Effect of hypervolaemic haemodilution on cerebral glutamate, glycerol, lactate and free radicals in heatstroke rats

In the present study, we attempted to assess the mechanisms underlying the neuroprotective effect of hypervolaemic haemodilution in rat heatstroke. In anaesthetized rats treated with normal saline (NS) immediately after the onset of heatstroke induced by T_a (ambient temperature) of 42 °C for 88 min, followed by T_a of 24 °C for 12 min, the values for MAP (mean arterial pressure), ICP (intracranial pressure), CPP (cerebral perfusion pressure), CBF (cerebral blood blow), brain PO₂ (partial pressure of O₂) and striatal glutamate, glycerol, lactate/pyruvate ratio, hydroxyl radicals and neuronal damage score were 42±3 mmHg, 33±3 mmHg, 9±3 mmHg, 109±20 BPU (blood perfusion units), 6±1 mmHg, 51±7 µmol/l, 24±3 µmol/l, 124±32, 694±22% of baseline and 2.25±0.05 respectively. In animals treated with 10% albumin immediately after the onset of heatstroke (T_a of 42 °C for 88 min), the values for MAP, ICP, CPP, CBF, brain PO₂ and striatal glutamate, glycerol, lactate/pyruvate ratio, hydroxyl radicals and neuronal damage score were 64±6 mmHg, 10±2 mmHg, 54±5 mmHg, 452±75 BPU, 15±2 mmHg, 3±2 µmol/l, 4±2 µmol/l, 7±3, 119±7% of baseline and 0.38±0.05 respectively. Apparently, the heatstroke-induced arterial hypotension, intracranial hypertension, cerebral hypoperfusion, cerebral ischaemia, brain hypoxia, increased levels of striatal glutamate, glycerol, lactate/pyruvate ratio and hydroxyl radicals, and increased striatal neuronal damage score values were all attenuated significantly by the induction of hypervolaemic haemodilution in rats immediately at the onset of heatstroke. These results demonstrate that the neuroprotective effect of hypervolaemic haemodilution is associated with a decrease in the elevation of glutamate, glycerol, lactate and free radicals in brain exposed to experimental heatstroke-induced cerebral ischaemia/hypoxia injury.