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 beneficial effects of ischemic preconditioning, we have characterized the production of diacylglycerol, the endogenous activator of PKC, and its molecular species composition in ischemic control and preconditioned hearts. Preconditioning was induced by 1 cycle of 5 min of ischemia followed by 5 min of reperfusion. In control and preconditioned groups, hearts were harvested under deep anesthesia at baseline (preischemia) and at 2, 5 and 10 min into the sustained coronary artery occlusion, i.e., preceding myocyte death. Diacylglycerol content and fatty acid composition were analyzed by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC), respectively. Myocardial diacylglycerol content was increased at 2 min into the sustained ischemia in the control group (481 +/- 34 vs 292 +/- 64 ng x mg(-1) at baseline; p < 0.05), but was comparable to the baseline value at 5 and 10 min. In the preconditioned group, diacylglycerol production remained unchanged throughout the 10-min test ischemia (317 +/- 17 at 2 min vs 312 +/- 38 ng x mg(-1) at baseline; p = NS). A detailed analysis of the molecular species composition at the time of 2 min revealed a reduced contribution of phosphatidylinositol to diacylglycerol production in preconditioned myocardium (global correlation coefficient 0.57 vs 0.66 in control myocardium) with a trend toward an enrichment of diacylglycerol composition with some species originating from phosphatidylcholine. Thus, our study revealed that brief preconditioning ischemia: (1) prevents the increase of diacylglycerol content in the early minutes of the sustained ischemia, and (2) emphasizes the contribution of phosphatidylcholine in diacylglycerol formation to the detriment of that of phosphatidylinositol.