Microdialysis-based analysis of interstitial NO in situ: NO synthase-independent NO formation during myocardial ischemia.
OBJECTIVE
Nitric oxide (NO) synthesis by NO synthases (NOS) requires oxygen. However, although counterintuitive, NO synthesis is increased in ischemic myocardium. Accordingly, mechanisms independent of the NOS pathway have been suggested to contribute to NO synthesis during ischemia. NO initiates detrimental as well as protective mechanisms in a concentration-dependent manner, thus aggravating or improving the outcome of ischemia. The aim of this study was to measure in situ interstitial NO concentrations in parallel to infarct size in anaesthetized pigs subjected to myocardial ischemia/reperfusion. The contribution of NOS-independent pathways to NO synthesis was studied using NOS blockade.


METHODS
Interstitial NO measurements, based on microdialysis combined with the oxyhemoglobin method, were made during 90 min of moderate or severe ischemia and subsequent reperfusion. To examine the effect of NOS inhibition, an initial 30-min ischemic period was followed 60 min later by a second 30-min ischemic period with intracoronary infusion of S-ethyl-isothiourea.


RESULTS
During ischemia, the interstitial NO concentration increased for about 30 min and then remained constant at this elevated level. The increase in NO concentration by 253+/-82 nmol/L during moderate and 565+/-169 nmol/L during severe ischemia correlated inversely with subendocardial blood flow (r=-0.76). NOS inhibition increased coronary arterial pressure and decreased the interstitial basal NO concentration and tissue nitrite content. However, it did not diminish the increase in interstitial NO concentration during ischemia.


CONCLUSIONS
NOS-independent pathways are significantly involved in NO synthesis during myocardial ischemia.
Martin
Claus
C
Institut für Pathophysiologie, Zentrum für Innere Medizin des Universitätsklinikums, Essen, Germany.
Schulz
Rainer
R
Post
Heiner
H
Boengler
Kerstin
K
Kelm
Malte
M
Kleinbongard
Petra
P
Gres
Petra
P
Skyschally
Andreas
A
Konietzka
Ina
I
Heusch
Gerd
G
D000818:Animals; D015415:Biomarkers / Q000032:analysis; D045604:Extracellular Fluid / Q000737:chemistry*; D007550:Isothiuronium / Q000031:analogs & derivatives / Q000494:pharmacology; D017551:Microdialysis; D018613:Microscopy, Confocal; D008929:Mitochondria, Heart / Q000201:enzymology; D023421:Models, Animal; D017202:Myocardial Ischemia / Q000378:metabolism*; D015425:Myocardial Reperfusion; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009569:Nitric Oxide / Q000032:analysis*; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010108:Oxyhemoglobins / Q000032:analysis; D013194:Staining and Labeling; D013552:Swine; D013556:Swine, Miniature
D015415:Biomarkers; D010108:Oxyhemoglobins; D007550:Isothiuronium; C007687:etiron; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase