Activation of nitric oxide synthase by ischaemia in the perfused heart.
OBJECTIVE
Recent data have indicated that the activity of nitric oxide synthase (NO synthase), the enzyme producing NO from L-arginine, could be modified by ischaemia. The aim of the present work was therefore to study whether ischaemia activated NO synthase.


METHODS
NO synthase activity was measured by the conversion of radioactive arginine into citrulline in extracts of isolated perfused rabbit hearts submitted to low-flow ischaemia and reperfusion.


RESULTS
When measured in heart homogenates, NO synthase activity was significantly increased during ischaemia. This activation was already detectable after 5 min of ischaemia and was maintained during the whole ischaemic period. After cell fractionation, NO synthase was recovered in cytosolic and membrane fractions. The increase in NO synthase activity by ischaemia was related to an activation of the cytosolic activity, while the membrane-bound NO synthase activity remained constant.


CONCLUSIONS
NO synthase activity in the heart is rapidly stimulated by ischaemia and this stimulation is maintained during the whole ischaemic episode. This activation is found only in the cytosolic fraction, whereas the particulate activity is not affected by ischaemia.
Depré
C
C
Hormone and Metabolic Research Unit, University of Louvain Medical School, Brussels, Belgium.
Fiérain
L
L
Hue
L
L
D000818:Animals; D001120:Arginine / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002956:Citrulline / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000032:analysis / Q000378:metabolism*; D008297:Male; D017202:Myocardial Ischemia / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000378:metabolism*; D010477:Perfusion; D011817:Rabbits
D007527:Isoenzymes; D002956:Citrulline; D001120:Arginine; D019001:Nitric Oxide Synthase