Purpose: The aim of the present study was to assess nitric oxide synthase (NOS) activity during a 25 min coronary artery occlusion and following preconditioning (PC) in anaesthetized dogs.
Methods: In three groups of control dogs (n=9), the hearts were removed following a) euthanasia, b) 5 min and c) 25 min occlusion of the left anterior descending coronary artery (LAD). Another four groups (n=12) were preconditioned by two 5 min periods of LAD occlusion interspersed with 5 min reperfusion intervals, and myocardial tissue samples were collected a) at the end of the second period of the PC occlusion, b) just prior to, c) 5 min and d) 25 min of the occlusion of the LAD. NOS enzyme activity (radioimmunoassay), myocardial superoxide production (DHE fluorescence) and plasma nitrate/nitrite (NOx) levels (Griess reaction) were determined.
Results: Compared with the sham operated dogs, occlusion of the LAD increased (at 5 min) and then decreased (at 25 min) NOS activity (3.1±1.2 vs. 7.3±0.9 and 2.7±0.7 pmol citrulline/protein, respectively). A similar biphasic pattern occurred in NOx levels. PC itself enhanced the activity of NOS enzyme and NO bioavailability, and these increases were maintained during a 25 min ischaemia (e.g. NOS activity was 6.7±1.2 and 6.7±0.8 pmol citrulline/protein at 5 and 25 min of the occlusion).
Conclusions: These results suggest that changes in NO availability during ischaemia and following PC are due to the rapid alterations in NOS activity.