Nuclear magnetic resonance investigation of the freezing of water in rat kidney tissues.

The proton linewidth and the integral of the absorption signal of water in rat kidney tissue have been measured at sub-zero temperatures. The water, fresh or stored at +4 degrees C for 24--48 h, shows a supercooling effect down to -10 degrees C to -14 degrees C. At -20 degrees C, 10--20% of the total tissue water remains unfrozen. The supercooling effect is diminished by prior storage at positive temperatures but completely eliminated by storage at several degrees below 0 degrees C. This suggests that the freezing behavior of tissue water varies with change in the physiological state of the tissue. Tissue samples stored at positive temperatures were observed to be more vulnerable than fresh tissue to freezing damage. Storage at several degrees below 0 degrees C for the same period of time appeared to be even more damaging.