[The protective effect of hypothermia in a new transient cerebral ischemic model of the rat--A 31P magnetic resonance spectroscopy in vivo study].

The energy state and intracellular pH of the rat brain during and after transient cerebral ischemia was measured by the method of 31P magnetic resonance spectroscopy in vivo for the purpose of the evaluation of the protective effect of hypothermia. The rat's chest was opened and the bilateral subclavian arteries were ligated. The transient cerebral ischemia was induced by occlusion of the bilateral cerebral arteries using the balloon occluders. The rat's brain was cooled to 20 degrees C by the surface cooling using the ice bags and was heated to 37 degrees C in the control group, respectively. The animal's temperature was adjusted and regulated by a water blanket placed under the animal's body. After 30 min cerebral ischemia, the level of phosphocreatine (PC) was decreased to 58 +/- 4% versus to 36 +/- 4%, 20 degrees C versus 37 degrees C, respectively (p < 0.01). ATP was decreased to 73 +/- 5% versus 52 +/- 4% (< 0.01). Intracellular pH was decreased from 7.23 to 6.48 at 20 degrees C, from 7.22 to 6.08 at 37 degrees C (p < 0.01). After 60 min ischemia, PC was decreased to 52 +/- 5% versus to 33 +/- 6%, 20 degrees C versus 37 degrees C (p < 0.01). ATP was decreased to 62 +/- 6% versus 36 +/- 6% (p < 0.01). At 37 degrees C either PC or ATP was not recovered to the pre-ischemic level. Intracellular pH was decreased to 6.38 at 20 degrees C, to 5.80 at 37 degrees C (p < 0.01). It is concluded the hypothermia saved the high energy phosphates and keeps intracellular pH high and this beneficial effects contribute the brain protection during cerebral ischemia.