The protection of ischaemic preconditioning can be reinstated in the rabbit heart after the initial protection has waned.
OBJECTIVE
Preconditioning the heart with 5 min of ischaemia followed by reperfusion renders the myocardium resistant to infarction from subsequent ischaemia. This protection lasts for about 1 h. The aim of this study was to test whether the protection could be reinstated with a second episode of preconditioning after protection from an initial episode had worn off.


METHODS
To induce infarction animals experienced 30 min of coronary artery occlusion and then 3 h reperfusion. Ischaemic preconditioning was accomplished with 5 min of coronary branch occlusion. In one group of rabbits the subsequent reperfusion period was prolonged to 2 h to permit protection to wear off before the 30 min coronary occlusion was initiated. In another group a second 5 min coronary occlusion was performed at the end of the 2 h reperfusion. After 10 min of reperfusion the 30 min ischaemic period began. Control animals experienced only the 30 min ischaemia and 3 h reperfusion. Infarct volume was measured with tetrazolium and expressed as a percentage of the ischaemic zone volume.


RESULTS
Average infarct size in seven control rabbits [36.0 (SEM 2.0)% of the ischaemic zone] was not significantly different from that in eight rabbits with the prolonged coronary occlusion occurring 2 h after the preconditioning stimulus [28.6 (2.9)% infarction]. In contrast infarcts were significantly smaller in the re-preconditioned group of seven rabbits [8.3 (4.2)%] and comparable to those previously seen with a single preconditioning stimulus followed 10 min later by the 30 min occlusion [6.1 (1.8)%].


CONCLUSIONS
The rabbit heart can be protected with a second preconditioning stimulus after protection from an initial period of preconditioning has subsided.
Yang
X M
XM
University of South Alabama, College of Medicine, Mobile 36688.
Arnoult
S
S
Tsuchida
A
A
Cope
D
D
Thornton
J D
JD
Daly
J F
JF
Cohen
M V
MV
Downey
J M
JM
D000818:Animals; D005260:Female; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology / Q000517:prevention & control*; D017202:Myocardial Ischemia / Q000473:pathology; D015425:Myocardial Reperfusion / Q000379:methods*; D009206:Myocardium / Q000473:pathology; D011817:Rabbits; D013997:Time Factors