[Nuclear magnetic resonance studies of effects of glycerol on brain edema]

Effects of glycerol on the state of water in edematous brain tissues were studied by the pulse FT NMR technique. Brain edemas were induced experimentally by cold injury and triethyl tin (TET) intoxication in Wistar rats. Ten percent w/v glycerol (1 g/kg body weight) were injected intravenously at 30 minutes before decapitation for the NMR measurements. Transverse relaxation times (T2) in the cerebral gray and white matter were measured by Meiboom-Gill pulse sequence at the resonant frequency of 100 MHz. Water content was calculated from the difference between wet and dry weight after heating in an oven at 95-100 degrees C for 72 hours after the NMR measurements. In the normal brain T2 value was 76.4 msec and 75.4 msec in the gray and white matter respectively. In the edematous brain, T2 separated into two components, one slow and one fast, corresponding with the increase of water content. Values of the slow component (slow T2) were characteristic of both types of brain edema. In the cold injury edema, slow T2 values became 105 msec in the gray matter and 96 msec in the white matter, while in the TET induced edema, it became 450 msec in the white matter. After glycerol infusion, slow T2 became faster in these regions in both types of brain edema, showing 92.1 msec in the gray matter and 88.1 msec in the white matter of the cold injury edema, and 388 msec in the white matter of TET induced edema. The degree of the changes of slow T2 values per unit change of water content was greater in the cold injury edema than in the TET induced edema. Serum osmolality elevated 23.8 mOsmol greater than the control value after glycerol infusion in this experiment. It is concluded from these findings that glycerol retracts free mobile water molecules from the edema fluid by osmotic pressure gradient.