ERK and p38 MAP kinase activation are components of opioid-induced delayed cardioprotection

Opioids have been previously shown to confer acute and delayed cardioprotection against a prolonged ischemic insult. We have extensively characterized the signal transduction pathway mediating acute cardioprotection and have suggested a role for extracellular signal regulated kinase (ERK) in this cardioprotection. Therefore, we attempted to determine a role for ERK and the stress activated MAP kinase, p38, in opioid-induced delayed cardioprotection by using selective inhibitors of these pathways. All rats were subjected to 30 min of ischemia and 2 h of reperfusion (I/R). Control animals, injected with saline 48 h prior to I/R, had an infarct size/area at risk (IS/AAR) of 61.6 ± 1.6. 48-h pretreatment with TAN-67 (30 mg/kg), a δ₁-opioid receptor agonist, maximally reduced IS/AAR (31.2 ± 6.5). The involvement of ERK was examined with PD 098059, a selective pharmacological antagonist which inhibits the upstream kinase, MEK-1, that phosphorylates and activates ERK. PD 098059 (0.3 mg/kg) did not alter IS/AAR when administered alone (60.7 ± 4.9). However, PD 098059 (0.3 mg/kg) administration 30 min prior to TAN-67 (30 mg/kg) completely abolished cardioprotection (61.0 ± 7.6). The selective p38 inhibitor, SB 203580 (1.0 mg/kg), had no effect on IS/AAR in the absence of TAN-67 (53.1 ± 2.3). Additionally, SB 203580 (1.0 mg/kg) when administered prior to TAN-67 (30 mg/kg) partially abolished cardioprotection (51.3 ± 6.4). These results suggest that both ERK and p38 are integral components of opioid-induced delayed cardioprotection and may act via parallel pathways. Received: 21 August 2000, Returned for revision: 13 September 2000, Revision received: 18 September 2000, Accepted: 20 September 2000