatography (TLC) and high-performance liquid chromatography (HPLC), respe ctively. Myocardial diacylglycerol content was increased at 2 min into the sustained ischemia in the control group (481 +/- 34 vs 292 +/- 64 ng.mg(-1) at baseline; p < 0.05),but was comparable to the baseline value at 5 and 1 0 min. In the preconditioned group, diacylglycerol production remained unch anged throughout the 10-min test ischemia (317 +/- 17 at 2 min vs 312 +/- 3 8 ng.mg(-1) at baseline; p = NS). A detailed analysis of the molecular spec ies composition at the time of 2 min revealed a reduced contribution of pho sphatidylinositol to diacylglycerol production in preconditioned myocardium (global correlation coefficient 0.57 vs 0.66 in control myocardium) with a trend toward an enrichment of diacylgrycerol composition with some species originating from phosphatidylcholine. Thus, our study revealed that brief preconditioning ischemia: (1) prevents the increase of diacylglycerol conte nt in the early minutes of the sustained ischemia, and (2) emphasizes the c ontribution of phosphatidylcholine in diacylglycerol formation to the detri ment of that of phosphatidylinositol.