THEODORE I. MALININ 
371 
the perfused hearts continue to pulsate until 
inorganic salt concentration is increased to 
31/2-4X "isotonic" levels. Gain and reduction 
of weight can be likewise produced by varying 
concentration of cryoprotective agents in the 
perfusate. 
Consideration of the response of whole organs 
to cryoprotective agents will not be complete 
without the mention of the physiologic peculiari- 
ties of some organs, as exemplified by the heart. 
The effect of cryoprotective agents on cardiac 
rat muscle has been studied by Karow.*^ He 
found dextran, DMSO and magnesium to be ef- 
fective cryoprotective agents, and glycerol an 
ineffective one. He attributed the ineffectiveness 
of glycerol to its high toxicity to rat heart. 
To be effective a cryoprotective substance 
must be in contact with the cells to be preserved, 
and must be present in sufficiently high con- 
centrations. It appears, in view of vascular- 
interstitial space equilibration, that the latter 
condition is not met in the case of cells in or- 
gans perfused with the usual concentrations 
(7-15%) of commonly used cryoprotective 
agents. If this is, in fact, the case, the failure to 
protect whole organs from freezing damage can 
be easily explained. If, on the other hand, com- 
monly used cryoprotective agents are intro- 
duced into the vascular tree in higher concentra- 
tions, irreversible injury due to direct toxic 
effects takes place. Thus, the major problem 
of freeze-preservation of organs remains un- 
solved. It is still impossible to prolong extra- 
corporeal life span of an extirpated organ by 
freezing. Hearts will not survive cooling below 
— 20°C despite the use of cryoprotective agents. 
Furthermore, even at this temperature resusci- 
tation cannot be achieved after storage of 20 
minutes. Kidneys will not survive freezing. On 
the other hand, the last two decades witnessed 
an impressive progress in cryobiology. Whole 
blood, bone marrow, lymphocytes, protozoa, dis- 
persed cells and micro-organisms are frozen 
and thawed routinely with remarkable success. 
Even though results of studies with freezing 
whole adult heart are far from encouraging, 
results obtained by Conway et al.'*« and Rey*^ 
with embryonic hearts indicate that there is 
probably no inherent peculiarity of cardiac tis- 
sue which would prevent it from being frozen 
and resuscitated on thawing. 
At this point, I would like to suggest a differ- 
ent approach to studies dealing with organ 
preservation. The detailed study of the vascular 
response to perfusion, introduction of cryo- 
protective agents, and to cooling and freezing 
itself must form the basis of this approach. The 
response of microvasculature to freezing and 
thawing must be studied directly in the organs 
being frozen, and not anatomically dissimilar 
structures. 
SUMMARY 
The research in organ preservation has been 
stimulated by a sheer pragmatic need for organ 
transplants used in an attempt to extend life in 
critically ill patients. It is hoped that this will 
continue to simulate advances in the field of 
organ preservation. 
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