Alpha(1)-adrenergic receptor-mediated increase in the mass of phosphatidicacid and 1,2-diacylglycerol in ischemic rat heart

1,2-Diacylglycerol (1,2-DAG) and phosphatidic acid (PA) are produced by pho spholipase C and D activity and play a key role as second messengers in rec eptor-mediated signal transduction. So far, Little is known about alteratio ns of endogenous 1,2-DAG and PA production during myocardial ischemia. Meth ods: Rat isolated perfused hearts were subjected to global ischemia, total lipids were extracted, and separated by thin-layer chromatography. The mass of PA and 1,2-DAG were quantified using laserdensitometric analysis of vis ualized lipids. Results: Compared to normoxic control values (1,2- DAG 713/-45 ng/mg protein, PA 171+/-11 ng/mg protein), the myocardial content of I ,2-DAG and PA was unaltered after 10 min of ischemia. Prolonged myocardial ischemia (20 min), however, which was accompanied by marked overflow of end ogenous norepinephrine, significantly increased the mass of both second mes sengers (1,2-DAG 1062+/-100 ng/mg protein, PA 340+/-29 ng/mg protein). The increase in PA and 1,2-DAG in response to ischemia was abolished by inhibit ion of ischemia-induced norepinephrine release as well as by alpha(1)-adren ergic blockade but unaffected by beta-adrenergic blockade. While inhibition of diacylglycerol kinase did not affect ischemia-induced increase in PA an d 1,2-DAG, inhibition of phosphatidylinositol-specific phospholipase C acti vity significantly suppressed ischemia-induced increase in 2,2-DAG but did not affect endogenous production of PA indicating phospholipase C-independe nt formation of PA and activation of both, phospholipase C and D, in the is chemic heart. Conclusions: Ischemia elicits an alpha(1)-adrenergic receptor -mediated increase in the mass of myocardial PA and 1,1-DAG. The increase i n endogenous PA is suggested to be due to the activation of myocardial phos pholipase D, whereas 1,2-DAG is formed predominantly by activation of phosp holipase C in the ischemic heart. (C) 1999 Elsevier Science B.V. All rights reserved.