Endotoxin and ischemic preconditioning: TNF-α concentration and myocardial infarct development in rabbits.

Ischemic preconditioning (IP) and prior exposure to lipopolysaccharides (LPS) reduce infarct size (IS) and serum tumor necrosis factor-α (TNF-α) concentration resulting from myocardial ischemia-reperfusion in rabbits. The decrease in TNF-α might relate to an induced TNF-α inhibitory serum activity (TNF-α-ISA). We analyzed TNF-α and TNF-α-ISA during 30 and 180 min ischemia and reperfusion, respectively, in anesthetized rabbits either untreated ( group 1, n = 7), preconditioned (5 and 10 min ischemia and reperfusion, respectively, group 2, n = 9), or exposed to LPS 72 h before ischemia ( group 3, n = 9). TNF-α-ISA was assessed by coincubating LPS-stimulated rabbit blood with serum of groups 1-3 and measuring TNF-α (WEHI assay). With a comparable area at risk, IS in group 1 was 36.9 ± 11.1 (SD)%, and it was reduced to 13.1 ± 11.6% and 17.3 ± 11.3% (both P < 0.05) in groups 2 and 3, respectively. TNF-α was increased during ischemia-reperfusion in group 1 but remained unchanged in rabbits subjected to IP or LPS. TNF-α-ISA was detected during ischemia-reperfusion in group 2 (29% and 38% of maximum inhibition, respectively) and during baseline, ischemia and reperfusion in group 3 (51%, 46%, 48% of maximum inhibition, respectively) but was absent in group 1. Cardioprotection by IP and LPS is associated with a reduced TNF-α and an induced TNF-α-ISA during ischemia-reperfusion.