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Experimental Research Laboratory, Division of Cardiology, University of Louisville and Jewish Hospital Heart and Lung Institute, Louisville, Kentucky 40292
Although
previous studies suggested that the protection of late preconditioning
(PC) against myocardial stunning is mediated by nitric oxide (NO),
direct evidence that exogenous administration of NO attenuates
myocardial stunning is lacking. Furthermore, although exogenous
NO administration was shown to elicit a late PC phase, it is unknown
whether NO donors also induce an early PC phase. Therefore, conscious
rabbits underwent two experimental stages (3 days of six 4-min
occlusion/4-min reperfusion cycles each) 2 wk apart. In
study
I, both stages were control stages (n = 7). In
studies
II and
III,
stage
I was the control stage. On
day 1 of stage
II, seven rabbits received infusion of
nitroglycerin (NTG; 2 µg · kg
1 · min
1
iv) during the ischemia-reperfusion sequence, starting 30 min before the 1st occlusion and ending 10 min after the 6th reperfusion (study
II). Another seven rabbits received
infusion of NTG (2 µg · kg
1 · min
1
iv) for 1 h followed by a 30-min washout interval and then underwent six 4-min occlusion/4-min reperfusion cycles
(study
III). In the control stage of all
three studies, recovery of wall thickening (WTh) after
occlusion/reperfusion cycles was markedly enhanced on
days
2 and
3 compared with
day
1, indicating late PC. In
study II, infusion of NTG during the
occlusion/reperfusion cycles on day
1 resulted in significant and
sustained enhancement in WTh recovery. A similar attenuation of
stunning was observed in study IV in six rabbits given intravenous
infusion of
S-nitroso-N-acetylpenicillamine (SNAP) during occlusion/reperfusion cycles. The magnitude of the protection afforded by NTG and SNAP was comparable to that afforded by
the late ischemic PC phase. In contrast, in
study
III infusion of NTG before
occlusion/reperfusion cycles did not enhance WTh recovery, indicating
that NTG failed to induce an early PC effect against stunning. This
study demonstrates that administration of hemodynamically inactive
doses of two unrelated NO donors alleviates myocardial stunning in
conscious rabbits, providing direct evidence for a protective action of
NO in this setting.
myocardial ischemia; reperfusion injury; left ventricular function; nitroglycerin
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