Role of Erk1/2, p70s6K, and eNOS in isoflurane-induced cardioprotection during early reperfusion in vivo

Purpose: Administration of isoflurane during early reperfusion after prolonged coronary artery occlusion decreases myocardial infarct size by activating phosphatidylinositol-3-kinase (PI3K) signal transduction. The extracellular signal-related kinases (Erk1/2) represent a redundant mechanism by which signaling elements downstream from PI3K, including 70-kDA ribosomal protein s6 kinase (p70s6K) and endothelial nitric oxide synthase (eNOS), may be activated to reduce reperfusion injury. We tested the hypothesis Erk1/2, p70s6K, and eNOS mediate isoflurane-induced postconditioning in rabbit myocardium in vivo. Methods: Barbiturate-anesthetized rabbits (n = 78) instrumented for measurement of systemic hemodynamics were subjected to a 30-min coronary occlusion followed by three hours reperfusion. Rabbits were randomly assigned to receive 0.9% saline (control), the Erk1/2 inhibitor PD 098059 (2 mg.kg(-1)), the p70s6K inhibitor rapamycin (0.25 mg.kg(-1)), the nonselective nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyll ester (L-NAME; 10 mg.kg(-1)), the selective inducible NOS antagonist aminoguanidine hydrochloride (AG, 300 mg.kg(-1)), or the selective neuronal NOS inhibitor 7-nitroindazole (7-NI, 50 mg.kg(-1)) in the presence or absence of 1.0 minimum alveolar concentration isoflurane administered for three minutes before and two minutes after reperfusion. Results: Brief exposure to 1.0 minimum alveolar concentration isoflurane reduced (P < 0.05) infarct size (21 +/- 4% [mean SD] of left ventricle area at risk, respectively; triphenyltetrazolium staining) as compared to control (41 +/- 5%). PD 098059, rapamycin, and L-NAME, but not AG nor 7-NI, abolished the protection produced by isoflurane. Conclusion: The results suggest that the protective effects of isoflurane against infarction during early reperfusion are mediated by Erk1/2, p70s6K, and eNOS in vivo.