Nuclear magnetic resonance evidence using D2O for structured water in muscle and brain.

The electric quadrupole moment of the deuterium nucleus provides a nuclear magnetic resonance (NMR) probe of electric field gradients, and thereby of organization of tissue water. 8-17% of H(2)O in rat muscle and brain was replaced by D(2)O from 50% deuterated drinking water. The peak height of the steady-state NMR spectrum of D in muscle water was 74% lower than that of an equal concentration of D(2)O in liquid water. Longitudinal NMR relaxation times (T(1)) of D in water of muscle and brain averaged 0.092 and 0.131 sec, respectively, compared with 0.47 sec in D(2)O in liquid water. Transverse NMR relaxation times (T(2)) averaged 0.009 and 0.022 sec in D(2)O of muscle and brain, respectively, compared with 0.45 sec in D(2)O in liquid water. These differences cannot be explained by paramagnetic ions or by magnetic inhomogeneities, which leaves increased organization of tissue water as the only tenable hypothesis. Evidence was also obtained that 27% of muscle water and 13% of brain water exist as a separate fraction with T(2) of D(2)O less than 2 x 10(-3) sec, which implies an even higher degree of structure. Each of the two fractions may consist of multiple subfractions of differing structure.