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 microg/kg) or
LY294002 (0.3 mg/kg) or the TOR inhibitor
rapamycin (3 microg/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 Ser9 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 GSKalpha (Ser21 or Tyr279) or phosphorylation of GSKbeta (Tyr216). These data indicate that OIC occurs via the phosphorylation of GSKbeta at Ser9 during reperfusion.