Cryopreservation of fetal rat liver tissue--a morphological investigation.

The present study was undertaken to define optimal conditions for cryopreservation of fetal rat liver tissue fragments. First, various cooling rates (1, 4, 10, 20 and 30 degrees C/min) and preserving temperatures (-20, -80 and -196 degrees C) were examined. Next, various concentrations of Me2SO (5, 10, 20 and 30 per cent vol/vol) were examined by freezing at a rate of 4 degrees C/min to -80 degrees C before transfer to -196 degrees C. All samples were preserved for at least one week. After recovery from cryopreservation, the fragments were transplanted into the spleens of syngeneic rats. Histological assessment of the grafts was made one month after transplantation. Consequently, the optimal cryopreserving conditions for fetal rat liver fragments were defined as follows: cooling rate was 1 to 10 degrees C/min, preserving temperature was at -196 degrees C, concentration of Me2SO was 20 per cent (final concentration: 10 per cent). In the long term observation, the stored liver fragments could be differentiated into adult hepatocytes and the surviving hepatocytes showed little difference from the nonfrozen controls, either histochemically or ultrastructurally. The surviving hepatocytes in the stored transplants were less numerous than in the nonfrozen ones and hepatic cell plates and sinusoids were nil.