X-Message-Number: 7686 From: (Brian Wowk) Newsgroups: sci.cryonics Subject: Re: Hextend as cryoprotectant? Date: 12 Feb 97 19:45:29 GMT Message-ID: <> References: <01bc18af$ee2cfb40$> In <01bc18af$ee2cfb40$> "JDY" <> writes: >I came across a news item at http://www.businesswire.com/cnn/btim.htm, >dated may 96. It's probably old news to most readers here, but it was new >to me. BioTime researchers were presented results at a meeting, and the >text mentioned experimental results which pointed to the possibility for >long term preservation of organs. My question is, would the solution >(hextend?) be useable as a cryoprotectant? Are any of the cryonics >organizations considering using it? Why or why not? Hextend (tm) is not a cryoprotectant per se, but a plasma volume expander (blood substitute) whose key ingredient is HES (hydroxyehtyl starch). HES is a very large molecule that does not penetrate cells, and whose cryoprotective effects are therefore confined to the extracellular and especially intravascular spaces. HES has been used as "nonpenetrating" cryoprotectant by organ cryopreservationists for at least 15 years. It has been used as a perfusate ingredient by most cryonics organizations for the past ten years ever since the pioneering work of Jerry Leaf and Mike Darwin who demonstrated that HES inhibits edema during blood washout with great effectiveness. Paul Segal and associates have since formed a remarkably successful company (Biotime) oriented around the development of commercial blood substitutes using HES as a colloid. > Additional research on the use of Hextend supplemented with >cold-protective agents was presented by Dr. Hal Sternberg, BioTime's >research vice president. He described experiments in which hamsters >were completely blood substituted at hypothermic temperatures with >BioTime solutions, and then placed in sub-zero freezing baths for >periods of up to 2 hours. These animals reached deep body >temperatures as low as -4 C, and then were revived to consciousness >and reactivity. These experiments are similar to the work of Audrey Smith 40 years ago, who demonstrated that hamsters could be recovered after partial freezing near 0'C. Hextend is being used essentially as a carrier solution in Dr. Sternberg's experiments to introduce "supplementary cold-protective agents" such as glycerol, which are the real cryoprotectants that penetrate and protect intracellularly. At last report to CryoNet, I believe Dr. Sternberg gave the opinion that more than 3% glycerol was fatal to whole hamsters. This is a factor of 20 short of the concentration required for recovery from deep sub-zero temperatures, so this work still has as a long way to go. *************************************************************************** Brian Wowk CryoCare Foundation 1-800-TOP-CARE President Human Cryopreservation Services http://www.cryocare.org/cryocare/ --------------------------------------------------------------------------- Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=7686