Canadian researchers have successfully transplanted ovaries and fallopian tubes into rats after the organs were frozen in liquid nitrogen and then thawed, boosting the prospect that one day more organs might be saved for transplant.
The work, described Thursday in the journal Nature, was carried out by a team led by Roger Gosden of McGill University in Montreal.
Although the frozen transplanted ovaries didn't all function as well as a control group of fresh organs, four out of seven were able to ovulate normally and one recipient became pregnant with two healthy fetuses, the scientists said.
Transplantation was made simpler by the fact that all the rats used for the experiment were genetically identical, eliminating the problem of organ rejection.
"The results are encouraging, but indicate that ovarian function is compromised to some extent by freezing," perhaps due to freezing within blood vessels, Gosden said. Advances in the freezing process may be able to overcome this problem, however.
Although scientists have been able to preserve some cells - red blood, sperm, eggs and embryos - through freezing, or cryopreservation, they haven't been able to protect larger masses of cells from the rigors of freezing and thawing.
Scientists believe that carefully frozen cells can exist in "suspended animation" for hundreds, even thousands, of years, and still remain viable when thawed.
The trick is to protect the cell structures and membranes with anti-freeze that's not toxic, while slowly dehydrating the cells to get most of the water out without forming ice crystals that can damage cell membranes and other structures.
Gosden has also been involved in experiments that froze and then transplanted small sections of ovarian tissue containing immature eggs into mice and sheep. Those tests resulted in the birth of live young.
For the latest experiment, the Canadian team ran an anti-freeze solution through the rats' right ovaries and fallopian tubes for 30 minutes before beginning a slow cooling process down to about 20 degrees Fahrenheit.
Vials containing the organs were stored overnight in liquid nitrogen before being rapidly thawed and the protective material removed before transplant. Each transplant operation took about two hours. Follow-up with the animals continued for 10 weeks.
"Frozen banking of reproductive organs could eventually be useful in breeding from endangered species and as a fertility treatment for women and children who have undergone sterilizing chemotherapy," the researchers said.
The researchers also believe their work advances the potential for doctors to eventually be able to bank frozen donor tissue and organs for long periods of time and to ship them over long distances.
"Our success with ovarian transplants should stimulate the improvement of cryopreservation techniques for other organs," Gosden and his colleagues said.
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