Opioid-induced cardioprotection occurs via glycogen synthase kinase β inhibition during reperfusion in intact rat hearts

Glycogen synthase kinase (GSK) inhibition produced by ischemic preconditioning has been previously shown to be regulated through phosphatidylinositol-3 kinase (PI3K). Therefore, we determined whether opioid-induced cardioprotection (OIC) occurs during reperfusion by altering GSK phosphorylation through PI3K and target of rapamycin ( TOR). Furthermore, we determined if selective GSK inhibitors, SB216763(SB21) or SB415286(SB41), emulate OIC. Rats were treated with the nonselective opioid agonist, morphine (MOR, 0.3 mg/kg), the delta-selective opioid agonist BW373U86 (BW, 1 mg/kg), or the GSK inhibitors, SB21 (0.6 mg/kg) or SB41(1.0 mg/kg), either 10 minutes before ischemia or 5 minutes before reperfusion. Five minutes before opioid or SB21 treatment, some rats received either the PI3K inhibitor wortmannin (15 mug/kg) or LY294002 (0.3 mg/kg) or the TOR inhibitor rapamycin (3 mug/kg). After 30 minutes of ischemia followed by 2 hours of reperfusion, infarct size was assessed. MOR, BW, SB41, and SB21 reduced infarct size compared with vehicle when administered before ischemia (42.9 +/- 2.6, 40.3 +/- 2.3, 46.6 +/- 1.6, 42.2 +/- 1.8 versus 60.0 +/- 1.1%, respectively; P < 0.001) and showed similar protection when administered 5 minutes before reperfusion (43.6 ± 2.3, 40.2 ± 2.6, 44.8 ± 2.8, 39.4 ± 0.8%, respectively; P < 0.001). Wortmannin, LY294002, and rapamycin were found to inhibit OIC; however, they did not abrogate SB21-induced infarct size reduction. At 5 minutes of reperfusion, both MOR and BW increased P-GSKbeta at Ser(9) in the ischemic zone compared with vehicle (181 +/- 20, 178 +/- 15 versus 75 +/- 17 DU, respectively; P < 0.05), and this effect was abrogated by prior administration of wortmannin or rapamycin in MOR-treated rats. Furthermore, no differences were seen in phosphorylation of GSKα (Ser(21) or Tyr(279)) or phosphorylation of GSKβ (Tyr(216)). These data indicate that OIC occurs via the phosphorylation of GSKβ at Ser(9) during reperfusion.