X-Message-Number: 27617
Date: Tue, 14 Feb 2006 19:06:21 -0800 (PST)
From: Doug Skrecky <>
Subject: urea as a novel cryoprotectant

J Exp Biol. 2005 Nov;208(Pt 21):4079-89.
Cryoprotection by urea in a terrestrially hibernating frog.

  The role of urea as a balancing osmolyte in osmotic adaptation
is well known, but this 'waste product' also has myriad other
functions in diverse taxa. We report that urea plays an important,
previously undocumented role in freezing tolerance of the wood
frog (Rana sylvatica), a northern woodland species that hibernates
terrestrially in sites where dehydration and freezing may occur.
Wood frogs inhabiting an outdoor enclosure accumulated urea to
65 mmol l-1 in autumn and early winter, when soil moisture was
scarce, but subsequently urea levels fell to approximately
2 mmol l-1 as the availability of environmental water increased.
Laboratory experiments showed that hibernating R. sylvatica can
accumulate at least 90 mmol l-1 urea under relatively dry, warm
conditions. During experimental freezing, frogs synthesized
glucose but did not accumulate additional urea. Nevertheless, the
concentrations of urea and glucose in some tissues were similar.
We tested urea's efficacy as a cryoprotectant by measuring lysis
and lactate dehydrogenase (LDH) leakage in samples of R. sylvatica
erythrocytes frozen/thawed in the presence of physiological levels
of urea or other osmolytes. In conferring protection against
freeze/thaw damage, urea was comparable to glycerol and as good as
or better than glucose, cryoprotectants found in freeze-tolerant
frogs and other animals. Urea treatment also improved the
viability of intact tissues frozen in vitro, as demonstrated by
post-thaw measures of metabolic activity and LDH leakage.
Collectively, our findings suggest that urea functions both as an
osmoprotectant and a cryoprotectant in terrestrially hibernating

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=27617