Sevoflurane postconditioning improves the spatial learning and memory impairments induced by hemorrhagic shock and resuscitation through suppressing IRE1α-caspase-12-mediated endoplasmic reticulum stress pathway

Severe hemorrhagic shock induces cognitive dysfunction by promoting cell death mediated by activating endoplasmic reticulum (ER) stress. Sevoflurane postconditioning prevents neuronal apoptosis against cerebral ischemia/reperfusion injury. It is unknown if this protective effect on hemorrhagic shock and resuscitation rats (HSR) is associated with ER stress attenuation. Male adult Sprague-Dawley rats were subjected HSR by removing 40% blood volume within 30 min, and 60 min later the animals were resuscitated with infusion of the removing blood in 30 min. Sevoflurane postconditioning was performed by inhaling sevoflurane at three different concentrations (0.5, 1.0, 1.5 MAC) at the onset of resuscitation for 30 min. Severe hypotension (mean arterial pressure 40-45 mmHg) occurred in the shock session for 60 min accompanying with significantly elevated lactate, decreased BE and pH values in arterial blood gas analysis. There were impaired spatial learning and memory following HSR indicated by persistently longer escape latency and lower correct rate, as well as less duration and crossing in the target quadrant by using Morris water maze and Y-maze tests. In the hippocampal CA1 region, there was significantly higher activity of caspase-3 induced by HSR. HSR also elevated the expression of inositol-requiring enzyme 1α (IRE1α) and caspase-12 in the hippocampus by western blot analysis. Sevoflurane postconditioning at 1.0 and 1.5 MAC significantly reversed these changes. These findings suggested that sevoflurane postconditioning could improve spatial learning and memory deficits induced by severe hemorrhagic shock and subsequent resuscitation. The suppression of endoplasmic reticulum stress provided critical contribution in neural apoptosis mediated by IRE1α-caspase-12 pathway.