J Mol Cell Cardiol 32, 1159–1167 (2000) doi:10.1006/jmcc.2000.1152, available online at http://www.idealibrary.com on Exogenous Nitric Oxide Can Trigger a Preconditioned State Through a Free Radical Mechanism, But Endogenous Nitric Oxide Is Not a Trigger of Classical Ischemic Preconditioning Atsushi Nakano 1 , Guang S. Liu 1 , Gerd Heusch 1,3 , James M. Downey 1 and Michael V. Cohen 1,2 1 Departments of Physiology and 2 Medicine, University of South Alabama, Mobile, AL, USA and 3 Department of Pathophysiology, University of Essen Medical School, Essen, Germany (Received 8 February 2000, accepted in revised form 31 March 2000) A. N, G. S. L, G. H, J. M. D M. V. C. Exogenous Nitric Oxide Can Trigger a Preconditioned State Through a Free Radical Mechanism, But Endogenous Nitric Oxide Is Not a Trigger of Classical Ischemic Preconditioning. Journal of Molecular and Cellular Cardiology (2000) 32, 1159–1167. Nitric oxide (NO) has been reported to play an important role in the late phase of ischemic preconditioning (PC) in the rabbit heart. However, the role of NO in the early phase of ischemic PC (‘‘classical PC’’) is controversial. Accordingly, the present study was designed to determine whether NO contributes to the cardioprotective effect of classical PC in rabbits. Isolated hearts experienced 30 min of regional ischemia followed by 120 min of reperfusion. Infarct size was measured with triphenyltetrazolium chloride. In control hearts infarction was 30.2±3.3% of the risk zone. PC with 5 min of global ischemia and 10 min of reperfusion reduced infarct size to 10.2±2.4% (P<0.05). Perfusion with 2 S-nitroso-N- acetylpenicillamine (SNAP), a NO donor, in lieu of ischemia mimicked PC (4.4±1.9% infarction, P<0.01 v control). To determine whether this protection was dependent on either protein kinase C (PKC) as has previously been demonstrated for classical PC or free radicals known to be produced during exogenous NO administration, ch- elerythrine (5 ), a PKC inhibitor, or N-(2-mercaptopropionyl)-glycine (300 ), a free radical scavenger, was administered with or shortly after SNAP. Neither drug had any independent effect on infarct size, and each blocked SNAP’s cardioprotection (31.0±5.1 and 25.7±5.2% infarction, resp.). N -nitro--arginine methyl ester (-NAME, 100 ), a NO synthase inhibitor, failed to block the cardioprotection from the above ischemic PC protocol (9.5±2.8% infarction, P<0.05 v control). -NAME alone had no effect on infarct size (30.6±2.7%). These results suggest that the beneficial effect of exogenous NO production during SNAP pretreatment is mediated by a protein kinase C- dependent pathway via MPG-sensitive oxidants. However, we were unable to show any contribution of endogenous NO to classical PC’s protection in isolated rabbit hearts. 2000 Academic Press K W: Free radicals; Ischemic preconditioning; -NAME; MPG; Nitric oxide; SNAP. Cells contain low basal levels of NO, but exposure to Introduction several vasoactive substances including bradykinin, acetylcholine, and serotonin results in marked ac- Nitric oxide (NO) is a physiologic autacoid formed in cells during the conversion of -arginine to - celeration of NO production. NO has multiple physiologic actions. 1 It maintains vascular and thus citrulline by NADPH-dependent NO synthase (NOS). Please address all correspondence to: Michael V. Cohen, MD, Department of Physiology, MSB 3024, University of South Alabama, College of Medicine, Mobile, AL 36688, USA. 0022–2828/00/071159+09 $35.00/0 2000 Academic Press