Regeneration of rat ovarian tissue grafted after exposure to low temperatures

Abstract A study has been made of the viability of rat ovarian tissue after exposure to -79°C and to -190°C for varying times and in different media. The material so treated was grafted usually autoplastically, into spayed rats and its functional activity assessed by examination of vaginal cycles and by histological studies at intervals after grafting. Ovaries chopped in serum , cooled slowly to -79°C and left at that temperature for 1 h or for 9 days gave functional autografts, but not after exposure to -190°C. The incidence of takes and the functional activity of the grafts was greater when the ovarian tissue was suspended in serum or saline containing 15% glycerol and cooled either to -79 or to -190°C for 1 h. Such material deteriorated during 9 days at -79°C but not at -190°C. A delay of 2 h between thawing and grafting reduced the incidence of takes with ovarian tissue suspended in saline containing 15% glycerol and cooled to -190°C. Increasing the glycerol concentration in the medium to 25 % before freezing also decreased the proportion of takes and delayed the appearance of activity of the grafts. Material cooled rapidly did not give functional grafts. The histological appearances suggested that, during the processes of freezing and thawing, a proportion of ovarian cells were destroyed and that eggs in all stages of development were particularly sensitive. Immature ovarian tissue had a greater capacity for reformation of oocytes than had adult tissue, but in either case the capacity to reform oocytes was exhausted within one month, whereas lutein tissue continued to increase for several months.