LAUSR

Objectives: Remote ischemic preconditioning (RIPC) is a practicable and noninvasive method to protect the heart against ischemia reperfusion injury. Unfortunately results from clinical studies are not convincing. Propofol is suggested to be an inhibiting factor of cardioprotection by RIPC, but the underlying mechanism is still unknown. We investigated whether after RIPC the release of humoral factors and/or the direct cardioprotective effect at the myocardium is inhibited by propofol. Design: Randomized, prospective, blinded laboratory investigation. Setting: Experimental laboratory. Patients/Subjects: Male Wistar rats. Interventions: Repetitive hind limb ischemia in rats—blood plasma transfers to isolated rat heart. Measurements and Main Results: In male Wistar rats (six groups, each n = 6/group), RIPC was induced by four cycles of 5 minutes bilateral hind limb ischemia alternately with 5 minutes of reperfusion. Blood samples were taken with (RIPC) and without RIPC (Con). Rats received continuous anesthesia with pentobarbital (Pento, 40 mg/kg body weight/hr) or propofol (Prop, 12 mg/kg body weight/hr), respectively. Cardioprotective properties of the blood plasma was investigated in the rat heart in vitro (six groups, each n = 6/group) perfused with Krebs-Henseleit buffer alone or with propofol (10 µM). Plasma was administered over 10 minutes before myocardial ischemia. All hearts underwent 33 minutes of global ischemia followed by 1 hour of reperfusion. At the end of the experiments, infarct size was determined by triphenyl-tetrazolium-chloride staining. RIPC plasma from pentobarbital anesthetized rats (Pento-RIPC) reduced infarct size from 64% (62–71%) (Pento-Con) to 34% (30–39%) (p < 0.0001). Infarct size with control plasma from propofol anesthetized rats was 59% (58–64%) (Prop-Con). RIPC plasma could not induce cardioprotection (Prop-RIPC: 63% [56–70%] ns vs Prop-Con). In contrast, RIPC plasma from pentobarbital anesthetized rats induced a significant infarct size reduction under propofol perfusion (Pento-RIPC: 34% [30–42%] vs Pento-Con: 54% [53–63%]; p < 0.0001). Conclusions: Loss of cardioprotection by RIPC during propofol anesthesia depends on inhibition of release of humoral factors.