X-Message-Number: 15702
Date: Tue, 20 Feb 2001 15:17:23 EST
Subject: oocytes & embryos

IVF.com has some interesting stuff on cryopreservation of human eggs and 
embryos. The relevance to cryonics is only tangential, but it reinforces some 
things we need to keep in mind about cryopreservation. One is that different 
workers may report substantially different experiences, in some cases 
seemingly contradictory, yet they can all be right in their own contexts. 
Another is that sometimes very small differences in technique can make large 
differences in outcomes or in consistency of outcomes. Also, thawing 
procedure can be more important than freezing procedure. And again--this 
relates to relatively simple systems, very small specimens, so that with 
brains we should expect much, much greater complications and extreme 
difficulty in getting uniformly good results across all brain regions, let 
alone all kinds of patients in many different circumstances. As the IVF 
writer says, "Cryobiology is all about compromise" and probably the best we 
can expect for many years is to moderate the average damage, somewhat 
reducing the burden on future technology.

Techniques used successfully have involved DMSO, gycerol, propanediol with 
sucrose, and glycerol with sucrose, all slow-freeze-rapid-thaw; and 
vitrification by extremely fast cooling.

Besides cryopreserving eggs, it is possible to use egg precursors, including 
ovarian tissue.

Another interesting note: "One approach has been to replace sodium as the 
principal cation in the cryoprotectant with choline in an attempt to shut 
down the sodium ion pumps in the oocyte membrane during cryoprotectant 
exposure, thus minimizing potentially deleterious 'solution effects' during 
cooling."  Notice--if sodium pumping is shut down, the K/Na ratio test, if 
applied at this time, would show an abnormal or "non-viable" result, which 
would be misleading. 

Robert Ettinger
Cryonics Institute
Immortalist Society

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