X-Message-Number: 15702 From: 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 http://www.cryonics.org Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=15702