Nitric oxide as a mediator of delayed pharmacological (A(1) receptor triggered) preconditioning; is eNOS masquerading as iNOS?
BACKGROUND
Nitric oxide (NO), synthesised from the inducible isoform of nitric oxide synthase (iNOS), is implicated in mediating second window of protection (SWOP)/delayed ischemic preconditioning. However the role of NO and iNOS in delayed pharmacological protection remains unclear and is the subject of this investigation.


METHODS
To test the hypothesis that iNOS is necessary for delayed pharmacological preconditioning, the adenosine A(1) receptor agonist, 2-chloro N(6) cyclopentyl adenosine (CCPA) (25 microg/kg i.v.) or saline was administered to wild type (WT) or iNOS gene knockout mice (KO). Twenty-four hours later, the hearts were isolated, Langendorff perfused and subjected to 35 min ischemia/30 min reperfusion prior to infarct size determination.


RESULTS
WT and KO control hearts had identical infarct sizes of 37 +/- 3% and 37 +/- 2%, respectively. CCPA significantly reduced infarct size in WT hearts to 22 +/- 2% and also, unexpectedly, in KO hearts (27 +/- 2%). This protection was abrogated with the non-specific NOS inhibitor, N(omega) nitro L-arginine methyl ester (L-NAME, 100 microM), and could be mimicked in naïve hearts with the NO donor, donor S-nitroso N-acetyl DL penicillamine (SNAP, 1 microM). Delayed protection appeared to be mediated by NO synthesis in both WT and KO hearts. Additional studies using Western blot analysis demonstrated endothelial NOS (eNOS) upregulation and increased NO(x) release in both WT and KO hearts.


CONCLUSIONS
This is the first study to demonstrate a role for eNOS in delayed A(1) receptor triggered (pharmacological) preconditioning, potentially representing a new pharmacological target for protecting the ischemic heart.
Bell
Robert M
RM
The Hatter Institute and Centre for Cardiology (Division of Medicine), University College London Medical School and Hospitals, Grafton Way, London WC1E 6DB, UK. hatter-institute@ucl.ac.uk
Smith
Christopher C T
CC
Yellon
Derek M
DM
D000704:Analysis of Variance; D000818:Animals; D001426:Bacterial Proteins; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D019157:Ischemic Preconditioning, Myocardial; D051379:Mice; D018345:Mice, Knockout; D009206:Myocardium / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D010477:Perfusion; D018047:Receptors, Purinergic P1 / Q000187:drug effects*; D012097:Repressor Proteins / Q000494:pharmacology*
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D018047:Receptors, Purinergic P1; D012097:Repressor Proteins; C069286:catabolite control proteins, bacteria; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse; D019331:NG-Nitroarginine Methyl Ester