Resuscitation from experimental heatstroke by brain cooling therapy

We have used hypothermic retrograde jugular venous flush to cool the brain previously and to provide better resuscitation than peripheral cold saline infusion during heatstroke in the rat. The current study was performed to assess the effects of brain cooling further on production of reactive nitrogen species, reactive oxygen species, tumor necrosis factor-alpha, and interleukin-10 in both serum and brain during heatstroke. Rats, under general anaesthesia, were randomized into the following groups and given: (a) 36 degrees C or (b) 4 degrees C saline infusion in the external jugular vein immediately after onset of heatstroke. They were exposed to an ambient temperature of 43 degrees C for exactly 70 min to induce heatstroke. When the 36 degrees C saline-treated rats underwent heat stress, their survival time values were found to be 21-25 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline greatly improved survival (226-268 min). Compared with the normothermic controls, the 36 degrees C saline-treated heatstroke rats displayed higher levels of brain temperature, intracranial pressure, serum and hypothalamic nitric oxide metabolite, tumor necrosis factor-alpha and dihydroxybenzoic acid as well as hypothalamic inducible nitric oxide synthase immunoreactivity. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and hypothalamic levels of local blood flow, and partial pressure of oxygen were all significantly lower during heatstroke. The cerebrovascular dysfunction, the increased levels of nitric oxide metabolites, tumor necrosis factor-alpha, and dihydroxybenzoic acid in both the serum and the hypothalamus, and the increased levels of hypothalamic inducible nitric oxide synthase immunoreactivity occurred during heatstroke were significantly suppressed by brain cooling. Although the serum and hypothalamic interleukin-10 maintained at a negligible level before stress, they were significantly elevated by brain cooling during heatstroke. These findings suggest that brain cooling may resuscitate persons who had heatstroke by decreasing overproduction of reactive nitrogen species, tumor necrosis factor-alpha, reactive oxygen species and cerebrovascular dysfunction, but increasing production of interleukin-10.