Effects of brain membranes on 1H nuclear magnetic resonance signal intensity of ethanol in vitro.

In vivo proton nuclear magnetic resonance (1H NMR) studies of ethanol in animal and human brains have shown that only a fraction of ethanol in brain is visible by NMR. The goals of these in vitro 1H NMR experiments were to determine: (1) whether the interaction of ethanol with brain membranes in vitro diminishes ethanol visibility; and (2) if a magnetization transfer (MT) effect can be observed for the interaction of ethanol with brain membranes in vitro. Furthermore, pilot studies were performed to determine if the brain membranes from rats chronically exposed to ethanol had a different effect on ethanol NMR visibility and spin-spin relaxation time (T2) than brain membranes obtained from control rats. Results show that the NMR visibility of ethanol is lower in rat brain membrane suspensions in vitro as compared to ethanol in saline solutions. The factors decreasing ethanol NMR visibility are T2 relaxation, water presaturation time, and off-resonance saturation by a frequency-dependent MT pulse. One-pulse NMR measurements without water presaturation showed that ethanol visibility was significantly increased by 15% in brain membrane suspensions of ethanol-fed rats, suggestive of decreased ethanol partitioning compared to controls. Furthermore ethanol in brain membrane suspensions from ethanol-fed rats showed smaller MT effects than from control rats. These results provide a mechanism for decreased NMR visibility of ethanol in brain, and suggest that chronic exposure to ethanol produces membrane changes which result in increased NMR visibility.