Cryopreservation of thyroid pieces--optimal freezing condition and recovery]

We have studied the cryopreservation of thyroid pieces for the purpose of autotransplantation. In this paper, the optimal freezing condition was investigated by comparing the survival cells of the cryopreserved thyroid pieces under various freezing conditions, including cooling rate, freezing medium, cryoprotectant, size of pieces and prefreezing incubation. The recovery regarded as survival rate was also evaluated. Based on the results, the optimal freezing condition was that 1 mm 3 of the thyroid pieces in the freezing medium, consisted of culture medium supplemented with 10% of fetal bovine serum and 10% of dimethylsulfoxide, were cooled slowly until -80 degrees C with prefreezing incubation at 4 degrees C for 1 hour and kept in liquid nitrogen for preservation. The number of survival cells under the optimal condition was 1.24-2.03 (1.71 +/- 0.40) x 10(6)/0.1 g tissue, and recovery was 25.2-58.0 (45.5 +/- 14.6)%. This high survival rate suggests the possibility that the cryopreserved thyroid pieces are utilized as the autografts maintaining the intact follicles.